Global shape integration optotypes for the clinical assessment of visual acuity and subjective refraction

Abstract

Purpose : Currently available optotypes rely on a resolution task to measure subjective refractive errors, visual acuity and/or contrast sensitivity. In order to further integrate global shape processing, we have investigated the usability of radial frequency (RF) pattern as optotypes to assess the visual acuity (VA) and subjective refraction (SR).

Methods : For VA testing, RF-patterns consisting of a base circle with a cross-sectional luminance profile of a Gaussian filter, were reduced in diameter using a psychophysical staircase method incorporating a 4AFC (experiment 1) or a 2AFC task (experiment 2). Similar to the Landolt C, the smallest detectable detail was five times smaller than the global diameter of the RF pattern. SR was assessed by the same optometrist, using an EDTRS layout existing of five lines with RF patterns, calculated to cover visual acuities between 0.2 to -0.2 logMAR. Optotypes to measure VA and SR were validated in 16 participants (mean spherical equivalent error M = -2.18 ± 3.07 D), using the standard Landolt C stimulus with the same psychophysical paradigms as described above. Power vectors (M, J₀ and J₄₅) from SR using RF and standard optotypes was evaluated based on Bland-Altmann-analysis.

Results : VA from the experiment 2 resulted in significant different values (ΔVA = 0.29 ± 0.04 logMAR, p < 0.001) compared to the standard procedure. However, the 4AFC task (experiment 1) does not show a significant difference (ΔVA = 0.02 ± 0.02 logMAR, p = 0.37) and good intra class correlation (ICC = 0.689), when compared to standard optotypes. No significant bias between RF and standard optotypes for the assessment of SR was observed. Limits of agreement are comparable to those from repeated measurements of the SR (M = ± 0.56 D, J₀ = ± 0.14 D and J₄₅ = ± 0.14 D). Best corrected visual acuity (BCVA), tested after standard SR, resulted in no significant difference compared to refraction based on RF pattern (ΔBCVA = 0.04, p = 0.23, paired t-test).

Conclusions : The current investigation showed that radial frequency patter (RF) can serve as visual stimuli for the assessment of the visual acuity and subjective refraction. We report values on the validity and showed an excellent agreement between the RF pattern and standard optotypes. Further studies could show their ability for the assessment of the contrast sensitivity function.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.