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Glaucoma in iridoschisis
Iridoschisis is a rare condition which typically affects the elderly and is often bilateral. It is associated with underlying angle-closure glaucoma in at least 90% of cases. It is thought that acute or intermittent angle-closure results in iris atrophy as a result of high IOP.
1Slit lamp biomicroscopy
•Shallow anterior chamber (Fig. 10.66A).
•Iridoschisis usually involves the inferior iris (Fig. 10.66B).
•The severity ranges from intrastromal atrophy to extensive splitting of the anterior leaf (Fig. 10.66C) and disintegrated iris fibrils.
2Gonioscopy shows a narrow occludable angle which may be associated with PAS.
3Treatment initially involves peripheral laser iridotomy. Subsequent treatment is aimed at limiting glaucomatous damage.
Fig. 10.66 Iridoschisis. (A) Shallow anterior chamber; (B) mild; (C) very severe
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Primary congenital glaucoma
Introduction
Genetics
Most cases of primary congenital glaucoma (PCG) are sporadic. In approximately 10% inheritance is AR with incomplete penetrance. To date, PCG has been linked to three loci: 2p21 (GLC3A), for which the responsible gene is CYP1B1, 1p36 (GLC3B) and 14q24 (GLC3C), for which the genes are not yet identified.
Pathogenesis
Impaired aqueous outflow in PCG is caused by maldevelopment of the angle of the anterior chamber, unassociated with any other major ocular anomalies (isolated trabeculodysgenesis). Clinically, trabeculodysgenesis is characterized by absence of the ciliary body band due to translucent amorphous material that obscures the trabeculum (Fig. 10.67B).
Fig. 10.67 (A) Normal infant angle shows the iris root, prominent ciliary body band but no discernible scleral spur and trabeculum; (B) angle in congenital glaucoma shows the iris root but not the ciliary body band due to translucent amorphous tissue that obscures the trabeculum
(Courtesy of K Nischal)
Classification
1 True congenital glaucoma (40%) in which IOP becomes elevated during intrauterine life.
2Infantile glaucoma (55%) which manifests prior to the third birthday.
3Juvenile glaucoma, the least common, in which the pressure rise develops after the third birthday but before the age of 16 years. Gonioscopy may be normal or reveal trabeculodysgenesis. Patients with normal findings are classed as having juvenile open-angle glaucoma that behaves like adult primary open-angle glaucoma.
Diagnosis
Although PCG is the most common of the congenital glaucomas, it is still a very rare condition, affecting 1 : 10 000 births; 65% of patients are boys. The clinical features depend on the age of onset and the level of IOP. Both eyes are affected in 75% of cases although involvement is frequently asymmetrical.
1Corneal haze is often the first sign noticed by the parents (Fig. 10.68A). It is caused by epithelial and stromal oedema secondary to raised IOP and may be associated with lacrimation, photophobia and blepharospasm (Fig. 10.68B).
2Buphthalmos is a large eye as a result of stretching due to elevated IOP prior to the age of 3 years (Fig. 10.68C). It is not usually reported by the parents unless advanced (Fig. 10.68D). As the sclera stretches it becomes thinner and translucent; the eye then takes on a blue appearance due to enhanced visualization of the underlying uvea. As ocular enlargement continues the anterior chamber deepens and in advanced cases the zonular fibres stretch and the lens may rarely subluxate. The increased axial length also causes axial myopia, which may give rise to anisometropic amblyopia.
3Breaks in Descemet membrane secondary to corneal stretching may be associated with a sudden influx of aqueous into the corneal stroma. Haab striae represent healed breaks in Descemet membrane and appear as horizontal curvilinear lines (Fig. 10.68E). Chronic stromal oedema may lead to permanent scarring and vascularization (Fig. 10.68F).
4Optic disc cupping in infants may regress once the IOP is normalized. Most normal infants exhibit no apparent cup; very few have
a cup–disc ratio greater than 0.3, unlike a high percentage of infants with PCG. In contrast to the adult eye, the scleral canal in the infant eye enlarges as part of the generalized enlargement of the globe and the lamina cribrosa may bow posteriorly in response to elevated IOP. Cup size may therefore be increased from neuronal loss, enlargement of the scleral canal, or both.
Fig. 10.68 Congenital glaucoma. (A) Corneal haze; (B) photophobia and blepharospasm; (C) buphthalmos; (D) severe buphthalmos and scleral thinning; (E) Haab striae; (F) corneal scarring and vascularization
(Courtesy of M Parulekar – fig. A; U Raina – figs B, C and F)
Management
Initial evaluation
The initial evaluation should be performed under general anaesthesia with intravenous ketamine, since this lowers IOP less than other agents. Examination of the optic discs should be undertaken first, followed by measurement of IOP and corneal diameters, and finally gonioscopy.
1IOP is measured with the Perkins tonometer (Fig. 10.69) or Tono-Pen® (see Fig. 10.7C).
2Corneal diameter is measured in both the vertical and horizontal meridian with callipers. A diameter >11 mm prior to the age of one year or >13 mm at any age should be viewed with suspicion. Diameters of 14 mm are typical of advanced buphthalmos.
3 Gonioscopy is performed with a direct goniolens.
Fig. 10.69 Measurement of intraocular pressure with the Perkins tonometer
Surgery
1Goniotomy is performed at the initial examination if the diagnosis is confirmed, provided there is sufficient corneal clarity and the angle can be visualized. The procedure involves making a horizontal incision at the midpoint of the superficial layers of the trabecular meshwork (Fig. 10.70). Although goniotomy may need to be repeated, the eventual success rate is about 85%. However, the results are poor if the corneal diameter is 14 mm or more because in such eyes the canal of Schlemm is obliterated.
2Trabeculotomy may be necessary if corneal clouding prevents visualization of the angle or when repeated goniotomy has failed. In this procedure a partial thickness scleral flap is fashioned (Fig. 10.71A and B), the Schlemm canal is found (10.71C), a trabeculotome is inserted and then rotated into the anterior chamber (Fig. 10.71D). The technique is highly demanding and requires previous experience and good anatomical landmarks to achieve predictable results. In addition, the Schlemm canal may be difficult to canalize because of hypoplasia or angle anomaly.
3Trabeculectomy is often successful, particularly when combined with adjunctive antimetabolites.
4Combined trabeculectomy and trabeculotomy has been used but its superiority to trabeculectomy alone is debatable.
Fig. 10.70 Goniotomy – arrow shows the cleft
(Courtesy of K Nischal)
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Fig. 10.71 Trabeculotomy
(Courtesy of K Nischal)
Follow-up
The patients should be reviewed 1 month after initial surgery. The IOP and corneal diameters should be monitored at regular intervals because progressive enlargement of the corneal diameter is as important a sign of uncontrolled congenital glaucoma analagous to progressive visual field loss in adult glaucoma. Cycloplegic refraction should be performed at 6-monthly intervals. About 50% of patients suffer visual loss from optic nerve damage, anisometropic amblyopia, corneal scarring, cataract and lens subluxation. A buphthalmic eye is also susceptible to traumatic damage.
Differential diagnosis
1Cloudy cornea at birth
•Birth trauma, which gives rise to corneal oedema due to breaks in Descemet membrane.
•Intrauterine rubella, which results in a cloudy cornea due to keratitis. Ten percent of infants with the rubella syndrome also have congenital glaucoma due to an angle anomaly similar to that found in PCG. This may be missed because the eye may not appear significantly enlarged, due to pre-existing microphthalmos.
•Metabolic disorders such as mucopolysaccharidoses and mucolipidoses.
•Congenital hereditary endothelial dystrophy.
2Large cornea due to megalocornea or very high myopia.
3 Lacrimation resulting from delayed canalization of the nasolacrimal duct.
4Secondary infantile glaucoma
•Tumours such as retinoblastoma and juvenile xanthogranuloma.
•Persistent hyperplastic primary vitreous.
•Retinopathy of prematurity.
•Intraocular inflammation.
•Trauma.
•Ectopia lentis.
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Iridocorneal dysgenesis
Posterior embryotoxon
Posterior embryotoxon is an isolated innocuous finding in 10% of the general population.
1Signs
•Thin grey-white, arcuate ridge on the inner surface of the cornea, adjacent to the limbus (Fig. 10.72A and B).
•It comprises a prominent and anteriorly displaced Schwalbe line.
2Associations
aAxenfeld–Rieger anomaly is always associated with posterior embryotoxon.
bAlagille syndrome is associated with posterior embryotoxon in 95% of cases. It is characterized by paucity of intrahepatic bile ducts, cardiopulmonary malformations, peculiar facies and vertebral defects. Optic disc drusen are also common.
Fig. 10.72 Axenfeld anomaly. (A) Posterior embryotoxon; (B) magnified view; (C) gonioscopy shows of strands of peripheral iris tissue extending to the cornea
(Courtesy of P Gili – fig. A; L MacKeen – fig. B)
Axenfeld–Rieger syndrome
Pathogenesis and genetics
Axenfeld–Rieger syndrome is a spectrum of disorders designated in current nomenclature by the following eponyms: (a) Axenfeld anomaly,
(b) Rieger anomaly and (c) Rieger syndrome. Gene loci have been mapped to 4q25 (PITX2 gene), 6p25 (FKHL7) and 13q14 (RIEG2). All patients with Axenfeld–Rieger syndrome, irrespective of ocular manifestations, share the following features:
•Bilateral developmental ocular anomalies which are not necessarily symmetrical.
•Frequent family history with AD inheritance.
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•No gender predilection.
•Frequent presence of systemic developmental defects.
•Associated glaucoma.
Axenfeld anomaly
This is characterized by posterior embryotoxon with attachment of strands of peripheral iris tissue (Fig. 10.72C).
Rieger anomaly
1Slit-lamp biomicroscopy
•Posterior embryotoxon.
•Iris stromal hypoplasia (Fig. 10.73A and B).
•Ectropion uveae (Fig. 10.73C).
•Corectopia and full-thickness iris defects (Fig. 10.73D).
2Gonioscopy in mild cases shows Axenfeld anomaly. In severe cases, broad leaves of the iris stroma adhere to the cornea anterior to Schwalbe line (Fig. 10.73E).
3Glaucoma develops in about 50% of cases, usually during early childhood or early adulthood due to an associated angle anomaly or secondary synechial angle closure. The elevation of IOP should initially be managed medically, although surgery may be required subsequently.
Fig. 10.73 Rieger anomaly and syndrome. (A) Mild iris stromal hypoplasia; (B) severe iris stromal hypoplasia; (C) ectropion uveae; (D) corectopia and full-thickness iris defects; (E) peripheral anterior synechiae; (F) facial and dental anomalies in Rieger syndrome
(Courtesy of U Raina – fig. F)
Rieger syndrome
Rieger syndrome is linked to the region of the epidermal growth factor gene on chromosome 4. It is characterized by Rieger anomaly in association with the following extraocular malformations:
1Dental anomalies consisting of hypodontia (few teeth) and microdontia (small teeth – Fig. 10.73F).
2Facial anomalies include maxillary hypoplasia, broad nasal bridge, telecanthus and hypertelorism (see Fig. 10.73F).
3Other anomalies include redundant paraumbilical skin and hypospadias. Hearing loss, hydrocephalus, cardiac and renal anomalies and congenital hip dislocation are rare.
Peters anomaly
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Peters anomaly is an extremely rare but serious condition which is bilateral in 80% of cases. It is the result of defective neural crest cell migration in the 6th to 8th weeks of fetal development, during which time the anterior segment of the eye is formed. It is not a homogeneous condition and may vary from mild to severe.
1Inheritance. Most cases are sporadic, although AR inheritance and chromosomal defects have been described.
2Signs
•Central corneal opacity of variable density (Fig. 10.74A).
•Underlying defect involving the posterior stroma, Descemet membrane and endothelium with or without iridocorneal (Fig. 10.74B) or lenticulocorneal (Fig. 10.74C) adhesions.
3Investigations. In severe cases ultrasound biomicroscopy is used to determine associated pathology prior to contemplating penetrating keratoplasty.
4Ocular associations occasionally present include Axenfeld–Rieger anomaly, aniridia, microphthalmos, persistent fetal vasculature and retinal dysplasia.
5Glaucoma occurs in about 50% of cases as a result of an associated angle anomaly in which there is incomplete development of the trabecular meshwork and Schlemm canal. Elevation of IOP is usually evident in infancy but may occasionally develop in childhood or even later. Treatment of glaucoma is very difficult and the prognosis tends to be worse than that of primary congenital glaucoma.
6Systemic associations include craniofacial anomalies, central nervous system anomalies, fetal alcohol syndrome, chromosome abnormalities, and ‘Peters plus’ syndrome (short-limbed dwarfism, cleft lip/palate and learning difficulties).
Fig. 10.74 Peters anomaly. (A) Corneal opacity; (B) iridocorneal adhesion; (C) lenticulocorneal adhesion
Aniridia
Genetics
Aniridia (AN) is a rare bilateral condition that may have life-threatening associations. It occurs as a result of abnormal neuroectodermal development secondary to a mutation in the PAX6 gene linked to 11p13. PAX6 is adjacent to gene WT1, mutation of which predisposes to Wilms tumour.
Classification
1AD form accounts for about two-thirds of cases and has no systemic implications. Penetrance is complete (i.e. all patients with the genotype will have the phenotype) but expressivity (severity) is variable.
2Sporadic, including WARG syndrome (Wilm tumour, Aniridia, Genitourinary abnormalities, mental Retardation), previously known
as Miller syndrome, accounts for about a third of patients. Children with sporadic aniridia have about a 30% chance of developing Wilms tumour.
3Gillespie syndrome accounts for only about 1% of cases. Inheritance is AR but not caused by PAX6 mutations. Cerebellar ataxia and mental handicap are features.
All patients with sporadic aniridia should have abdominal ultrasonography (to detect Wilms tumour) every 3 months until 5 years of age, every 6 months until 10 years of age and annually until 16 years of age or until molecular genetic analysis confirms an intragenic mutation without extragenic involvement.
Diagnosis
1Presentation is typically at birth with nystagmus and photophobia. The parents may have noticed absence of irides or ‘dilated pupils’.
2Aniridia is variable in severity, ranging from minimal, detectable only by retroillumination, to partial (Fig. 10.75A) and total (Fig. 10.75B).
3 Gonioscopy even in eyes with ‘total’ aniridia usually shows a hypoplastic or rudimentary frill of iris tissue (Fig. 10.75C).
4Lids often show meibomian gland dysfunction.
5Cornea
•Tear film instability, dry eye and epithelial defects are common.
•Limbal stem cell deficiency may result in ‘conjunctivalization’ of the peripheral cornea.
•Total corneal central stromal scarring and vascularization may occur in end-stage disease.
•Other lesions include opacity, epibulbar dermoids, microcornea, sclerocornea and kerato-lenticular adhesions.
6Lens changes include cataract, subluxation (usually superiorly – Fig. 10.75D), congenital aphakia and persistent pupillary membranes.
7Fundus may exhibit foveal hypoplasia (Fig. 10.75E), optic nerve hypoplasia and choroidal coloboma.
Fig. 10.75 Aniridia. (A) Partial; (B) total; (C) open angle and remnants of the iris root; (D) superior subluxation of a cataract; (E) foveal hypoplasia; (F) angle closed synechially by iris rudiments
(Courtesy of R Curtis – fig. C; L MacKeen – fig. D)
Glaucoma
Glaucoma occurs in approximately 75% of patients and usually presents in late childhood or adolescence. It is caused by synechial angleclosure secondary to the pulling forward of rudimentary iris tissue by contraction of pre-existing fibres that bridge the angle (Fig. 10.75F).
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Treatment is difficult and the prognosis guarded.
1Medical treatment is usually the initial approach although it is usually eventually inadequate.
2 Goniotomy may prevent subsequent rise in IOP if performed before the development of irreversible synechial angle-closure. 3 Combined trabeculectomy-trabeculotomy may be successful although trabeculectomy alone is seldom beneficial.
4Artificial filtering shunts may be effective in established cases.
5Diode laser cycloablation may be necessary if other modalities fail.
Management of aniridia
1 Opaque contact lenses may be used to create an artificial pupil and improve vision and cosmesis.
2Lubricants are frequently required for associated keratopathy.
3 Cataract surgery is often required. Care must be taken to minimize trauma to the limbus and preserve stem cell function.
4Limbal stem cell transplantation with or without keratoplasty may be required.
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