Optic nerve hypoplasia and micropapilla
Optic nerve hypoplasia is an uncommon defect in which the optic nerve fails to develop normally, leading to blindness. One or both eyes may be affected. Micropapilla refers to a smaller than normal optic disc, and is not associated with loss of sight.
The mode of inheritance is unclear.
Depending on the degree of hypoplasia (underdevelopment), an eye may be partially or completely blind. Usually if only one eye is affected, your dog will compensate for the decreased vision to the point that you are unaware of any abnormality. You may notice that the pupils of your dog's eyes are different sizes - the pupil of the affected eye will be larger.
If both eyes are affected, your dog will have some loss of sight or will be blind.
This condition is suspected when a dog is visually impaired from birth. Based on clinical and ophthalmoscopic examination, your veterinarian will determine if optic nerve hypoplasia is the cause. This condition must be distinguished from micropapilla, a normal variation of optic disc appearance where the disc is smaller but vision is normal.
There is no treatment. With their acute senses of smell and hearing, dogs can manage well despite reduced vision. You can help your visually impaired dog by developing regular routes for exercise, maintaining your dog's surroundings as consistently as possible, introducing any necessary changes gradually, and being patient.
With unilateral involvement, clinically you will see ipsilateral mydriasis, blindness, and absence of menace reflex and of direct pupillary light reflex, with normal consensual reflex in affected eye following stimulation of normal eye. If both eyes are affected, there will be bilateral mydriasis, no menace response, and reduced or absent pupillary light reflexes.
Ophthalmoscopic examination reveals a variable reduction in optic disc size, with normal or tortuous -appearing retinal vessels. Optic nerve hypoplasia may be difficult to differentiate from micropapilla on a routine ophthalmoscopic screening examination.
Affected dogs and close relatives should not be used for breeding.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Ackerman, L. 1999. The genetic connection. p 159-160. AAHA Press. Lakewood, Colorado. This reference contains a comprehensive list of breeds in which optic nerve hypoplasia or micropapilla have been seen. .