Normative best-corrected values of the visual image quality metric VSX as a function of age and pupil size

Abstract

The visual image quality metric the visual Strehl ratio (VSX) combines a comprehensive description of the optics of an eye (wavefront error) with an estimate of the photopic neural processing of the visual system, and has been shown to be predictive of subjective best focus and well correlated with change in visual performance. Best-corrected visual image quality was determined for 146 eyes, and the quantitative relation of VSX, age, and pupil size is presented, including 95% confidence interval norms for age groups between 20 and 80 years and pupil diameters from 3 to 7 mm. These norms were validated using an independently collected population of wavefront error measurements. The best visual image quality was found in young eyes at smaller pupil sizes. Increasing pupil size caused a more rapid decrease in VSX than increasing age. These objectively determined benchmarks represent the best theoretical levels of visual image quality achievable with a sphere, cylinder, and axis correction in normal eyes and can be used to evaluate both traditional and wavefront-guided optical corrections provided by refractive surgery, contact lenses, and spectacles.

Comparison of Wavefront-guided and Best Conventional Scleral Lenses after Habituation in Eyes with Corneal Ectasia

“…Although the total magnitude (RMS) of higher-order aberrations was reduced to within normal levels for 85% of eyes, the distribution and magnitude of individual aberration terms residual through the wavefront-guided lenses interacted visually such that logVSX for the majority of eyes did not reach the objectively optimized levels of best-corrected normal eyes. 46 Considering, the realistic variability of subjective refraction, 14 eyes reached the logVSX limits (−0.580 ±0.239; 5 mm pupil diameter) calculated from the typical subjective refraction of 200 young normal eyes. 56 This indicates that further improvement in visual quality is possible as wavefront-guided corrections continue to be improved and might involve, for example, targeting particular aberrations such that the residual distributions of higher-order aberrations better resemble those of normal eyes.…”

“…While the pattern of results for logVSX agrees with the other outcomes and best visual image quality was provided by the wavefront-guided lenses, the majority (18) of eyes did not reach the high logVSX levels theoretically obtained by objectively bestcorrecting normal eyes. 46…”

“…49 In this study, the magnitudes and distributions of residual higher-order aberrations, through best conventional lenses, interacted such that all eyes remained outside the objectively optimized logVSX levels of best-corrected normal eyes. 46…”

“…In (B) two eyes of a subject are plotted in the same color; right eyes solid; left eyes dashed; symbols indicate severity grade of posterior radius of curvature. 33 Age-matched 95% limits are for objectively best-corrected normal eyes (Hastings et al 46 ). Table 1.…”

Combining optical and neural components in physiological visual image quality metrics as functions of luminance and age

“…Additionally, the convention of reporting wavefront error at a common pupil size (American National Standards Institute, 2004) across individuals has meant that normative values of best-corrected visual image quality as a function of age were defined at fixed pupil sizes (Hastings, Marsack, Thibos, & Applegate, 2018). Although these have often been clinically satisfactory at the level of an individual patient, we also desire metrics that respect real-world physiological conditions.…”