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   Table of Contents      
CURRENT OPHTHALMOLOGY
Year : 1993  |  Volume : 41  |  Issue : 2  |  Page : 51-70

Current concepts in the diagnosis and management of developmental glaucomas


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
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Source of Support: None, Conflict of Interest: None


PMID: 8262604

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  Abstract 

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 2019 Sep 18];41:51-70. Available from: http://www.ijo.in/text.asp?1993/41/2/51/25621



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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 Top


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 Top


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 Top


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 Top


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 Top


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 Top


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 Top


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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    Figures

  [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]
 
 
    Tables

  [Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]


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