Contrast sensitivity functions measured using simple optics and computer testing

Purpose: Contrast sensitivity function (CSF) testing is a common approach to assessing clinical changes to specific aspects of spatial vision. Different stimulus presentations and testing procedures, however, yield significant differences in CSF curves that are more a feature of the method than the observer. In this study, we designed a simple optical device for measuring CSF that could be directly calibrated and compared with a commonly used computer-based system. Methods: Twenty-one participants (M = 28.95 +/- 10.34 years; 66.7% female; 81.0% non-Hispanic White; best corrected visual acuity 6/9 or better) provided photopic CSFs (from measurements at 1.6, 3.2, 8, 16 and 24 cycles per degree, with spatial frequency presentation randomised) using both the Metropsis test platform and a simple optical device over two test sessions (one session/method, randomised, counterbalanced) separated by 1-7 days. The optical system used 520 nm lasers that were made Lambertian using two integrating spheres with a 3.5 degrees circular exit port. These beams were combined with a beam splitter that allowed constant measurement of light output and contrast modulation using sine-wave gratings on glass. In Metropsis, 2 degrees Gabor stimuli were presented for 0.5 s with either a vertical or a horizontal orientation via a two-alternative forced choice paradigm with contrast modulated until four (first) and eight (last) reversals were complete. Results: Both methods took approximately the same amount of time to generate a CSF and yielded curves that were consistent with past studies using similar methods but different from each other. The optical system showed a 3.5 times higher maximum sensitivity and yielded higher test-retest reliability. Conclusions: Using simple optics to measure CSF yields low noise, high sensitivity and reliability. The ability to calibrate the stimuli directly is an advantage over computer-based methods.

Automated summary

This study designed a simple optical device for measuring CSF and compared it with a computer-based system, finding slightly different results between the two methods, with the optical system showing higher sensitivity and test-retest reliability. Using simple optics to measure CSF reduces noise, increases sensitivity and reliability, and allows for direct calibration of stimuli.