EYE Flashcards
What is the cause of glaucoma?
The correct answer is decreased outflow of aqueous. Glaucoma is an increase in IOP which is dependent on production of aqueous and outflow of aqueous. Clinical increases are always from decreased outflow although treatment can be aimed at either increasing outflow or decreasing production of aqueous.
You are examining the eyes of a dog with all the signs of Horner’s syndrome. After instilling topical hydroxyamphetamine, there is no change. You then instill topical phenylephrine and in 5 minutes, the eye returns to normal. What can you conclude about this dog’s Horner’s?
The answer is that he has a post-ganglionic lesion. Hydroxyamphetamine acts by encouraging release of norepinephrine from the neuromuscular junction. If there is a pre-ganglionic lesion, NE will still be released by the postsynaptic neuron and signs will resolve. If there is a post-ganglionic lesion, there will be no NE to release. Also, with a post-ganglionic lesion, denervation hypersensitivity to NE occurs. As a result, adding phenylephrine topically can cause a rapid response. With pre-ganglionic lesions, the response usually takes greater than 20 minutes.
Meibomian glands produce which portion of the tear film?
The correct answer is lipid. There are three layers of the tear film. The mucous portion lies against the cornea and keeps the tear film adhered to it. This is made by conjunctival goblet cells. The aqueous portion has nutritional and immunologic factors and is in the middle. It is produced by the lacrimal gland and the gland of the 3rd eyelid. The lipid portion of the tear film is the most outer part, and it allows for even spreading and prevents evaporation of tears. It is produced by the meibomian glands.
A 3-year old cat is squinting both eyes on examination. The conjunctivae are inflamed. Fluorescein stain of the eyes reveals small branching superficial dendritic ulcerations. The owner states that the cat has been playing around some bushes in the backyard as he recently became an outdoor cat approximately 3 weeks ago. What is the best treatment for this cat?
Dendritic ulcers in cats are almost pathognomonic for feline herpes virus 1. The clinical signs this cat is exhibiting are likely from a latent herpes virus the cat had contracted as a kitten. Treatment for this condition includes topical antibiotics. Antivirals would also be useful for treatment and as a preventative. Flare-ups can sometimes be triggered by stress. Treatment with dexamethasone and grid keratotomies are both contraindicated in feline herpetic keratitis. Conjunctival grafts would only be indicated in severe cases.
Taurine deficiency in cats causes what abnormality in the eye?
The answer is central retinal degeneration. Cats with taurine deficiency can develop feline central retinal degeneration (FCRD) in addition to cardiomyopathy. This is because photoreceptors contain large amounts of taurine, and cats cannot synthesize it. The classic lesion is an elliptical area of tapetal hyperreflectivity starting in the area centralis dorsolateral to the optic disk that progresses to a horizontal band and eventually can involve the entire fundus.
A 1-year old female Golden Retriever presents with bilateral exophthalmos that has taken place over the past 2 days. It is not painful, and no swelling is evident. The dog is otherwise healthy. What condition do you suspect?
The answer is extraocular polymyositis. Extraocular polymyositis is a condition seen primarily in young Goldens and they present with the signs above. It is kind of similar to masticatory muscle myositis in that it occurs due to an autoimmune reaction against muscle antigens. It is treated with prednisone +/- azathioprine. The condition can be differentiated from these other conditions because orbital neoplasia and retrobulbar abscesses are usually unilateral. Abscesses are usually accompanied by more systemic signs. Orbital neoplasia is usually more slowly progressive and seen in older animals. Lymphoma could present in a similar fashion but is less likely in such a young dog with no other signs.
