The cornea is the front, transparent part of the eye. By remaining transparent, light can enter the eye and this enables us to see. When fluid accumulates within the cornea, this swelling (oedema) results in loss of transparency and clouding of the cornea which in turns affects our vision.

How do I know if I have corneal oedema?

You may develop a gradual blurring of vision. In mild cases of corneal oedema, this typically occurs in the morning upon waking up. Vision gradually improves over the course of the day.

As the corneal oedema worsens, the vision may be constantly blurred. Patients may see halos around streetlights or car headlights, especially at night.

In advanced cases of corneal oedema, the surface of the cornea may develop blisters ("bullae") that result in pain, with risk of infection and irreversible scarring of the cornea. This is a condition that is termed "bullous keratopathy".

A layer of cells (endothelial cells) on the inner surface of the cornea work like a pump, pumping fluid out of the cornea to maintain its transparency. Without this function, the cornea becomes swollen with water, resulting in corneal oedema. The cornea loses its transparency and becomes hazy, resulting in a loss of vision.

Corneal oedema can be caused by any condition that affects the functioning of these endothelial cells:

• Fuchs' endothelial dystrophy, an inherent disorder of the cells on the inner surface of the cornea. This usually affects both eyes.
• Unhealthy corneal cells prior to eye surgery or multiple eye surgeries. Subsequently, any procedure within the eye (such as cataract, glaucoma or retinal surgery) can result in corneal oedema.
• Eye trauma causing damage to the corneal cells.
• Acute or chronic glaucoma. High pressures in the eye can damage corneal cells.
• Inflammation of the eye, especially long-term or chronic inflammation, can affect the functioning of the corneal cells resulting in corneal oedema. In these cases, the corneal oedema may not clear even after the pressure or inflammation has been controlled.
  

Diagnosis can usually be made when an ophthalmologist examines the cornea. Measurements of the thickness of the cornea, and microscopic photographs of the cells on the inner lining of the cornea can aid diagnosis.

Treatment of corneal oedema depends on the cause of the oedema, as well as how advanced the swelling is. Patients with high eye pressures or eye inflammation need treatment for those conditions in order to prevent corneal oedema from worsening.

In patients with mild corneal oedema and minimal blurring of vision, concentrated ("hypertonic") saline eyedrops and ointment can help reduce the corneal swelling and improve vision.

However, as the corneal oedema becomes more advanced, corneal transplant surgery may be needed to replace the inner lining of cells of the corneal in order to restore transparency to the cornea. This form of partial corneal transplant, where only the inner lining of cells is transplanted, can be performed with different techniques such as DSAEK (Descemet Stripping Automated Endothelial Keratoplasty) and DMEK (Descemet Membrane Endothelial Keratoplasty).

Uncommonly, in advanced cases of corneal oedema where there is severe scarring of the cornea, a full-thickness corneal transplant (known as Penetrating Keratoplasty) may be required.