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30 Cards in this Set
- Front
- Back
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Rules for letter chart VA
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Use a chart that follows Bailey-Lovie design principles (e.g., ETDRS chart)
Logarithmic size progression, task the same at each level Have best refractive correction in place Constant luminance (recommended 160cd/m2 ) 80-320cd/m2 OK Patient must be able to read ALL letters on top row and NO letters in the bottom row Give credit for every letter read correctly Consistent administration Do not point to individual letters If you isolate or underline rows to help place-keeping, be consistent Encourage guessing in a consistent manner If patient gets 3 of 5 correct (>50%) in their last row always ask “Can you guess at any letters at all in the next row?” |
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Why distance VA should be measured at 4m
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4 meter viewing distance achievable in most rooms
Convenient to allow +0.25 D for close (4m) viewing distance Mathematically similar to 40 cm test distance used for near vision Metric units used for all other ophthalmic measurements |
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Describe the Berkeley Rudimentary Vision Test. Indicate the kinds of visual acuities it measures, the test distances it uses, and the visual acuity ranges that are achieved.
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pairs of 25 cm square cards hinged together
Single tumbling E card pair ( 4 different sizes) 100M, 25M, 63M, 40 M) Grating card pair (4 different sizes) 200M, 50M, 125M, 80M Basic Vision card pair White Field Projection (black with white quad field , Black with white hemifield) Black White Discrimination Black card and white card TEST DISTANCES 100 cm for STE 25 cm for STE, Grating , WFO, BWD ACUITY RANGES Beyond limit of letter charts (limit LC VA = logMAR 1.6 20/800 ( BRVT begins at STE LogMAR = 1.4) Allows acuity scores much less than logMAR = 2,0 (20/2000) STE acuity to logMAR = 2, .6 (20/8000) Grating acuity to logMAR=2.9 (20/16000) WFP and BWD do not give a measure of VA. Used if VA not measurable with grating card pair |
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List 4 different purposes for conducting a visual field examination using a tangent screen. For each, indicate how you select the test target parameters
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Screening - for unsuspected disease moderate visibility target
demonstrate blind spot diagonal sweeps or large zig-zag Investigation - for suspected disease test as sensitive as possible target just visible in region being investigated Monitoring - for change in known disease use same conditions as last time If previous conditions were not appropriate then do second field test with optimal conditions This becomes the new baseline Functional fields - for predicting practical problems Large easy to see targets) Might change illumination conditions Might use white photopic backgroundwith black targets |
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Describe the Pelli-Robson Test
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Large letters all the same size 6 letters across
Contrast varies Each group of three letters has same contrast. Progressively reduces Viewing distance should not be distant (1 meter recommended, closer is OK) |
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How do the results from the Pelli Robson chart correspond to the Contrast Sensitvity Function?
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The result from the Pelli Robson chart shows the peak of the contrast sensitivity function
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List four different purposes for taking VA
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Treatment decisions (refraction, magnification)
Checking vision is “normal” Quantifying effect of ocular disorder or disease Monitoring stability of vision Predicting functional abilities at visual tasks Quantifying loss for compensation or benefits Standards for eligibility for jobs, privileges |
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How do spectacle lenses affect the VF?
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HIGH PLUS LENS (hyperope)
Blind spot smaller and more central ( less eccentric) Scotomas smaller. Scotomas less peripheral than retinal lesions Ring Scotoma Ring scotoma moves with eye movement. HIGH MINUS LENS (myope) Blind spot larger and less central (more peripheral) Scotomas larger than retinal lesion. Scotomas more peripheral than retinal lesions Unable to stimulate peripheral retina through spec lens |
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Contrast sensitivity.is often assessed by comparing high-contrast letter-chart acuity and low-contrast letter-chart acuity.
How are these measurements be related to the CSF? |
Differences in letters seen for high and low contrast gives info about the slope of the CSF as it approaches the cut off spatial frequency
Hi contrast VA = cut off SF Low contrast VA gives Spat Freq limit at a certain height up the slope. Height up the slope is determined by the contrast of the low contrast chart Join these two points and it gives slope of CSF curve in right side |
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The United States law that defines Statutory Blindness, gives the visual acuity requirement as
best corrected visual acuity in the better eye must be |
worse than 20/200
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The United States law that defines Statutory Blindness, gives the visual field requirement that, for the field in the better eye.
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maximum diameter is equal to or less than 20 degrees in all 8 major meridians
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The visual acuity criterion for “blindness” used by the World Health Organization (WHO) is that best corrected acuity is
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worse than 20/400
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In 2007, The Social Security Administration issue new rules so that now an acceptable criterion for Statutory Blindness
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worse than 20/100
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How many people would you expect to be legally blind?
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0.2%
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How many people would you expect to be totally or functionally blind?
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15%-20% of the legally blind
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How many people would you expect to be visually impaired?
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2% total
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List the reasons for preferring to trial lenses, rather than a phoropter
when refracting low vision patients |
Better to use trial lens system than phoropter
Observe eye movements and viewing strategies Observe nystagmus, change with monocularity, fixation etc Observe closing eyelids, actively or passively Allows patient to alter head and eye posture Allows abrupt changes in large steps of power Avoids vignetting of pupil by phoropter aperture |
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On the Bailey Lovie Chart, the visual task is essentially the same at each size level so that size is the only significant variable from one level to the next.
List the chart design features required to bring about this standardization of the task on letter charts |
Charts should have task the same at each size level
ie., size only significant variable from one level to the next FOR LETTER CHARTS THIS REQUIRES a. Same number of letters at each size level b. Logarithmic size progression (constant ratio) c. Spacing between-letters and between-rows proportional to letter size d. Letters balanced for legibility (rows equally difficult) |
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How many mm in 1M
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1.45mm
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List the advantages of doing an over-refraction using Halberg Clips (or similar) rather than using a trial frame
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In high powers, better control of positioning and aberrations
Old Rx and New Rx expected to have -Similar vertex distance -Similar lens tilt -Similar aberration distribution and field properties Changes in Rx are of usually of modest magnitude -Work with lower power lenses (available in 0.25D steps) -Less precision needed positioning lenses -Less precision needed for axis (of over-refraction cyl) Easier demonstration of the effect of changes -Verify changes Patient sees the impact |
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What are the differences between the Bailey Lovie Chart and the ETDRS
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4x5 letters in BL (British non serif) 5x5 letters in ETDRS Sloan letters) 4 meter test dist for ETDRS
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How to make the a chart as good as the Bailey Lovie Chart
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Log size progression
Same number of optotypes per row Spacing between rows and between letters proportional to size Mix of optotypes about equally difficult in each row |
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Many visually impaired patients report that their visual abilities are especially sensitive to lighting levels. Describe a methodology for systematically assessing the effects of retinal illuminance on visual acuity and contrast sensitivity, and when would you use such a method.
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Use dark gray filters
Test VA and CS with and without filters Note differences due to filter. Neutral NOIR U23 (1.6% or 2% neutral) or other very dark filter VA drops by 10 letters, CS by 0.12 log units |
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What is the major difference between square wave gratings and sine wave gratings for the Contrast Sensitivity Function?
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there is no low frequency roll off for square wave grating
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For VA = 20/20, what is the expected “cut-off spatial frequency ” in cycles per degree?
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30 cpd
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What is the spatial frequency at the peak of the normal CSF?
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5cpd
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What do measurements of low contrast visual acuity tell you about the CSF?
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Diff in VA at two different contrasts indicates slope of curve on right side of CSF
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Describe the Berkeley Discs Test of Contrast Sensitivity, and comment on the potential advantages of this test. You do not need to specify contrast levels.
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3 cards, 6 sides
A 3x2 grid (6 cells) on each card face. Some cells have a disc of selected contrast (actually 3 discs on each side) and subjects task is to locate the discs. (Cells about 3” or 75 cm square and discs 2” or 50mm in diam) First card is screening card (S card 0.0, 0.6, 1.2 and 0.3, 0.9 and 1,5) Two other cards. One for high CS, the other for medium and low CS One card does in-between steps at medium &low CS end, (A card 0.15, 0.75, 1.35 and 0.45, 1.05 and 1.65) The third card does extra contrast at the good CS end (B card 0.75, 1.85 and 1.80 and 1.05, 1.65 and 1.95) |
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What are the parameters for testing Legal Blindness?
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Goldmann III 4e on white background of 10 cd/m2
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What are the four color vision tests you can use?
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D15 Panel
Portnoy Test for RG defects Bernson Achromatopsia Sloan achromatopsia test |
