Pet owners often think that as their pets get older they develop cataracts because they notice a grey color in their eyes; although dog's can certainly develop cataracts it is far more common that they are experiencing something called lenticular sclerosis.
Lenticular sclerosis is a normal aging change that occurs, resulting in the lens of the eye appearing progressively more grey in color as the pet ages. This change usually occurs fairly gradually and most owners notice it only when it gets to the point where it starts to affect their pet's vision or becomes visibly noticeable under close scrutiny. Middle aged to older pets are all affected and both eyes undergo this change at the same time. The pet's pupil is still able to react to light and vision is still possible during the early and middle stages of lenticular sclerosis. Cataract surgery is usually not recommended for this phenomenon unless the lenticular sclerosis has progressed to the point of complete blindness at the very end stage of this degeneration.
A typical cataract, conversely, will come on very rapidly and result in complete opacity of the lens. This means that a normally clear lens and normal looking eye will have a large milk colored disc present in the center of the eye. No light is able to penetrate this lens resulting in complete blindness in the affected eye. It is more common to see this occurring in one eye, but it can occur in both eyes simultaneously. Cataracts can occur at any age. Sometimes there can be an underlying medical cause (like diabetes mellitus) or sometimes these can be congenital. Surgery is usually recommended to restore vision, especially in young dogs with juvenile cataract formation.
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How badly is the vision affected in a pet undergoing lenticular sclerosis? This is very hard to determine because nobody really knows how well pets can truly see. I believe most of us feel our pets can see fairly well, but I believe we also overestimate the importance of vision in our pets. Most scientific studies have proven that our pets vision is very mediocre, at best. Once lenticular sclerosis starts, mediocre vision can only get worse. It seems to me that our pet's night vision is affected when lenticular sclerosis progresses. Most owners report that their pets see better during the daytime versus the night time as they age. It is very hard to relate our pets' vision to our own because the anatomy of our human eye is different than the dog's or cat's eye. We have the presence of a macula in the retina of our eye, allowing for extremely acute, precise vision and optimum focus. Pets lack this anatomical structure, so trying to relate our vision to their vision is guesswork. In addition, dogs and cats rely on their sense of smell as their primary sense organ so are less affected than their human counterparts when vision decreases.
There has recently been some discussion about an eyedrop that claims to reverse cataracts called Ocluvet, but there is no controlled scientific studies that this works.
