Congenital Ocular Anomalies in Cats
Congenital abnormalities of the eyeball or its surrounding tissue can be evident in a kitten shortly after birth, or may develop within the first six to eight weeks of life. Most defects are genetically inherited; for example, photoreceptor dysplasia, which is indicated by pupils inability to contract normally in response to light, is more prone in Abyssinian, Persian, and Domestic Shorthair cats. This affects the cat's ability to see in both low light and daylight.
Ocular abnormalities can also develop spontaneously (e.g., colobomas of ther anterior) or occur in utero. Exposure to toxic compounds, lack of nutrients, and systemic infections and inflammations during pregnancy (such as panleukopenia) are other potential risk factors for ocular abnormalities.
Symptoms and Types
There are a variety of abnormalities that can affect a cat's eye or surrounding tissues. The following are some of the more common issues and their corresponding signs:
- Colobomas of the lid
- May appear as notch in eyelid, or tissue of the eyelid may be missing
- Often affects the upper lid
- Variable eyelid twitching and watery eyes
- Inherited in Burmese, Persian, and Siamese cats
- Colobomas of the iris
- Misshapen iris
- Sensitivity to bright light
- Persistent pupillary membranes (PPM)
- Fetal tissue will remain on the eye after birth; rare in cats
- Variable iris defects
- Variable cataracts
- Variable colobomas of the uvea
- Tumor-like cysts on eyelid(s) conjuctiva, or cornea
- Variable eyelid twitching and watery eyes
- Iris cysts
- Often not visible, as the cyst is located behind the iris
- May not have symptoms besides slight bulging of the iris, unless the cyst is interfering with the field of vision
- Congenital glaucoma (high pressure within the eye) with buphthalmos (abnormal enlargement of eyeball)
- Enlarged, red, and painful eye
- Congenital cataracts
- Cloudiness in the eyes
- Often inherited
- Other congenital issues
- Lack of pupils or abnormally-shaped pupil
- Lack of tear duct openings
- Lack of iris
- Persistent hyperplastic tunica vasculosa lentis (PHTVL) and persistent hyperplastic primary vitreous (PHPV)
- Begins in utero, with progressive atrophy of the vascular system that supports the eye lens
- Retinal dysplasia
- Appears as folds or rosette shapes on the retina
- Affects kittens that have been exposed and infected with feline leukemia or feline panleukopenia, either while in utero or after birth
- Photoreceptor dysplasia
- Night blindness (when rods are affected)
- Day blindness (when cones are affected)
- Slow or absent pupillary reflex to light (when pupil does not contract or dilate normally)
- Involuntary eye movement
- Rod-cone malformation
- Initially pupillary dilatation (2-3 weeks), followed by retinal degeneration (4-5 weeks), and then night and day blindness (8 weeks)
- Inherited in Persians, Abyssinians, and American mixed-breeds
In addition, hereditary defects, such as corneal opacities, cataracts, retinal detachement, and dysplasia, are often associated with the following factors:
- Abnormally small eyes
- Missing eyeball
- Hidden eyeball (due to other eye deformities)
- Spontaneous malformations of unknown causes
- Uterine conditions (e.g., infections and inflammations during pregnancy)
- Exposure to toxins during pregnancy
- Nutritional deficiencies during pregnancy
You will need to provide as much of your cat's medical history as you have available to you, such as in utero conditions (i.e., whether its mother was ill, her diet, etc.), and the cat's development and environment after birth. After taking a thorough history, your veterinarian will test the health of the eye.
A Schirmer tear test may be used to see if your cat's eyes are producing an adequate amount of tears. If abnormally high pressure in the eye (glaucoma) is suspected, a diagnostic tool called a tonometer will be applied to your cat's eye to measure its internal pressure. Abnormalities within the eye, meanwhile, will be examined with an indirect ophthalmoscope and/or a slitlamp biomicroscope.
An ultrasound of the eyes may also reveal problems with the lens of the eyeball, the vitreous humor (the clear fluid which fills the space between the lens and retina), the retina, or other problems that are taking place in the posterior (back) segment of the eye. In the case of iris cysts, ultrasound will help your doctor determine if the mass behind the iris is in fact a cyst or a tumor. Cysts do not always behave uniformly: some grow, while others shrink. In most cases follow-ups to check the progress of the cyst will be the extent of treatment, until further intervention is warranted.
Another useful diagnostic method called angiography can also be used for viewing problems in the posterior of the eye, such as detachment of the retina and abnormal blood vessels in the eye. In this method, a substance that is visible on X-ray (radiopaque) is injected into the area that needs to be visualized, so that the full course of blood vessels can be examined for irregularities.
Treatment will depend on the specific type of eye abnormality that is affecting your cat. Depending on your veterinarian's experience with eye diseases, you may need further treatment with a trained veterinary ophthalmologist. Surgery can repair some congenital birth defects, and medicines can be used to mitigate the effects of some types of defects. Congenital keratoconjunctivitis sicca (KCS), commonly known as dry eye, can often be medically treated with tear substitutes in combination with antibiotics. Other medicines called mydriatics may be used to increase vision when congenital cataracts are present in the center of your cat's eye lenses.
In cases of photoreceptor dysplasia, there is no medical treatment that will delay or prevent its progress, but cats with this condition generally do not suffer from any other physical abnormality and can learn to manage their environment very well, as long as they are able to depend on their environment being stable and safe.
Living and Management
Congenital KCS requires frequent checkups with a veterinarian to monitor tear production and the status of the external eye structures. Abnormalities such as congenital cataracts, PHTVL, and PHPV require checkups twice yearly to monitor progression.
In addition, since most congenital ocular anomalies are hereditary, you should not breed a cat that has been diagnosed with any of these disorders.