The relationship between scotopic viewing conditions and the need in some patients for a relatively more myopic correction has been known for some time. This study compared clinical refraction findings, as measured under standard examination conditions with findings under conditions of decreased illumination and contrast, using an innovative mirror/lens system to control contrast while maintaining average luminance nearly constant. Changes in refractive findings were statistically (p < 0.003) and clinically significant (mean change = 0.65D, SD = 0.20) . This indicates that decreasing the contrast of test letters in this manner can be a clinically useful aid to determination of refractive correction under conditions of low illumination and contrast.
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