Eye Disease: Part One

An old saying states that the eye is the window to the soul. It may be more accurate to say that the eye is the window to the brain. It is connected by a nerve directly to the brain, and is responsible for converting outside stimuli to images that can be interpreted by the overall organism.

 

The eye is a delicate and complicated organ. Like any intricate structure, it can also be subject to a variety of issues, in animals as well as humans. If you note that something seems off with your pet’s eyes, it is important to seek prompt veterinary care. While most ocular illnesses can be treated, they can be painful, and may cause permanent damage if not addressed. When you bring your cat or dog to a vet for an eye issue, the exam may involve a few extra sections. A complete ophthalmic exam begins with a visual exam of the eye.

 

This starts with the veterinarian closely looking at both eyes and their surrounding tissues, to observe any overall abnormalities. Typically, several reflexes will be checked, including whether the pet blinks when a hand is brought near the eye, and whether the pupils contract in response to a bright light. He or she will then use an ophthalmoscope, a device that uses magnification and light to observe the interior of the eye. Next, some or all of the following tests may be performed. The first is called a Schirmer tear test. A small strip of paper is tucked into the inside of the eyelid, and left in for a full minute. At the end of this time, the distance that tears have wicked up the paper is measured. This tests whether tear production is adequate in the eye. A fluorescein stain test may then be performed. A drop of a bright yellow dye is placed in the eye, or a damp dye-impregnated strip may be touched directly to the white of the eye. Then the eye is thoroughly flushed with saline solution, and the eye is examined with a blue light. If the cornea (the clear front part of the eye) is intact, the water soluble dye with completely wash off the eye. If there is a scratch on the cornea, this ulceration will show up bright yellow. The final ophthalmologic test is called tonometry, and involves tapping a special device on the eye to measure the pressure inside it (called intraocular pressure). Depending on the type of device used, the eye may or may not need to be numbed with a topical medication first. In most cases, a combination of these tests can diagnose the underlying issue. In certain situations, more advanced tests or even referral to a veterinary opthalmologist may be necessary.

So what sorts of eye diseases may affect our pets? This post is the first in a series which will describe some of the more common ocular disorders in cats and dogs, starting with some of the tissues surrounding the eye itself.

Entropion

This term refers to an anatomic abnormality in which the eyelids curl inward. This allows eyelashes, hair, or skin to rub directly on the surface of the eye, and can cause irritation or even ulceration of the front of the eye. Most pets with entropion come to the vet because one or both eyes appears red and inflamed. Usually, the condition can be diagnosed by a close visual exam of the eyes. A fluorescein stain will usually be performed as well, to see if the cornea is ulcerated. The other previously described tests may also be performed in order to rule out any other concurrent problems.

Oftentimes, entropion is congenital, meaning that the pet was born with it. Certain breeds, like bloodhounds, mastiffs, chow chows, and shar peis, are more prone to entropion than others. Some cases of entropion can be secondary to injury. There is also a special type called spastic entropion, which is caused by pain. When the eye is irritated, the animals clamps it tightly shut, which can cause the eyelids to curl inward. This creates a cycle of irritation and worsening entroption. Spastic entropion usually improves when numbing drops are applied to the eyes.

So how is entroption treated? In the case of spastic entropion, the underlying painful condition needs to be treated, and then the entropion will resolve. In any case of entropion which has caused corneal ulceration, medications may be needed to prevent secondary infection. For anatomic or primary entropion, the main treatment is surgical.

If a young puppy is diagnosed with entropion, definitive surgical correction should not be performed right away. Some puppies may “grow into” their eyelids, and the condition may resolve. And permanent surgery could create more issues if their skin is still growing. Instead, a temporary “tacking” procedure is usually performed. Essentially, skin sutures or staples are used to pull the skin around the eyes back, which uncurls the eyelids. These are replaced every few weeks as the puppy grows. If definitive correction is still needed when the dog is older, a surgery is performed in which a thin strip of skin below the eyelid is removed, permanently unrolling the eyelids.

Most pets with entropion do quite well following the procedure. If the condition is left untreated for too long, not only will the pet be in pain, but the front of the eye may become permanently scarred and pigmented, which can affect vision. Therefore, it is essential to address entropion in a timely fashion.

Ectropion

This condition is the opposite of entropion — a condition in which the eyelids roll outward.

It is less likely to cause problems. However, if severe, the eyes may not be properly protected, and can become irritated. If ectroption is causing long term issues, a different type of surgical procedure can be performed to correct it.

Oddly, some breeds are prone to entropion and ectropion at the same time. These breeds often have a characteristic “diamond eye” appearance, with the upper eyelid prone to rolling inward, and the lower eyelid prone to rolling outward. Since entroption and ectropion can be hereditary, if a line of dogs is repeatedly developing these issues, their breeding plan may need to be reassessed.

Cherry Eye

This is a common term for a prolapsed gland of the third eyelid. Dogs and cats have an extra structure within the eye that humans do not, called the third eyelid or nictitating membrane. This is a piece of cartilage at the inner corner of the eye, and contains a gland which produces a significant amount of their tears. Prolapse is a term which means that a structure has slipped out of place. Usually, the third eyelid is barely visible. If the gland is prolapsed, it will appear as a rounded, pinkish mass at the inner corner of the eye. It may occur on just one side, or on both.

It is not completely understood why certain dogs and cats develop cherry eye, but there seems to be a hereditary component. It is more common in dogs, and typically occurs within the first few years of life.

Although not immediately painful, prolonged or severe cherry eye can cause incomplete eyelid closure, dry eye, and conjunctivitis (inflammation of the lining of the eye and eyelids). The main form of treatment for cherry eye is surgical correction. The gland cannot be simply removed, as tear production in the affected eye will then be insufficient. Instead, there are several techniques used to replace the gland into a more normal location and keep it there. This type of surgery has a high success rate, although there is always a small risk of the gland re-prolapsing, or developing delayed onset dry eye.

Tune in next time for more ocular issues! In the next post, we’ll delve into some common causes of conjunctivitis in both cats and dogs.

 

 

References

Church, M., & Herring, I. (2016, August 19). Third Eyelid Gland Prolapse. Retrieved February 4, 2019, from https://www.vin.com/Members/Associate/Associate.plx?DiseaseId=142.

Stanley, R. (2011, July 8). Entropion. Retrieved February 4, 2019, from https://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1204.