Year : 1995 | Volume
: 43 | Issue : 4 | Page : 159--176
Principles and paradigms of pediatric cataract management
Surendra Basti1, Mark J Greenwald2,
1 From the Cornea and Anterior Segment Service, L.V. Prasad Eye Institute, Hyderabad, India
2 Division of Ophthalmology, Children's Memorial Hospital, 2300, Children's Plaza, Chicago, IL 60614, USA
L.V. Prasad Eye Institute, Road No. 2, Banjara Hills, Hyderabad 500 034
Propensity for increased postoperative inflammation and capsular opacification, a refractive state that is constantly in a state of flux due to growth of the eye, difficulty in documenting anatomic and refractive changes due to poor compliance, and a tendency to develop amblyopia, makes management of cataract in the child different from that in the adult. The recent past has unraveled several caveats of pediatric cataract management - the importance of atraumatic surgery and complete removal of lens matter, benefits of in-the-bag intraocular lens(IOL) implantation, role of titrating IOL power to counter refractive changes due to growth of the eye, prudery of continuously following these eyes for early detection of aphakic glaucoma and benefits of some surgical innovations. Although these promise to significantly improve our management of pediatric cataract, their long-term benefits are yet to be determined. We will also have to harness newer techniques, especially in the areas of wound construction and capsule management, and will have to develop effective strategies for the refractive management of infantile aphakia.
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Basti S, Greenwald MJ. Principles and paradigms of pediatric cataract management.Indian J Ophthalmol 1995;43:159-176
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Management of the child with cataract poses many challenges to the ophthalmologist. Methods of evaluation need to be modified for patients who are frequently unable or unwilling to provide basic cooperation. Surgical removal of the cataract calls for techniques that counter the tendency toward increased posterior capsular opacification in young eyes. Choosing a modality of aphakic correction requires careful consideration of the change in refraction these eyes may undergo as they grow to maturity. Most importantly, there is all along the danger of amblyopia from visual deprivation looming large.
Over the years, there has constantly been a search for new techniques that more effectively manage pediatric cataracts. Within the past two decades, major advances in adult cataract management have provided numerous new options, including refinements in microsurgical technique, better quality intracameral pharmacologic agents, and improved implantable lenses. The pediatric cataract surgeon now faces the challenge of determining how best to draw on these advances to the benefit of children, always keeping in mind that their eyes are not only smaller than adult eyes, but also different in many important ways.
This article seeks to elaborate on the various options available for pediatric cataract management, and to spell out when possible what paradigms are established or emerging for care of the child at various stages of development.
EVALUATION OF THE CHILD WITH CATARACT
Only a small minority of pediatric cataracts present clinically with subjective complaints relating to vision. Often the first sign is a white or partially white pupil noted by the parents. Strabismus may be the initial manifestation, especially in unilateral cases, and nystagmus or poor visual fixation may herald the presence of bilateral lens opacities in infancy. Increasingly congenital cataracts are detected by pediatricians, who in recent years have been well trained to inspect the red fundus reflex in every newborn. A significant fraction of childhood cataracts are detected in the course of routine school or preschool vision screening.
It is important to quantify the visual acuity of the child with cataract as precisely as possible. With patient effort, most developmentally normal children over three years of age and even many two-year-olds can be tested reliably using Snellen optotype equivalents: both letter identification (either "HOTV" with matching card or tumbling E with directional pointing) and picture naming (with Allen cards or similar symbols) should be tried. Presentation of test characters in isolation (as opposed to full lines) is generally sufficient for this purpose. Infant visual acuity can be estimated with good accuracy in many cases using preferential looking (with Teller cards) or visual evoked potential recording. Successful application of either of these methods requires that the eye under study be capable of some degree of visual fixation.
The quality of visual fixation is also of great importance in patients older than about age 3 months. The examiner must note carefully the presence or absence of nystagmus or other unsteadiness (preferably under monocular as well as binocular viewing conditions), and also whether the child will alternate fixation between the two eyes. The latter question can be answered by simple observation and cover testing when constant strabismus is present, and in other cases by optically inducing ocular misalignment with a 10- or 20-diopter vertical prism held before one eye. The ability to maintain alignment with fusional control, even for brief periods, should also be carefully looked for and documented in the strabismic child, and stereopsis measurement should be attempted in every patient cooperative enough for acuity testing.
It is essential to examine the anterior segment. This can be done in conventional manner using the slit lamp (facilitated by having the child kneel on the exam chair) with most children age 3 years and older. Most infants under 6 months of age can be adequately immobilized for examination with a hand-held slit lamp or simple magnifying lens by securely wrapping the arms and body in a sheet or special restraining device and retracting the lids with an appropriately sized speculum. Between 6 months and 3 years it is often necessary to use oral sedation (chloral hydrate, 50 to 100 mg/kg body weight) or to resort to examination under general anesthesia.
Corneal diameter needs to be measured or estimated as reliably as possible. A cornea that is less than 9.0 mm at (full term) birth, less than 10.5 mm at age 6 months, less than 11 mm above age 1 year, or more than 0.5 mm smaller than its contralateral fellow, should be taken as evidence of microphthalmos.
The quality of the red fundus reflex must be critically assessed in every child with cataract, noting the size and location of opacities viewed against retroillumination, and whether any light is transmitted through them. The direct ophthalmoscope, held a few inches from the eye, is the best instrument for this purpose. When possible, at least the posterior pole of the fundus should be assessed by indirect ophthalmoscopy, looking particularly for underdevelopment or malformation of the disc or macula and the presence of abnormal pigmentation. B-scan ultrasonography is necessary if no fundus view is obtainable.
Even cataracts that permit fairly good light transmission and vision often make retinoscopic refraction virtually impossible. Given that reliable subjective refraction is usually very difficult if it can be done at all in children under age 10 years, pinhole acuity testing represents a very valuable way to estimate the potential visual benefit of optical correction for the child with cataract. It is important to perform this maneuver when cooperation permits, because early in the course of cataract formation there may be significant changes in the refractive power or accommodative range of the lens.
Intraocular pressure measurement should be done on every eye with a cataract. Schiotz tonometry is quite adequate for this purpose, and can sometimes be accomplished in the awake infant under 6 months old (aided by giving a bottle to suck on). If necessary this part of the assessment can be deferred to the operating room when surgery is indicated.
When intraocular lens (IOL) implantation is under consideration, keratometry and A-scan axial length measurements are needed. If an appropriate inventory of lens powers is available, these tests can be done in the operating room immediately prior to surgery. Use of a standard keratometer on an adjustable height table is made possible by turning the child's head to the side.
DIFFERENTIAL DIAGNOSIS AND ASSOCIATED CONDITIONS
Cataracts are more often attributable to a specific cause in children than in adults (although still a majority of pediatric cases are idiopathic); careful consideration of possible etiologies is therefore routinely indicated, although this need not require an extensive laboratory work-up.
One of the most frequent identifiable sources of childhood cataract is autosomal dominant familial transmission. Both mother and father should be examined if possible for asymptomatic opacities that may show the child's problem to be hereditary. Siblings should also be checked, although autosomal recessive and X-linked inheritance of cataract is relatively uncommon.
Trauma, both blunt and penetrating, is an important cause of cataract in childhood. Often a history of injury is lacking, either because there was no adult witness, or because the injury resulted from physical abuse that has been denied by the caretaker responsible. Lens dislocation, angle recession or iridodialysis, and retinal hemorrhages or rhegmatogenous retinal detachment are associated findings that should immediately suggest traumatic origin.
The morphology of the lens opacity may help elucidate its origin [Figure:1]. Unilateral cataracts occupying primarily the posterior cortex (with or without extension forward to involve the nucleus) are usually the result of isolated, idiopathic, sporadic malformation involving the posterior capsule: either posterior bulging of abnormally thin capsular membrane (posterior lenticonus or lentiglobus), or fibrous thickening of the capsule resulting from persistent hyperplastic primary vitreous (PHPV). Bilateral posterior polar cataracts (with or without associated lenticonus) are typically familial. Bilateral or unilateral anterior polar opacities are usually idiopathic, while bilateral anterior lenticonus is most often associated with Alport's syndrome and anterior subcapsular localization suggests association with atopic dermatitis. Nuclear, lamellar, and diffuse multipunctate cataracts [Figure:2] may result from a wide variety of causes including chromosomal abnormalities (Down's syndrome), metabolic disturbances (particularly hypocalcemia and hypoglycemia) and hereditary transmission, but very often no etiology can be determined.
In contrast to posterior cortical cataracts associated with lenticonus or PHPV, and in marked contrast to the adult situation, isolated true posterior subcapsular (PSC) opacification is seldom seen as a sporadic idiopathic occurrence in childhood. Unilateral occurrence should prompt a careful search for evidence of trauma. Bilateral PSC cataract may result from chronic uveitis, metabolic disorders (including galactosemia and diabetes mellitus), prolonged corticosteroid treatment for chronic disease, radiation treatment for malignancy (whole body or regional involving any part of the head), or nonaccidental injury (child abuse). PSC opacification is also seen in older children and young adults with atopic dermatitis and type 2 (central) neurofibromatosis.
Other ocular abnormalities associated with cataract often provide important diagnostic clues or require attention as problems in their own right. Elevated intraocular pressure may accompany congenital cataract associated with rubella infection or Lowe's syndrome. Posterior segment malformation can be detected by ultrasonography in some cases of PHPV. Rhegmatogenous retinal detachment occurs in a significant number of patients with cataract caused by atopic dermatitis. Pigmentary retinopathy may be visible in eyes afflicted with rubella or other congenital infection. Signs of uveitis (sometimes quite subtle) indicate the presence of an underlying disorder such as juvenile rheumatoid arthritis (particularly characterized by the presence of iris-lens synechiae and band keratopathy), Fuch's heterochromic iridocyclitis, or pars planitis (intermediate uveitis) Microphthalmos, a common feature of serious ocular malformation, is also often seen in otherwise well-formed and healthy eyes with idiopathic and familial bilateral congenital cataracts, and with unilateral cataracts that are idiopathic or attributable to PHPV. Microphthalmos is very seldom associated with cataracts caused by posterior lenticonus or metabolic disturbances.
When cataract in childhood is associated with a dysmorphic syndrome or systemic disease, some extraocular abnormality is usually fairly obvious and evident at the time of diagnosis. Nevertheless, every child with cataract should have a thorough systemic history and physical examination by a pediatrician or other qualified specialist, and laboratory evaluation as indicated based on positive findings. In the absence of specific historical or physical evidence of a systemic problem, laboratory evaluation can usually be limited to a few simple tests, chosen on the basis of the specific clinical situation.
Serologic screening for congenital infection (TORCH titers, including testing for rubella and syphilis) is indicated for any infant with cataract of uncertain origin., It is particularly important to identify the baby with rubella prior to surgery, because exposure of operating room personnel to aspirated lens material containing the live virus may cause harm. TORCH testing in older children often gives misleading results, and should be reserved for cases in which there is specific clinical evidence for one of these conditions.
Urine testing for reducing substance (using Clinitest tablets on a specimen obtained after milk feeding) should be done to rule out galactosemia in any infant with bilateral cataracts in otherwise normal eyes. Although this is a rare condition (1-3% of pediatric cataracts)' it is important to detect early in infancy, when elimination of lactose from the diet may reverse or arrest lens opacification (particularly if it has not progressed beyond the characteristic "oil droplet" nuclear lesion). Early diagnosis is also critical to general health and development in cases caused by galactose transferase enzyme deficiency. Quantitative testing of red blood cells for transferase and for galactokinase (deficiency of which causes cataract and galactosuria, but no other systemic problem) can be used to confirm the diagnosis of galactosemia or rule it out if urine test results are positive or equivocal, or if clinical concerns warrant further investigation., Both forms of galactosemia are autosomal recessive genetic disorders, fully expressed only in the homozygous state. It has been shown, however, that bilateral zonular or PSC cataract formation in older children and young adults may be associated with heterozygosity for galactokinase deficiency, and possibly stabilized or reversed by dietary modification. Some authorities suggest RBC galactokinase assay in such cases to identify patients with subnormal enzyme levels, although the yield is low and results are often difficult to interpret. Lactose restriction has also been advocated for mothers of galactosemic children during subsequent pregnancies.
Rarely if ever is cataract the initial sign of abnormal glucose or calcium metabolism, but because screening for serum levels of these substances is so routine, it is usually included in the evaluation of any child with bilateral isolated cataracts of possibly metabolic origin.
Lowe's oculocerebrorenal syndrome is a rare but important multisystem disorder that may initially show no abnormality except for bilateral congenital cataracts, typically occupying small, flattened lenses., Males affected with this X-linked recessive condition manifest moderate to severe developmental delay and behavior problems beginning in late infancy, along with nephropathy characterized by aminoaciduria and metabolic acidosis. Carrier mothers have minor lens opacities. Boys with consistent ophthalmologic findings should have urine screening for protein and amino acids and serum electrolyte and bicarbonate measurement not only at the time of diagnosis, but again at age 1-2 years.
SURGICAL INDICATIONS, TIMING, AND VISUAL PROGNOSIS
Surgery is nearly always indicated for total cataract in childhood. Regardless of the degree of amblyopia that may persist after treatment, recovery of some useful vision can be anticipated. In unilateral cases with severe amblyopia, it can at least be expected that there will be expansion of the binocular perimeter by addition of the temporal monocular crescent of the amblyopic eye's field (which is relatively resistant to the effect of unilateral visual deprivation).
Deciding whether to operate on a child with partial lens opacification can be very difficult. Some partial cataracts are extremely harmful to developing vision (especially in unilateral cases), and must be removed urgently for optimal visual outcome. In other cases, untreated partial cataracts, unilateral as well as bilateral, have only a minor effect on vision, and the child's visual development may be more threatened by the possibility of postoperative problems than by the original condition. Finally, there is a third group of cases in which unilateral partial cataracts have already damaged sight beyond the possibility of recovery, even with highly aggressive treatment; arguably these eyes also should be left alone if they can be identified.
The ophthalmologist attempting to resolve this dilemma should first take into account whatever historical information is available. A large percentage of childhood cataracts are acquired after birth. If the parents or pediatrician are reasonably certain lens opacification they now see was not present at a particular earlier age, greater optimism is warranted than if they report having seen the abnormality since birth. Recovery of decent central vision is very unlikely if surgery on a truly congenital unilateral amblyogenic cataract is delayed beyond 4-6 months of age. A history of recent trauma with compatible physical findings also bodes well for visual recovery, provided the eye otherwise remains healthy and adequate refractive correction can be maintained postoperatively.
Visual function and ocular motility assessment can provide valuable guidance, even with preverbal patients. Favorable signs in the presence of a unilateral cataract include preservation of central steady fixation (even if only on a light), and maintenance of intermittent binocular fusion in the child with strabismus, or stereopsis in the child with straight eyes; these capabilities are usually lost in the context of significant amblyopia. Surgery can be safely deferred in many such children who demonstrate retention of good binocular function.
Nystagmus or lack of visual fixation in an infant more than 3 months old with bilateral cataracts implies that significant visual deprivation has occurred and that surgery is indicated, but does not necessarily mean that postoperative vision will remain poor. The absence of nystagmus and the presence of reasonably good fixation in such an infant (ideally supplemented by documentation of normal for age acuity with Teller Cards or VEP) suggests that visual potential is good, and may in fact favor close observation over immediate intervention. For an infant less than 3 months old, little can be inferred on the basis of fixation behavior or motility, and even testing with Teller Cards or VEP is usually uninformative; surgical decision making in the newborn period must therefore rely on other clinical findings (see below).
The decision to operate on bilateral partial cataracts after infancy should take into account the impact of the condition on the child's normal activities. A toddler who navigates well and recognizes family members easily, a preschooler who plays with other children and views picture books normally, and a school age child who functions without significant difficulty in the classroom may all be best served by postponing consideration of surgery. It must be kept in mind that mild to moderate reduction in acuity is much less bothersome to a child who has experienced it from an early age than to an adult who acquires it after decades of experience with normal vision.
As in the case of differential diagnosis, cataract morphology has considerable relevance to surgical indications and visual prognosis. A generally reliable rule of thumb holds that severe amblyopia usually results only from cataracts that completely block light transmission through the central 3 mm of the lens. Thus most polar opacities (particularly those involving only the anterior capsule), smaller nuclear cataracts, and lamellar cortical opacities that transmit light centrally usually can be left alone at least until the child reaches a developmental stage that permits reliable assessment of visual impairment. Posterior cortical cataracts (especially those resulting from posterior lenticonus) usually do not become visually significant until months or years after birth, in which case the likelihood of a good visual outcome is considerably better than for a comparable congenital opacity.
Other physical abnormalities associated with a childhood cataract may have substantial impact on visual potential and suitability for surgery. PHPV involving the posterior segment generally indicates a poor functional prognosis. Traumatized eyes with significant corneal scarring tend to end up with seeing considerably less well after cataract surgery than those with intact corneas. On the other hand, mild to moderate microphthalmos does not in itself seem to have much impact on ultimate visual acuity. Concurrent uveitis or glaucoma, if appropriately managed intra- and postoperatively, also does not as a rule have serious negative implications for vision.
Finally, thought should be given to overall health and developmental prognosis before subjecting a young child to cataract surgery. The visual needs of an immature patient with very short life expectancy or very limited mental potential may not justify a procedure that would certainly be performed on an otherwise normal child. Intraocular surgery on a violently self-abusive, severely retarded individual may even be contraindicated. The medically fragile child can pose anesthetic risks that require deferment of treatment, or consideration of bilateral operations under a single general anesthesia.
The timing of surgery for pediatric cataract can be a matter of considerable importance. When amblyogenic lens opacification is detected in a newborn or infant judged to have good visual potential, initial surgical treatment should be done within a few days if at all possible. In symmetrical bilateral cases, the second eye should be operated on within a week of the first. When there is significant asymmetry, the more involved lens is generally removed first; surgery on the second eye may then be deferred until after the first eye receives aphakic correction, or longer if the visual function of the still phakic eye is established to be better than that of the initially operated eye. Older children presenting with severe opacities are somewhat less demanding of urgent attention, but should nevertheless go to the operating room within a week or two if treatment of amblyopia is planned.
It is often advantageous to plan elective surgery for non-amblyogenic cataract (see above) so as to avoid the age range of 1-4 years, within which postoperative care can be very difficult. Elective surgery on the second eye of a bilaterally affected child over age 4 is best deferred until the first eye is fully healed and seeing comfortably with whatever form of aphakic refractive correction has been selected.
When surgery for partial cataract is delayed for an extended period after diagnosis, some children may benefit from instillation of mydriatic drops to permit vision through a larger unopacified area of the lens. An agent with relatively little cycloplegic effect should be chosen (e.g. tropicamide or phenylephrine), and used 1-3 times per day. If no visual benefit can be documented, discontinuation after a short trial is justifiable.
If observation is the course chosen for an infant or child with partial lens opacities, it is extremely important to ensure that findings are reassessed on a frequent regular basis. Although most pediatric cataracts change very gradually or not at all, they can progress at times with astonishing rapidity (from barely visible to total opacification in a matter of weeks or even days). In infancy, examination should be repeated every few months. Older children ought to be seen at least once or twice a year. Most importantly, the family should be instructed to report at once any change in the appearance of the pupil, the development or worsening of strabismus, or evidence of deteriorating vision. The cooperative child should be asked to check monocular vision by covering each eye in turn for a moment every few weeks. Similarly close observation is warranted for the apparently uninvolved eye in unilateral cases.
SURGICAL MANAGMENT: GENERAL APPROACHES
It has often been said that removal of the cataract itself is the least of the problems in pediatric cataract management. While still containing some truth, this statement needs to be qualified in the present era. Techniques used in the past such as discission, needling, and the Scheie procedure were indeed easy surgically. Their inadequacies, however, made postoperative management far from easy. All of these approaches left behind a large part or the whole of the posterior capsule as well as lens cortical remnants. In a very large percentage of cases, this subsequently led to reopacification with obscuration of the visual axis, renewing the threat of amblyopia and necessitating further surgical treatment. Residual lens material also predisposed to postoperative uveitis and to aphakic glaucoma.
Disadvantages of the above mentioned surgical procedures stimulated pediatric cataract surgeons to turn to newer techniques, developed initially for other purposes, that avoided some of the drawbacks of the older methods. The two approaches most widely used today are lensectomy with anterior vitrectomy (adapted from techniques originated by vitreoretinal surgeons) and modern extracapsular cataract extraction (based on techniques developed by adult cataract surgeons). A new and promising approach is extracapsular cataract extraction combined with primary posterior capsulotomy and anterior vitrectomy.
Lensectomy With Anterior Vitrectomy (LAV)
Introduction of instruments with cutting and aspirating capabilities such as the automated vitrector in the 1970s provided a valuable new approach to removal of pediatric cataracts., Since the perils of leaving behind residual lens material were well recognized, surgeons attempted to achieve nearly complete removal of the lens and found the automated vitrector ideally suited for this purpose. Over the years, two approaches have been used with the LAV procedure: limbal and pars plicata. The pars plicata technique was introduced earlier. This method permits complete removal of all lens material; also, since all manoeuvers are performed in the posterior chamber, there is less risk of damage to the iris and corneal endothelium. Since most anterior segment surgeons are not entirely comfortable with pars plicata/pars plana surgery, the limbal approach to LAV was developed and refined by pediatric cataract surgeons, and rapidly became the dominant technique of childhood cataract extraction in the 1980s. The peripheral portion of the capsular bag is retained in this procedure, thus providing the option of subsequent IOL implantation. As traditionally performed, however, the amount of capsule left behind by this procedure is relatively meager.
Extracapsular Cataract Extraction (ECCE)
The development of manual and automated instruments that irrigate and aspirate lens cortex through separate channels was one of the innovations that helped revolutionize adult cataract surgery in the 1970s and 1980s. The posterior capsule is left intact in modern as in older extracapsular cataract procedures, but because of the high degree of control made possible by newer equipment and the routine use of the operating microscope, removal of cortex is more nearly complete, and the incidence of reopacification in adult eyes operated on with this technique is considerably lower than was seen in the past.
Motivation to apply modern ECCE to pediatric cataract surgery came from several considerations: First, despite the reported low incidence of complications following LAV, some surgeons continued to feel uneasy about possible late consequences of removing substantial amounts of vitreous from young eyes. Second, the advent of Nd:YAG laser capsulotomy technique offered a relatively non-invasive means of dealing with posterior capsule opacification after ECCE., Finally, modern ECCE was developed in conjunction with major advances in IOL implantation, and is optimally suited to this method of dealing with aphakia. As pediatric cataract surgeons have turned increasingly to the use of IOLs, ECCE has looked more and more attractive. The risk of reopacification remains a significant concern however, particularly in patients under age 2 years. Experience to date with Nd:YAG capsulotomy in children has shown mixed results, with recurrence of opacification [Figure:3] requiring repeated laser treatment and sometimes surgical capsulectomy and vitrectomy as a secondary procedure in a some cases.[47, 48]
Extracapsular Cataract Extraction With Primary Posterior Capsulotomy and Anterior Vitrectomy (ECCE+PPC+AV)
The rationale for combining controlled posterior capsulotomy and vitrectomy with ECCE [Figure:4] is to circumvent the need for secondary surgical procedures after extracapsular cataract extraction, while retaining a capsular bag that is suitable for IOL implantation. Although technically challenging when placement of an IOL is included, this approach has been mastered with experience by a number of surgeons. It seems to be more effective than procedures that leave the vitreous undisturbed in preventing reopacification. Early results have been encouraging, with maintenance of an unobstructed visual axis [Figure:5] in most cases reported to date.
MANAGEMENT OF APHAKIA
The risk of amblyopia mandates prompt optical correction following pediatric cataract removal. Pediatric cataract surgeons are now fortunate to have an unprecedented range of options for this purpose, including spectacles, various types of contact lenses, corneal refractive surgery (epikeratophakia) and intraocular lens implantation.
Glasses have a considerably larger role to play in the postoperative management of pediatric than adult cataract. Children under age 10 years with bilateral aphakia generally adapt very readily to the magnification and distortions produced by high plus spectacle lenses, and many who can wear contact lenses nevertheless prefer glasses because of their convenience. Unilateral childhood aphakes generally suffer loss of binocularity if they must rely on glasses, and find the qualities of spectacle-corrected aphakic vision objectionable in comparison to the preserved phakic vision of the fellow eye, but occasionally even for these patients glasses can be used successfully to enable the treatment of amblyopia in a situation of contact lens intolerance.
Aphakic spectacles are readily obtainable throughout most of the world at reasonable cost, but expense may be considerable if aspheric lenses that reduce thickness and optical aberrations are desired, or if repeated loss or breakage occurs (not unusual with children). Most adolescents object to aphakic glasses because of their appearance and interference with athletics. For infants following cataract surgery, spectacle fitting is quite difficult, both because their faces are poorly suited to supporting the weight of high power lenses, and because the powers required (frequently in excess of +20 D) are hard to obtain. One option that may be considered is the use of high power Fresnel membrane lenses applied over lower plus spectacle lenses.
For several decades contact lenses (CLs) have been the dominant means of optical correction for pediatric aphakia in North America and Europe.[39, 52, 53] Most American pediatric ophthalmologists favor silicone elastomer lenses (Silsoft, Bausch and Lomb, Rochester), which are commercially available in powers up to +32 D, are relatively easy for parents to handle, and can be worn continuously for a week in most cases. Aphakic CLs produce only a small degree of aniseikonia (which can be eliminated if necessary by adding extra plus power to the lens and neutralizing with minus spectacle overcorrection), making binocular fusion possible in unilateral cases, although only a minority of these achieve stereopsis.
Disadvantages of the Silsoft lens include its high cost and limited durability; replacement is usually necessary after about six months of wear because of surface deterioration. Very young users of all types of CLs suffer from the burden of relatively frequent lens loss and the need for unpleasant physical restraint during insertion and removal. Lens fitting and retention are especially a problem after penetrating injury because of corneal irregularities. When CL wear must be initiated in the 1-4 year old range, problems are greatly magnified by the child's typically very strong resistance; patients and families that have become accustomed to lenses during infancy are much more likely to manage adequately during this period, although they still usually report increased difficulty of compliance compared with the first year of life. Finally, the frequency of infectious keratitis in CL-wearing pediatric aphakes may be higher than for other categories of lens wearers, especially when hygienic conditions are suboptimal.
Overall, the success rate for contact lens correction of pediatric aphakia has been good to excellent under favorable circumstances, although less than desirable for certain groups of patients, particularly toddlers and preschool children who undergo surgery for traumatic cataract.
In developing countries and for poorer residents of more affluent societies, however, the disadvantages of this approach frequently outweigh its benefits.
Epikeratophakia, introduced in the early 1980s, initially appeared to offer great promise in the correction of pediatric aphakia [Figure:6]. Its theoretical advantages included permanent maintenance of optical correction without use of a non-tissue intraocular prosthesis, and the prospect of modifying power by simple surgical exchange of the tissue lenticule applied to the corneal surface., Regrettably, most surgeons' experience with this technique was disappointing. Interface scarring and uneven quality of commercially available freeze-dried lenticules proved to be serious problems and deterrants to widespread use. Discontinuation of production by the major supplier of lenticules effectively eliminated the option of epikeratophakia in the early 1990s.
The appeal of using the IOL for aphakic correction stems from its ability to provide continuous, optically optimal refractive correction immediately following surgery, without dependence on compliance by the patient and family. Although IOLs were first tried in children in the late 1950s, pediatric usage has lagged far behind implantation in adults. This fact is in part a reflection of the basic conservatism of most pediatric cataract surgeons, who wished to see ample confirmation of the safety and efficacy of IOLs in adults before subjecting children to their widespread application. It also reflects skepticism engendered by the frequency of complications and poor outcomes seen after early IOL use in children. Ophthalmologists now recognize, however, that many of the early problems with pediatric lens implantation were attributable to employment of procedures and lens designs that are no longer considered applicable. Early experiences served as crucibles for the conception of newer and much improved techniques. Recent reports in the literature indicate very encouraging short- to intermediate-term results following childhood cataract surgery with IOL use,,,, , ,  and have considerably decreased the controversy surrounding it. Still, the relative novelty of this technique, and the very long life expectancy of children who will be subjected to it, warrant a continuing degree of caution in its application. It will probably take several decades before we definitively know the role of IOL implants for the correction of pediatric aphakia.
Currently the greatest negative of IOL implantation in childhood, aside from the general unavailability of large scale long-term follow-up data, is the problem of application to infants, who are among those most in need of improved techniques for aphakic correction. The small dimensions of the infant eye, the many significant differences between its tissues and those of the mature eye, the magnitude of the changes it will undergo during completion of development, and its tendency to react intensely to the presence of an intraocular foreign body all conspire to thwart the pediatric cataract surgeon who attempts to apply presently available implant techniques to the youngest patients.
SPECIAL TECHNICAL CONSIDERATIONS
Although nuances of pediatric anesthesia are well outside the scope of this article, the discerning surgeon would do well to be familiar with some of the broad guidelines that govern successful general anesthetic use for cataract surgery. It is recommended that General Anesthesia (GA) for children be undertaken only with a minimum hemoglobin of eight grams per deciliter, although exceptions to this rule can and sometimes should be made if there is real urgency to correct the ophthalmologic problem. Children with homocystinuria have thrombotic tendencies when under GA, and measures to prevent and manage these need to be taken when operating upon such patients with cataract. In order to decrease the forces exerted on the globe by the extraocular muscles, it is recommended that the child be paralyzed and ventilated throughout the surgical procedure. This is said to be especially important during insertion of an implant.
Wound Construction and Closure
Decreased scleral rigidity and thin sclera in children mandate special attention to wound construction and closure during pediatric cataract surgery. The tendency toward collapse of the anterior chamber and prolapse of iris tissue can be countered to a great extent by constucting wounds that snugly fit instruments and permit essentially closed-chamber techniques. For example, if an irrigation/aspiration handpiece is being used for cortical aspiration, a 3-mm wound will minimize fluid loss and shallowing of the anterior chamber. Some surgeons, recommend creating a separate limbal stab wound for passing an anterior chamber maintainer to provide continuous infusion and prevent collapse of the anterior chamber.
Self-sealing sutureless wound construction has recently achieved great success and popularity in adult cataract surgery., Although one study has documented secure self-sealing of sutureless wounds following pediatric ECCE with posterior capsule preservation and IOL insertion, other surgeons who applied these techniques to children's eyes found a need to suture the wound at the conclusion of surgery because of aqueous leakage., A high frequency of wound leaks was also reported in a prospective study investigating the role of sutureless wound construction in childhood, with wound leaks seen in 100% of eyes of patients below 11 years of age who underwent ECCE+PPC+AV+IOL. The incidence of leakage was 33% in eyes of the same age group that had intact posterior capsule at conclusion of surgery. The explanation for this divergence between adult and pediatric experience probably is that low scleral rigidity in children causes fish-mouthing of the internal aspect of the wound, with inadequate apposition of the corneal flap to the overlying stroma [Figure:7]. Proper closure of such wounds using sutures requires a technique that ensures proper positioning of this flap. Although decreased induction of astigmatism associated with sutureless cataract wounds makes them appealing for use in adults, the occurrence and value of a similar effect in children has yet to be established. Based on the outcome data cited above, their use may not be appropriate to pediatric lens extraction.
A majority of pediatric cataract surgeons utilize 10-0 monofilament nylon for wound closure in lens extraction with or without IOL implantation, conforming to adult surgical practice. A distinct disadvantage of this material in pediatric use, however, is the difficulty of removing sutures that cause unacceptable persistent astigmatism or irritation, which usually requires general anesthesia because of insufficient patient cooperation. A substantial minority of surgeons therefore opt for absorbable sutures, most often polyglactin (Vicryl), generally either 8-0 braided or 10-0 monofilament. A single 7-0 Vicryl suture works well with the small wound required for LAV. Although the rapid healing of wounds in childhood makes the risk of dehiscence after suture resorption relatively low, some surgeons who prefer nylon argue that the more durable material provides useful added protection against accidental trauma to the eye in the months following surgery, particularly for the larger wound required for IOL insertion.
Use of Viscoelastic Agents
Viscoelastic substances can serve as highly useful adjuncts to performance of pediatric cataract surgery, particularly when IOL implantation is involved. The maneuvers most dependent on these agents are capsulorhexis and IOL insertion. Controlled anterior capsulorhexis is greatly facilitated by forcing the lens posteriorly and reducing its anterior convexity. This is best achieved with a highly retentive viscoelastic such as sodium hyaluronate 14 mg/mL (Healon GV, Pharmacia ophthalmics, Uppasala). Injection of viscoelastic between the anterior and posterior capsular leaflets after cortical aspiration adds significantly to the ease with which posterior capsulorhexis can be accomplished, and the implant inserted.
Management of Anterior Capsule
Handling the anterior lens capsule presents a particular challenge for the pediatric implant surgeon. Creation of an appropriate capsular opening is critical to enable lens placement "in the bag". Most surgeons now agree that the traditional "can opener" technique is not adequate for this purpose. In recent years, the technique of continuous curvilinear capsulorhexis (CCC) has gained many adherents among adult cataract surgeons. When this procedure is attempted in the usual manner on the pediatric lens, however, outward spiralling of the capsular tear typically occurs, making lens placement in the bag difficult or impossible. CCC can be used on very young eyes, but its successful application demands specifically pediatric experience and modification of technique. Tractional force must be directed centripetally at all times, rather than circumferentially. A novel and promising approach to capsulorhexis has recently been developed using an animal model that simulates the high degree of elasticity of the child's anterior capsule, but this technique has yet to prove itself clinically.
Some surgeons have reported good results from using suction /cutting vitrectomy instrumentation to create an anterior capsular opening [Figure:8]. This approach is somewhat more forgiving than capsulorhexis, yet provides similar resistance to radial tearing; it has worked well in the authors' experience. Vitrector capsulotomy requires orientation of the cutting port directly posteriorly toward the intact capsule, then applying brief bursts of full suction (250 mm Hg) to engage and cut tissue.
Choice of IOL
Of available lens materials, only polymethyl methacrylate (PMMA) has so far stood the test of time adequately to be considered appropriate for implantation in eyes with a life expectancy of many decades. Three-piece (with PMMA haptics; haptics made of polypropylene may not be biologically inert,), and one-piece (preferably newer models with haptics chemically modified for increased flexibility) C-loop designs have been the choice of most pediatric cataract surgeons in recent years.,
Wilson has shown that lens sizes of 12 mm are generally suitable for posterior chamber implantation in eyes more than 2 years old, with capsular fixation. Optic diameter and design do not appear to be particularly critical; despite the relatively large resting size of most children's pupils, edge effects seem not to represent a problem with smaller optics.
Selection of lens power has been one of the most controversial topics relating to pediatric IOL implantation. It is well known that the power required for aphakic correction declines precipitously during the first year of life, and to a considerable further degree during the ensuing childhood years. Thus, a pseudophakic eye that is emmetropic at age 1 year may become 5-10 diopters myopic by maturity. There is, however, a lack of long-term follow-up data on which to base predictions of the ultimate refraction of an eye that receives an IOL early in childhood. (The change that will occur may be different for pseudophakic than for aphakic eyes, given the dynamic control of ocular growth under the influence of visual experience). Furthermore, if an eye is rendered significantly ametropic at an early age, supplemental refractive correction in spectacle or contact lens form becomes essential to ensure optimal visual development, neutralizing much of the advantage of using an IOL.
Considerable polarity is seen with regard to the choice of appropriate power of the IOL for implantation in children. Surgeons have chosen lens powers to make the eye hypermetropic, emmetropic and even myopic. In their study on the growth of the eye after birth, Gordon and Donzis demonstrated that approximately 90% of the growth of the eyeball is complete during the first 18 months after birth. Since the overall increase in axial length from this age upto age eleven is close to two millimeters, many surgeons today veer towards making the eye hypermetropic by two diopters in children between two and four years of age. This reduces the residual myopia that occurs with growth of the eye which can be large, particularly if the eye is corrected for myopia. Exception to this rule is made for the child with unilateral cataract whose other eye needs optical correction for significant myopia or hyperopia; in such a case it seems appropriate to place the pseudophakic eye 1-2 diopters closer to emmetropia than the phakic eye.
Prior to the development of CCC, most IOLs were, almost by default, left partly or wholly supported by the ciliary sulcus. Since uveal tissues in the child are highly reactive, reliable in-the-bag placement has been viewed as a highly desirable goal by pediatric cataract surgeons. The significantly lowered incidence of severe postoperative uveitis described in several recent reports of childhood IOL implantation,,  seems largely attributable to improved success in achieving full capsular support for implants. Many surgeons, however, still consider the ciliary sulcus to be an acceptable alternative site of lens implantation in eyes that lack adequate capsule for in-the-bag implantation. Most do not consider anterior chamber IOL placement in a child, even in the absence of adequate capsular support.
A new technique developed by Gimbel consists of in-the-bag IOL placement followed by posterior curvilinear capsulorhexis (PCCC) and capture of the IOL optic by the PCCC [Figure:9], [Figure:10]. This approach was premised on the belief that 360 degree apposition of the anterior and posterior capsular leaflets would lead to formation of a Sommering's ring configuration anterior to the IOL and that lens epithelial cells would be kept in the anterior chamber, where they would be carried away with the aqueous fluid. Gimbel's preliminary results appear to support this view. Several issues still need to be resolved, however. The procedure is technically very challenging. There is a risk of inadvertantly exerting severe traction on the vitreous during PCCC (although this in theory should be prevented by prior copious injection of high viscosity viscoelastic between the capsule and the vitreous). There is also a possibility that late contraction of the capsular ring may cause displacement of the haptics, or even their extrusion from the bag. Clearly, more experience and longer follow-up are necessary before this approach can be fully evaluated, but it does show promise as a means of maintaining a clear visual axis and optimal IOL centration in very young eyes.
Postoperative examination of the young child is frequently limited in extent. Confirmation that the anterior chamber is formed and the red reflex visible may be all that is possible on the first postoperative day, but fortunately more than this is seldom mandatory. Inspection of the posterior pole of the fundus can and should be done before initiating visual rehabilitative measures. Intraocular pressure routinely ought to be measured at least once or twice a year after surgery, with the aid of sedation or general anesthesia if necessary.
Most pediatric cataract surgeons use a combination corticosteroid-antibiotic drops following surgery. The frequency can be 2 to 4 times a day for 1 to 2 weeks postoperatively in eyes undergoing LAV. More intensive steroid treatment and a cycloplegic is indicated in pseudophakic eyes. Gimbel et al believe that compared to other cycloplegics, atropine reduces the incidence of fibrin reaction in the postoperative period. In eyes showing intense or fibrinous inflammatory reaction in the anterior chamber, some surgeons prefer to increase topical medication, while others employ oral prednisone or methyl prednisolone, beginning at a dose of 1-2 mg/kg body weight per day and tapering rapidly over the second to third postoperative weeks.
Activity limitation is difficult to enforce with young children. It is the authors' practice to keep water out of the eye for one week after surgery, and to refrain from rough play and sports for 2-4 weeks. An eye shield is worn while sleeping until 1 month after surgery. Children are advised to use protective eyewear for sports indefinitely after cataract surgery, but there is no specific activity prohibition beyond 1 month postoperatively.
It is crucial to provide at least approximate optical correction of refractive error as soon as possible after cataract surgery in childhood, in order to minimize disruption of the process of visual development. Uncorrected aphakia is in many cases as damaging to vision as the cataract itself. Spectacle or contact lens correction of aphakia should be provided before the end of the second postoperative week. Ametropia exceeding 1 diopter of hyperopia or 4 diopters of myopia in a pseudophakic eye should be corrected with glasses or contact lens. Bifocal correction to optimize both near and distance vision may be helpful for visual rehabilitation of preschool children, and should definitely be provided for school age children.
Occlusion therapy for documented or presumed amblyopia is the last and often the most critical element of postoperative care in cases of unilateral or asymmetric cataract. Self-adhesive patches applied to the better-seeing eye are conventionally used, but other methods (e.g., spectacle mounted occluders, opaque or severe blur-inducing contact lenses) can be helpful in selected cases. (Atropinization of the better eye usually does not prove adequate treatment for deprivation amblyopia.) For infants under age 6 months, a few hours of patching a day is appropriate. Beyond age 6 months, occlusion for half the waking hours or more should be the goal. Between age 1 and 3 years, patching is typically very difficult, and may lapse altogether. From 3 to 5 years, though, effective amblyopia therapy is usually possible, and significant improvement in acuity can often be obtained even if earlier efforts met with failure. One to three hours of occlusion daily to maintain vision at the best level achieved ought to be continued until about 10 years of age.
With conscientious and persistent postoperative effort, ultimate visual acuity of 20/70 or better can be achieved in most children whose treatment for cataract is initiated within a few months after the onset of significant visual deprivation., , , ,  Dramatic improvement in deprivation amblyopia typically occurs within a month or two after starting effective treatment. If an eye operated on for unilateral cataract shows no evidence of useful central vision after 6 months of intense occlusion effort, it is probably best to discontinue treatment.
Co-existing Cataract and Microphthalmos
The presence of significant micropthalmos in an eye with cataract has prompted most surgeons to refrain from implantating an IOL during cataract extraction. Choosing the proper implant power for these eyes becomes problematic, since presently available IOL power calculation formulas become increasingly inaccurate for very short eyes. Also, the physical dimensions of adult-size IOLs may not be appropriate for microphthalmic anterior segments. Reports of increased postoperative glaucoma frequency associated with decreased corneal diameter raise additional concerns about the long-term safety of implantation in this context., Two published reports, however, indicate encouraging results in such cases., Continued observation of operated eyes is necessary to determine long-term results of IOL implantation in such eyes.
Anterior and Posterior Lenticonus
The term lenticonus refers to localized outpouching of the anterior or posterior lens capsule, usually in the central region. The capsule is thinner than normal in the involved area, and the bulging adjacent lens cortical material, although usually clear at birth, contains atypically formed and arranged lens epithelial cells that often opacify over time.
Anterior lenticonus is usually associated with Alport's syndrome but can be idiopathic. It may cause disabling visual symptoms that justify surgical removal of the lens even in the absence of opacification., Posterior lenticonus (or lentiglobus) is responsible for the most common form of unilateral developmental cataract in normal sized eyes. It is sometimes associated with a persistant hyaloid artey remnant. The presence of posterior lenticonus has been documented in the newborn, but it also has been reported to develop during infancy in a lens that was previously observed to be normal.
IOL implantation is usually the strongly preferred means of aphakic correction for eyes with posterior lenticonus and cataract, because the patients tend to present in the 1-4 year age range, are unilaterally involved, and have a good visual prognosis. Unfortunately, surgical handling of the abnormally thin and ectatic posterior capsule can be difficult, and it frequently ruptures,, potentially making in-the-bag lens placement difficult.
Lenticular subluxation with associated cataract is most often seen in multisystemic syndromes such as Marfan's disease, Wiel-Marchesani syndrome and homocystinuria. When lens removal is necessary (either because of cataract formation or because lens displacement creates an insurmountable obstacle to refractive correction), it is best accomplished using the pars plicata or limbal lensectomy with vitrectomy, followed by optical rehabilitation with spectacles or contact lenses.
Secondary IOL Implantation
Experience with secondary IOL implantation in childhood remains very limited, although in the future demand for this procedure is likely to become great. A few encouraging results have been reported., For now, however, the possibility of serious complications from additional major intraocular surgery weighs against its use except in cases where it appears to represent the only hope of overcoming or preventing severe amblyopia.
Infection and Inflammation
Infectious endophthalmitis is a rare complication of pediatric cataract surgery, with an incidence similar to that reported for adults. Treatment is similar: sampling of aqueous and vitreous for culture (under general anesthesia), followed by intravitreal injection of vancomycin 1mg plus either ceftazidime 2.25 mg or amikacin 0.4 mg. The added value of intravenous, subconjunctival, and topical antibiotics is debatable. In cases that do not respond within a few days after intravitreal injection, surgical vitrectomy should be considered.
Intense sterile inflammation, often associated with a large fibrin clot in the anterior chamber [Figure:11], is relatively common following cataract surgery with IOL implantation in early childhood. Hypopyon is rarely seen in such cases. If doubt exists, treatment for infection is appropriate. Meticulous removal of viscoelastic after lens implantation and use of large doses of intraoperative and postoperative corticosteroid and atropine (0.5% in infants and 1 % in older children) can help prevent or mitigate this occurrence.
Reopacification is a very frequent problem after pediatric cataract surgery., , [97 99] In infancy the rate of occurrence is nearly 100 percent unless a generous posterior capsulotomy and anterior vitrectomy is performed; cortical proliferation can span across formed vitreous quite readily at this young age. Older children show progressively less tendency to reopacify,, ,  but the rate remains considerably higher than for adults. Lack of a clear pupillary space not only poses a direct threat to visual development, but by making accurate retinoscopic refraction difficult it may further interfere with successful visual rehabilitation.
Secondary capsulotomy with the Nd:YAG laser sometimes provides a permanent solution to this problem, but in the youngest children reopacification may develop repeatedly sometimes necessitating secondary surgical membranectomy and vitrectomy are performed.,, 
The possibility of glaucoma developing months to years after surgery for childhood cataract must always be kept in mind., , ,  Because measurement of intraocular pressure in young children is difficult and tends to be done infrequently, delay in diagnosis is common. An important initial clue is often provided by the documentation of more rapid than expected decline (myopic shift) in aphakic refractive power.
Most cases of postoperative pediatric glaucoma are open angle. Because the risk of this complication seems to be significantly higher for eyes that had small corneal diameters, nuclear cataracts or PHPV, it may represent a disturbance of trabecular meshwork function developmentally related to the underlying lens disorder rather than simply a consequence of surgery. Treatment with standard medical and surgical approaches is very often unsuccessful, even when antimetabolites are used in conjunction with filtering surgery. Implantation of an aqueous shunt (Molteno or Krupin implant) is more likely to correct the problem, and may be the most appropriate initial operative therapy. In some cases, repeated cyclodestructive procedures prove necessary.
Pupillary block glaucoma caused by vitreous filling the pupillary space may occur following lensectomy with anterior vitrectomy for cataract or PHPV in infancy. In fact, occupation of the pupil by formed vitreous is seen at several years of age in most eyes that have had this surgical procedure before age 6 months. Presumably tertiary vitreous is still developing in the young infant, and increases in volume to replace the material removed surgically. Peripheral iridectomy or iridotomy with or without repeat vitrectomy usually lowers elevated pressure in such cases. Prophylactic peripheral iridectomy should probably be performed as a part of any cataract operation in infancy.
Retinal detachment was a common and much feared complication after pediatric cataract surgery in the past.,,  Frequently the problem did not develop until the child had reached adolescence or young adulthood, and repair was often unsuccessful. Since the advent of current techniques of lens aspiration, retinal detachment appears to occur much less often, but it must be kept in mind that the oldest patients who have been treated with present day procedures are only now approaching age 20.
Cystoid macular edema is very seldom a clinical problem following pediatric cataract surgery, even in eyes in which an anterior vitrectomy has been performed.,  Bullous keratopathy is another complication of adult cataract surgery that rarely is seen in children in the short term. The increased endothelial cell density in children is likely to be responsible for this.
Long-term follow-up of operated eyes is necessary to determine the actual incidence of this complication after pediatric cataract surgery.
HORIZONS AND VISTAS
Pediatric cataract surgeons now stand at the threshold of a new era, filled with the kind of promise and excitement that greeted adult cataract surgeons nearly two decades ago as they entered the age of modern extracapsular surgery and intraocular lens implantation. We are fortunate to have the opportunity to build on the immense progress that has taken place in the field since then. It is well to remember, however, the many technical options that have been tried and abandoned in recent years past, and to temper our enthusiasm for innovation with appropriate restraint when we consider that our patients will live with the results of our efforts long beyond the end of our professional lifetimes.
There are a number of specific areas in which the future will hopefully bring solutions to current problems or concerns. One major wish, of course, is for confirmation of the long term safety of current techniques and devices used in IOL implantation. If no unexpected significant incidence of late complications in either adults or children emerges over the next 15 years, we may well witness almost as complete a substitution of pseudophakia for aphakia in children as has occurred in adults over the past 15 years. Longer observation will also provide much needed further information concerning the refractive maturation of pseudophakic eyes.
Technical advances specifically developed for pediatric IOL surgery are much awaited, particularly with reference to wound construction and capsule management. Better techniques for managing pseudophakia in infant eyes are needed before this "last frontier" of lens implantation can be conquered. Secondary IOL surgery, particularly in eyes with little or no residulal lens capsule, represents an important challenge for future surgeons. Perhaps key developments will also occur in the design of implants themselves-one can conceive of models that permit secondary modification of refractive power, for example. Finally, it is not unreasonable to hope for new keratorefractive approaches to aphakia that may fulfill the promise epikeratophakia could not keep. Whatever happens, pediatric cataract surgeons can at least expect to live in an interesting time for many years to come.
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