opticnervehypoplasia

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Canine Optic Nerve Hypoplasia

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Optic nerve hypoplasia is the underdevelopment of the optic nerve leading to blindness. It usually occurs as single abnormalities but can be seen with other ocular defects. Because blindness in one eye is compensated by sight in the other, hypoplasia affecting only one eye often will go undetected. The nerve may also be impaired by inflammation (optic neuritis), swelling (papilledema), or shrinkage (optic atrophy). Affected eyes have reduced numbers of retinal ganglion cell axons. Resting pupil size may be normal (regulated from the opposite eye) or dilated (with bilateral optic nerve hypoplasia). On ophthalmoscopic examination the retina appears normal as do the retinal blood vessels but the number of arterioles and veins may be reduced, it also reveals a small or barely detectable optic nerve which appears to be grey in colour.

It is best to withhold affected dogs from breeding programs, since the condition is known to be inherited in certain breeds (Miniature and Toy Poodles, German Shepherd and numerous other breeds), while in others it is associted with other inherited eye disorders and a broad range of disorders of the central nervous system. The cause is unknown in most cases. There is no treatment.

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Canine Optic Nerve Hypoplasia

related term: micropapilla
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What is optic nerve hypoplasia?
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 opticnervehypoplasia

opticnervehypoplasia

affected. Micropapilla refers to a smaller than normal optic disc, and is not associated with loss of sight.

How is optic nerve hypoplasia inherited?
The mode of inheritance is unclear.

What breeds are affected by optic nerve hypoplasia?
The condition occurs in the toy, miniature, and standard poodle and in the German shepherd. It occurs sporadically in other breeds as well. (See reference below for a comprehensive list.)

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.

What does optic nerve hypoplasia mean to your dog & you?
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.

How is optic nerve hypoplasia diagnosed?
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.

FOR THE VETERINARIAN: 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.

How is optic nerve hypoplasia treated?
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.

Breeding advice
Affected dogs and close relatives should not be used for breeding.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources
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. .

Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.

This database is funded jointly by the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.
Permission to reprint is granted by
Alice Crook, DVM Coordinator, Sir James Dunn Animal Welfare Centre
Atlantic Veterinary College University of Prince Edward Island