Key takeaways
Coloboma describes the presence of an abnormal hole, or thinning, in part of the eye.
- Colobomas are rare in dogs but, where present, are most commonly found in the iris and eyelid margin
- Colobomas are a developmental disorder which are normally inherited
- Dogs with iris colobomas present with an abnormally shaped pupil and may be sensitive to bright light
- Dogs with eyelid colobomas present with a visible defect in the eyelid margin as well as symptoms of persistent eye irritation including weeping, redness, itchiness, and recurrent ulceration
- Treatment of lid colobomas involves treating the symptoms with medication
- Some cases of lid colobomas can be surgically repaired
- Iris colobomas are not repairable, but usually cause mild symptoms
- The prognosis for all colobomas is good
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A closer look: Coloboma in Dogs
Iris colobomas reduce the ability of the iris to constrict in response to bright light, resulting in squinting in sunlight. This is sometimes a concern in working dogs, but most iris colobomas present with mild symptoms.
Lid colobomas are less common in dogs and the severity varies depending on the size of the defect. Small defects do not result with many symptoms, while larger defects trigger chronic irritation of the eye and surrounding tissue. Dogs showing symptoms of squinting in bright light or unusually shaped eyelids require prompt veterinary examination to rule out more serious underlying conditions.
Colobomas can be found in other areas of the eye such as the lens, but are not detectable without specialist ophthalmic equipment.
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Risk factors
Cases of eyelid coloboma can lead to several secondary conditions, such as chronic ulceration, corneal edema (cloudy eye), and blindness, as the protective nature of the eyelid is not present.
Some colobomas are seen as part of the condition known as Collie Eye Anomaly, a group of genetic eye abnormalities found most commonly in Collies and other shepherd dogs.
At-risk breeds include:
- Australian shepherd dogs
- Border Collie
- Nova Scotia Duck Tolling Retriever
Possible causes
Symptoms vary slightly depending on location.
Testing and diagnosis
Many colobomas are self evident. Further investigation of colobomas involves:
- Physical examination
- Ophthalmic examination
Steps to Recovery
Treatment options depend on the type, and extent of coloboma.
In cases of lid coloboma, options include:
- Treatment of secondary conditions including antibiotics, lubricants, anti-inflammatories, and pain relief
- Surgery to repair the defect in the eyelid
In cases of iris colobomas, options include:
- Avoid bright sunlight
- Dog sunglasses
Colobomas are a lifelong condition, but the prognosis for function is good in most dogs.
Prevention
Colobomas are inherited conditions, although the exact combination of genes is not known. Prevention of colobomas involves not breeding affected dogs. Some colobomas are subtle and an ophthalmic (eye) examination is recommended in at-risk breeds before breeding.
Is Coloboma in Dogs common?
All types of colobomas are rare in dogs. Of coloboma types, iris colobomas are the most common form.
Typical Treatment
Treatment options depend on the type, and extent of coloboma:
- Treatment of secondary conditions
- Surgery to repair the defect in the eyelid
- Avoid bright sunlight
- Dog sunglasses
