Effect of target spatial frequency on accommodative response in myopes and emmetropes

Abstract

This study investigates whether systematic differences exist between the accommodation response/stimulus curves of emmetropes and myopes when the targets are sinusoidal gratings, in particular whether myopic accommodation is relatively less effective when presented with targets of high spatial frequency due to increased tolerance to defocus blur. Ten emmetropes (overall mean sphere +0.19 D, range -0.37 to +1.37 D) and 10 myopes (overall mean sphere -2.89 D, range -1.13 to -6.63 D) viewed Gabor targets with dominant frequencies 1, 4, 8 and 16 c/deg. Maximal grating contrast was 80% and the full, green, stimulus field was 6 deg. Subjects were aged between 18 and 37 years. A further high-contrast 6/30 optotype target was included for comparison purposes. Viewing was monocular, the other eye being occluded. Stimulus demand was varied with trial lenses over the nominal range 0 to 6.0 D and the corresponding accommodation responses were recorded with an open-view, Shin-Nippon SRW-5000 auto-refractor. The resulting accommodation response/stimulus curves were characterized by their slopes over the stimulus range 1.5 to 6.0 D and by an "error index" indicating the extent to which the responses differed from the ideal 1:1 response/stimulus line. No significant differences were found between the mean accommodative behavior of the two refractive groups for any target. There were, however, substantial inter-subject differences. Some subjects in both groups showed more accurate responses with the higher spatial-frequency targets, while others showed optimal response at intermediate frequencies. Although it has been reported in the literature that, in comparison to emmetropes, myopes have reduced sensitivity to blur and response/stimulus curves of lower slope, the present study failed to demonstrate any reduction in their responses to gratings of relatively high spatial frequency. For each target the two refractive groups showed similar accommodative behavior.

Immature visual neural system in children reflected by contrast sensitivity with adaptive optics correction

“…Nevertheless, we should point that some potential uncorrected defocus might still exist and thus affect subjects' performance. However, such uncorrected defocus, if existed, was likely to have no notable effect on the comparison of CSFs between children and adults in the current study: Firstly, it has been shown that defocus has larger effect on visual performance with AO-correction than that without AO-correction414647. Thus, if the uncorrected defocus affected children more, we would expect less benefit from AO correction in children, which was not the case in our study.…”

Subjective versus Objective Accommodative Amplitude

“…Although this methodology may have impacted subjective amplitudes, it is not believed to have had an impact on the objective measurements of accommodative amplitude, given the previous evidence that a large range of spatial frequencies stimulate accommodation equally. 32 To further support this, objective proximal stimulated amplitudes were measured in two adults and one five year old subject using the 1.5 mm letter from the present study design versus a 0.7 mm letter for comparison. No appreciable differences in measured amplitude were found when comparing letter sizes (differences ranged from a 0.36 D decrease in amplitude with the smaller letter to a 0.14D increase in amplitude with the smaller letter across subjects).…”

Accommodative Responses Under Different Stimulus Conditions

“…5Y7, 21,22 However, the results of some studies were inconsistent when the slope was used alone to assess the difference in accommodative response between refractive groups, especially between myopes and emmetropes. 5Y7, 21,22 However, the results of some studies were inconsistent when the slope was used alone to assess the difference in accommodative response between refractive groups, especially between myopes and emmetropes.…”