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A. P. Ginsburg, S. V. Subramaniam; Visual Acuity, Contrast Sensitivity and Night Driving Visibility in Complaining LASIK Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1575. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relationship between loss in visual acuity (VA), contrast sensitivity (CS) and night driving visibility distances in LASIK patients with unsatisfactory visual outcomes.
This was a retrospective case control study of 21 patients who underwent bilateral conventional LASIK (Mean age = 39 ± 10.3 years). Binocular data with best correction was compared with 29 age-matched controls (Mean age = 44.9 ± 12.9 years). VA was measured using the ETDRS chart, CS by the Functional Acuity Contrast Test (FACT) chart and visibility distances of road signs/hazards by the Night Driving Simulator (NDS).
The mean logMAR VA of LASIK subjects was 0.056 ± 0.23 and that of the controls was -0.05 ± 0.06. CS was lower in LASIK subjects than the controls by 0.3 log units (50% loss) or more from 3 to 18 cpd under all visibility conditions (p=0.001). Decrease in night driving visibility for identification of road targets was greater than 25% compared to age-matched controls (p<0.001). Loss in NDS distances correlated better with loss in CS than with loss in VA. The best correlations were observed at the middle spatial frequencies of 3 and 6c/d (p<0.01), which is the peak of the human contrast sensitivity function (CSF). Regression predicted an increase in night driving identification distance loss by 37-40% in rural roads and 28-29% in city roads for an average increase in CS loss of 0.3 log units at 3 and 6c/d.
Standard VA alone may be insufficient in assessing functional aspects of vision such as night driving visibility in complaining LASIK subjects. Sine-wave grating CS, in addition to VA testing, can be useful in evaluating the quality of functional vision in such patients.
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