Cornea

What is the cornea?

The cornea is the clear front dome that covers the front part of the eye, and through which all the light must pass in order to make it to the inside of the eye. The cornea is an extraordinary structure, which remains clear, in the absence of illness and injury, for the whole of your life.

The cornea is the most important refracting surface in the eye, in other words it is the one that produces most of the important focusing of light so that you can get clear vision.

The cornea can become injured, either perforated or lacerated with sharp injuries, damaged with blunt injuries, or with chemical injuries or burns. Although the cornea has capacity to heal, mostly the healing process reduces the clarity of the cornea and makes it less useful for getting clear vision.

The cornea is remarkable in that its clarity is created by relative dehydration. This is in spite of the fact that it contains the watery inside of the eye behind it and tears in front of it, but many of the structures keep water from entering the cornea and making the cornea disorganised and opaque. Loss of the barrier functions in the front or behind make the cornea swell and make it lose clarity, and the eye lose sight.

Corneal infections

Corneal infections occur sometimes when the eye has been injured, or has sutures in it, or has a disease, and sometimes because the eye has been exposed to unusual organisms. Contact lens wear is something that produces an increase risk of infection in the cornea and patients who wear contact lenses need to be aware that they need to seek help rapidly should their eye become sore or red.

Corneal infections, for the most part, can be treated quite well with topical antibiotics. Antibiotics in the form of drops can get high concentrations in the cornea, can be effective at treating most infections, although there are still some particularly difficult infections, including fungal infections and acanthamoeba, which are difficult for medicines to heal.

The main problem with cornea infections is the scarring and damage that occurs, and hence the distortion and loss of quality of vision.

Fuch's endothelial dystrophy

Fuch’s endothelial dystrophy is one of the corneal dystrophies, but the most common one, and produces a change to the endothelium, or the under surface layer, usually starting in the centre of the cornea. The effect mostly for the patients is a scattering of light and haloes or stars around lights at night, but it can progress to being more significant visual loss and eventually to thickening of the cornea, where it is not possible to get clear vision.

Fuch’s endothelial dystrophy is relatively common, but mostly fairly mild. It has an inheritance and there is no treatment available for it, apart from resolving the problem with the cornea once it becomes damaged. Resolution comes in the form a corneal graft – either all of the cornea (penetrating keratoplasty) or only the endothelial layer (Endothelial transplantation).

Fuch’s endothelial dystrophy can get worse with glaucoma and may be worse after cataract surgery and injury to the eye.

Corneal Transplants

Corneal transplants are the oldest and most common organ transplants, but are unusual as we do not match the donor to the recipient. In other forms of transplant great care is taken in matching the donor to the recipient to reduce the chances of rejection. This is not helpful for corneal transplantation.

Corneal transplants, because they have no blood supply, are much less prone to rejection and there has not been any strong evidence to show that matching the blood type (or other immune markers) has any value in improving the outcome of corneal transplants.

Corneal transplants are performed in the operating theatre, under local anaesthetic usually, and they involve the removal of the existing cornea, or at least the central part of it, and replacement with a donor cornea. A donor cornea can now be stored for up to a month in a particular transport medium and donor corneas are now usually in good health and can bed in quite nicely to the recipient.

Corneal transplants require sutures to hold them in place and those sutures will often stay in place around twelve months from the operation.

It is rare to get substantially better vision within 6 months after a corneal transplant, although it does depend on how poor the vision is to start with. Often the visual recovery is quite prolonged so it is important to consider the recovery period in the surgical planning for a corneal graft.

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