Optic nerve hypoplasia

From Dog
Optic nerve hypoplasia in a 1-year-old Poodle with right-eye visual impairment and left-eye blindness[1]

Optic nerve hypoplasia is a rare autosomal-recessive genetic ophthalmic disease of dogs[2] characterized by optic nerve developmental failure.

This disease can occur either as an isolated unilateral or bilateral ocular anomaly[3] or as a component of the syndrome of septo-optic dysplasia, which has evolved to include microphthalmia, retinal dysplasia, retinal detachment, midline brain malformations, hydrocephalus and hypopituitarism[4].

Optic nerve hypoplasia is thought to be inherited in Miniature Poodles and has been seen occasionally in several canine breeds, including Beagle[5], Dachshund[6], German Shepherd, Miniature Schnauzer, Rough Coated Collie, St. Bernard, Bouvier des Flandres[7], Pekingese[8], Belgian Sheepdog[9], Miniature and Toy Poodle, Russian Wolfhound, Tervuren, English Cocker Spaniel, and Pyrenean Mountain Dog[10].

Clinically affected dogs present at a young age with ipsilateral or bilateral mydriasis, blindness, menace deficit, and absent direct pupillary reflex, but with a normal consensual reflex in the affected eye following stimulation of the normal eye[11][12]. The pupils of the affected eyes will not respond quickly, if at all, to light. When light is shone into the eyes, the normal reduction in pupil size does not occur. When examined closely, the pupils will appear to be excessively dilated. In some cases, the dog may develop cataracts[13].

Diagnosis is suggested by a history of visual impairment from birth and clinical findings[14].

A definitive diagnosis requires histological evaluation of the optic nerve, showing vacuolation and a general paucity of neurons in ganglion cells of the retina[15]. The optic nerve foramen/canal may be markedly narrowed in some affected animals.

A differential diagnosis would include Collie eye anomaly[16].

The prognosis is poor in most cases and there is no treatment.

References

  1. Grahn, BH & Sandmeyer, LS (2009). Diagnostic ophthalmology. Can Vet J 50(5):543–544
  2. Vite, Ch (2004) Developmental disorders. In: Braund's Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment. IVIS, Ithaca, New York, USA
  3. Negishi H et al (2008) Unilateral optical nerve hypoplasia in a Beagle dog. Lab Anim 42(3):383-388
  4. Borchert M & Garcia-Filion P (2008) The syndrome of optic nerve hypoplasia. Curr Neurol Neurosci Rep 8(5):395-403
  5. Belhorn RW. (1974) Survey of ocular findings in eight- to ten-month-old Beagles. J Am Vet Med Assoc 164:1114-1116
  6. Meyer W. (1977) Studies on morphology and reproduction in relation to merle colour. Thesis. Tierarztliche Hochschule Hannover
  7. Rensburg IBJv, Petrick SW, Lugt JJvd, et al (1992) Multiple inherited eye anomalies including persistent hyperplastic tunica vasculosa lentis in Bouvier des Flandres. Progress in Veterinary & Comparative Ophthalmology 2:133-139
  8. Turnquist SE, Pace LW, Sardinas J. (1991) Unilateral optic nerve hypoplasia and hydrocephalus in a Pekingese. Cornell Vet 81:305-311
  9. Hogan D, Williams RW. (1995) Analysis of the retinas and optic nerves of achiasmatic Belgian sheepdogs. J Comp Neurol 352:367-380
  10. Saunders L. (1952) Congenital optic nerve hypoplasia in collie dogs. Cornell Vet 42:67-80
  11. Boroffka SA, Verbruggen AM, Boeve MH, et al (1998) Ultrasonographic diagnosis of persistent hyperplastic tunica vasculosa lentis/persistent hyperplastic primary vitreous in two dogs. Vet Radiol Ultrasound 39:440-444
  12. Spiess BM, Leber-Zurcher AC. (1992) Oscillating potentials on the B-wave of the ERG in the dog. Schweiz Arch Tierheilkd 134:431-443
  13. LIDA
  14. Grozdanic SD et al (2012) Rapid diagnosis of retina and optic nerve abnormalities in canine patients with and without cataracts using chromatic pupil light reflex testing. Vet Ophthalmol Dec 10
  15. da Silva EG et al (2008) Distinctive histopathologic features of canine optic nerve hypoplasia and aplasia: a retrospective review of 13 cases. Vet Ophthalmol 11(1):23-29
  16. Mizukami K et al (2012) Collie eye anomaly in Hokkaido dogs: case study. Vet Ophthalmol 15(2):128-132