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Gareth D Hastings, Jason D Marsack, Raymond A Applegate; Normative values of the visual image quality metric VSX as a function of age and pupil size. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1122. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The visual image quality metric Visual Strehl (VSX) combines a comprehensive description of the optics of an eye (wavefront error (WFE)) with an estimate of the neural processing of the visual system, and has been shown predictive of subjective best focus and well correlated with change in visual performance. Given the demonstrated capability of VSX to quantify the visual quality of optical corrections, especially where residual diopters and RMS WFE fail to do so, this study aimed to establish normative values of best-corrected VSX as a function of pupil size and age.
Previously collected WFE data from the Texas Investigation of Normal and Cataract Optics (TINCO) study, recorded on one dilated eye of 146 subjects from 20 to 80 years of age, were fit with tenth-order Zernike expansions and scaled to 7, 6, 5, 4, and 3 mm diameters. A set of 95454 sphere, cylinder, and axis combinations were searched for the prescription (termed best-corrected) that provided best visual image quality for each eye at each fixed pupil size. Because physiological pupil size decreases with natural aging, VSX was also calculated for physiological pupil sizes under a range of luminances (10-4 to 104 cd/m2) as a function of age. Towards validation of the presented norms, VSX was calculated for an independently collected WFE dataset and compared with the confidence intervals (CI) of the corresponding norms.
Best corrected VSX as a function of age and pupil size quantitatively agreed with the prevailing qualitative understanding of image quality, that is, best visual image quality was found in young eyes (20 to 30 years old) at small pupil diameters (3 mm), and VSX decreased as age increased and as pupil size increased, with pupil size causing a more rapid decrease. Both variables had statistically significant influence (p<0.0001); multiple regression is logVSX = 0.414 – 0.005*age – 0.122*pupil size. When natural decrease in pupil size with age was considered, VSX was almost constant across age for most luminances.
The 3-D relation of best-corrected VSX, age, and pupil size is presented and 95% CI norms are provided for age groups between 20 and 80 years and pupil sizes from 3 to 7 mm. These norms can be used to evaluate both traditional and wavefront-guided optical corrections provided by refractive surgery, as well as contact lens and spectacle corrections.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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