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Vivek Labhishetty, Arijit Chakraborty, William R Bobier; Is blur sensitivity altered in progressive myopic children?. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4755. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Reduced sensitivity to blur leads to large accommodative response lags in progressive myopes. This altered accommodative behavior is associated with a large depth of focus (DOF). However, most of the studies on blur sensitivity were done on adults where the progressive nature of myopia was attenuated considerably. While DOF measures are lacking in school aged progressive myopes, their blur detection and discrimination capacities appear to be similar to their non-myopic peers. Accordingly, the current study objectively quantified DOF in school aged myopic children, as well as their non-myopic peers and adults. Blur detection ability was determined using a psychophysical design.
Blur sensitivity measures were taken from 12 children (8-13 years, 6 myopes and 6 emmetropes) and 6 naïve adults (20-35years). Objective DOF was measured using a dynamic photorefractor which monitored changes in both accommodation and pupil size to step changes in the lens induced defocus (0 to ±1.50D, 0.25 steps) while the subjects viewed a high contrast target through a Badal optical system at both 2 and 4D demands. Blur detection thresholds (BDT) were tested using the same high contrast target in a 2 alternate forced choice paradigm (2AFC, reference and test targets) at both 2 and 4D demands. The rendered blur on the test target was altered using a 2 down-1 up staircase design (0.1D steps) and BDT was calculated by averaging the last 5 reversals.
Accommodative response lags and DOF were significantly larger in myopic children compared to the adults and non-myopes (F = 35.2; p < 0.0001). However, blur detection thresholds were similar across the three subject groups (F = 1.80; p = 0.19). Furthermore, blur sensitivity was poorer at 4D demand compared to the 2D demand across all the three subject groups (F (DOF) = 107.6; p < 0.0001; F (BDT) = 642.3; p <0.0001).
When limited to blur only cues, the findings of a large DOF coupled with high accommodative lags suggests that progressive myopes are less sensitive to retinal defocus. However, progressive refractive error and age had no influence on the ability to detect blur. Taken as a whole, the reduced sensitivity to the defocus in a growing myopic eye appears to be compensated by some form of an adjustment in the higher visual processes, for instance, perceptual adaptation to preserve the subjective percept of clarity even with a poor retinal image quality.
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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