Bullous keratopathy

Bullous keratopathy, also known as oedematous keratopathy, involves a corneal imbalance caused by fluid entering the cornea due to a change in the endothelium, the internal cellular layer. Because of a endothelium dysfunction, aqueous humour enters the cornea, particularly the most superficial layers at the start, formed by microvesicles or bullae, which is where its name comes from.

When this corneal oedema develops, the cornea loses its transparency, affecting the eyesight.

Because we keep our eyes closed for a long time at night, the patient initially starts to notice blurred vision in the morning when they wake up. Closing the eyes prevents the normal evaporation of intracorneal fluid and the cornea thickens. 

Subsequently, the sensation of blurred vision extends throughout the day. Cornea vesicles or bullae start to appear, which finally break causing intense pain. If the patient is not treated, this situation is prolonged with chronic pain until cicatrisation occurs and the symptoms gradually disappear although the patient's vision is very affected. 

The cause of the bullous keratopathy is the imbalance of the most internal cellular layer of the cornea, called the endothelium. The corneal endothelium is a layer of cells whose role is to act as a barrier stopping the aqueous humour, a liquid occupying the anterior chamber of the eye, from entering the inside of the cornea and making it opaque, as it is like water causing mist on the glass of a watch if it gets inside.   

Any illness or external cause that changes the normal functioning of the endothelium will lead to a corneal endothelium with bullous keratoplasty.

The most common causes are congenital dystrophies of the endothelium, such as Fuchs' dystrophy, and surgical traumas caused during cataract surgery. We must remember that we are born with a number and density of endothelial cells that gradually decrease throughout life.

These cells do not have the proven capacity to regenerate themselves under normal conditions, which is even a small reduction in the number of cells will lead to the onset of bullous keratopathy.

No preventive surgery can be performed on people with the congenital disease, although in recent years a lot of work has been done on learning about the function of the corneal endothelium and developing pharmacological treatments to improve its repair mechanisms.

However, in cases secondary to surgical trauma, the use of a refined surgical technique and protective substances during surgery evidently prevents the intraoperative endothelial lesion and any complications arising therefrom. 

Treatment for bullous keratopathy is a cornea transplant, generally in the form of a posterior lamellar transplant, known as DSAEK or DMEK in English. 

In the surgical procedure, the surgeon delicately removes the damaged endothelium and replaces it with a healthy endothelium from a donor, placing it in position using a gas or air bubble. The patient must stay on bed rest for a few days to help the bubble holding the transplant to stick to the posterior face of the cornea and so that it does not come away, a complication that can be fixed by injecting more gas. This type of lamellar transplant is performed under local anaesthesia and only a few hours or a day is required to check it properly.

In the large majority of cases, the recovery of the cornea's transparency is excellent, and vision is completely restored if there are no concomitant pathologies affecting the retina or the optic nerve. The transplant may be rejected, but this is very uncommon. In cases where the bullous keratoplasty has existed for a long time and there is cicatrisation on the most superficial layers of the cornea, a full corneal transplant must be considered, which extends the post-operative and visual recovery time as sutures are required, although the prognosis is usually very good if proper postoperative follow-up is properly undertaken. 

Currently, in some special cases of Fuchs dystrophy where there is a endothelium dysfunction, the central endothelium is surgically removed and an eyedrop is administered to facilitate endothelial cicatrisation, with promising results, although this is still being studied by the ophthalmic scientific community. 

In cases where a transplant is not considered, the use of a therapeutic contact lenses as a type of bandage combined with hypertonic sodium chloride solutions to eliminate the corneal oedema may be represent a conservative treatment.