The eyes have it
Many of my clients are surprised when I discuss a referral to a Veterinary ophthalmologist. Animal eye problems are a great part of our practice. Complicated eye
issues can be referred to a specialist, but we can help the majority at our own practice.
How does a dog’s vision compare with that of a human? While there are individual breed differences, we know a lot about how dogs see. The eye chart at our office has different size cats on it, but the use of the chart does not tell us much since our patients can’t tell us what they can see. We may do such things as drop a cotton ball and watch to see if the dog follows it. We may also approach the eye with a Q-tip and see if the dog reacts before we touch the eyeball. Most dogs have good distance vision, especially if the object is moving. Since the eyes are angled out more than ours, dogs have a wider field of vision, meaning that they have good peripheral vision. Looking at the retinas of dogs, they have more rods than cones. This means that their night vision is better, but color vision is not as differentiated. While dogs see color, they do not see the variety that we do. Red is a real problem and probably looks black to them.
The most common eye issues in dogs involve the exterior parts of the eye—the lids, the conjunctiva and the cornea. The signs an owners might see are red eyes, swollen lids, gray corneas and signs of eye pain, such as rubbing or closed lids.
Conjunctivitis can be infectious or inflammatory. The most common type is inflammatory, caused by allergens or irritants in the air. The conjunctiva turns red and there is a discharge. The eyelids may become crusty as well. Viruses and bacteria can cause these same symptoms; treatment involves flushing the eyes and either antibiotics or cortisone.
The lids can be affected by allergy, causing them to swell. Antihistamines will decrease
the swelling. Quite commonly the lids will develop masses called tumors. They are
almost always benign. Small masses can be left as long as they don’t bleed a lot. Larger
masses are excised with plastic surgery and usually heal well.
The cornea is the glassy covering of the front of the eye. Any disease of this tissue is called keratitis. Abrasions and ulcerations of the cornea are frequent occurrences. Scratches by cats, branches, or other sharp objects and even soap from bathing can lead to ulcerative keratitis. These will usually heal with proper treatment unless the insult is too deep, which can result in a perforation allowing the fluids inside to leak out. If this occurs, an ophthalmologist will need to do surgery.
As we go inside the eye the first hard structure we meet is the lens. The purpose of the
lens is to focus light rays on the retina to make a clear image. As the lens ages, it
becomes permeable to water. Some gets into the lens and changes it from clear to a
grayish hue. This is called nuclear sclerosis and, though it will not cause blindness, it will cause some decrease in sight in low light situations.
Cataracts occur when the lens becomes crystalline and gradually opaque. We occasionally see cataracts in young dogs as well as in diabetics. Usually cataracts are part of the aging process. They usually are bilateral and may cause blindness if the whole of both lens are involved. Dogs that have bilateral cataracts are no longer consigned to blindness. Veterinary ophthalmologists can remove the lens allowing these animals to see fairly well.
Tunie sees pretty well, looking out the window at all the dogs passing by at the condo.
Lots of barking. She has enjoyed meeting the many dogs living at Mountainview. Oliver and Tunie are still chasing each other around the apartment. I’m glad we put
soundproofing under the new floor so the downstairs neighbors can have peace.
I hope the winter will prove to be happy and healthy for all my readers.
Dr. Segall can be reached Tues thru Thurs mornings at The Hudson Valley Animal Hospital, 4 Old Lake Rd Valley Cottage, NY (845) 268-0089 ex 3.