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12 Cards in this Set
- Front
- Back
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What are the 3 components of the precorneal tear film?
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Lipid layer - most anterior
Aqueous layer - middle Mucous layer - most posterior |
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What is the lipid component made of?
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Fatty acids
Cholesterol -waxes and cholestery esters |
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What are the fxns of the Lipid layer?
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-basic purpose to stabilize the film esp. in between blinks
--TBUT - tear break up time: 10< is normal ---<10 sec dry eyes |
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What do the physical-chemical properties of esters allow lipid layer to do?
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-flow from their ducts to the eyelid edges
-form a film over the aqueous layer and maintain contact w/ it -adhere to the eyelid skin and act as a barrier to the aqueous layer -form a water-tight seal when the lids are closed |
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What are some pathological conditions of the lipid layer?
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Meibomian gland dysfunction - excessive production of keratin occurs in ductal epithelium
--keratin alters lipid composition resulting in more rapid TBUT |
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What purpose do Lipids play in the retina?
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important supporting role in visual transduction
-the % of FA in both retina and photoreceptor membranes resemble each other --both have high [cervonic acid] (highly unsaturated) which helps the cell membranes to be especially fluid |
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What is the lipid content of the rods and cones?
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15% of wet weight vs 1% in most cells
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What does high [cervonic acid] provide in the eye?
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high fluidity of discs contribute to the important rotational and lateral movements of rhodopsin needed for phototransduction
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Cervonic acid is vunerable to destruction by oxidative processes. What protects it?
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Vitamin E - absorbs free radicals that are found in the active forms of oxygen and peroxides
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What is the loss of night vision called and what causes it?
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Nyctalopia - vit A deficiency
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What can happen after nyctalopia if the vit a deficiency is not treated?
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Xerophthalmia or dry eyes
-hardening of the corneal conjuctiva w/ the loss of conjuctival secretions -rare in US |
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What adverse side effects come from taking excessive Vit A?
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>10000IU - abdominal pain, blurred vision, drowsiness, headache, irritability, nausea, vomiting
-increased gluconeogenesis -increased protein turnover |
