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J. C. Rabin, D. Ivan, J. Gooch, R. Rubin, S. Linnemeyer, M. Foxworth; Beyond 20/20: New Metrics for Quantifying Subnormal and Supernormal Vision. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5516.
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© ARVO (1962-2015); The Authors (2016-present)
Sensitive metrics to quantify enhancements and decrements in vision are needed to complement recent advances in wavefront technology, refractive surgery and treatment of eye disease. While visual acuity (VA) remains the cornerstone of clinical vision care, symptoms can prevail and performance can suffer despite normal VA. We describe theory, sensitivity and application of a multi-dimensional approach to quantify quality-of-vision (QOV) in optical, retinal and post-retinal conditions.
QOV tests include: (1) Monocular and binocular contrast sensitivity (CS) and reaction time with FDA-recommended sine-wave gratings (0.9, 3, 6, 12 & 18 cycles/deg Gabor, Best-Pest detection; Cambridge Research Systems Ltd); (2) Photopic letter CS (20/50 letter chart, PrecisionVision®); (3) Simulated night vision goggle (NVG) VA and CS (letter chart with 4 cd/m2 low luminance green filter); (4) Higher order aberrations (RMS; WavescanTM) quantified as an aberration ratio (AR): log(measured RMS/expected RMS for same pupil size). Sensitivity of QOV tests (percent >2SD below normal mean) was determined for keratoconus and PRK patients (n=204) meeting the current 20/20 VA standard; while specificity (percent normals within 2SD of mean) based on CS normative data (n=98) and patients pre-operative to PRK (n=74).
Mean specificity of grating CS is 98% across five spatial frequencies (SFs) and 99% when expressed as the sum of log CS (sumCS) across five SFs. The high specificities of AR (97%), letter CS (96%), and NVG VA and CS (95%) confirm that all QOV metrics have a low false positive rate (mean=2.7%). In keratoconics with 20/20 VA moderate sensitivity is achieved with AR (60%) and the new metric sumCS (47%) while letter CS (25%), NVG VA (24%) and NVG CS (19%) show lower sensitivity. Consistent with minimal symptoms, test sensitivity in PRK patients with 20/20 was low (AR 19%, NVG VA 9%, letter CS 8%, NVG CS 6%, 12 cycles/deg CS 5%, sumCS 4%) but higher than the sample of visually normal observers. Individual cases of glaucoma and retinopathy show prolonged CS reaction times.
Grating and letter CS, simulated NVG (low luminance) VA and CS, and the aberration ratio can disclose potential decrements in visual function despite 20/20 VA. High sensitivity and specificity are achieved with this QOV battery, with contrast specific and global reaction time promising to be additional sensitive metrics. The sum of log CS values across the CS function is a sensitive, computationally-simple metric of QOV.
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