There are several additional services that we at Butler Creek Animal Hospital offer that diagnostically are very important in treating your pet's illnesses. Many of these can be done during your appointment because we know that time may be of the essence for some.
Eye injuries and conditions are fairly common in dogs as well as cats! Some injuries occur while playing outside or with a housemate and often result in scratches or ulcers in the eye. Alternatively, other conditions may be genetic in origin. There are a variety of diagnostic tools used to assess these injuries/conditions.
A fluorescein stain is indicated anytime a dog has a red or painful eye, or if any corneal irregularities or trauma to the eye are noted. Fluorescein staining is also used to determine if the duct that allows the passage of tears from the corner of the eye to the nose is open and working. (This duct is why our nose runs when we cry). There are no real contraindications to performing this test in a dog with eye problems.
Fluorescein staining of the cornea identifies abrasions, scratches, ulcerations, and lacerations present in the cornea on the surface of the eye. Early treatment is crucial in promoting repair and healing of corneal ulcers and injuries, and in preventing rupture of the eye. Fluorescein is also important in revealing if the duct from the eye to the nose is open and draining properly.
Initially, the surface of the eye is cleaned of any mucous or discharge. The eyelids are opened and a drop of fluorescein stain is dropped on the surface of the eye. The eyelids are then closed to allow the stain to flow over the entire surface of the eye. If the duct from the eye to the nose is being evaluated, the opening of the nostril is examined for evidence of fluorescent green stain showing up at the tip of the nose.
If the cornea and surface of the eye are to be examined, the fluorescein is flushed out of the eye with eyewash. The eye is then examined with either a penlight or special cobalt blue filtered light to detect the presence of the green stain on the eye. The stain adheres to any areas where the surface layer of the cornea (the epithelium) is missing and where the underlying layer (corneal collagen or stroma) has been exposed. This test outlines the extent of any ulceration and permits a more accurate assessment of the size, depth, and type of ulcer. This test usually takes less than five minutes.
How is a fluorescein stain done?
Schirmer Tear Test
The Schirmer Tear Test (STT) is most commonly used to assess tear production and diagnose keratoconjunctivitis sicca (KCS), also known as "Dry Eye". The test should be carried out in every case with eye discharge, conjunctivitis, and keratitis (inflammation of the cornea). The strips have a line of blue dye at the bottom and are calibrated with a millimeter scale.
To perform the test, the veterinarian will gently pull out the lower eyelid slightly and place the notched section into the lid, making contact with the cornea. This is left in place for sixty seconds then the distance traveled by the dye carried by the tears on the test strip is recorded.
Test Result Interpretation
15+ mm - Normal tear production
10 - 14mm - Considered borderline
5 -10 mm - Dry eye
<5 mm - Severe dry eye
Note: Some animals, especially cats, have very low values (many are 0mm) when they are stressed in a clinic environment yet have no clinical signs of KCS.
Tonometry is performed using an instrument called the tonometer and measures intraocular pressure (IOP) to diagnose glaucoma. Glaucoma is caused by the buildup of fluid within the eye. Abnormally high pressure can damage the optic nerve, leading to vision loss. It is also useful in identifying low IOP, which may occur with anterior uveitis (inflammation within the eye) or following intraocular surgery. Low IOP is also associated with dehydration.
TonoVET Demonstration Video
The TonoVET we use performs rebound tonometry, a process where the instrument applies a rod of a certain weight to the surface of the cornea. The distance that the rod indents the cornea is inversely related to the pressure within the eye. In other words, the softer the eye, the more the rod indents the cornea. The harder the eye and higher the IOP, the less indentation occurs.
Results are given in mmHg. Normal values vary between species of animals and sometimes vary between breeds and individuals. Results can also be affected by the technique used to measure them, so values are usually given as a range. In dogs and cats, pressures between 10 - 25 mmHg are considered normal, however, values that differ > 8 mmHg between eyes are considered significant.