Collie Eye Anomaly, also known as CEA, is an inherited disease causing defects in the formation of the eye. CEA has now been determined to be a genetic disorder.
Several forms of the disease are recognized, but the most common is a lesion on the back of the eye called choroidal hypoplasia (CH). All dogs affected by CEA have choroidal hypoplasia, by definition. CEA is not a progressive disease like prcd-PRA and most affected dogs may only have mildly impaired vision. More severely affected dogs may have pits (colobomas) affecting the retina and nearby tissues and in the most severely affected eyes, retinal hemorrhaging and detachments can occur, resulting in blindness.
Varying degrees of CEA and definitions are listed below:
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Choroidal Hypoplasia, Chorioretinal Change, Choroidal Dysplasia:
These
refer to abnormalities in the coloring or pigmentation of the choroid or
central layer of the eye's lining. This is the most common abnormality
found in CEA and all dogs with CEA have CH. However it is the least
harmful and mildest form of CEA. Most dogs with this form function
normally with no ill-effects or loss of vision.
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Coloboma, Ectasia, Staphyloma:
While not completely synonymous, these terms all refer to a
cupping or bulging in the eyeball usually in the area of the optic
nerve. Colobomas are the most common more serious complication of CEA.
Colobomas can be described as a pit in the eye or a blister at the back
of the eye that you can see with an ophthalmoscope. Colobomas vary and
can be small or large and occur in approximately 25% of dogs with CEA.
Interestingly, you cannot have CEA without CH and won’t have coloboma without CH.
A third set of complications which occur exclusively in dogs with coloboma include retinal detachment or hemorrhaging in the eye. About 5-10% of dogs with CEA have these severe complications, which can lead to blindness. These percentages are based on experience with the Collie Breeds.
Vascular Disease, Tortuous Blood Vessels: These terms describe defects in the vessels of the eye, which are responsible for its blood supply or "nourishment." These may be malformed, undersized, or even lacking.
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Retinal Detachment:
Loosening or separation of the innermost, or retina, layer from the wall
of the eye. This may involve a tiny area or the entire retina. It can be
either one or both eyes. The complete detachment of the retina results
in blindness in that eye.
There is usually no significant visual deficit with CH or coloboma, but may lead to a blind spot in the eye. These conditions usually do not affect the working ability of a dog.
Fortunately, there is now a DNA test which will confirm whether or not a dog is clear, a carrier or affected. For information on DNA testing please click on the link on the menu bar to the left.