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26 Cards in this Set

  • Front
  • Back
What is contrast?
created by difference in the amount of reflected light from two adjacent surfaces. (change in luminance)
How can a pt have 6/6 vision and still have visual complaints concerning contrast?
visual acuity charts are all 100% (or close) contrast LogMAR, snellen.... etc
retina's ability to detect differences in brightness or shading varies
Why is contrast important in vision testing?
can some times be detected before acuity is affected
- very sensitive indicator of visual dysfunction
What ocular conditions can affect contrast sensitivity?
corneal edema
optic nerve probs
contact lenss
retinal probs
refractive surgery
Would you be able to use contrast as a differentiating element for disease processes?
No - loss is too similar between different disorders
What is the threshold contrast?
lowest visible contrast
If a pt lowest visible contrast is 5%, what is their contrast sensitivity?
100/5 = 20%
High contrast threshold = what type of sensitivity
inverse relation
therefore low sensitivity
What is spatial frequency?
square wave or sine wave gratings that use cycles to measure image size.
Higher spatial frequency = what type of image size
What is a VISTECH chart used for?
constrast sensitivity assessment
How is the VISTECH chart structured? (in terms of contrast and spatial freq )
letter to letter = decrease in contrast
line to line = increase spatial
Why is uniform lighting important when assessing contrast?
shadows and glare will affect results
How does the patient give results in VISTECH
pt determines if lines point L, R, UP, DOWN, or BLANK
WHAT DOES TJE vectorvision chart look like
similar to vistech chart except pt determines from which set of circles (top or bott) which one HAS gratings in it
How is Pelli-Robson chart structured
groups of 3 letters with same contrast which decreases by group

2 wrong out of 3 = they didnt get itt
WHat is the value of normal binocular contrast>?
Normal monocular contrast?
0.15 higher than binocular
What is precision vision chart
similar to pelli-robson but uses LH symbols
What is an important aDVANTAGE OF The precision vision chart concerning differing patient acuities
there is a differing acuity equivalents at differnt distances
If tested at 2m, what is the symbol size equivalent to in precision vision testing?

1m: 6/60
2m: 6/30
4m: 6/15
How would you record results for precision vision contrast testing?
- 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
Your young patient sees 18 symbols on precision vision at 1m. Is this typical of young normal sighted pts? If not then what is?
not normal

young normal sighted see 25-30 at 1m, 20-25 at 3m
What type of results should be noted as abnormal in vectorvision?
difference of 2 or more patches between the curves of both eyes
a one patch difference at 3 or more spatial frequencies
Your patient is not getting good results at high spatial frequencies. What do you postulate is the reason for this?
check the refraction bitch
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.
Nothing. This is normal with age