Corneal anomalies: causes, symptoms, diagnosis, treatment

Anomalies in the development of the cornea are expressed by changes in its size and shape.

Megalocornea - a giant cornea (diameter over 11 mm) - is sometimes a familial hereditary anomaly. In this case, there is no other pathology.

A large cornea can be not only a congenital but also an acquired pathology. In this case, the cornea increases in size secondarily in the presence of uncompensated glaucoma at a young age.

Microcornea - a small cornea (5-9 mm in diameter) - can be either a unilateral or bilateral anomaly. In such cases, the eyeball is also reduced in size (microphthalmos), although there are cases of a small cornea in normal-sized eyes. With an unusually small or large cornea, there is a predisposition to the development of glaucoma. As an acquired pathology, a decrease in the size of the cornea is accompanied by subatrophy of the eyeball. In these cases, the cornea becomes opaque.

Embryotoxon is a ring-shaped corneal opacity located concentrically to the limbus. It is very similar to arcus senilis. No treatment is required.

A flat cornea can be combined with microcornea, its refraction is reduced (28-29 diopters), there is a predisposition to increased intraocular pressure due to narrowing of the anterior chamber angle.

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Iris pathology associated with posterior embryotoxon

Rieger's anomaly

• Hypoplasia of the mesodermal layer of the iris.
• Iridotrabecular bands to the Schwalbe line.
• Posterior embryotoxon.
• Ectropion of the choroid.
• Coloboma of the iris.
• High myopia.
• Retinal detachment.
• Glaucoma - at least 60% of cases.
• Corneal opacities are usually small in size and located at the periphery.
• Posterior keratoconus.
• Cataracts are local opacities in the cortical layers of the lens that have little effect on visual acuity.
• Optic disc anomalies: oblique optic disc, myelinated fibers.

Rieger's syndrome

Rieger syndrome is characterized by ocular symptoms of Rieger anomaly and systemic manifestations including:

• hypoplasia of the upper jaw;
• short philtrum;
• dental pathology - small, conical-shaped teeth with wide gaps in the dental row, partial anodontia;
• umbilical and inguinal hernias;
• hypospadias;
• isolated hormonal deficiency;
• heart valve defects.

Pathology of chromosome 6, deletion of chromosome 13 (4q25-4q27) was detected. The disease is inherited in an autosomal dominant manner. Concomitant glaucoma occurs with a frequency of 25 to 50%.

In most cases, the disease is inherited in an autosomal dominant manner; in 30%, newly occurring mutations and sporadic occurrence of the anomaly occur.

Other syndromes involving anterior segment developmental disorders include:

• Michel syndrome. A disease with an autosomal recessive type of inheritance. Combines cleft lip and palate in combination with epicanthus, telecanthus, ptosis, telangiectasias of conjunctival vessels, peripheral corneal opacities, iridocorneal adhesions and decreased intelligence.
• Oculo-dento-digital syndrome. An autosomal dominant syndrome that includes microphthalmos, iris hypoplasia, persistent pupillary membrane, small nose and hypoplasia of the alae nasi, narrowing and shortening of the palpebral fissure, telecanthus, epicanthus, sparse eyebrows, enamel hypoplasia, camptodactyly or syndactyly. The combination of anterior chamber angle abnormality with iridodysgenesis predisposes affected individuals to glaucoma.

Total corneal remodeling

Flat cornea

The diagnosis of flat cornea is made when the corneal curvature is in the range of 20-40 D. Keratometry data usually do not exceed the corresponding sclera indicators. The anomaly can be either unilateral or bilateral. Flat cornea may be accompanied by infantile glaucoma, aniridia, congenital cataract, ectopia lentis, coloboma, blue sclera symptom, microphthalmos and retinal dysplasia. The type of inheritance can be either autosomal dominant or autosomal recessive.

Local and diffuse corneal opacities

• Congenital glaucoma.
• Sclerocornea.
• Corneal dystrophies (in particular, congenital hereditary endothelial dystrophy).
• Severe dysgenesis of the anterior segment of the eye.
• Chemical damage.
• Fetal alcohol syndrome.
• Infectious keratitis (see Chapter 5).
• Non-infectious keratitis (see below).
• Diseases of the skin.
• Mucopolysaccharidosis.
• Cystinosis.

Peripheral corneal opacities

Dermoid

Dermoid cysts, localized on the periphery of the cornea, usually contain connective collagen and epithelial tissue, which gives them the appearance of dense whitish formations. Epibulbar dermoids are located on the conjunctiva, sclera, cornea or in the limbus area. They can be an isolated pathology, or they can be part of the symptom complex of circular dermoid syndrome - damage by dermoids of the entire limbus circumference, 360°. Sometimes corneal dermoid cysts are combined with dermoids of the conjunctiva and sclera, causing the appearance of corneal astigmatism, amblyopia and strabismus.

Sclerocornea

Congenital bilateral vascularized peripheral corneal opacity, often asymmetrical. In 50% of cases, the disorder is sporadic, and in 50%, it is inherited in an autosomal recessive manner. May be accompanied by other pathologies of the visual organ, including:

• microcornea;
• flat cornea;
• glaucoma;
• anterior chamber angle dysgenesis;
• strabismus;
• nystagmus.

In rare cases, it accompanies such general disorders as:

• spina bifida;
• mental retardation;
• cerebellar pathology;
• Hallerman-Streiff syndrome;
• Mietens syndrome;
• Smith-Lemli-Opitz syndrome;
• osteogenesis disorder;
• hereditary osteomyodysplasia - with this syndrome, if glaucoma is not added, high visual acuity is usually maintained.

Central corneal opacity

Peters Anomaly

Usually a bilateral disorder characterized by central corneal opacities with a clear periphery. Corneal changes are often accompanied by cataracts. The anomaly may be isolated or combined with other visual pathologies, including:

• glaucoma;
• microcornea;
• microphthalmos;
• flat cornea;
• colobomas;
• mesodermal dystrophy of the iris.

In some cases, this pathology is part of the symptom complex of Peters syndrome "plus", which includes short stature, cleft lip or palate, hearing problems and developmental delays.

Other syndromes characterized by Peters anomaly:

• fetal alcohol syndrome;
• ring pathology of chromosome 21;
• partial deletion of the long arm of chromosome 11;
• Warburg syndrome.

Treatment of Peters' anomaly is aimed at identifying and treating concomitant glaucoma and, if possible, ensuring transparency of the optical center of the cornea. The results of penetrating keratoplasty for Peters' anomaly remain unsatisfactory. Most authors indicate that keratoplasty is indicated only in cases of severe bilateral corneal damage. In case of opacities of the central zone of the cornea and lens, optical iridectomy may be performed.

Posterior keratoconus

A rare congenital bilateral syndrome that does not tend to progress. The curvature of the anterior surface of the cornea is not changed, but thickening of the corneal stroma is noted, due to which the curvature of its posterior surface increases. As a result of these changes, myopic astigmatism occurs.

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Primary pathology of the anterior chamber angle

The posterior border of Descemet's membrane is marked by Schwalbe's ring. Its anterior edge, which appears as a narrow grayish-white line, can be seen during tonioscopy and is known as the posterior embryotoxopa.

Posterior embryotoxon is present in the gonioscopic picture of many healthy eyes. However, in cases of developmental disorders of the anterior segment, posterior embryotoxon is included in the symptom complex of several known syndromes.

Axenfeld anomaly

Axenfeld anomaly includes posterior embryotoxon in combination with iridogoniodysgenesis (fusion of the iris root with the Schwalbe ring). It may be sporadic in origin or may be inherited in an autosomal dominant manner. Glaucoma develops in 50% of cases.

Congenital glaucoma

It is a blockade of the trabecular zone by cellular elements that were not absorbed during embryogenesis.

Alagille syndrome

An autosomal dominant disorder characterized by congenital intrahepatic bile duct hypoplasia causing jaundice. Posterior embryotoxon is visible in over 90% of patients. The fundus is paler than normal. Optic disc drusen are often present. Associated disorders include spinal malformations (butterfly-shaped anterior arches), cardiovascular malformations, deep-set eyes, hypertelorism, and pointed chin. Associated pigmentary retinopathy may be caused by vitamin A and E deficiencies.