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Alexandra V Kalpadakis-Smith, Vijay Tailor, Annegret H Dahlmann-Noor, D Sam Schwarzkopf, John A Greenwood; The acuity and crowding deficits in strabismic amblyopia are stronger in the fovea than the visual periphery. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5960.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is characterised by reduced acuity in one eye, despite optical correction. When associated with strabismus, foveal vision is further impaired by crowding. In unaffected vision, crowding is minimal in the fovea but rises in the periphery – an effect attributed to receptive field size increasing with eccentricity. Whether acuity and crowding are further elevated in the amblyopic periphery is unclear. We investigated the peripheral deficit pattern to gain insight into the changes associated with amblyopia across the visual field.
We tested 8 participants with typical vision (aged 20-44 years) and 8 with strabismic amblyopia (aged 19-43). Participants reported the orientation of a Landolt-C target, either in isolation (acuity) or surrounded by 4 flanker Cs (crowding). Stimuli were presented monocularly in the fovea and periphery (2,4,8,12°), either to the amblyopic eye or to the dominant eye for controls. A modified QUEST procedure was used to measure the minimum gap-size threshold for isolated and crowded targets. Eye movements were recorded to ensure fixation.
Characteristic of amblyopia, acuity thresholds were elevated in the fovea (M=4.3’ ±4.5’ SD) compared to control participants (0.9’ ±0.3’). Amblyopic acuity thresholds were also increased across peripheral vision (e.g. 12° nasal: 14.7’ ±8.5’) compared to controls (7.7’ ±1.9’). Crowded gap-size thresholds were further elevated in the amblyopic fovea (10’ ±10.3’), with controls showing minimal foveal crowding (1.3’ ±0.3’). Crowding was elevated in all eccentric locations in the amblyopic (e.g. 8° temporal: 38.4’ ±9.4’) compared to the control periphery (9.6’ ±6.4’). Although thresholds were elevated across the amblyopic visual field, the greatest deficit was foveal: amblyopic thresholds for acuity and crowding were on average 4.7× and 9× those of controls, respectively. For peripheral acuity, this elevation dropped to 3× controls at 2° and to ×1.8 at 12°. Peripheral crowding dropped even more rapidly to 1.2× at both 2° and 12°.
The greatest elevations in acuity and crowding are found in the fovea. Although these deficits persist in the periphery, their magnitude is reduced, particularly for crowding. Given the potential link between crowding and receptive field size, we are exploring whether this deficit pattern is associated with fMRI measures of population receptive field size.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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