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Sanjeev Kasthurirangan, Carrie Garufis; Letter Based Contrast Sensitivity Assessment for Clinical Trials. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1088.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast sensitivity (CS) is a key assessment in intraocular lens (IOL) clinical trials, but a typical CS test with spatial frequency gratings needs a large sample size (122 subjects per ANSI Z80.12 Multifocal IOL guidance) and the test repeatability depends on the subject’s ability to understand the methodology. In this study, common letter based tests were used for a simpler assessment of contrast sensitivity.
31 pseudophakic subjects provided measurements for best corrected 100% contrast visual acuity (VA), 25% contrast VA, 10% contrast VA, threshold contrast for a 20/40 letter and grating contrast sensitivity (CS) at 1.5, 3, 6, 12 and 18 cycles per degree (CPD) with an electronic clinical trial suite (CTS, M&S Technologies) under mesopic conditions. All the testing were repeated with +0.25D, +0.50D and +0.75D defocus lenses to assess the effect of induced refractive error. Subjects included 61% females, aged 61 to 82 years and spherical equivalent refraction from -2.25D to +0.75D.
All the letter tests showed reduction in performance for +0.50D and +0.75D defocus (p<0.01 in all cases). However, for +0.25D defocus, 100% and 25% contrast VA showed a reduction (p<0.02), but not 10% contrast VA (p = 0.32) and contrast threshold test (p = 0.06). For grating CS, only at 0.75D defocus and only spatial frequencies of 6 CPD (difference: -0.18 logunit) and 12 CPD (difference: -0.21 logunit) were statistically significant (p<0.05). For each defocus level, mean scores from all the letter tests when plotted together as spatial frequency (i.e. visual acuity) vs. contrast sensitivity showed a linear relationship (r2 > 0.93 for all defocus levels). For this combined data, two metrics (slope and area under the curve) showed 40% and 48% change, respectively, for +0.75D defocus.
Contrast sensitivity loss due to small amounts of defocus was detected better by a combination of letter based tests compared to a standard grating contrast sensitivity test.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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