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48 Cards in this Set
- Front
- Back
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What is visual acuity
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1. The ability to distinguish object details and shape
2. Assessed by the smallest identifiable object that can be seen at a specified distance |
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What are cones
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1. Used for fine detail and colour vision
2. Decreased sensitivity in low illumination 3. Has fewer intermediate connections than rods30 sec of arc in size |
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What are rods
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1. We have a much higher ratio to bipolar and ganglion cells
2. Increased sensitivity in low illumination 3. Lower resolution but increased sensitivity than cones |
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types of visual acuity
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1. Minimal resolvable
2. Minimum visible 3. Minimal discernable |
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What is minimal resolvable
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1. Identifies features of a target
2. Normal can resolve 30 – 60 seconds of arc 3. Typical description of VA |
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What is Minimal visible acuity?
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1. Single line or spot on a white background
2. Normal’s can see 1 sec of arc 3. Even those with poor vision can see minimal visable |
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What is Minimal discernable or hyperacuity
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1. Ability to detect a shift in a line
2. Normal’s can detect 2 to 10 seconds of arc |
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What is the arc seconds of the Snellen E
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1. 5 seconds of arc
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what is acuity as a ratio
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2. d/D
3. where d= the viewing distance 4. D= the distance were the letter spokes subtend 1 min of arc on the retina |
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What is legal blindness
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1. 6/60
2. 6/15 in one eye only on snellen |
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which eye do you test first
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1. right first or the amblyopic eye, so if that is the left eye then do that
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what do they do if they are not 6/6
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2. pinhole -> allows direct path of light to retina rather than distortion of the light rays from the surface f the eye. If improves uncorrected refractive error
3. +/- .50 4. single letters- eliminates crowding can help with amblyopics |
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What types of Nystagmus are there
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1. Manifest-present when binocular
2. Latent- becomes apparent when 1 eye is occluded 3. Can have both |
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What do you do if patient has Nystagmus
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1. allow head posture, may have a point where it is minimized
2. often have reduced acuity start higher up on chart 3. will have better acuity at near 4. use hi plus lens 5. /genie paddle 6. use vectograph with polarized glasses 7. red green duochrome with red filter glasses will only see one or the other but done with both eyes open to minimize nystagmus |
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what are the infancy version of LH
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lighthouse
symbols no crowding not a lot of choices |
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Ffooks symbols
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1. variety of shapes
2. patient has shapes to hold 3. good for children who need tactile stimuli 4. no crowding, not a lot of shapes, usually done at 1m |
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what do you do if they cannot read the largest letter
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1. use low vision charts
2. walk to chart, only top number changes 3. count fingers 4. hand motion 5. light projection 6. light perception 7. no light perception |
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Disadvantages of tumbling E
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1. lateral directions
2. only 4 posibilities 3. often no crowding, which can help discover mild amblyopia 4. little form of discrimination, E is constant |
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what visual acuity tests are used for literates
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1. snellen
2. sloan 3. LogMAR 4. ETDRS |
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Near vision tests
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1. Sloan
2. Rosenbaum 3. Fonda-Anderson 4. Lebensohn chart 5. Maclure reading book |
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Visual aquity for prelierates
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1. HOTV
2. LH symbols (Lea) 3. Follows a face 4. Heidi Paddles 5. Fixation Patterns |
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What are disadvantages of Snellen chart
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1. Different number of letters per line
2. Size gap between letters inconsistent 3. Some letters easier than other 4. Minimal angle of resolution varies from line to line |
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Explain Sloan
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1. After snellen
2. Mostly same amount of letters on each line 3. Gaps between each letter is one letter size 4. Same difficulty of letters 5. Minimal angle of resolution varies from line to line |
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Log mar
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1. MAR minimum angle resolvable
2. Letters on each line are 1.2589x the letters on the previous chart 3. Logarithmic progression 4. Most designed |
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ETDRS
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1. Consistant number of letters, gap size, letter difficulty
2. Crowing effect exists uses logMAR 3. Calibrated in lanes for 8 feet |
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How many letter per line do you have to get to get the line
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3
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If patient improves near vision in amblyopia
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Will be first to improve and this is encouraging
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Where do you test for sloan
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@40 cm, does not have logarithmic progression, has crowding
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what is the rosenbaum test
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tumbling e
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what is the fonda-anderson
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test
print in a variety sizes and different source of print, i.e. phone book, bible. |
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HOTV
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1. Preliterate
2. logMAR 3. more difficult for kids to name in comparison to LH 4. has matching card 5. HOTV are reversible 6. Agreeable with adult vision 7. One and 4 chance of getting it right |
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LH (Lea symbols)
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1. Easier for younger kids to name
2. Logarithmic 3. Crowding 4. Can point |
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Follows a face
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1. Reflex present between 6 weeks and 2 months
2. no glasses 3. if not there by 4 months 4. write as f/f face light toy |
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Heidi Paddles
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1. can be adapted fo preferential looking test using a blank
2. largest heidi tests monocularity |
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Fixation Patern
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1. central
2. maintained 3. steady 4. if strabismus will they let either eye turn equally 5. does the eye fix centrally or eccentrally C UC 6. steady or nstagmus S or US 7. does the eye maintain when occluder removed or give up to the better seeing eye M UM immediately = amblyopia held briefly = some amblyopia through a blink = likely equal |
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why do we need to be careful of Microtropia
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because they always have a dominant eye and will often not hold at all despite having equal visual acuity. Results in a high false positive rate on these individuals
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what is induced Tropia test
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used on orthotropic patients
16/10 pd prism placed in front while looking at an accommodative target should induce vertical diplopia if eye picks second image, fixation is maintained within that eye. Alternates freely if no shift upward, cover fixating eye and allow the prism to pick up fixation how long is it held need to make sure that they hold through a smooth pursuit can be used in distance |
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What tests can we use for preferential looking
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1. Heidi padles
2. Teller cards 3. Cardif cards |
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How do you use teller
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1. performed at 38cm
2. monoculary 3. don’t be biases 4. have to get the answer right 3x to get the card |
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what are the advantages and disadvantages of teller
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1. relatively inexpensive
2. assigns a value to acuity allows comparison between visits 3. cumbersome and requires tech to perform 4. overestimates acuity 5. requires parents to help |
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electrophysiology
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1. measured VEP, visually evoked potential
2. can be done on infants 3. uses electrodes 4. measures signam to the brain 5. good for low vision 6. see if pathway is intact or if its slow 7. expensive 8. need someone well trained |
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What are cardif cards
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1. similar to teller
2. uses pictures 3. performed at 50cm 4. 3 cards at same level have to get 2 out of 3 |
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what are the advantages and disadvantages of Cardiff card
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1. well organized
2. quick and easy 3. gives a measure, better than fixation pattern 4. overestimats acuity 5. no crowding what type of vision is it really measuring |
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what is postrotary Nystagmus
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1. test when you suspect blindness
2. mom holds baby 3. rotate on stool, if turning right should show left beating Nystagmus 4. normas have 3-5 seconds after stop 5. blind continues 15-30 seconds after stopping 6. can be used for child with ET to fully abduct |
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Optokinetic Nystagmus and three tests
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1. evoked by images moving across your visual field
2. peripheral type of stimulus target moved right saccadic left movements 3. tests subcortically 4. adults will attempt to blur image and not respond if attempting to malinger 5. child has to be attentive 6. catford drum- minimal dots variable sizes rotated 7. okn tape 8. okn drum |
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candy beads
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1. need to have pincher reflex, 4-6 months
2. good to displayreduced vision in one eye (amblyopia to parents) |
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Allen Pictures
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1. supposed to be equivalent to snellen
2. images are not mathematically constructed 3. can show difference between 2 eyes but not really a number 4. gives false acuity 5. symbols are out of date (i.e. phone) 6. best possible is 20/30 7. |
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tumbling E
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1. can be used on illiterate adults
2. mathematically constructed letter 3. presented at different size and direction 4. can cause language barriers |
