Influence of spatial distribution with blur on fluctuations in accommodation.

PURPOSE

We investigated the influence of spatial distribution of retinal image with blur on the waveform of microfluctuations in accommodation.

METHODS

We studied changes in accommodation in 8 young emmetropic subjects (21.88 +/- 2.36 years old), who viewed monocularly a target with the natural pupil. The spatial frequency of the target was varied from 0.85 to 15 cpd in 7 steps, and the blur intensity was increased in 7 steps to obtain a Gaussian distribution of retinal image. Continuous accommodation signals were recorded using an eye-tracking infrared optometer with a sampling frequency of 40.98 Hz, and analyzed with a fast Fourier transform (FFT) analyzer. The power spectra of the low frequency component (LFC, < 0.6 Hz) and the high frequency component (HFC) at approximately 1.9 Hz were calculated for each target with a frequency resolution of 0.02 Hz.

RESULTS

Microfluctuations in accommodation increased as the blur was increased and decreased at further increases in blur intensity level. Microfluctuations peaked at a lower blur level as the spatial frequency was increased. Power spectral analysis revealed that these changes in the microfluctuations could be attributed mainly to increases of power in the LFC.

CONCLUSIONS

Blurring of the edge and reduction in contrast provided accommodative cues, inducing microfluctuations in accommodation, and the LFC increased as the target sharpness was reduced, possibly in an attempt by the accommodation system to maintain the sharpness of the retinal image under poor stimulus conditions. However, when the blur level was increased, the amount of blur was indistinguishable and microfluctuations in accommodation decreased.