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Clara Mestre, Sonisha Neupane, Vivian Manh, Kristina Tarczy-Hornoch, T Rowan Candy; Vergence and accommodation responses in the control of intermittent exotropia. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2607.
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© ARVO (1962-2015); The Authors (2016-present)
To determine how young patients with intermittent exotropia (IXT) use vergence and accommodation when controlling their deviation.
Vergence and accommodation responses of 25 subjects with IXT (5-31 years) and 17 age-matched typical participants were recorded using simultaneous Purkinje image eye tracking and eccentric photorefraction (PowerRef3). They watched a movie on a 7x7 cm screen, moving between 80 and 33 cm, in binocular and monocular viewing. Data were averaged over 2s windows of stable gaze and refraction during the 8s periods at each viewing distance. Periods of deviation were identified objectively using gaze position in monocular viewing. Fusional ranges were measured at the 80cm distance with a Risley prism. Fusional limits were defined objectively as the last prism for which subjects maintained alignment. Accommodative change during this test was assessed as the difference in refractive state between no prism and the fusional limit prism.
18 IXT participants were aligned throughout the binocular periods at distance and near viewing. Across all participants, vergence and accommodative responses to the change in binocular viewing distance were 10.20±1.96pd and 1.52±0.51D for IXTs, and 10.25±1.75pd and 1.44±0.38D for controls. Responses in monocular viewing were reduced to 6.95±5.23pd and 1.00±0.51D for IXTs, and 4.79±2.13pd and 1.03±0.34D for controls. For participants who deviated spontaneously in binocular viewing at 80cm and had uncorrected hyperopia of <1D, the mean change in eye alignment was 18.39±8.15pd, accompanied by 0.09±0.23D of accommodative change. This was similar to the change in refractive state during monocular viewing at 80cm of control subjects (-0.01±0.12D). 12 IXT patients and 9 controls had fusional divergence limits of 10.12±6.35PD and 8.62±3.80PD, respectively, beyond their dissociated position with refractive changes <0.64D. Fusional convergence limits from the dissociated position were 32.60±10.41PD for IXTs and 21.93±9.52PD for controls (3 reached the maximum prism), typically with <1.00D increase of accommodation.
Most emmetropic or optically corrected IXTs were aligned in binocular conditions with wide fusional ranges, accompanied by only small changes in refraction. This suggests accommodative convergence is not uniquely responsible for control of the deviation in IXT and alignment is not achieved at the expense of focus.
This is a 2021 ARVO Annual Meeting abstract.
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