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51 Cards in this Set
- Front
- Back
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Define Visual Acuity.
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The ability to distinguish object details and shape.
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What is the function of cones in the retina?
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- Red, Green, Blue
- color (day) vision and fine detail |
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What type of cell is responsible for night vision?
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Rods
- increased sensitivity in low illumination |
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How to convert degrees to sec of arc (")?
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1 degree = 60 min of arc = 3600 sec of arc
(60 sec of arc = 1 min of arc) |
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Name three types of visual acuity?
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1. Minimum Resolvable/Separable
2. Minimum Visible 3. Minimum Discernible |
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What is minimum resolvable acuity used for?
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- features of a target
- typical description of "visual acuity" - normal ~30-60 sec of arc |
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How to test minimum visible acuity?
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- single line or dot on a white background
- normal 1 sec of arc |
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How to test minimum discernible acuity?
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- vernier
- detect a shift or break in a line - normal ~ 2-10 sec of arc |
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What type of visual acuity does a typical vision chart test?
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minimum resolvable
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What does the acuity ratio represent (numerator = ? denominator = ?)?
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Numerator = viewing distance
denominator = distance where the letter spokes subtend one minute of arc on the retina |
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Patient has 6/12 acuity. A person with 6/6 vision can see the same target ___ m away.
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12
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Minimum Angle of Resolution (MAR) = ?
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D/d instead of d/D
* 6/6 MAR = 1 * 6/12 MAR = 2 |
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What is the MAR for a person with 6/48 vision?
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MAR = 8
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Define legal blindness.
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6/60
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What can you do to try to improve patient's vision if they do not see 6/6?
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- Pinhole
- single letters - +/- 0.50 lenses |
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What do you do when patient's vision is reduced below the largest line on the ETDRS chart?
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Resort to low vision ETDRS, or walk to the chart by meter
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Patient's vision is reduced below largest line; low vision chart is not available, and walking to chart has not helped. What then can you do to determine the vision of this patient?
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- Count fingers (CF)
- Hand motion (HM) - Light Projection (where is the light coming from?) - Light perception (light at all?) - No Light Perception (NLP) |
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What are the disadvantages of using a Snellen Acuity chart?
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- different number of letters per each line
- inconsistent size gap between letters - some letters easier than others - MAR varies from line to line |
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What was fixed in the Sloan chart compared to the Snellen? What is the one disadvantage?
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- same number of letters on most lines
- gap between letters is one letter size - same difficulty letters BUT - MAR still varies from line to line |
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What is unique about Log MAR acuity testing?
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Log units used to yield exponential change from one line to the next
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Letters on each line are _____ X the height of the letters on the line below it.
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1.2589
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What type of visual acuity would have Log MAR a negative value?
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Better than 6/6
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What does ETDRS stand for?
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Early Treatment Diabetic Retinopathy Study
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Name all lines (acuity) of the ETDRS chart.*******
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6/60
6/48 6/38 6/30 6/24 6/18 6/15 6/12 6/9.6 6/7.5 6/6 6/4.5 6/3.8 6/3 |
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How many letters on one line does a patient need to see correctly in order to "get" that line? (On ETDRS)
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3/5
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A patient read 3/5 letters on the 6/60 line correctly
The same patient read 2 letters correctly on the line directly below when using pinhole aid What is the VA? |
6/60 -2,+2 pinhole
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What is the preferred near vision test for literates?
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Sloan @ 40 cm
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What might be a disadvantage of using the Sloan near vision test?
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No logarithmic progression
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What are some near vision tests for literates (other than Sloan)?
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- Rosenbaum - variety of objects
- Fonda-Anderson - variety of sizes print ex. phone book - Maclure Reading Book - different levels of reading ability and different size print |
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Name some visual acuity tests for preliterates.
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- HOTV (Log MAR)
- LH (Lea) symbols (preferred) - Follows a Face - Heidi Paddles - Fixation Pattern |
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What are the problems associated with the HOTV test for preliterates?
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- unreliable - difficult for kids to name therefore point to match letters on a card
- 25% chance of getting it right just by guessing |
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What are LH symbols used for? What are advantages/disadvantages?
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LH symbols - Lea symbols
- used as an acuity test for prelit - heart, house, square, circle - easier than HOTV - logarithmic - crowding effect - problem: 25% chance to get it right |
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At what age should a child be able to follow a face?
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4 months
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What do Heidi Paddles measure?
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monocular - fix and follow
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When is fixation pattern test used?
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if strabismus is present - check to see if they will let either eye turn equally (if yes: most likely equal vision)
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How is a fixation pattern test performed?
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- occlude straight (fixing) eye
- does the questionable eye now fix centrally or eccentrically - steady? or nystagmus? - upon removal of occluder - does eye still maintain fixation? - if uncovered eye deviates instantly = amblyopia "Central Steady Maintained" |
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Why are microtropias hard to measure in fixation pattern test?
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have a dominant eye but equal vision - seem like they will not hold at all but really they have equal vision
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When is the induced tropia test used?
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On ortho patients. Determines whether they have better vision in one eye or not
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Describe the method of the induced tropia test
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on straight patients
- 10-16 D BU or BD prism placed in front of eye while viewing an accommodative target - patient should have induced vertical diplopia - if patient spontaneously shifts eye upward to pick up fixation then fixation is maintained in that eye (alternates freely) - if eye under prism does not shift upward, cover fixing eye and allow eye under prism to pick up fixation - remove cover - is fixation held? briefly? through blink? through pursuit? |
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Why is it important to get the patient to hold through smooth pursuit in an induced tropia test?
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false negatives possible when done just to a stationary target
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What is preferential looking? Give an example of a test that can be done in clinic which demonstrates this
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Grating type of acuity
ex - Teller cards |
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What does VEP stand for?
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Visually Evoked Potential
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What is a VEP?
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VEP records brain response to visual stimuli
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What is postrotary nystagmus?
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induced nystagmus by focusing on a rotating target
- normals stop nystagmus after 3-5 seconds of stopping - blind - nystagmus continues for 15 to 30 sec |
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Optokinetic Nystagmus =
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Nystagmus induced by moving images across visual field
- eyes follow right and jerk left - adults can intentionally blur image and have no response |
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When are Candy Beads used?
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4-6 months of age - have pincher control
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When are Allen symbols used?
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get a rough estimate of difference between 2 eyes
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What is similar about Sheridan Gardener and Lighthouse test?
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single letter or single picture as stimulus
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What are the two types of nystagmus?
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1. Manifest - present when patient sing binocular vision
2. Latent - always there but only becomes apparent when one eye is occluded Can also have some latent with manifest nystagmus |
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What are the testing procedures for a patient with nystagmus?
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- allow head posture
- start higher up on chart since they usually have reduced acuity - measure monocularly and binocularly |
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What are methods of occlusion for a patient with nystagmus?
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1. High plus lens - blurs vision significantly but still allows some light to the eye
2. Vectograph slide - polarized lens only allows some letters to be perceived with one eye 3. Duochrome - half red half green 4. hold hand in front of but not completely covering 5. translucent occluder |
