Cataracts

Dear Dr. Jody:  Our eight year old bulldog, “Porkchop”, has gradually developed a cloudy appearance in both eyes.  She doesn’t seem painful at all, but she has started bumping into walls in dim light.  Are these cataracts, and if so, what can we do about them?

The inner anatomy of the eye is very complicated.  A simplified explanation is that the outer, clear layer of the eye (the part that your contact lenses adhere to) is called the cornea.  The coloured part of the eye is called the iris, and the little black “hole” in the middle of the iris is called the lens.  In front of the lens is a chamber of fluid called the aqueous humor, and behind the lens is another chamber of fluid, called the vitreous humor.

The lens is not really just a little black hole in the iris.  It is actually a little fibre-filled sac that can quickly change shape in response to different conditions.  It is this dynamic little Smartie-shaped structure that allows you to focus on objects at different distances.

As dogs age, more and more fibres are deposited inside the lens.  Because the lens cannot grow and become larger to accommodate these fibres, the fibres become more compacted together and give the lens a cloudy appearance.  This cloudy lens is not necessarily a cataract, and is usually a condition called lenticular sclerosis (which essentially means “fibrous lens”).  Most dogs can still see quite well through these cloudy lenses, and they are not painful.

Cataracts on the other hand, while they can develop as a result of age, more often develop for other reasons including genetics, trauma, or disease such as diabetes.  In diabetic patients, not only is blood sugar elevated beyond the normal range, but eye glucose is also elevated.  Excess glucose in the aqueous chamber of the eye is absorbed by the lens where it is converted into sorbitol.  The sorbitol within the lens then osmotically draws water into the lens.  This concoction results in the formation of a completely opaque cataract, which the dog cannot see through.  It is not unusual for diabetic cataracts to develop quickly – at times within several hours.

While not all cataracts are painful, many are.  Often, the body’s immune system recognizes the abnormal consistency of the lens as foreign, and mounts an immune response against it.  This causes a great deal of inflammation within the eye, and consequently the eye becomes very uncomfortable.  Additionally, the abnormal lens can loosen from the tissue strands that hold it in place within the iris.  This process, known as a lens luxation, causes the cataractous lens to float free within the front chamber of the eye.  This acutely painful condition requires immediate medical attention.  If the lens slips into the front chamber of the eye, it can obstruct the normal drainage of fluid from the eye and cause a sudden increase in pressure within the globe – a highly painful condition known as glaucoma.

Eyes are wonderfully complex structures that are beautifully designed.  However, sometimes even the smallest of changes can lead to permanent vision loss or intense pain.  If you believe that the appearance of your dog’s eyes has changed in any way, it is important to consult your veterinarian immediately.  While some lens opacities are a normal, non-painful result of the ageing process, many are not.  In some cases, even though the dog does not act painful, there can be significant inflammation within the eye that, if not diagnosed and treated quickly, can progress to permanent loss of vision or even the need to remove the eye surgically.