Cataracts

A cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Early on in the development of age-related cataract the power of the crystalline lens may be increased, causing near-sightedness (myopia), and the gradual yellowing and opacification of the lens may reduce the perception colors. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated. Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian Cataract, and can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the historical surgical procedure of couching) in ancient times were regarded as a blessing from the heavens, because it restored some perception of light in the bilaterally affected patients.

Causes
Cataracts can be congenital, age-related, of genetic origin (the most common cause), caused by trauma, by dietary deficiency (some kitten milk replacement formulas have been implicated), by electric shock, or by toxin. The patient with a cataract is not able to see through the opacity. If the entire lens is involved, the eye will be blind.

Diabetes mellitus in dogs
Many things can cause the lens to develop a cataract. A special cause is Diabetes Mellitus. In this condition the blood sugar soars as does the sugar level of the eye fluids. The fluid of the eye’s anterior chamber (see illustration above) is the fluid that normally nurtures the lens but in the diabetic pet the lens can only utilize so much sugar. Excess absorbed sugar is transformed into sorbitol within the lens which unfortunately draws water into the lens causing an irreversible cataract in each eye. Cataracts are unavoidable in diabetic dogs no matter how good the insulin regulation is; diabetic cats have alternative sugar metabolism in the eye and do not get cataracts.

Condition
The area of the lens involved by the cataract amounts to a spot that the cannot be seen through. If the cataract involves too much of the lens, the animal may be blind in that eye and, of course, there could be cataracts in both eyes which means the pet could be rendered completely blind.
A cataract can “luxate” which means that it can slip from the tissue strands that hold it in place. The cataractous lens can thus end up floating around in the eye where it can cause damage. If it settles so as to block the natural fluid drainage of the eye, glaucoma (a build up in eye pressure) can result, leading to pain and permanent blindness. A cataract can also cause glaucoma when it absorbs fluid and swells so as to partially obstruct fluid drainage from the eye.
Cataracts can begin to dissolve after they have been present long enough. This sounds like it could be a good thing but in fact, this is a highly inflammatory process. The deep inflammation in the eye creates a condition called “uveitis” which is in itself painful and can lead to glaucoma.
A small cataract that does not restrict vision is probably not significant. A more complete cataract may warrant treatment. Cataracts have different behavior depending their origin. If a cataract is of a type that can be expected to progress rapidly (such as the hereditary cataracts of young cocker spaniels) it may be of benefit to pursue treatment when the cataract is smaller and softer, as surgery will be easier.

Treatment
Cataract treatment generally involves surgical removal or physical dissolution of the cataract under anesthesia. This is invasive and expensive and is not considered unless it can restore vision. A complete examination of the eye is performed by a veterinary ophthalmologist. If a cataract is present, it is not possible to see the retina through it; a test called an “Electroretinogram” is done to determine if the eye has a functional retina and could benefit from cataract surgery. Ultrasound of the eye can be used to look for retinal detachments. If the eye has a blinded retina, there is no point to subjecting the patient to surgery.

Prevention
Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts. Regular intake of antioxidants (such as vitamin C and E) may be helpful.