Most of us will see a variety of eye complaints in all species almost every week. It therefore helps to have a reliable tool kit available to help you check the eye in order to make an accurate diagnosis. The good news is that most of the diagnostic equipment required for the basic ophthalmic examination is inexpensive and readily available.
Posted: 15 December 2018
In this article, we take a quick look at 5 of the most commonly used special diagnostic procedures we should all be using.
The pre-corneal tear film is essential in maintaining normal corneal health. Insufficient tear formation can lead to painful and debilitating complications, so it’s essential we are able to identify abnormalities early before any long-term damage can occur.
We can all make a qualitative assessment of the tear film by looking at the luster of the corneal surface, but in order to make a quantitative assessment we need the Schirmer tear test. The diagnosis of "dry eye" can easily be missed if this test is not routinely used.
The Schirmer tear test measures only the aqueous aspect of tears, and should therefore be carried out before you place any drops (fluorescein/local/atropine) into the eye. It’s easy to perform and produces clinically relevant results within seconds. The test strips have a numbered ruler on the strip, which is impregnated with a blue dye that travels up the strip as the tears are absorbed.
Reading and understanding intraocular pressure measurements is an important part of eye examinations in many patients. Subtle elevations in the intraocular pressure can be significant, and the repeated measurement of glaucomatous eyes under medical treatment is essential to ensure the treatment you presctibe is effective. The most effective way to do this in practice is by using instrument tonometry.
Applanation tonometers, such as the ‘tonopen’, calculate the intraocular pressure from the force required to flatten (applanate) a constant area of the cornea. They tend to be accurate and easy to use. They are affordable and readily available from most veterinary equipment suppliers, and have made it much easier to diagnose and treat animals with glaucoma. Make sure that you keep the patient relaxed, as if they are stressed, the results can read high. When restraining the animals, be gentle as you open the eyelids. If you are suspicious that there was excessive eyelid pressure or patient restraint, retest.
16.8 ± 4.0 mm Hg in dogs
20.2 ± 5.5 mm Hg in cats
Direct ophthalmoscopy is used more frequently in general practice than indirect ophthalmoscopy. It produces a direct optical image of the patient's eye, with the fundus image being upright and magnified.
There are however some limitations with direct ophthalmoscopy, such as;
Indirect ophthalmoscopy complements direct ophthalmoscopy. To perform indirect ophthalmoscopy a fairly bright light source is directed into the eye. A condensing lens is introduced between the light source and the eye. Incident light is condensed to illuminate the fundus. The reflected light then is condensed by the same lens to form a virtual, inverted, and reversed image between the lens and the light source.
The advantages of indirect ophthalmoscopy are;
There are a few disadvantages, the main one being that since is provides less magnification than the direct ophthalmoscopy, you may miss some of the finer detail.
When the indirect ophthalmoscope is used, the lens is usually held close to the cornea initially to permit observation of the ocular fundus and then moved away from the eye until the image is maximum size.
Examination of the cornea is incomplete without using topical ophthalmic stains. Fluorescein is probably the most popular, and is used to highlight the existence or absence of corneal ulcers. For topical use, fluorescein impregnated paper strips are sometimes preferred to fluorescein solution to ensure sterility.