Congenital Nystagmus
Nystagmus is an involuntary movement of the eyes associated with vestibular or visual stimuli.
Is Nystagmus Always Abnormal?
No. Normal vestibular nystagmus occurs when you move your head in any direction. When the head is move in the horizontal plane to the right, the eyes will stay focused on an object in their visual field, and as the head moves out of that field, the eye will suddenly jerk in the direction of that movement. This is referred to as physiologic or vestibulo-ocular nystagmus. This type of nystagmus will also occur in a blind dog.4
Abnormal Nystagmus
Abnormal nystagmus is characterized by the presence of continual jerk nystagmus with the head motionless in any position. This is a spontaneous or resting nystagmus.4
Congenital nystagmus in dogs is usually associated with ocular abnormalities and visual defects.1 Because the fast movement is recognized more easily, it is used to name the nystagmus. Fluttering or flickering movements are sometimes seen in Siamese cats with strabismus. If the cat fixes its sight on an object, the nystagmus disappears. This problem of nystagmus does not seem to cause problems in cats.2
The movement is either smooth and equal in both directions (pendular nystagmus), or alternates between a slow drift and a quick, jerk-like movement (jerk nystagmus)). Pendular nystagmus is usually seen in congenitally blind eyes.
This type of nystagmus is observed in Collies with known congenital and hereditary eye disorders.3
Horizontal Nystagmus
Horizontal nystagmus is a side-to-side movement most often seen in cats and dogs with vestibular disease. The "fast" component always "kicks away" from the side of the brain where there is a lesion; then this is followed by a slower return phase.5
Rotatory Nystagmus
Rotatory nystagmus involves more violent movement of the ball and usually indicates a more severe brain damage.
Animals with congenital eye abnormalities such as microphthalmia, persistent pupillary membrane, and cataracts, or conditions with a very early onset of blindness often show abnormal eye movements of wandering nature termed as "searching nystagmus."6
The Biard dog is affected by an autosomal recessively inherited retinal disease with severe, early-onset visual impairment and blindness. The cause is thought to be a genetic defect. Most affected dogs have nystagmus. Puppies can be diagnosed using electroretinography procedure.7
Treatment of Nystagmus
Gene therapy is a promising tool for treatment of genetic disorders in which the gene defect is known. In the eye, this therapy seems exceptionally promising and has already been shown in practice.
Acquired Nystagmus
Dogs with ear diseases such as otitis media or otitis externa often have balance problems. Balance is governed primarily by semicircular canals which are located in the inner ear. These balance problems may be characterized by head tilt, circling, incoordination, and nystagmus].8 Untreated ear diseases can lead to erosion of the skull bones and meningitis (inflammation of the brain).
References:
1. Canine ophthalmology: an atlas and text. K. C. Barnett, Jane Sansom, Christine Heinrich
2. Ophthalmology for the veterinary practitioner. Frans C. Stades, Milton Wyman, Michael H. Boevé, Willy Neumann, Bernhard Spiess
3. UC Davis book of dogs: the complete medical reference guide for dogs and puppies. Mordecai Siegal, Jeffrey E. Barlough
4. Small animal ophthalmology secrets. Ronald C. Riis
5. Dictionary of Veterinary Nursing. D. R. Lane, S. Guthrie, S Griffith
6. Small animal ophthalmology: a problem-oriented approach. Robert L. Peiffer, Simon M. Petersen-Jones
7. Retinal degenerations: mechanisms and experimental therapy. Matthew M. LaVail, Joe G. Hollyfield, Robert Eugene Anderson
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