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E. Lee, G. Ong, S. Rajak, A. Casswell; Changes in Chromatic and Achromatic Contrast Sensitivities Following Tropicamide Administration . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4603.
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Purpose: To determine the effects of tropicamide on chromatic and achromatic contrast sensitivities over the physiological range of spatial frequencies. Methods: 26 healthy volunteers (19 females & 7 males) with a mean age of 32.9 years were recruited. Any ophthalmic history and their refractive status was noted. One eye of each patient was examined on two occasions; once with, and once without, one drop of 1% tropicamide being administered to that eye 30 minutes previously. The order of the examinations was randomised for each patient; for the group whose "with tropicamide" examinations were performed first, at least 48 hours was left before they returned for the "without prior tropicamide" examinations. The testing regime, and environment (including room luminance) was controlled and maintained constant throughout the study. During each testing session the uni–ocular best corrected visual acuity (BCVA) using a Bailey–Lovie chart, and pupil diameter were recorded. Chromatic and achromatic contrast sensitivities were then examined using the Sussex Grating Machine (a computerised, cathode–ray–tube based gratings system, which presents sinusoidal gratings on a high–resolution colour monitor). The luminance of the screen is kept constant. Achromatic contrast sensitivity was measured at seven spatial frequencies, between 0.66 and 25 cycles per degree (cpd). Colour Contrast Threshold (CCT) was measured along the red–green (constant S–cone) and tritan (constant L/M–cone) confusion axes. A modified double staircase reversal algorithm was used to accurately determine thresholds, under computer control. The mean differences in the "with" and "without" prior tropicamide measurements were tested for statistical significance at the 95% level using two–tail paired t–tests. Results: Following tropicamide administration mean pupil diameter increased from 4.1 mm to 7.2 mm (p<0.001) and mean BCVA was reduced by 0.07 LogMar units (p<0.001). Achromatic contrast sensitivity was also significantly reduced following tropicamide at 2.20 cpd (p=0.01), 3.40 cpd (p=0.01), 10.00 cpd (p=0.04), 17.00 cpd (p=0.04) and 25.00 cpd (p<0.01). There was no difference in contrast sensitivity at the lower spatial frequencies (0.33 and 0.66 cpd). Colour contrast thresholds were not significantly altered following tropicamide administration. Conclusions: Achromatic contrast sensitivity was significantly reduced at intermediate and high spatial frequencies, following one drop of 1% tropicamide, in our population of healthy volunteers. No significant changes were seen at low spatial frequencies, and in colour discrimination.
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