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AMBLYOPIA - 2

AMBLYOPIA - 2. Ralph P. Garzia. Non-visual acuity deficits in amblyopia. reduced contrast sensitivity deficient accommodative skills amplitude, facility, lag deficient oculomotor skills fixation, pursuits, saccades spatial uncertainty spatial distortion eccentric fixation.

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AMBLYOPIA - 2

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  1. AMBLYOPIA - 2 Ralph P. Garzia

  2. Non-visual acuity deficits in amblyopia • reduced contrast sensitivity • deficient accommodative skills • amplitude, facility, lag • deficient oculomotor skills • fixation, pursuits, saccades • spatial uncertainty • spatial distortion • eccentric fixation

  3. Amblyopia & contrast sensitivity Note the differences in CSF function between amblyopes

  4. Amblyopia& accommodation normal accommodative stimulus-response curve

  5. Amblyopia & accommodation Amblyopic accommodative stimulus-response curve

  6. Accommodation & amblyopiaEffects of eccentric fixation Normal accommodative responses as a function of amount of eccentric fixation or retinal eccentricity

  7. Accommodation & amblyopia • Latency • increased • Gain • reduced • Amplitude • reduced • Facility • reduced

  8. Amblyopia & fixation instability fixating a + > steady fixation >

  9. Amblyopia & steady fixation EOG’s more instability > with greater acuity loss > >

  10. Amblyopia & smooth pursuits EOG of smooth pursuit to sinusoidal stimuli • acceleration • uniform velocity • saccadic intrusions

  11. Amblyopia & saccades Dysmetria multiple small saccades in the direction of the target displacement

  12. Oculomotor deficits in amblyopia • Fixation • unstable • increased drift amplitude • Saccades • increased latency • decreased peak velocity • dysmetric • Pursuits • increased number of loses of fixation • increased number of saccadic intrusions • decreased gain

  13. Snellen Acuity vs grating acuity Anisometropic amblyopes A’s cluster on the 1:1 line Strabismic amblyopes S’s are far to the right normal eyes > Strabismic amblyopes: • oculomotor problems • spatial distortion problems

  14. Oculomotor effects • Snellen vs. grating acuity • VEP’s • CSF • Interferometry What these have in common is a spatially redundent pattern.

  15. Amblyopia and visual acuity behavior Typical letter confusions made by amblyopic eyes Note the confusion • similar shapes • sequence errors • transpositions What’s the VA?

  16. Characteristics of visual acuity measurements in amblyopia • crowding effects • distortions / misperceptions • loss of place / out of order • noisy • short and long term variability

  17. Amblyopia and visual acuity behavior Typical letter confusions made by amblyopic eyes Note the confusion • similar shapes • sequence errors • transpositions What’s the VA?

  18. Amblyopia & contour interaction Test stimulus used to determine contour interaction

  19. Contour interactionnormal eyes and amblyopic eyes Contour interaction as multiples of gap width (critical detail) normal eyes > amblyopic eye > ci effects are similar in normal & amblyopic eyes as a function of visual acuity

  20. Psychometric chart • Landolt C’s are the targets • There are 8 at each VA level • There are equal spacing between each of the test optotypes (C’s) and the nearest contour on all 4 sides • Spacing is equal to the overall size of the test optotypes or 5x’s the critical detail

  21. Psychometric or “S” graph • Normal eye has a steep function • Amblyopic eye has a very gradual drop-off of visual acuity

  22. Crowding phenomenon • Entire chart vs. • Whole line vs. • Single letter

  23. Eccentric fixation & visual acuity combine all the lines and get a best fit curve or linear formula: MAR’=.4(ef∆)+1 e.g. ef=1deg=1.75∆ MAR’=.4(1.75)+1 MAR’=0.7+1=1.7’ VA=20/34

  24. Visuoscopy central fixation > nasal eccentric fixation >

  25. Haidinger’s brushes Fixate on the dot: where are the brushes perceived

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