POSTERIOR CORNEAL DYSTROPHIES

Cornea Guttata of vogt
This condition is characterised by drop-like excrescences involving the entire posterior surface of Descemet's membrane. These are similar to Hassal- Henle bodies which represent the age change and are mainly found in the peripheral part. Cornea guttata may occur independently or as a part of early stage of Fuch's dystrophy. The condition usually occurs in old age and is more common in females than males. It rarely affects the vision and hence treatment is usually not required.

Fuch's epithelial-endothelial dystrophy
Fuchs dystrophy is frequently seen as a slowly progressive bilateral condition affecting females more than males, usually between fifth and seventh decade
of life. Primary open angle glaucoma is its common association.

Clinical features can be divided into following four stages:
1. Stage of cornea guttata. It is characterised by the presence of Hassal-Henle type of excrescenses in the central part of cornea. A gradual increase of
central guttae with peripheral spread and confluence gives rise to the so called 'beaten-metal' appearance. This stage is asymptomatic.

2. Oedematous stage or stage of endothelial decompensation is characterised by the occurrence of early stromal oedema and epithelial dystrophy. Patients complains of blurring vision.

3. Stage of bullous keratopathy. This stage follows long-standing stromal oedema and is characterised by marked epithelial oedema with formation of bullae, which when rupture cause pain, discomfort and irritation with associated decreased visual acuity.

4. Stage of scarring. In this stage epithelial bullae are replaced by scar tissue and cornea becomes opaque and vascularized. The condition may sometimes be complicated by occurrence of secondary infection or glaucoma.

Treatment is as follows :
1. In early oedematous stage use of 5 percent sodium chloride (hypertonic saline) may be of some use.
2. Bandage soft contact lenses provide some relief from disturbing symptoms in bullous keratopathy stage.
3. Penetrating keratoplasty is the treatment of choice when the visual acuity is reduced markedly.

Posterior polymorphous dystrophy
It is a dominantly inherited dystrophy of endothelium and Descemet's membrane. It is characterised by lesions with variable appearance, such as vesicles, curvilinear lines or geographical opacities at the level of Descemet's membrane. The condition is very slowly progressive and thus usually asymptomatic. Corneal oedema sometimes may occur, requiring keratoplasty.
Rarely it may be complicated by secondary glaucoma.

Congenital hereditary endothelial dystrophy (CHED)
This is a rare dystrophy associated with scanty or absent endothelial cells and thickened Descemet's membrane. The basic endothelial deficiency results in diffuse milky or ground glass opacification and marked thickening of corneal stroma. It may be inherited both dominantly and recessively.