The cornea is an amazing biological structure. It is the clear window that has the strongest lens power in the eye. It achieves this by virtue of its curved surface, which allows light to be focused on the back of the eye. It has to be transparent and perfectly regular. It achieves this with the layers of cells within it, that are perfectly arranged in an orderly pattern. Additionally there are no blood vessels present to obscure the clarity, and the surface is lubricated with mucus tears and meibomian gland oily secretions.
When the surface of the cornea is breached, it becomes vulnerable to infection by bacteria, viruses and fungi. Infection leads to inflammation which leads to scarring and tissue damage. On the back of your hand this would be fine; but in the eye this is a very serious matter as these changes can lead to loss of vision. Even if the infection is brought under control, the resulting scarring can be a real problem.
Infections typically occur in contact lens wearers, following trauma, or with underlying disorders such as dry eye, blepharitis or corneal melting disorders, which may breach the surface layer. Sometimes there can be abrasions caused by lashes rubbing and breaking down the surface (See lid Malpositions).
These serious eye infections need to be treated with intensive fortified antibiotics
and managed by a specialist. The case on the right is an acanthamoeba infection.
Pain, which may be quite severe, worsening vision, redness and discharge, which may either be watery or purulent.
This problem needs to be treated as an emergency by an ophthalmologist. A sample will be taken from the surface of the eye and sent for culture in the laboratory. This helps to identify the organism and to test its sensitivity to various antibiotics.
The aims are to get the infection sterilized and under control, and then to prevent further inflammation and scarring.
Most infections are caused by bacteria, which will need to be treated with fortified antibiotics. These are not available over the counter or at the GP.
Often drops will need to be instilled up to every 15 minutes day and night for the first 24-48 hrs. If this is a problem, admission to hospital may be required.
Less common infections with fungi or yeasts and an organism called acanthamoeba may occur. These may require longer-term treatment with specialized antimicrobial drugs taken as eye drops and by mouth.
Once things are under control, steroid drops will often be given. These reduce the inflammation and scarring.
Marginal keratitis is an inflammation of the cornea, which is the front clear window of the eye. Typically there is an infiltration of the cornea with inflammatory cells at the junction between the cornea and sclera, where the cornea turns into the white part of the eye. The surface of the cornea is not breached and the area is not infected. The cause of the inflammation is from toxins produced by bacteria called staphylococci that colonise the lids. Typically there is a concurrent problem with chronic blepharitis.
Recurrent episodes of redness. A watery discharge and discomfort.
This condition settles very quickly with steroid drops. Attention to lid hygiene will help prevent recurrence. Sometimes a course of antibiotics such as doxycyline for six weeks helps.