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Lorraine A. Duffy, Mhairi M. Day, Dirk Seidel, Lyle S. Gray, Niall C. Strang; Accommodation Response Thresholds And Peripheral Refraction In Emmetropes And Myopes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):844.
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© ARVO (1962-2015); The Authors (2016-present)
The accommodation response threshold (ART) describes the required change in stimulus vergence to produce an accommodation response. The aim of this study was to measure ART for axial and peripheral retinal stimuli and relate this to axial and peripheral refraction measures in emmetropes (EMMs) and myopes (MYOs).
5 EMMs and 5 MYOs participated with informed consent. ARTs were measured in the right eye while subjects viewed circular annuli containing a 4cpd vertical sine wave grating in a +5D Badal system. Targets were presented at the open-loop accommodation level and MYOs axial refractions were fully corrected using disposable soft contact lenses. Targets subtended 1deg and achieved retinal stimulation at 0, 4 and 8deg and target vergence varied sinusoidally with a frequency of 0.5Hz. For each trial, 10 continuous measures of accommodation of 16s duration were recorded and power spectra were obtained from fast Fourier transform analysis. The 10 spectra for each stimulus condition were averaged and the power for bins at 0.43-0.55Hz was summed. ART was defined as the stimulus amplitude at which a significant increase in power occured compared to a stationary target (0Hz). Peripheral retinal defocus was calculated based on refraction measures obtained using a Grand Seiko FR-5000 autorefractor at the open-loop accommodation level. Pupils were dilated with phenylephrine 10% and the instrument was rotated to obtain measures at 0, 5 and 10deg nasal and temporal along the horizontal meridian.
Mean±SD central ART (0.42±0.08D) was similar in both refractive groups (p>0.05) . ARTs increased linearly with eccentricity in EMMs (0.06D/deg, R2=0.99) and MYOs (0.11D/deg, R2=0.99). MYOs showed significantly higher ARTs than EMMs at 4 and 8deg (p<0.05). Peripheral defocus did not change significantly up to 10deg retinal eccentricity and was similar in MYOs and EMMs (p>0.05).
Peripheral ARTs in MYOs are not affected by the peripheral refraction. This would suggest that the cause of higher peripheral ARTs in MYOs is neural in nature. The findings suggest that the accommodation control mechanism in myopes integrates information over an extended retinal area which could explain increased accommodative microfluctuations previously reported in this refractive group.
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