Corneal Dystrophies are corneal abnormalities with are genetically inherited and non inflammatory in nature. Inheritance is usually complex, with often “incomplete penetrance” which means that even those who have the gene anomaly may not have (express) the problem, but could still be a carrier.
There are many very rare dystrophies, and they can be divided into which part of the cornea they affect- the cornea can be thought of as being composed of five different layers.
- Epithelium – The outermost layer of the cornea, composed of cells, attached to the next layer by the Epithelial Basement Membrane.
- Bowmans Layer – a strong layer of connective tissue
- Stroma – The bulk of the cornea, composed of connective tissue fibrils in an extremely regular arrangement, and bathed in a fluid matrix.
- Descemets Layer – Another strong layer of connective tissue.
- Endothelium – A single layer of cells lining the back of the cornea, which control the hydration, these are never replaced throughout life, so any losses are covered by their neighbours spreading out to fill any gaps.
A few of the more common Dystrophies (or perhaps less uncommon).
Map/Dot/Fingerprint Dystrophy, also called Cogan’s Microcystic Dystrophy
This goes by a variety of names, but lately it has been deemed not to be a dystrophy- it may have a very slight familial tendency, but is now more thought to be due to damage to the epithelial basement membrane. This is a common problem in young mothers who get a corneal abrasion from a baby’s fingernail. This can result in a recurrent erosion, whereby the cornea heals, but the epithelial cells later “fall off” again. This can be treated initially with ocular lubricants, particularly at night time (when the epithelium can stick to the eye lid). If recurrence continues, sometimes corneal scraping or excimer laser can remove the cells in the hope that when they regenerate, their strength will be normal. This condition seems to be more common in diabetics.
Reis Bückler’s dystrophy.
This relatively common dystrophy generally presents in early childhood. Examination shows superficial ring shaped opacities in the cornea, usually mostly at the corneal centre. These rings can coalesce to give the cornea a honeycomb appearance. Most patients develop severe attacks of recurrent epithelial erosions. Usually some patients require either a full, or lamellar corneal graft if vision is severely affected. Unfortunately the condition can recur in the new donor graft.
This very rare dystrophy usually appears early in life, and is characterised by tiny cysts within the corneal epithelium, only visible with a particular slit lamp illumination technique (retro illumination). The lesions are more numerous between the eyelids, and extend across the cornea. This condition generally doesn’t affect vision, though it may cause mild irritation of the anterior eye.
This affects the stroma of the cornea, the middle layer and presents usually with recurrent corneal erosions. White criss-crossing lines are visible within the stroma of the cornea, at various depths. This condition normally shows up by age 10, and by age 30 the lattice like opacities, combined with a general haze can affect vision enough to require a full thickness keratoplasty. Recurrence of the condition in the donor graft can occur.
Fuchs Endothelial Dystrophy.
This is perhaps one of the most under diagnosed eye problems. Symptoms can be misty vision, particularly on waking, but possible remaining throughout the day in more advanced cases. The cause of the misty vision is the failure of the corneal endothelium to maintain the hydration levels of the cornea- it becomes waterlogged, and loses clarity. Treatments include hypertonic saline- more salty tears help to draw water from the cornea. A hair dryer blown gently into the eyes can dry out the tears, and again help to remove water from the cornea. The only sure way to fix this condition is with a corneal transplant, which may become necessary, should the vision be too badly affected or if the condition becomes painful- sometimes water blisters can erupt on the surface of the cornea, exposing corneal nerves and causing pain.