Abstract
Purpose: :
The magnitude of the accommodation microfluctuations has been found to increase when viewing a target through a 0.5mm pinhole and this has been attributed to an enlarged depth of focus. Increases in the size of depth of focus have been found in myopes when compared with emmetropes. The aim of this study is to investigate the interaction between depth of focus and refractive error by measuring changes in accommodation microfluctuations induced by a range of pinhole sizes in emmetropic and myopic eyes.
Methods: :
Thirty subjects (14 emmetropic/16 myopic) viewed a high contrast (80%) Maltese cross target (angular subtense 15 deg) monocularly through a +5 D Badal lens. The target was placed at a stimulus vergence which produced an accommodation response equal to the open loop level. A Maxwellian View system imaged pinholes of size 0.5, 1, 2, 3, 4 and 5 mm in a random order at the nodal point of the eye. Myopic subjects were fully corrected using daily disposable soft contact lenses. Accommodation responses were measured continuously at a sampling rate of 52 Hz using a modified open view Shin–Nippon SRW–5000 autorefractor. Two minutes of data were recorded for each pinhole size.
Results: :
There was no significant variation in the static accommodation response level with changing pinhole size (p = 0.956). The mean rms of accommodation microfluctuations increased significantly as pinhole size reduced (p < 0.0001).The microfluctuations while viewing through the 0.5 mm pinhole were significantly larger than through all other pinholes (Scheffe Post Hoc, p < 0.02) and the microfluctuations through the 1 mm pinhole were significantly larger than the 4 and 5 mm pinholes (Scheffe Post Hoc, p < 0.03). These increases were mediated by the low frequency component (p<0.01). There was no significant difference in the microfluctuations between emmetropes and myopes (p = 0.07). Cluster analysis revealed two distinct subject groups, 21 subjects showed an average increase in mean rms of 0.05 ± 0.04 D compared to 9 other subjects who showed an average increase in mean rms of 0.19 ± 0.04 D. There was a significant difference in the behaviour of these 2 groups (p < 0.0001). The latter group comprised of 4 emmetropes and 5 myopes.
Conclusions: :
The magnitude of accommodation microfluctuations was found to increase in all subjects while viewing targets through pinholes of < 2mm diameter. The magnitude of the increases were subject dependent but unrelated to the refractive error of the subjects. This suggests that the importance of retinal image blur as an accommodation controller may vary between subjects irrespective of their refractive error characteristics.
Keywords: myopia • refractive error development