Effect of target luminance on microfluctuations of accommodation

Abstract

It is feasible that small temporal variations in steady-state accommodation may provide feedback to the accommodation control system through changes in retinal image contrast and that this feedback may be used to maintain an optimal accommodation response. The complex waveform of microfluctuations is dominated by two distinct regions of activity; a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.0 < or = HFC < or = 2.3 Hz). Whereas the HFCs appear to be correlated with some intraocular manifestation of arterial pulse the contribution of the LFCs to the control of steady-state accommodation is unclear. The present study investigates the effect of target luminance on the waveform of accommodative microfluctuations. Three young emmetropic observers viewed monocularly a high contrast (90%) Maltese cross target placed at a vergence equal to their dark-focus level of accommodation in a Badal stimulus system. The luminance of the target was varied from 0.002 to 11.63 cd m-2 in nine equal logarithmic steps. Five continuous accommodation signals were collected for each viewing condition at a sampling rate of 102.4 Hz, and average power spectra subsequently calculated with a frequency resolution of 0.1 Hz. One-way ANOVA revealed a significant variation in the root-mean-square (r.m.s.) value of the microfluctuations (F = 19.795, d.f. 124, P = 0.0001) which could be attributed mainly to increases in the r.m.s. value for the two lowest luminances (0.002 and 0.004 cd m-2). Power spectrum analysis revealed that these changes in the microfluctuations could be attributed to increases of power in the LFC.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between object spatial profile and accommodation microfluctuations in emmetropes and myopes

“…These theories are supported by findings showing that the magnitude of the accommodation microfluctuations vary systematically with target characteristics such as target luminance (Day, Seidel, Gray, & Strang, 2009a;Gray, Winn, & Gilmartin, 1993b), the spatial frequency (SF) content of the stimulus (Niwa & Tokoro, 1998) as well as with variations in ocular depth of focus induced by alterations in pupil size (Campbell et al, 1959;Day et al, 2009a;Gray, Winn, & Gilmartin, 1993a;Stark & Atchison, 1997).…”

“…The shallower contrast gradient available at luminances e0.002 cd/m 2 is caused by a reduction in the SF content available to the accommodation error detector (Day et al, 2009a). Accommodation microfluctuations are found to increase in magnitude at these lower luminance levels, and it is thought that the microfluctuations increase because larger changes in focus are required to produce alterations in the contrast gradient detectable by the accommodation controller (Day et al, 2009a;Gray et al, 1993b).…”

Microsaccades drive illusory motion in theEnigmaillusion

“…The two groups reported contradictory results: According to Zeki, the illusion could be seen through the pinhole [and thus the percept was not caused by accommodation fluctuations (23)], whereas Gregory reported that the pinhole abolished the illusion (26). The logic underlying these experiments was problematic, however, because a pinhole does not optically mitigate accommodation fluctuations (51,53,54). Although a small pinhole will prevent large accommodative responses (such as those related to shifting one's gaze between objects located at different distances), it does not eliminate the accommodation fluctuations found during visual fixation.…”

“…Zeki used both 1.6-and 2.2-mm pinholes (23), whereas Gregory used a 4-mm pinhole (26). Moreover, as pointed out by Mon-Williams and Wann (17), the 4-mm pinhole used by Gregory (26) was too big to prevent even large accommodative responses (51).…”

“…Although a small pinhole will prevent large accommodative responses (such as those related to shifting one's gaze between objects located at different distances), it does not eliminate the accommodation fluctuations found during visual fixation. Specifically, pinholes larger than 2 mm have no effect on the fluctuations, whereas pinholes smaller than 2 mm increase the power and amplitude of the fluctuations (51,53,54). Zeki used both 1.6-and 2.2-mm pinholes (23), whereas Gregory used a 4-mm pinhole (26).…”