1
20 200
“BE SURE TO NOTIFY YOUR OPHTHALMOLOGIST OF ANY EYE PROBLEMS THAT YOUR DOG HAS...”
2
20 100
3
20 70
4
20 50
This test evaluates tear quantity rather than quality, so your dog could have tear-related problems even with a normal Schirmer Tear Test. Tears con- sist of water, fatty oils and mucus; the components can become offset due to the blockage of the glands that produce them. The absence of one or more of these components can cause a variety of problems for the eye. FLOURESCEIN STAIN Flourescein Stain is used both to check the cornea for ulcers and to eval- uate the nasolacrimal duct. The stain usually comes as an orange strip that turns fluorescent green when moist- ened. It can be applied to the eye either by touching the strip gently to the eye (usually in the sclera, or white part of the eye, because the point of contact can retain stain) or by placing the strip in a syringe of saline, mixing and then placing a drop in the eye. As the dog blinks, the stain is moved across the surface of the eye and down into the nasolacrimal duct, which connects the eye to the inside of the nasal cavity (this is why your nose runs when you cry— tears drain out through your nose). Bright green liquid should eventually show up in the dog’s nose, showing that the duct is clear. The stain will stick to defects on the cornea, such as ulcers. After apply- ing the stain, the veterinarian will shine a black light on the eye to look for spots where it has been taken up. Corneal ulcers are painful and prone to secondary bacterial infections, but with proper care and treatment can be resolved within a few weeks (depend- ing on the severity of the ulcer). Some ulcers can eat all the way through the cornea, which risks rupture of the eyeball. INTRAOCULAR PRESSURE Intraocular pressure is tested with an instrument called a tonometer.
The two most commonly used in veterinary ophthalmology are the TonoVet ® and TonoPen ® . TonoVet uses a tiny metal probe with a plastic end that is bounced off the surface of the eye. The rebound allows the device to cal- culate the pressure inside the eye. The probes are discarded after each patient to prevent contamination between ani- mals. The end of a TonoPen is covered with a disposable tip and then tapped on the surface of the eye to allow the device to calculate the intraocular pres- sure. Both tonometers require multiple taps to give a final reading, and provide feedback on the standard deviation of the data (basically, it tells you how accurate your results are). These tools can be finicky and it may take a couple attempts to get a good reading, espe- cially if the dog is fussing and moving around. Discomfort can be reduced by using a drop of topical anesthetic in each eye, but the process does not dam- age the eye. A normal eye pressure is between 10 and 20 millimeters of mercury (the units for measuring pressure). Low pressure readings can indicate uveitis, or inflammation inside the eye. High pressure readings indicate glaucoma and untreated high intraocular pres- sure will damage the optic nerve and eventually cause the eye to go blind. It is also very painful. Glaucoma is caused by excess fluid in the eye, either due to excessive fluid produc- tion or poor drainage. The ophthal- mologist will examine the eye to figure out what is causing the pressure to be so high. DILATION Atropine sulfate drops are used to dilate the eyes so that the irises are out of the way, allowing the vet to see more of the structures inside the eye. There are some situations in which the eyes should not be dilated, such as nar- row-angle glaucoma. Be sure to notify
5
20 40
6
20 30
your ophthalmologist of any eye prob- lems that your dog has now or has had in the past so that he or she can determine the appropriate way to approach the eye exam. ANTERIOR EYE EXAM The front portion of the eye is exam- ined using a slit lamp, which combines a microscope with a light source that has multiple settings. This light source is more crisp and precise than a pen light, which allows the veterinarian to closely examine the cornea (outer surface, inner surface and depth), the aqueous humor (liquid in the front of the eye) and the lens. POSTERIOR EYE EXAM The back portion of the eye (behind the lens) is examined with special lens- es and a light source (often a head lamp, but the slit lamp light source can also be used). These lenses allow the veteri- narian to evaluate the vitreous humor (fluid in the back, main portion of the eyeball), retina and optic nerve. Because our dogs are usually conscious for eye exams, there is always some motion, even if the dog is really well behaved. This adds an extra level of challenge to examining the retina and ocular nerve, because the vet may only get brief glances of them before having to readjust the lens. It is definitely an art (as is the entire eye exam), which is why it is best to take your dog to a board certified ophthalmologist for eye problems. Ideally your dogs should have their eyes examined every year by an oph- thalmologist to catch any changes or problems early on.
70 • S how S ight M agazine , A pril 2017
Powered by FlippingBook