Pigment is a brown discoloration, composed of melanin granules. In this disease, the clear surface of the eye, the cornea, is affected. Another name for this condition is corneal melanosis.
Corneal pigment deposits result from pigmented cells from the peripheral tissues of the eye into the normally clear cornea. It rests in deep epithelial layer and/or surface of the layer underlying it, the stroma.
Brown color change to the corneal surface is present. The coloration can be more apparent in certain light conditions. Other signs of corneal inflammation can accompany the pigment, including blood vessels. The pigment can become so severe as to impair vision, especially when it involves the central cornea.
Chronic irritation, from inward turning of the eyelid margins allowing hairs to rub on the corneal surface (entropion), poor blink response allowing exposure, chronic corneal ulceration, or diminished tear production allowing drying of the corneal surface can contribute to the condition. In rare cases, even when the underlying cause has been corrected, pigment will continue to form.
Evaluation includes measurement of tear production, application of fluorescein stain and close examination of position of the eyelids, both at rest and when blinking. Corneal sensitivity may be tested. Photos may be taken to document current appearance. Examinations over time are indicated to monitor for progression.
Control of the underlying condition(s) is usually the first step, with some cases requiring eyelid surgery and other cases requiring tear stimulating medications. In some cases, medications, such as Tacrolimus or Cyclosporine, are helpful to reduce pigmentation or prevent progression.
Pigment is only rarely surgically removed, and only if it is significantly impairing vision, since these surgeries weaken the cornea, leave scarring, can have healing complications or recurrence of pigmentation.
The pigmentation is likely to progress if the condition causing the pigment deposition is not successfully treated. Many pets need life-long, consistent medical treatment to prevent progressive damage.