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| CURRENT OPHTHALMOLOGY |
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| Year : 1993 | Volume
: 41
| Issue : 2 | Page : 51-70 |
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Current concepts in the diagnosis and management of developmental glaucomas
Anil K Mandal
VST Centre for Glaucoma Care, L.V. Prasad Eye Institute, Hyderabad, India
Correspondence Address:
Anil K Mandal
L.V. Prasad Eye Institute, Road No. 2, Banjara Hills, Hyderabad - 500 034
India
 Source of Support: None, Conflict of Interest: None  | Check |
PMID: 8262604 
Developmental glaucoma is a global problem and has a broad range of ocular manifestations and is sometimes associated with systemic disorders and syndromes. It poses a major diagnostic and management problem to the ophthalmologists. A proper diagnostic evaluation under general anesthesia is advisable for all children who do not cooperate for an office examination. Surgery remains the principal therapeutic modality in the management of developmental glaucoma and medical therapy is limited to a supplemental role while the child is being prepared for surgery. Conventional angle incision surgery (goniotomy and trabeculotomy ab externo) is uniquely valuable in the management of primary developmental glaucoma, while combined trabeculotomy cum trabeculectomy offers the best hope of success in advanced cases. In recent years, artificial drainage devices such as the Molteno implant seem to be promising for safe and effective pressure control in children with refractory developmental glaucoma. Visual rehabilitation involves correction of refractive errors, removal of opacities in media (i.e. cataract or corneal scarring) and aggressive amblyopia therapy. Early diagnosis, prompt institution of therapy combined with commitment from the family for postoperative follow-up care are critical for the restoration of good visual function. Keywords: Developmental glaucoma, congenital glaucoma, buphthalmos, goniotomy, trabeculotomy, combined trabeculotomy and trabeculectomy
How to cite this article:
Mandal AK. Current concepts in the diagnosis and management of developmental glaucomas. Indian J Ophthalmol 1993;41:51-70 |
How to cite this URL:
Mandal AK. Current concepts in the diagnosis and management of developmental glaucomas. Indian J Ophthalmol [serial online] 1993 [cited 2021 Dec 8];41:51-70. Available from: https://www.ijo.in/text.asp?1993/41/2/51/25621 |
Developmental glaucoma refers to glaucoma associated with developmental anomalies of the eye that are present at birth. These include both primary congenital glaucoma (isolated trabeculodysgenesis) and glaucomas associated with systemic developmental anomalies or those of the eye. It is an uncommon disease and its impact on visual development is extreme. The primary objective in the management of developmental glaucomas is to normalise and permanently control the intraocular pressure thereby preventing loss of visual acuity; to preserve the visual field and ocular integrity; and to stimulate the development of binocular stereoscopic vision. Clinicians should be familiar with the pathology, pathogenesis and the clinical course of the ailment before they can treat it. The aim of this communication is to highlight current concepts in the diagnosis and management of developmental glaucomas.
| I. PATHOLOGY AND PATHOGENESIS | |  |
The embryologic basis of all developmental glaucomas is fetal maldevelopment of the iridocorneal angle, called goniodysgenesis:
Trabeculodysgenesis Maldevelopment of the trabecular mesh-work
Iridodysgenesis : Maldevelopment of the iris
Corneodysgenesis : Maldevelopment of the cornea
These may appear either singly or in combination. Isolated trabeculodysgenesis is the hallmark of primary developmental glaucoma.
Barkan (1955) initially assumed that a thin imperforate membrane covering the anterior chamber angle of the eyes prevents aqueous humour outflow and leads to increased intraocular pressure [1].The presence of "Barkan's membrane" was subsequently championed by Worst in 1966 [2],[3] However, light microscopy as well as electron microscopic studies provided no evidence of a membrane in any of the specimens [4],[5],[6][7],[8],[9],[10].
Based on the clinical and histopathological observations of the current concepts of normal anterior segment development, the mechanism of developmental glaucomas has been attributed to a developmental arrest, late in gestation, of certain anterior segment structures derived from neural crest cells (Angular neuro-cristopathies) [11]
Anderson (1981) [4] provided histopathological proof that in eyes with primary congenital glaucoma, the iris and ciliary body have the appearance of an eye in the seventh or eighth month of gestation rather than one which is at full term development. The iris and ciliary body fail to recede posteriorly and the iris insertion and ciliary body overlap the posterior portion of the trabecular meshwork. He believed that in infantile glaucoma, the thickened trabecular beams prevent the normal posterior migration of the ciliary body and iris root. Thus, observations suggest that the developmental immaturity of the outflow system renders it functionally incompetent [12]
High intraocular pressure causes corneal clouding, rapid enlargement of the globe and limbal stretching. The corneal diameter can enlarge upto as much as 16 to 17mm. There may be stretching of the Descemet's membrane, the corneal endothelium resulting in linear ruptures (Haab's striae) which can lead to corneal stromal and epithelial edema as well as corneal scarring if the problem is chronic. Sclera also expand slowly under the influence of increased intraocular pressure and the associated scleral thinning brings about increased visibility of the underlying uveal tissue in neonates and causes the sclera to appear blue. Thus, in the advanced stages of the disease, the eye is enlarged in all dimensions, resembling an ox eye (Buphthalmos). The optic nerve head in neonates and children is more vulnerable to increased intraocular pressure than adults and in advanced stages of the disease, the disc may show complete cupping. However, optic disc cupping may be reversible with normalization of intraocular pressure particularly in the early stage. Such reversal is very unusual in adults with intraocular pressure induced optic disc damage.
| II. CLINICAL PRESENTATION | | |
The classic triad [13] of manitestations that lead the clinician to suspect congenital glaucoma include:
Epiphora (i.e. excessive tearing),
Photophobia (i.e. hypersensitivity to light) and
Blepharospasm (i.e. squeezing of the eyelids)
These symptoms are due to corneal irritation that accompanies corneal epithelial edema caused by elevated intraocular pressure.
The parents may first notice that their baby keeps its eyes closed [Figure - 1] when exposed to sunlight. Their usual reaction is to provide some shade, in the belief that the baby is merely showing normal sensitivity to light. In severe cases, the baby keeps its eyes closed constantly and hides its face even from ordinary lighting. The child may become irritable to the point of burying his or her head in a pillow to avoid the pain of photophobia [14]sub .[Figure - 2].
The parents may notice clouding of the black part of the eye with or without an increase in the size of the eye ball [Figure - 3][Figure - 4]. Primary infantile glaucoma may also present as a "red eye" mimicking conjunctivitis and delaying correct diagnosis [15],[16],[17]
Enlargement of the eye occurs under the influence of elevated intraocular pressure with major enlargements occuring at the corneo-scleral junction. Younger children are more likely to have a corneal haze while older children more commonly present with frank corneal enlargement or buphthalmos [18] [Figure - 5]. As the axial length of the globe increases, myopia and astigmatism result. Myopic astigmatism and anisometropia are particularly common in cases of unilateral or asymmetric primary developmental glaucoma. Pain is unusual in older children with primary developmental glaucoma.
| III. THE DIAGNOSTIC EXAMINATION | | |
In order to arrive at a proper diagnosis, an examination under general anesthesia is advisable for all children who do not cooperate in an office examination.
A. INITIAL EXAMINATION (Office examination)
During the initial office visit, the examiner may be able to observe the degree of photophobia, blepharospasm and tearing. Ideally, the examiner captures the infant's open eye attention so as to observe the corneal size and clarity without touching the baby's face [19] Adequate examination including applanation tonometry can be performed in waking infant who is kept hungry and fed at the time of the test.
Usually a complete ocular examination including slit lamp examination, applanation tonometry, gonioscopy and optic nerve head evaluation can be performed in the office in children over the age of 5 years and with some training in children as young as 3 years. If necessary, a mild sedative, such as chloral hydrate syrup (25-50mg/kg body weight) can be given (chloral hydrate can mildly lower IOP), but this is usually unnecessary if patience and gentleness are excercised. Visual field examination can be performed at 5-6 years of age but the patient's short attention span and poor fixation often prevent a detailed study. The older and more cooperative the child, the more detailed the examination.
B. EVALUATION UNDER GENERAL
ANESTHESIA (EUA)
The basic equipment necessary to perform an adequate examination under anesthesia to ascertain the correct diagnosis includes the items listed in [Table - 1].
The following examinations are performed as listed in [Table - 2].
1. External Examination
It is important to detect and exclude the other conditions associated with epiphora, photophobia and blepharospasm as mentioned in [Table - 3].
The most common cause of epiphora in the newborn and the infant is blocked tear duct (CNLDO). Photophobia is not associated with this problem. CNLDO is differentiated from congenital glaucoma in that the former condition is associated with fullness of the lacrimal sac which is often accompanied by chronic muco-purulent discharge.
2. Corneal Assessment
The cornea is examined to document the presence or absence of breaks in Descemet's membrane (Haab's striae) and corneal enlargement in order to distinguish the glaucomatous signs from other corneal abnormalities listed in [Table - 4].
The corneal diameter is measured with calipers, from white to white along the horizontal meridian, as the vertical meridian is artifactiously narrowed by encroachment of sclera at the superior limbus.
The normal neonatal horizontal corneal diameter is approximately 10 to 10.5mm, increasing by 0.5 to lmm in the first year [16]. Enlargement of corneal diameter to more than 12mm in the first year of life is highly indicative of developmental glaucoma [13]. Corneal enlargement due to increased intraocular pressure predominantly occurs before the age of 3 years [20] but the sclera may be deformable until about 10 years [21].
Increased intraocular pressure also stretches the corneal endothelium and Descemet's membrane, resulting in breaks in these layers known as Haab's striae [17],[20] [Figure - 6]. These are typically horizontal and linear when they occur centrally in the cornea but parallel and curvilinear to the limbus when they occur in the periphery [17],[20],[22]. Birth trauma (forceps injury) may also cause tears in Descemet's membrane with resultant corneal oedema and clouding mimicking primary infantile glaucoma. There is no unequivocal way of determining whether breaks in Descemet's membrane are due to birth trauma or increased intraocular pressure. It has been stated that Descemet's membrane breaks resulting from birth trauma are oblique or vertically oriented [23] Obstetrical corneal trauma is usually unilateral and more commonly affects the left eye because of higher incidence of left occiput anterior presentation of the infant's head at birth. There are attendant signs of periorbital skin changes as a result of trauma (bruising), normal intraocular pressure and no corneal enlargement [20].
3. Refraction
Determination of refractive error (if media clarity permits), and in particular assessment of astigmatic change by streak retinoscopy, are methods used to recognise ocular enlargement and distortion for the purpose of diagnosis and to establish a baseline against which to judge future progression.
In particular cases of congenital glaucoma, while myopia is a common finding, its magnitude does not usually reach the expected value due only to the exaggerated enlargement of the eye ball. The final refraction will also be influenced by other changes induced by the disease in other eye structures such as:
(a)A more flattened cornea (eyeball enlargement and corneal growth cause its flattening)
(b)Decrease in lens thickness (when the eyeball enlarges, the scleral ring adjacent to the ciliary body also increases its diameter causing stretching of the zonular fibres, thus decreasing the lens thickness)
(c) Deep anterior chamber due to relative backward positioning of the lens, which influences refraction of the eyes affected by congenital glaucoma.
All these factors contribute to the so called "emmetropisation" which is constituted by harmonization among the different, interdependent parameters that have an influence on ocular refraction.
4. Tonometry
Intraocular pressure should be measured with a Perkins hand-held applanation tonometer [Figure - 7] or electronic tonometer (tonopen). Indentation tonometry (Schiotz) is very unreliable in children because the foot plate is not adapted to the very disturbed corneal curvature and because scleral rigidity is not known. In cases of scarred and edematous corenas, the MackayMarg tonometer is generally considered the most accurate [24],[25],26] but it is no longer being manufactured.
All anesthetics alter intraocular pressure of patients with infantile glaucoma [27] seemingly in the plane of anesthesia and as a direct effecf on the cardio-vascular tonus [28]. A rapid lowering of intraocular pressure occurs particularly with halothane (fluothane) [27],[28],[29] and readings 15-20mm below the (true) measurement can be obtained [37] Agents which achieve only light anesthesia and those that induce deeper anesthesia only slowly such as diethylether, cyclopropane [28] or ketamine, allow the intraocular pressure to be measured somewhere between the artifically elevated intraocular pressure of the "excitement" stage of anesthesia or the actual intraocular pressure elevating effect of cyclopropane or succinyl choline [28] (atleast transiently), and the artificially lowered intraocular pressure of deep anesthesia, especially with halothane. Standardisation of anesthesia for intraocular pressure measurement for diagnosis and follow-up of infantile glaucoma is obviously highly desirable and inconsistent readings should always be interpreted considering the patient's general stage of anesthesia and the specific anesthetic used [28].
The normal intraocular pressure in an infant under halothane anesthesia is said to be approximately 9-10 mm Hg [30] and a pressure of 20mm Hg or greater should arouse suspicion [30]. The most reliable method of measuring intraocular pressure is probably with the child awake, in a cooperative patient, and the Perkins tonometer has been found to be particularly suitable in this situation [31]. In one study, the mean intraocular pressure in unanesthetised newborns was 11.4 ± 2.4mm Hg [32].
There is no ideal method to measure intraocular pressure. Our preference is the hand-held Perkins applanation tonometer used at the earliest stage of inhalation anesthesia before intubation to reduce errors releated to anesthesia, relying on the rest of the examination to interpret the importance of the intraocular pressure reading.
5. Slit Lamp Examination or Examination
under Microscope
This portion of the examination is best performed with a portable hand held slit lamp or binocular operating microscope. The corneal findings are judged under magnification and stereopsis. The anterior chamber in primary congenital glaucoma is characteristically deep, especially when the globe is distorted. The iris is typically normal, although it may have stromal hypoplasia with loss of the crypts. Other developmental glaucomas are characterised by a spectrum of changes in the anterior segment structures.
6. Gonioscopy
Evaluation of the anterior chamber angle is essential for the accurate diagnosis of developmental glaucoma. The Koeppe (14-16mm) lens provides the surgeon with the appropriate view of the angle [Figure - 8]. If corneal clouding is marked, it could preclude a view of the angle. Anterior chamber angle in childhood differs significantly from that of adults. In the normal newborn eye, the iris usually inserts posterior to the scleral spur. Trabecular meshwork appears more transluscent than that of the adult.
Gonioscopy of the eye with primary congenital glaucoma reveals an anterior insertion of the iris directly into the trabecular meshwork [4],[33][Figure - 9]. This iris insertion is most commonly flat, although a concave insertion may also be seen. The surface of the trabecular meshwork may have a stippled appearance and the meshwork may appear thicker than normal. Sometimes, loops of blood vessels from the major arterial circle and fine fluffy tissue may be seen in the angle on gonioscopy.
7. Ophthalmoscopy
Evaluation of the optic disc is an essential part of the examination and other causes of optic nerve head abnormalities must be excluded, as listed in [Table - 5].
Ophthalmoscopy under GA is easy and is done best through a semi-dilated pupil. If surgery is contemplated, mydriasis can be obtained by using a drop of 1 % cyclopentolate and a good view can be facilitated by the use of Koeppe contact lens, which neutralises irregular corneal reflexes and also improves the view through a mildly dilated pupil allowing one to see the entire nerve head in one field.
The optic nerve head in normal newborn is typically pink but may have slight pallor and a small physiological cup is usually present [34]. A cup-disc ratio greater than 0.3 and asymmetry are suggestive evidence of developmental glaucoma. The infant glaucomatous cup is more commonly round, steep-walled and central and the cup tends to enlarge circumferen
tially with the progression of glaucoma. To provide records for future comparison, it is best to make a careful drawing or to take photographs of the optic nerve head.
8. Ocular Fundus Photography
This is best done when infant is anesthetized using a hand-held Kowa camera or a specially adapted fundus camera is positioned vertically to obtain fundus pictures.
9. Ultrasonography
Ultrasonic ocular biometry has been recommended by some investigators for routine use in diagnosis and follow up of congenital glaucoma [35],[36],37],[38] Normal axial length in an infant ranges from 17.5 to 20mm and increases to 22mm in length by one year of age. Results confirmed the clinical value of echographic biometry for both the diagnosis of developmental glaucoma in cases with borderline intraocular pressure, and that of glaucoma in the fellow eye of patients with presumed unilateral disease. The method has proved its efficiency in the follow up of patients with developmental glaucoma who had undergone surgery [35],[36],[37],[38].
C. INTERPRETATION OF THE EXAMINATION
FINDINGS
After successful completion of the examination under anesthesia, one is left with little doubt about the diagnosis of primary infantile glaucoma when one comes across the typical findings of corneal enlargement, optic nerve head changes and buphthalmos in an infant [19] (See Chart 1). It is always advisable to postpone the diagnosis and therapy for 3 to 4 weeks until a repeat examination under anesthesia is done when the examiner comes across atypical findings in the first attempt but in case all other features are suggestive and intraocular pressure is normal, the examiner may assume a normal intraocular pressure because of the artificial lowering of the intraocular pressure during anesthesia and proceed with surgery. It is also important to inform the parents about the possible diagnosis of primary infantile glaucoma before the examination and to obtain a consent in case surgery is indicated. This will allow the surgery to be performed in the same sitting which would save the child from the harmful effects of repeated anesthesia within a short time. The appropriate therapy can also be instituted at the earliest.
| IV. FACTORS INFLUENCING THERAPEUTIC DECISIONS | | |
The choice of therapy in developmental glaucomas depends on a variety of factors (See chart 2). The most important of these is the structural defect [39],[10] associated with the elevated intraocular pressure. In addition, age, corneal clarity and associated systemic syndromes can influence the choice of therapy.
A. STRUCTURAL DEFECTS
1. Isolated Trabeculodysgenesis
It is the hallmark of primary developmental glaucoma and is highly responsive to goniotomy and trabeculotomy ab externo.
2. Irido-Trabeculodysgenesis
When other defects are associated with trabeculodysgenesis, the success rate of goniotomy and/or trabeculotomy is lowered. In iridodysgenesis, where the only iris defect is hypoplasia of the anterior stroma, good response to surgery has been reported. However, when the iris defect is abnormal vessels that appear to wander somewhat irregularly across the surface of the iris, then the prognosis is extremely grave. In such cases, multiple surgeries are usually needed.
3. Irido-Corneo-Trabeculodysgenesis
In patients with Axenfeld-Rieger's anomaly, surgical therapy does not have good prognosis and medical therapy is used initially. Often, medical therapy too is unsuccessful, therefore, surgical intervention becomes necessary. In such cases, surgery should be tailored to the specific cause.
B. AGE
The age of the child at the onset of glaucoma is also a factor in choosing appropriate therapy. In general, children under the age of 3 years are best treated surgically. Children over 3 years of age deserve a trial of medical therapy unless a specific defect of trabeculodysgenesis is seen.
C. CORNEAL CLARITY
In situations, where corneal clouding prevents adequate visualisation of the trabecular meshwork, goniotomy is technically impossible. Trabeculotomy ab externo has to be performed as the initial surgical procedure [41],[42]
D. CORNEAL DIAMETER
Corneal enlargement is a poor prognostic factor in the management of the developmental glaucoma [43]. It is generally accepted that the success of goniotomy is not as good in eyes with significant buphthalmos. Barkan [44] felt that eyes with corneal diameter greater than 15mm are not suitable for goniotomy. I feel that in patients with significant increase in corneal diameter, goniotomy is technically difficult to perform and ab externo combined trabeculotomy cum trabeculectomy should be the initial procedure of choice.
E. SEVERITY OF GLAUCOMA
In advanced cases of developmental glaucoma, I prefer to perform ab externo combined trabeculotomy cum trabeculectomy, because it offers the highest success rate in such a situation.
F. SYSTEMIC SYNDROMES
1. Sturge-Weber Syndrome
When glaucoma is present in infancy, developmental anomalies that obstruct the aqueous outflow are thought to predominate [45] and goniotomy or trabeculotomy is the surgical procedure of choice. When glaucoma in Sturge-Weber syndrome has its onset in later life, it is thought to be predominantly because of elevated episcleral venous pressure [45]. Angle defect is less severe and sometimes minimal. In such patients medical therapy should be tried first. If medical therapy fails, surgery should be performed on these eyes [46],[47],[48], I prefer to use a technique combining ab externo trabeculotomy and trabeculectomy in such cases. I feel that a combined surgical approach offers the best hope of success in such a condition.
2. Lowe's Syndrome
Hemorrhage frequently accompanies surgery, therefore medical therapy should be tried initially. If it fails, surgery may be attempted but prognosis is poor [49].
| V. THERAPY | | |
Primary congenital glaucoma is essentially a surgical disease. Medical threapy is accorded a supportive role to reduce the intraocular pressure temporarily, to clear the cornea, and to facilitate surgical intervention. For the most part, medical management for congenital glaucoma is used only to prepare the child for surgery [28],[50]
A. MEDICAL THERAPY
1. Miotics
Pilocarpine may be used at 1 to 2% concentration topically every 6 to 8 hours but topical application of miotics is not very effective because of the abnormal insertion of the ciliary muscle into the trabecular meshwork. [7],[10].
2. Beta Blockers
Timolol, the most commonly used medication for treatment of developmental glaucoma, is a non-selective beta 1 and beta 2 adrenergic blocker that reduces intraocular pressure by reducing aqueous inflow.
Timolol in 0.25% and 0.5% solution may be used cautiously in children with developmental glaucoma [51],[52]. Although it has not yet been approved for use in children, studies have shown minimal side effects in short term-use. Selective beta blockers like betaxolol may be safer than timolol in children with asthma [53].
3. Carbonic Anhydrase Inhibitors (CAIS)
Acetazolamide either alone or in combination with miotics, in an oral dose of 10 to 15mg/kg of body weight every 6 hours is safe and well tolerated by the infants. It lowers intraocular pressure and reduces corneal edema as a prelude to surgery [28],[54]. Side effects from short-term use of carbonic-anhydrase inhibitors in infants and young children are rare.
B. SURGICAL THERAPY
1. Goniotomy
After the introduction of clinical gonioscopy, Otto Barkan (1936) modified the de Vincentiis' operation (1892) by using a specially designed glass contact lens to visualise the angle structures while using a knife to create an internal cleft in the trabecular tissue. He called the operation "goniotomy" [19],[44],[55],[56],[57],[58],[59],[60],[61]
The objective of goniotomy is to incise the obstructing tissue that causes the retention of aqueous and thereby restore the access of aqueous to Schlemm's canal, thus maintaining the physiological direction of the flow.
Results of goniotomy reported by various authors show a near uniform success rate of 80% in primary infantile glaucoma [60],[62],[63],[64],[65],[66],[67][68],[69],[70] Goniotomy appears to be as effective as external trabeculotomy in this condition. It appears that goniotomy is most successful in patients in whom glaucoma is recognised early and treated between I month and 1 year of age. Early diagnosis and prompt treatment of this disease are important if good results are to be obtained. The severity of the filtration angle defect must also be considered in determining success with goniotomy.
2. Trabeculectomy Ab Externo
Trabeculectomy ab externo or external trabeculotomy as practised today is an alternative to goniotomy for the surgical treatment of congenital and childhood glaucomas. It can be used even when corneal haze prevents an adequate gonioscopic view which is a prerequisite for performing goniotomy.
Simultaneously and independently described by Buriani [71],[72] and Smith [73] in 1960, trabeculotomy ab externo has given results better than goniotomy. On March 25, 1960, without the aid of an operating microscope, the first external trabeculotomy was performed by Burian on a young girl with Marfan's syndrome and glaucoma [71]. At about the same time in London, Redmond Smith, another early microsurgeon, developed an operation that he called "Nylon filament trabeculotomy [73]. This involved cannulating Schlemm's canal with a nylon suture at one site and threading the suture circumferentially, then withdrawing it at another site and pulling it tight like a bowstring. The surgical technique of trabeculotomy ab externo is basically a combination of that originally evoked by Burian and Smith and modified by Harms [74],[75], Damnheim [76], [77] and McPherson [78],[79],[80]
Advantages
My preferred operation is trabeculotomy ab externo, which has a number of major advantages [81]sub over the alternative operation of goniotomy.
(i) A trabeculotomy is anatomically more precise in rupturing the inner wall of the Schlemm's canal and trabecular meshwork, creating continuity between the anterior chamber and Schlemm's canal.
(ii) Trabeculotomy is easier for a well-trained microsurgeon because it does not require the introduction of sharp instruments across the anterior chamber.
(iii) There is no need for the surgeon to adapt to the visual distortion produced by the operating gonio-prism.
(iv) Success of trabeculotomy depends only on the type of angle anomaly and is not on the severity of glaucoma, the size of the cornea or the presence of corneal edema, all of which have been reported to influence the success of goniotomy [16],[82]
(v) Trabeculotomy produces less surgical trauma as the anterior chamber is entered only briefly. There is lower incidence of postoperative cataract and fewer postoperative complications [81].
(vi) Trabeculotomy has a higher documented success rate than goniotomy [16],[43],[78],[82],[83]
In patients with a scarred and edematous cornea, the goniotomist has the choice of either operating with no view of the operation site or doing a trabeculotomy. Most surgeons would prefer to do a trabeculotomy than operate "blind". Thus the goniotomist, who may have little experience with trabeculotomy, uses this procedure in difficult eyes. This is an argument for using trabeculotomy in all cases and gaining experience with the procedure in easier and more predictable operations.
The popularity of trabeculotomy ab externo as an initial procedure in the surgical management of developmental glaucoma has been championed by a number of authorities [27],[41],[62],[72],[74],[75],[76],[77],[78],[79],[80],[81],[82],[83],[84],[85].
3. Combined Trabeculotomy cum
Trabeculectomy (Combined Trab-Trab)
I prefer to use a technique combining ab externo trabeculotomy with trabeculectomy in most cases of developmental glaucoma.
The trabeculotomy is performed to remove the possible obstruction to the aqueous outflow by a congenital angle deformity while the trabeculectomy is included to bypass the episcleral venous system. In other words, the combined procedure is designed to deal with both possible mechanisms associated with some forms of developmental glaucoma, eg. The Sturge-Weber syndrome [86].
In my observation, compared to the Western population, a larger number of Indian patients present with corneal clouding and edema in which goniotomy is technically impossible [135]. External trabeculotomy is the initial procedure of choice. Another important consideration is that while most patients had symptoms suggestive of congenital glaucoma at birth or within 6 months of birth, patients usually present late because of poverty, illiteracy, ignorance and inadequate eye care facilities in remote corners of the country. In such advanced cases, I prefer to perform combined trabeculotomy cum trabeculectomy which offers the best hope of success.
Surgical Technique
The patient is usually a child and general anesthesia is required.
After the child is anesthetised, the operative field is prepared with antiseptic solution.
A surgical microscope designed for ophthalmic surgery is a must.
A limbus-based conjunctival flap is raised (7mm from the limbus) with blunt-tipped westcott scissors and plain forceps and the dissection is usually done in the episcleral plane [Figure - 10]. Hemostasis is meticulously maintained throughout the dissection of the conjunctival flap. The author uses a bipolar underwater cautery in an effort to minimize trauma to the tissue [Figure - 11].
Retracting the conjunctival flap gently towards the pupil, light cautery is applied on the sclera to outline the sides of a 4mm equilateral triangle with its base at the limbus.
A one-half thickness scleral incision is then made with a razor-blade chip along the V outlined by cautery. Here we must bear in mind that the sclera in a buphthalmic child is usually much thinner than the adult eye.
A partial thickness scleral flap is then dissected toward the limbus using a No. 57 Beaver blade. The flap is held with Pierse-Hoskins forceps during the dissection.
The author perfers triangular flap as it allows adequate exposure of the Schlemm's canal and involves less scleral dissection than a rectangular flap [Figure - 12].
Care should be taken to maintain the same plane while dissecting the scleral flap, especially near the limbus.
Surgical landmarks and anatomy of the limbal region should be carefully identified before one can proceed to the next step [Figure - 13].
Closest to the limbus is a transparent band of deep corneal lamellae. Behind that is a narrow greyish blue band, which represents the trabecular meshwork, following which is the white, opaque sclera. The junction of the posterior border of the trabecular band and the sclera is the external land-mark to the scleral spur and the land-mark to the canal of Schlemm [Figure - 13]. In most eyes, this is situated between 2 and 2.5 mm behind the surgical limbus.
A 2x2mm trabeculectomy flap is outlined without penetrating the anterior chamber [Figure - 13]
A central radial incision is then made across the scleral spur [Figure - 13] The objective of this radial incision is to cut the external wall of Schlemm's canal and to avoid entering the anterior chamber. It is importnat to bear in mind that Schlemm's canal is separated from the anterior chamber only by the trabecular meshwork.
This is the most delicate step in the operation and demands the most micro surgical skill. Under high magnification the radial incision is gradually deepened with a razor blade-chip until it is carried through the external wall of Schlemm's canal, [Figure - 13] at which point there is gush of aqueous, occasionally mixed with blood. In my experience, a drop of aqueous is more common than a drop of blood. The dissection is carefully continued through the external wall until the inner wall of the canal becomes visible. The inner wall is characteristically slightly pigmented and is composed of criss-crossing fibers. Vannas scissors are used to enlarge the lumen of the canal. Some surgeons confirm passage into the canal by passing a 6-0 nylon suture into the canal, as described by Smith [73].
The internal arm of the trabeculotome is introduced into the canal using the external parallel arm as a guide.[Figure - 14][Figure - 15][Figure - 16][Figure - 17].
Once 90% of the trabeculotome is within the canal, it is rotated into the anterior chamber and rotation is continued until 75% of the probe arm length has entered the chamber. Then the rotation is reversed and the instrument is withdrawn. About 2 to 2 1/2h clock hours of the internal wall of Schlemm's canal and trabecular meshwork are disrupted by the movement of the trabeculotome into the anterior chamber. The trabeculotome is then passed into the Schlemm's canal on the other side of the radial incision and rotated into the anterior chamber. In total, about 100° to 120° of trabecular meshwork is ruptured by this technique.
The most difficult pass for a right-handed surgeon is to introduce the internal arm of trabeculotome into the Schlemm's canal to the right of the radial incision. This pass should therefore be done first while the chamber is deep and clear of blood.
It is important that no force be used when introducing the probe into the canal, as this will create a false passage. If the probe does not slip easily down the canal, it should be withdrawn and dissection of the outer canal continued until the surgeon is satisfied that all fibres of the outer wall are removed. The probe is then reintroduced into the canal. As the probe passes into the anterior chamber, rupturing the inner wall of the canal, there should be some slight resistance and there may be a little intracameral bleeding [Figure - 18] from the inner wal1 [78],[79][80]. This bleeding is typical and perhaps even a favourable sign indicating that communication has been created between canal of Schlemm and the anterior chamber. This bleeding is innocuous and almost always clears by the following day.
The important point is that the probe should pass with ease along the canal and from the canal into the anterior chamber without forcing it.
The probe is swept in a plane parallel to the iris. As the probe is swung from the canal into the anterior chamber, the surgeon should carefully watch the iris for movement, particularly if the probe passes easily. Movement of the iris or totally unresisted passage of the probe implies that the probe is in the anterior chamber and touching the iris roof. If not corrected this may cause an iridodialysis. The probe should be immediately withdrawn without continuing its entry into the anterior chamber and replaced, keeping the tip of the probe slightly anterior so that it does not prematurely rupture the inner wall.
The cornea should also be carefully monitored to, ensure that the probe does not rip through the sclera, cornea and Descemet's membrane. This is easy to detect because small air bubbles appear in the cornea as the probe rutpures through corneal lamellae. The probe needs to be repositioned, pushing the tip a little posteriorly.
The trabeculotomy has been completed and now trabeculectomy has to be performed. The incision into the anterior chamber is deepened by careful dissection with the microblade until the opening is large enough to introduce a straight or angled Vannas scissors, with which the anterior incision is completed. Then the radial incision and finally the posterior incision just anterior to the scleral spur and parallel to the limbus are made, and trabecular block is removed. The iris blocks the trabecular opening maintaining the anterior chamber, which should remain formed throughout the procedure.
An iridectomy is then made. It is imperative that the base of the iridectomy opening is wider than the trabeculotomy opening to prevent the iris pillars from being pushed into this opening postoperatively:
The scleral flap is then closed with three 10-0 nylon sutures one at the apex and one on each lateral side of the triangular flap [Figure - 19].
The conjunctiva and Tenon's capsule are then closed with a running suture of absorbable material (eg. 6-0 vicryl).
In highly buphthalmic eyes, the Schlemm's canal may not be located with certainity. In such cases, it is possible to convert the procedure to a trabeculectomy by removing a block of deep limbal tissue beneath the scleral flap.
• Some surgeons prefer to perform a paracentasis opening with a beveled corneal incision at the beginning of the surgery. In such a situation, the anterior chamber is reformed with BSS and 'patency of the trabeculectomy can be tested at the conclusion of the surgery. The author, however, does not favour a paracentasis opening.
If bilateral surgery is needed, both procedures may be done at the same operating sessions, but for each eye an entirely different set of gowns, gloves, drops, instruments, and irrigating solutions is necessary.
A drop of antibiotic steroid preparation is instilled into the conjunctival sac and a patch and shield are applied to the eye.
Postoperative Care
The dressing is removed on the first postoperative day. A steroid antibiotic combination is prescribed to be used four times a day. A cycloplegic (e.g. cyclopentolate 1% BID) is used only if the eye is significantly irritated or if there is any significant circumcorneal injection. The child is seen weekly at office examinations, and an attempt is made to measure the intraocular pressure with a Perkins hand-held applanation tonometer or the pneumotonometer. Examination under anesthesia is repeated 3 to 4 weeks after surgery. If all is stable, the patient is scheduled for another evaluation under anesthesia in 3 months. The evaluations are repeated at quarterly intervals for the first year after surgery (See Chart 2).
After the first year, examinations are biannual until the child is old enough to cooperate fully with an office examination. These patients should be followed up for an indefinite period to determine whether or not adequate control of intraocular pressure has been achieved.
Complications
Complications of combined Trab-Trab are listed in [Table 6].
In my experience, a small hyphema is almost invariable. Rarely, does the hyphema require a washout of the anterior chamber.
A slightly stripped Descemet's membrane may occur if the trabeculotome is too far anterior when it is rotated into the anterior chamber. In 21 consecutive surgeries, I came across first one case of Descemet's stripping [Figure - 20]. This was of no clinical significance.
Over filtration leading to shallow or flat anterior chamber is a common sequelae. In this same series, I had three cases of flat anterior chamber; two formed spontaneously and one required reformation of anterior chamber.
Peripheral anterior synechiae may form in the region of the trabeculotomy.
Results
Children with primary infantile glaucoma with postnatal onset and no other ocular abnormalities, after surgery within the first year of life enjoy a success rate that approaches 100%. In patients with SturgeWeber syndrome, although early results are encouraging, failure rate increases with longer follow up [86].
A retrospective analysis of the results of primary trabeculotomy cum trabeculectomy in 21 consecutive eyes of 15 patients with advanced developmental glaucoma and corneal clouding revealed good intraocular pressure control without additional antiglaucoma medication in 85.71% of eyes with a mean follow up of 1.5 years. (Range = 1.3 to 2 years) while 14.29% (3 eyes) of the eyes required additional single topical medication.
4. Drainage Implant Surgery for Developmental
Glaucomas
Surgical management of developmental glaucoma, which cannot be controlled by conventional techniques described earlier, poses a difficult problem [87],[88],[89],[90]. Although postoperative subconjunctival 5-fluorouracil injections increase the success rate of filtering surgery in poor prognosis patients [91],[92] its administration in many young patients and children may not be practical. Drainage implant surgery appears to be a viable option for the management of such patients [93],[94],[95],[96] Pediatric Molteno implants with smaller (8mm in diameter) plates and baby Baerveldt glaucoma implants are specifically designed for this purpose.
Preliminary data analysis from a prospective, randomised clinical trial of single versus double plate Molteno implantation conducted at the Doheny Eye Institute under the University of Southern California indicates consistently lower intraocular pressure with the double plate model. Further, two stage installation of the system is associated with fewer postoperative complications. Hence a double plate Molteno implantation in a two stage technique is recommended in refractory developmental glaucomas, whenever technically feasible (Dale Heuer, D. Minckler and G. Baerveldt; Personal communication 1992).
With continued evolution, artificial drainage devices should become an even more valuable part of the glaucoma surgical armamentarium for the management of patients of refractory developmental glaucoma with poor surgical prognoses.
5. Cyclodestructive Procedures
If the artificial glaucoma drainage implants fail to control intraocular pressure the prognosis for vision in that eye becomes extremely poor. If the intraocular pressure is still unduly high, a cyclodestructive procedure should be considered, preferably cyclocryotherapy [97],[98],[99],[100],[101],subtherapeutic ultrasound [102],[103],[104] or Nd: YAG laser cyclodestructionlo [105],[106],[107],108],[109]. The most widely used procedure is cyclocryotherapy.
A contact transscleral Nd: YAG laser with a free running thermal mode is currently being evaluated for cycloablation but the optimal technique for children and young patients with developmental glaucoma has yet to be elucidated.
Cyclodestructive procedures should be applied with caution and in a titrated regimen. Parents should be warned of the high risk of phthisis bulbi following these procedures. If cyclocryotherapy is needed in infants and children, I prefer a technique called "minicyclocryotherapy". Although this may require a series of treatments, it appears to control intraocular pressure with fewer complications.
| VI. LONG-TERM FOLLOW UP AND PROGNOSIS | | |
Between three and six weeks after surgery, the postoperative control of the glaucoma must be judged. The degree of relief from photophobia, tearing, and blepharospasm usually reflects the effectiveness of surgery and may reasonably predict whether or not additional surgery will be required. Children with developmental glaucoma must be re-examined periodically and for an indefinite period to determine whether or not adequate control of intraocular pressure has been achieved.
Most of the examination can be done in an office setting. Examination under anesthesia often allows more careful gonioscopy, in addition to other measurements.
Each follow-up evaluation should include the following parameters:
1. Visual acuity evaluation 6. Refraction
2. External examination 7. Gonioscopy
3. Appearance of the 8. Tonometry
filtering bleb 9. Ultra sonographic
4. Corneal assessment biometry
5. Ophthalmoscopy 10. Disc photography
1. Visual Acuity Evaluation : Techniques vary greatly with the age of the patient. In infants, good fixation and following and the absence of nystagmus are important indicators of good visual function. In children over 3 years of age, visual acuity and eventually visual fields can also be determined.
2. External Examination : This is important to detect evidence of associated abnormalities, inflammation or lacrimal duct obstruction.
3. Appearance of Filtration Bleb : This should be noted in order to assess the effectivity of the surgery performed [Figure - 21].
4. Corneal Assessment : The degree of corneal haze or edema is noted [Figure - 22] and calipers are used to measure the corneal diameter.
5. Ophthalmoscopy : The optic disc is examined to determine if the optic cup has remained the same, is enlarged, or regressed [27].
6. Refraction : Retinoscopy of the eye can be compared to previous measurements of myopia and astigmatism.
7. Gonioscopy: Postoperatively , gonioscopy provides the most important anatomic information about the status of an anterior chamber angle treated with goniotomy or trabeculotomy ab externo.
8. Tonometry: Tonometry is performed at an appropriate stage of anesthesia [30] (or on the peaceful, awake infant), but the significance of the intraocular pressure reading must be balanced carefully against the other clinical signs, if it is not in keeping with them.
9. Ultrasonographic Biometry: The A scan ultrasound can be utilised to compare axial length to presurgical readings.
10. Disc Photography: To provide records for future comparision, it is best to make a careful drawing or preferably to take photographs of the optic nerve head.
A decrease in cupping can occur within hours or days after intraocular pressure control in the very young. This is especially marked in infants below 1 year of age.
In properly selected patients, namely those with isolated trabeculodysgenesis, surgical treatment (Trabeculotomy ab externo or goniotomy) is amazingly successful [69],[80] [Figure - 23]. However, it should be kept in mind, that increase in intraocular pressure can occur at any time in the life of a patient and life-long follow up is a must. The most important parameters in the follow-up examinations are:
cupping of the optic disc visualised by ophthalmoscopy,
axial length values measured by ultrasonographic biometry,
intraocular pressure measured by applanation tonometry, and
visual field evaluation (if possible).
| VII. CONCLUSION | | |
The responsibility of the surgeon does not stop with surgery and it is also very important not to be lulled into a false sense of security by surgical control of intraocular pressure. Visual rehabilitation is as important in the management of the disease as is intraocular pressure control. Visual rehabilitation involves correction of refractive errors [Figure - 24][Figure - 25], correction of opacities in the media such as corneal scarring and cataract, and orthoptic treatment to stimulate the development of binocular stereoscopic vision (See Chart 2). Anisometropia and amblyopia must also be aggressively managed to give these children the best chance for good vision in both eyes. These should be undertaken at as early an age as possible.
An attempt should be made to familiarise the parents with the protracted nature of the illness, the prognosis, the frequent necessity for repeated surgery and the life long need for continued examinations. Parents are often quite young, and often emotionally and economically ill-equipped to cope with the problems that have suddenly and dramatically occurred. Their guilt must be assuaged, particularly if a family history of congenital glaucoma exists. The parents should be advised that the disease has occurred because of factors beyond their control.
The parents should be familiarised with the various agencies that will afford financial assistance when necessary, for it is difficult to obtain retroactive help. Time and effort well spent will reward the ophthalmologist many times over at a later date, particularly when medical and/or surgical progress is not good.
In all ophthalmic surgery it is important that the appropriate operation be chosen and performed with technical perfection. Some complications are inevitable. In general ophthalmic practice, most surgery is performed in the geriatric age group and although the visual penalty paid by the patient for such complications may at times be severe it may not be of long duration. In young patients with developmental glaucoma, it will span a lifetime. Therefore, careful attention to detail and precise technique is of utmost importance in the management of these children. I believe that neither goniotomy nor trabeculotomy or combined trabeculotomy cum trabeculectomy should be attempted by the occasional surgeon. These highly specialised operations are best performed at eye institutes or ophthalmic centres where there is sufficient volume to ensure safe anesthesia and skillful surgery; and should be performed only by surgeons who are prepared to manage childhood glaucomas and follow them life long. Whenever possible these patients should be referred to such institutes.
It must be recognised that in some eyes the prognosis for long-term vision is poor regardless of the technical skill and heroic efforts of both parents and physicians. However, in such patients one should not give up the battle. The longer the child can be kept seeing, the better he will function in the adult world. The blind person who has at one time actually seen a tree or mountain or highway or building or busy intersection will be able to cope in a sight-oriented world better than one who was never able to form these mental images.
Persistence is therefore important. Fortunately, with early diagnosis and microsurgical techniques the disease in a large majority of these eyes can be controlled if not completely cured. However, in few patients who continue to show poor response to surgery such operations will delay the inevitable end, blindness, and allow the child to develop visual images that will be valuable to him in later life.
Eventually, the glaucomatous child will require repeated counselling in terms of the social aspects. His poor vision will need explanation to the parents and teachers to avoid excessive dependence. He may require the help of visual aids, his cosmetic blemishes will need correction where possible and advice may be required even in the selection of a mate.
Acknowledgements : This work was supported by a grant from the Hyderabad Eye Research Foundation, Hyderabad, India.
The author acknowledges the secretarial assistance of Ms. K. Malini and Mr. Siva Rama Sarma.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10], [Figure - 11], [Figure - 12], [Figure - 13], [Figure - 14], [Figure - 15], [Figure - 16], [Figure - 17], [Figure - 18], [Figure - 19], [Figure - 20], [Figure - 21], [Figure - 22], [Figure - 23], [Figure - 24], [Figure - 25], [Figure - 26], [Figure - 27]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]
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