Coloboma

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Persistent pupillary membrane and uveal coloboma and contralateral microphthalmia in an Australian Shepherd dog[1]
Iris coloboma in an Australian Shepherd dog[1]

Coloboma are a genetic ocular defect characterized by maldevelopmental of the eyelid[2], iris[3], lens, retina[4] or optic nerve[5].

Typical colobomas develop secondary incomplete closure of the optic fissure, and atypical colobomas develop secondary to a lack of tissue induction.

Although coloboma are commonly reported in dogs associated with Collie eye anomaly it has also been observed in other dog breeds, such as the merle Australian Shepherd dog where it occurs in association with microphthalmia as as an incompletely-penetrant recessive trait[6][7].

Optic disc coloboma have been reported in the Beagle[8].

Lenticular colobomas are uncommon and typically manifest at the 6 o'clock position or may be atypically located. They may occur as a primary condition or associated with other congenital ocular anomalies, including uveal colobomas[9].

Unless a coloboma is extensive and allows phacodonesis, treatment is usually not required[10].

References

  1. 1.0 1.1 Ashgi
  2. Carter JD (1973) Surgery of congenital eyelid defects. Vet Clin North Am 3(3):423-432
  3. Barnett KC & Knight GC (1969) Persistent pupillary membrane and associated defects in the Basenji. Vet Rec 85(9):242-248
  4. Lahav M et al (1973) Clinical and histopathologic classification of retinal dysplasia. Am J Ophthalmol 75(4):648-667
  5. Grahn BH et al (2003) Diagnostic ophthalmology. Bilateral lenticular coloboma and cortical cataracts. Can Vet J 44(3):245-246
  6. Gelatt KN et al (1981) Inheritance of microphthalmia with coloboma in the Australian shepherd dog. Am J Vet Res 42(10):1686-1690
  7. Gelatt KN & McGill LD (1973) Clinical characteristics of microphthalmia with colobomas of the Australian Shepherd Dog. J Am Vet Med Assoc 162(5):393-396
  8. Briziarelli G & Abrutyn D (1975) Atypical coloboma in the optic disc of a Beagle. J Comp Pathol 85(2):237-240
  9. Davidson MG & Nelms SR (1999) Diseases of the lens and cataract formation. In Gelatt KN, ed. Veterinary Ophthalmology 3rd ed. Philadelphia: Lippincott, Williams & Wilkins. pp:797–825
  10. Gelatt K (1991) The canine lens. In: Gelatt KN, ed. Veterinary Ophthalmology, 2nd ed. Philadelphia: Lea & Febiger. pp:429–460
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