Section: Veterinary Care In-depth
Veterinary care includes diagnostic tests and subsequent treatment recommendations.
Diagnosis In-depth
Diagnostic tests are needed to recognize cataracts and exclude other diseases. These tests may include:
A complete eye examination. Most veterinarians have the tools with which to confirm the presence of a cataract in the lens, but it is often necessary to visit a veterinary ophthalmologist to have a more thorough examination performed using specialized ophthalmic equipment. Such an examination includes fluorescein staining of the cornea, Schirmer tear test, slit lamp biomicroscopy, tonometry, and possibly examination of the retina.
Cataracts are classified as incipient (very small), immature (encompassing more, but not all of the lens), mature (encompassing the entire lens) and hypermature (the lens is beginning to shrink down and slowly resorb). The eye exam is important for staging the cataracts and for detecting ancillary or underlying diseases.
Blood tests are necessary to search for diabetes and other underlying systemic diseases. Laboratory tests are also used to assess general health prior to cataract removal surgery.
An ocular ultrasound is performed if the retina cannot be examined because the cataract is too opaque, and if surgery is being considered. Prior to surgery it is important to determine if the retina is normal or healthy. If a retinal detachment or changes in the vitreous (jelly-like substance behind the lens) are found, then surgery to remove the cataract may not be worthwhile.
An electroretinogram (ERG) is also frequently performed prior to cataract surgery in order to evaluate the function of the retina. An ERG is especially important in determining underlying retinal disease masked by the cataracts (if the lens is too opaque for all the retina to be examined). If the ERG is abnormal, then the cat is not a good candidate for cataract surgery.
To understand the importance of evaluating the rest of the eye and especially the retina prior to surgery, consider this analogy: A cataract is like a physical barrier to light, similar to a cover over the lens of a camera. This barrier can be physically removed by surgery. In contrast, the retina is like the film in the camera, and the rest of the eye is the camera itself. If the camera or the retina is not working properly, then removing the lens cover (cataract) will not improve the animal's vision. The rest of the camera must be working well and the film must be good before removing the barrier over the lens will be worthwhile.
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