Corneal disease
What is it?
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| The crystal clear normal cornea |
The normal cornea
The normal cornea is the clear watch-glass like window overlying the coloured part of the eye, the iris.
The cornea allows light to enter the eye and its curved surface helps bring the light to a focus inside the eye. Any alteration in the transparency or smoothness of the cornea affects vision.
Corneal structure
There are 5 layers in the cornea:
- The surface epithelium
- Bowman's membrane
- The corneal stroma
- Descemet's membrane
- The endothelium
Corneal disease
There are four main types of corneal disease:
- Secondary surface changes
- Change in shape
- Change in transparency
- Infection
Secondary surface changes
Several conditions lead to damage of the surface of the cornea. These include:
- Dry eye
- Blepharitis
- Abnormal eyelid position and function
Change in corneal shape
The most common abnormality of corneal shape is keratoconus, also known as 'conical cornea'.
Changes in corneal transparency
There are many diseases in which the cornea becomes less transparent. The most common are:
- Keratoconus or conical cornea
- Fuchs' corneal dystrophy
- Pseudophakic bullous keratopathy
- Corneal dystrophies
Keratoconus
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| Keratoconus - conical cornea. |
Keratoconus is a disease in which the surface of the cornea becomes progressively steeper and irregular, and the corneal stroma thinner and scarred.
The cause of keratoconus remains obscure. It usually begins in the teenage years and is more common in people with multiple allergies.
In most cases vision can be corrected with glasses or contact lenses, but in severe disease corneal transplantation is required.
Fuchs' corneal dystrophy
This common disease is essentially a premature aging of the corneal endothelium. The main function of the endothelium is control of the amount of water in the cornea.
Failure of the endothelium leads to swelling and loss of transparency of the cornea. In severe cases the cornea becomes so swollen that blisters or 'bullae' form.
Pseudophakic bullous keratopathy (PPBK)
PPBK occurs when the endothelium of the cornea is damaged; usually during cataract surgery. As in Fuchs' corneal dystrophy, endothelial loss leads to swelling and loss of corneal transparency.
Corneal dystrophies
Corneal dystrophies are conditions in which parts of the cornea lose transparency. There are multiple causes and patterns. The most common diseases are:
- Reis-Bucklers dystrophy
- Granular corneal dystrophy
Infection
Many infectious agents can cause corneal disease. The most important by far is the Herpes Simplex virus.
Herpes eye disease has two common forms:
- Epithelial ulceration, known as a dendritic ulcer
- Sterile inflammation of the stroma, known as disciform keratitis