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S. A. Koopmans, K. W. van Gaalen, N. J. Jansonius, T. T. Terwee, A. C. Kooijman; A Comparison of Widely Used Clinical Contrast Sensitivity Tests: Effect of Defocus on Contrast Sensitivity Measured in Healthy Phakic Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2785.
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In this study, we compared contrast sensitivity (CS) values of several contrast sensitivity tests with each other. To extend the range in which comparisons could be made, we also measured CS in a slightly defocused state. In a CS test with gratings, defocus reduces the amplitude of the gratings on the retina. The amount of reduction depends on the spatial frequency. In CS tests using other types of stimuli the dependency on defocus is less straightforward.
48 healthy phakic subjects, age 20-35 years and 55-70 years, participated. Optimal refraction and visual acuity were determined with an ETDRS chart. CS was measured with a computerized test with vertical sine-wave gratings (6 cpd) generated on a CRT (Cambridge Research Systems, Rochester, UK; Von Bekesy tracking method). CS was measured with five different chart tests: the Pelli Robson (PR) CS test, two low contrast ETDRS-like optotype charts (2.5% and 10%), and two edge CS tests (GECKO and GECKO-100). CS tests where performed monocularly in mesopic (3 cd/m2) and photopic (160 cd/m2) conditions, without cycloplegia, at the optimal refractive state of the eye and at -1D and +1D defocus. The dominant eye was tested.
We calculated the correlation coefficients between CS values of the various chart tests and the values obtained from the CRT test at 6 cpd. The correlation coefficient in the mesopic condition ranged between r = 0.38 and r = 0.79 and in the photopic condition between r = 0.29 and r = 0.70. In mesopic conditions, the best correlation in the younger group was found between PR and the CRT test at 6 cpd (r=0.79), which was second best in the elderly group (r=0.54). In photopic conditions, the correlation between PR and the CRT test at 6 cpd was best in the elderly group (r= 0.57) and second best in the younger group (r=0.64). The CS values at +1D defocus were significantly lower than the CS values in optimal focus in both age groups and light conditions.
In this study, CS values were measured with a variety of available contrast sensitivity tests. CS values in the -1D defocus condition were not significantly lower than at optimal focus. This is in agreement with earlier research. Effects of defocus in the mesopic condition were larger than in the photopic condition. Overall, the CS values measured with the PR showed the best correlation with the CRT test at 6 cpd.
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