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Vision Testing

We are often asked what our pets can see. In our eye diseases section we discuss Normal Animal Vision.

When we examine an animal with an eye problem which either is or potentially may affect vision most owners want to know how much vision has been lost. Unfortunately the individual best positioned to answer that question is the pet – unfortunately they rarely do so however!

Since we cannot have the animal read an eye chart and expect them to tell us which lines they cannot see we are forced to use other tactics to evaluate vision.

Routinely we assess their ability to see and react to objects moving in their visual field as well as test whether they can get around in a visual obstacle course. Your own observations of their behavior at home are very valuable in this regard.

We also are presented with animals with no obvious ocular abnormalities that we can see and then we have to use other diagnostic tests (for instance electroretinography) to de4termine if the eye is working as it should.

To assess the animal’s refractive state (like getting your eyes refracted or checked for a new lens prescription at the optometrist) we use an objective test called retinoscopy.

Retinoscopy is a non-invasive method which is similar to looking at the eye with an ophthalmoscope. Retinoscopy can be performed in just a few minutes using a retinoscope and series of lenses held near to the eye.

The technique may be carried out without dilating the pupil in some cases – in other animals dilating drops may have to be applied to the eye (take about 20 minutes to dilate the pupil) to allow an unobstructed view of the retina.

Retinoscopy allows the ophthalmologist to very quickly get an accurate measurement of whether the animals cornea and lens are bending (refracting) light normally to focus on the retina and assess if any astigmatism is present. Just as with people, animals may have refractive errors of the sort which in people would be corrected with eye glasses, contact lenses and in some cases corneal refractive surgery like LASIK (LAser in SItu Keratomeilusis).

In the past in veterinary ophthalmology we have not seen the need to correct visual refractive problems. After all we assume that few dogs or cats need to read books or drive cars! However we are increasingly recognizing that for some animals (especially working and sporting dogs) acute vision does make a difference. We are now able to make visual corrections using soft contact lenses and goggles designed to fit our patients.

Similarly we now routinely implant intraocular lenses after cataract surgery in dogs and cats (and we have even examined these for cataract surgery in horses – these appear to be beneficial in most animals in improving post-operative vision.

We have not yet reached the stage of recommending LASIK for pets (the cost is still rather prohibitive even in people) but in the near future who knows?