The ocular fundus is the back of the eye opposite the cornea and includes the retina, the membrane between the retina and the white of the eye (the choroid), and the optic disk (the spot where the optic nerve enters the eye). The choroid contains the tapetum (a reflective structure at the back of the eye that improves vision in dim light), the blood vessels that supply the retina, and colored (pigmented) cells. Diseases of the ocular fundus may occur on their own or as a part of generalized diseases.
Possible underlying causes for diseases of the retina in all species include:
Inflammation of the retina and choroid is frequently a result of a generalized, body-wide infection. It is important as both a convenient diagnostic clue and a predictor of visual function. Unless the abnormalities are widespread or involve the optic nerve, they often are “silent” and produce no signs.
During eye examinations, your veterinarian will look for certain characteristic lesions in the eye. These include “bullet-hole” lesions (which suggest infection with equine herpesvirus), diffuse lesions (which may be caused by inflammation or severe head trauma), and “horizontal band” lesions (which may be caused by blockage of the blood vessels).
Inflammation of the retina and choroid may be present with bacterial (leptospirosis), algal, and fungal infections, and blood infections (septicemia) in foals, or caused by trauma or parasites (for example, onchocerciasis). Therapy is directed at the underlying generalized disease.
When the retina become detached, it is separated from the back of the eye and from part of its blood supply, preventing it from functioning properly. In horses, detachment of the retina most frequently occurs with trauma, eye surgery, and equine recurrent uveitis.
Signs that the retina has become detached include excessive or prolonged dilation of the pupil, pupils of different sizes, vision impairment, and bleeding within the eye. Eye examinations need to be performed to confirm the diagnosis.
Detachments of the retina are treated medically with therapy directed at the primary disease or surgically to correct the detachment. Your veterinarian will select the treatment approach most appropriate for your horse’s condition.
Also see professional content regarding disorders of the retina in animals.