The Cornea & External Disease

What the cornea does

Light enters the eye through the cornea first. Because it is curved, it bends that light and provides most of the eye’s focusing power. It must stay perfectly clear and smooth to give sharp vision.

Diseases of the cornea and the eye’s surface (the “external” eye) are treated by cornea specialists.

Cross-section of the eye showing the clear dome of the cornea at the front — The cornea is the clear dome at the very front of the eye, the first surface light passes through.

Five thin layers

The cornea is only about half a millimeter thick, yet it has five layers. The outer surface protects the eye, the middle gives it strength and clarity, and a single inner layer of cells constantly pumps fluid out so the cornea stays clear.

Cutaway of the cornea showing its layers, from the surface epithelium through the thick stroma to the single inner layer of endothelial cells — From top to bottom: the protective epithelium, Bowman’s layer, the clear stroma, Descemet’s membrane and the endothelium. Full transplants (PK) replace every layer; DALK replaces the front layers; DMEK and DSAEK replace only the inner layers.

Simulated view with corneal disease — Race day with an irregular or swollen cornea, as in keratoconus or Fuchs’ dystrophy: ghosting, haze and glare. Drag to compare. Simulation for illustration only.

Simulated healthy vision — Race day with an irregular or swollen cornea, as in keratoconus or Fuchs’ dystrophy: ghosting, haze and glare. Drag to compare. Simulation for illustration only.

Common corneal conditions

Dry eye & ocular surface disease

An unstable tear film or irritated surface can cause burning, grittiness and fluctuating vision.

Keratoconus

The cornea gradually thins and bulges into a cone shape, distorting vision. It often begins in the teens or twenties.

Fuchs’ dystrophy

The inner pumping cells slowly fail, so the cornea swells. Vision is often worst in the morning.

Scars & infections

Injuries and infections such as corneal ulcers can leave the cornea cloudy or irregular.

Growths on the surface

Growths such as a pterygium can spread onto the cornea and affect comfort and vision.

Healing problems

Some eyes struggle to heal the surface layer, which leaves the cornea vulnerable.

How it can be treated

1
Medical care
Lubricating and prescription drops, ointments and treatment of the eyelids and tear film.
2
Specialty contact lenses
Custom lenses can smooth an irregular cornea, such as in keratoconus, and sharpen vision.
3
Corneal crosslinking
Special drops and ultraviolet light strengthen the cornea to help slow or stop keratoconus from progressing.
4
Corneal transplant
Replacing damaged tissue with healthy donor tissue. Today, often only the affected layers are replaced (DMEK, DSAEK or DALK) instead of the full thickness (PK).