A Message from the Vet - May 2013
A Closer Look at the Eye

Most eye problems should be seen and evaluated by a veterinarian as soon as possible. With some eye conditions such as glaucoma, hours can mean the difference between recovered vision and permanent blindness.

When your pet presents with an eye problem, the eye exam may seem very confusing. The first part of the exam is a thorough history. The vet will ask if your pet's behavior has changed with regard to vision, activity level, and pain level. Decreased vision may be evident by bumping into things. Some aging changes or conditions affect vision only in times of low light such as evenings. Pain may be evident by decreased appetite, decreased activity level, excessive panting, or squinting.

Once a thorough history is obtained, the doctor will then examine the eye and the surrounding tissue. Any deviation to one side or abnormal movement of the eye is noted. The eyelids are next in line and are evaluated for squinting, swelling, or possible masses. Squinting may be a sign of pain, while swelling may indicate inflammation or infection.

Next they will evaluate the conjunctiva. The conjunctiva is the pink tissue that lines the inside of the eyelid and covers the sclera (the white of the eye). The cornea (the clear part of the eye) is inspected for any cloudiness, defects, or pigmentary changes. Your vet may apply a dye called fluorescein to the cornea to highlight any cuts or ulcers.

Looking through the cornea, the vet will examine the iris. This is the colored portion of the eye. It contracts or relaxes to allow light to enter the eye, and forms the pupil. The pupil is the dark center that may change in size as the iris contracts or relaxes. When a bright light is shown to one eye, the iris contracts in response; this is called a pupillary light response. Normal animals will also show a consensual pupillary light response, which is when the other eye not exposed to the light also shows contraction of the iris. The pupillary light response is important in providing information about how the nerves are functioning, and helps to determine if the retina and the brain are receiving information appropriately.

The liquid part of the eye, called the aqueous, is normally clear, but in some diseases it can become cloudy. The vitreous is the jelly-like part of the eye that gives it shape. It too should be clear of any particles, blood, or bubbles. In between the aqueous and vitreous is the lens. The lens is disc-like and helps to focus the light before it hits the retina. Changes in the lens or its capsule may be related to inflammation, cataracts, or normal aging changes.

To visualize the back of the eye, the doctor may need to dilate your pet's pupil. This exam evaluates the retina, the blood vessels, and the optic nerve. The retina is formed by a layer of light receptors lining the back part of the eye. There are many vessels that cross the retina. The size and shape of these vessels are examined, and the retina is checked for any spots or hemorrhages. The optic nerve is the only nerve that is visible on physical exam.

Some additional tests that may be used are the schirmer tear test or a pressure test. The schirmer tear test helps to determine if there is a decrease in the production or quality of tears. A pressure test will check the pressure in the eye. An increase in pressure may indicate glaucoma, while a decrease in pressure may suggest inflammation.

When it comes to eye problems, it is usually better to be safe and have your pet examined as soon as possible. With the proper diagnosis and prompt therapy, your pet will have the best chance at keeping his or her vision healthy for a lifetime.

Candice Denham, DVM

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Last updated 2014 May 10.