Pet’s Eyes: The Big Picture
Sight is a very important sense to your pet dog, cat, or rabbit. I want to provide a broad overview of what is normal appearance and anatomy, then discuss the most common ocular diseases, and to finally make you aware of some ocular emergencies.
Like humans, our pet’s eyes have corneas, the clear front outer wall that is made up of several layers of tough connective tissue covered with a thin layer of skin cells. The iris, the colored part you can see through the cornea, regulates the amount of light coming through the lens which can change shape and focuses that light onto the retina. The retina is composed of light-sensing cells that create the impulses which are sent to the brain. There is also a third eyelid, which humans don’t have, that helps to spread the tear film and can slide up and cover the cornea to help prevent corneal injuries.
A healthy eye is one that is bright and shiny, looks moist, has no red inflammation, and the eyelids are held open. Any deviation from normal should catch your attention and rechecking a couple times that day may reveal a temporary resolving condition or one that is escalating to one of the following conditions.
Red Eye, or ConjunctivitisM, is a very common eye disease that can have many causes. Eye infections, allergies, or exposures to irritating substances are common. Cats can have lifelong recurring feline herpes viral conjunctivitis that is very common. Trauma to the cornea like scratches and ulcers are also common in pets. Sometimes internal eye problems like inflammation, termed uveitis, can also cause external eye redness. Uveitis can happen even when dogs develop cataracts. The treatments are many and varied and depend on the diagnosis by our veterinarians.
Dry Eye in one or both eyes is a common condition of mostly adult and senior dogs, but can be congenital. A decrease in tear production from one of several causes is at fault. Chronic eye irritation and redness with thick yellow-green mucous is often a tip-off to dry eye. Fortunately, today we can control dry eye in 90% of dogs with lifelong medications that can usually be given once daily. Dry eye in cats can be more challenging.
Glaucoma can be identified by a chronically red sclera (white of the eye), a continuously enlarged pupil, and an eye that may even appear larger than the opposite one. Pressure within the eye can be increased many fold leading to significant pain and loss of vision. We do have medical treatments for the various types of glaucoma, and sometimes surgery by our three local veterinary ophthalmologists can be helpful to alleviate this painful condition. Certain breeds like cocker spaniels and others are predisposed.
Cataract of the Lens occurs in many pets as a congenital or acquired condition. The proteins of the normally clear lens undergo changes that lead to a lens that becomes opaque to varying degrees. There is surgery to replace the lens with a plastic one just like for our eyes. However, if one eye is still normal or has partial vision, many pets adapt and seem to do well without surgery
Entropion is common condition in many breeds in which the eyelids roll under and inward against the eye with lashes and hairs rubbing the cornea until an ulcer develops. Outward rolling eyelids (Ectropion) predisposing to eye irritation also occurs. Both conditions are correctable with surgery at our clinic, as is the excision of usually benign eyelid tumors which grow out of the oil gland ducts and look like a wart on the lid margin.
Ocular Emergencies. Many of the conditions above should be examined fairly soon, but there are a few true ocular emergencies. One might be an eye with continuous squinting that never opens even in a darker room. Severe deep ulcers and penetrating injuries can cause this, especially with a globe that is smaller and requires immediate care. Glaucoma with severely elevated pressure can rapidly lead to blindness and requires immediate attention. In breeds with bulging eyes, like Pekinese and Pugs, the eyeball will actually pop out of the socket, which is definitely an acute emergency. Because time can be of the essence with severe eye problems, our office makes every attempt to schedule our clients’ pet’s serious acute ocular problems that day or as soon as possible. On weekends or after hours, care can be received at our local emergency hospitals. For very serious eye problems, the emergency service at the Pittsburgh Veterinary Specialists and Emergency Clinic can transfer pets to their three veterinary ophthalmologists for expert care.
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