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26 Cards in this Set
- Front
- Back
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What is contrast?
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created by difference in the amount of reflected light from two adjacent surfaces. (change in luminance)
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How can a pt have 6/6 vision and still have visual complaints concerning contrast?
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visual acuity charts are all 100% (or close) contrast LogMAR, snellen.... etc
retina's ability to detect differences in brightness or shading varies |
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Why is contrast important in vision testing?
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can some times be detected before acuity is affected
- very sensitive indicator of visual dysfunction |
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What ocular conditions can affect contrast sensitivity?
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MS
corneal edema optic nerve probs cataracts contact lenss retinal probs glaucoma keratoconus refractive surgery |
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Would you be able to use contrast as a differentiating element for disease processes?
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No - loss is too similar between different disorders
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What is the threshold contrast?
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lowest visible contrast
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If a pt lowest visible contrast is 5%, what is their contrast sensitivity?
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100/5 = 20%
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High contrast threshold = what type of sensitivity
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inverse relation
therefore low sensitivity |
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What is spatial frequency?
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square wave or sine wave gratings that use cycles to measure image size.
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Higher spatial frequency = what type of image size
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smaller
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What is a VISTECH chart used for?
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constrast sensitivity assessment
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How is the VISTECH chart structured? (in terms of contrast and spatial freq )
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letter to letter = decrease in contrast
line to line = increase spatial |
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Why is uniform lighting important when assessing contrast?
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shadows and glare will affect results
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How does the patient give results in VISTECH
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pt determines if lines point L, R, UP, DOWN, or BLANK
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WHAT DOES TJE vectorvision chart look like
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similar to vistech chart except pt determines from which set of circles (top or bott) which one HAS gratings in it
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How is Pelli-Robson chart structured
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groups of 3 letters with same contrast which decreases by group
2 wrong out of 3 = they didnt get itt |
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WHat is the value of normal binocular contrast>?
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1.50
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Normal monocular contrast?
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0.15 higher than binocular
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What is precision vision chart
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similar to pelli-robson but uses LH symbols
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What is an important aDVANTAGE OF The precision vision chart concerning differing patient acuities
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there is a differing acuity equivalents at differnt distances
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If tested at 2m, what is the symbol size equivalent to in precision vision testing?
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6/30
1m: 6/60 2m: 6/30 4m: 6/15 |
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How would you record results for precision vision contrast testing?
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- need distance (plotted at top)
- number of shapes correctly identified (/30) on y-axis plot the point that corrersponds to those two numbers and draw a straight line horizontally to obtain contrast sensitivity |
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Your young patient sees 18 symbols on precision vision at 1m. Is this typical of young normal sighted pts? If not then what is?
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not normal
young normal sighted see 25-30 at 1m, 20-25 at 3m |
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What type of results should be noted as abnormal in vectorvision?
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difference of 2 or more patches between the curves of both eyes
OR a one patch difference at 3 or more spatial frequencies |
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Your patient is not getting good results at high spatial frequencies. What do you postulate is the reason for this?
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check the refraction bitch
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Your patient is 65 years old. They show a large drop in contrast starting around the mid to high spatial frequency range. What is going on.
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Nothing. This is normal with age
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