Amblyopia Flashcards
1
Q
what is amblyopia and its prevalence?
A
- Deficit in visual acuity with no detectable organic cause
- Prevalence 2-3%
– 6-10 million Americans
– 60,000 children per year
– leading cause of monocular vision loss in children - Amblyopia is always associated with a history of an early sensory anomaly
– Strabismus
– Form Deprivation (media opacities)
– Anisometropia, Astigmatism, High hyperopia
2
Q
What is amblyopia also associated with?
A
Prevalence of 3.2%
(<20/30 in 3654 adults; Attebo et al., 1998)
50% associated with anisometropia
27% associated with strabismus and anisometropia
19% associated with strabismus
4% associated with visual deprivation
3
Q
VA in amblyopia
A
- Reduced visual acuity
– Acuity of 20/40 or worse in the weaker eye
– and/or a minimum acuity difference of 2 lines on the acuity chart between eyes
– Measured with recognition acuity tasks (letters or optotypes)
4
Q
Errors with snellen in VA testing
A
- Wide range of errors: miss some large letters & read some smaller ones
- Miscalls are not confusion letters
- Read letters out of order, fewer or more in number
- End-of-row letters more often correct
- Abnormal head position during acuity testing
5
Q
Visual Acuity Testing in Amblyopia
A
- Vision indistinct (not helped by pinhole).
- Line of letters has local compressions and expansions. Separation difficulty or crowding effect found mainly in strabs
- Living with the preferred eye patched, even with fairly good acuity in amblyopic eye, is more bothersome to Strab than Aniso.
- Trend toward non-acuity definitions of amblyopia
6
Q
Spatial uncertainty and distortion with amblyopia
A
- Not sure where some objects are located in space (uncertainty)
-Strabismics show spatial uncertainty AND distortion
-Anisometropes show only spatial uncertainty
7
Q
Contour Interaction and Visual Acuity testing
A
- S-chart: 21 slides that span 20/9 to 20/277 VA
- At each acuity level, the amount of contour interaction is constant
- Visual acuity responses for both eyes of an amblyope tested with S-chart
- The flatter curve for the amblyopic eye reflects the marked variability in acuity responses
8
Q
Visual Acuity Characteristics in Amblyopia
A
- Single optotypes underestimate acuity loss compared to chart acuity tests
- Contour interaction
- Crowding effect in normals is exaggerated in amblyopia
9
Q
Snellen v grating acuity in amblyopia
A
- Grating acuity underestimates loss of Snellen acuity
- Anisometropia
– reduced Snellen VA is proportional to reduced grating VA - Strabismus
– Snellen VA is affected more than grating VA
10
Q
Visual Acuity in
Amblyopia between Snellen and vernier
A
- Grating, vernier and Snellen are linearly related for anisometropes
- Only vernier and Snellen are linearly related for strabismics
- Both grating acuity and Vernier acuity have a strong correlation with optotype acuity
- The loss in Vernier acuity is almost directly proportional to the loss in optotype acuity
– exponent of the power function indicated by the best-fitting line is 1.15 - The loss in grating acuity is on average smaller than the corresponding loss in optotype acuity
– exponent of the best-fitting power function is 0.65, but the correlation value is high
11
Q
Optotype acuity for strabismics vs strabismic anisometropes
A
- For all groups, the loss in grating acuity is less than the loss in optotype acuity.
- Strabismics shallower slope than the whole abnormal population; exponent is 0.31.
- Strabismic anisometropes differs in the intercept of the fitted line – on average, the grating acuity of members was roughly 15% lower than for the whole abnormal population, for any given level of optotype acuity, (prevalence of points in the plot that fall below the line).
12
Q
Relationship between aniso, strab w/ aniso, strab, sporadic strab, eccentric fixators, deprivation amblyopia
A
- For all groups, the loss in grating acuity is less than the loss in optotype acuity.
- strab aniso and strab deviate from the overall trend
- The relationship between grating and optotype acuity in amblyopes with strabismus is different from the relationship in other amblyopes
13
Q
Ratio of grating to Vernier acuity
A
- Development of Vernier and grating acuity
– By 6 mo, ratio 2:1
– By 4 yr, ratio 4:1
– Adult ratio 10:1
14
Q
Contrast sensitivity functions in amblyopia
A
- A grating can be detected if it is visible in any part of the field of view it covers
- Details in letters (optotypes) are hard to see due to local
distortions of the image
15
Q
sensitivity ratio vs spatial frequency
A
- Marked losses of threshold contrast sensitivity in
amblyopia - Reduction in contrast sensitivity is greatest at high spatial frequencies
- Loss of CSF at high SF increases with severity of amblyopia
- Reduced CSF is a neural loss in foveal function
