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