What is a corneal erosion?
The cornea is the clear structure at the front of the eye, in front of the iris (the coloured part), and it starts the process of focusing light into the eye. It is made of highly modified skin tissue and is richly supplied with nerves. It therefore is very good at detecting pain from an injury or foreign body.
The outer layer, or epithelium, is easily damaged but actually is remarkably good at repairing itself. However sometimes, usually following an injury by a sharp object such as a fingernail, the epithelium does not repair properly. In this instance damaged epithelial cells are replaced by abnormal cells in which links allowing cells to join to neighbouring cells are missing. Normal cells are a bit like lego bricks and can link onto each other giving strength to the structure. Cells lacking this ability are therefore weak and easily break off.
During sleep, the back surface of the eyelid is in contact with the corneal epithelium, and if this contact becomes dry, then the cornea may stick to the eyelid. On awakening and opening the eye, the eyelid may then pull a chunk of abnormal corneal cells off the cornea. This causes intense pain, usually accompanied by sensitivity to light, and may actually be worse than the original injury. Usually, the pain from an erosion will last up to 24 hours.
Why does it recur?
Each time an erosion occurs it acts as a fresh injury, and causes more abnormal epithelial cells to be produced. What is needed is a period of about 3 months for the cornea to heal enough to produce normal cells that have the processes, or links, to enable them to join to each other. In some cases the cornea may require even longer.
What is the treatment?
Treatment is centred around preventing an erosion long enough for the cornea’s epithelial cells to heal fully, and produce ‘normal’ cells with a means of linking firmly with adjacent cells. This requires two things; first, the eye needs to be kept moist through the day, and second, some form of barrier between the cornea and eyelid during sleep.
The method that is usually first tried is a combination of Viscotears Gel four times a day to the affected eye and Lacrilube ointment in the eye just before going to sleep. The Viscotears helps to lubricate the eye through the day, and the thicker Lacrilube provides a barrier between the eye and the lid over night.
This treatment is continued until a 3 month period, during which there has been no erosion has elapsed, and then treatment is suspended.
What if the erosion recurs?
The same treatment is commenced but this time the goal is a 6 month erosion-free period. Again, if this is achieved, treatment is suspended and we wait and see if the cornea has healed.
If this fails there are a number of other treatment options. One is simply to continue with this routine of overnight lubrication. Alternatively, a bandage contact lens can be used. This is a special soft contact lens that can be worn continually day and night for a period of up to 30 days, and provides a physical barrier between the cornea and eyelid. This can be done either by us as optometrists, but not through the NHS and therefore fees are payable, or by referring you to the eye department at hospital (the RVI in Newcastle).
There are further, surgical options, for cases which do not respond to the treatments already outlined above. These involve causing the cornea to scar and therefore bind the layers of cells together. This can be achieved by either micro-puncture or by laser, but both of these options are surgical and therefore carry a small risk.
The vast majority of cases of recurrent corneal erosion respond well to treatment, usually to the regime of lubricant gel and ointment, and only a very small number remain unresponsive to treatment. There is no adverse effect on vision. Rarely, corneal erosions can occur spontaneously without history of an injury, and in both eyes; this may be due to an inherited defect in the cornea called epithelial basement membrane defect, but treatment is essentially the same.