Effect of pupil size on optical quality parameters in astigmatic eyes using a double-pass instrument

Abstract

Purpose: To objectively determine the effects of pupil size on optical quality parameters in astigmatic eyes using a double-pass instrument.

Methods: We examined twenty-two eyes of 22 healthy volunteers (mean age ± standard deviation, 27.1 ± 2.8 years) who had no ophthalmic diseases other than refractive errors (manifest cylinder ≤ 0.25 diopters (D)). After we fully corrected cycloplegic refraction, we created with-the-rule astigmatism of 1, 2, and 3 diopters in these eyes and then quantitatively assessed the modulation transfer function (MTF) cutoff frequency and the Strehl2D ratio with 2-, 4-, and 6-mm pupil sizes using the Optical Quality Analysis System.

Results: The MTF cutoff frequency and the Strehl2D ratio decreased significantly as the amount of astigmatism increased at each pupil size (P < 0.001 for 2, 4, and 6 mm, analysis of variance). They also decreased significantly with an increase in pupil size at each diopter of astigmatism (P < 0.001 for 0, 1, 2, and 3 D). Multiple comparisons demonstrated a significant difference between measurements made for a 2-mm pupil and for a 6-mm pupil at each diopter of astigmatism (P < 0.001 for 0, 1, 2, and 3 D, Dunnett test) and those made for a 4-mm pupil and for a 6-mm pupil at each diopter of astigmatism (P < 0.001 for 0 D, P < 0.05 1, 2, and 3 D).

Conclusions: Eyes with larger pupils had lower optical quality even when they were astigmatic. It may be necessary to correct the preexisting astigmatism to acquire excellent visual performance, especially in astigmatic eyes with larger pupils.

Figure 1

Point spread function (PSF) (left) and modulation transfer function (MTF) (right) images of 3 diopters of astigmatism obtained by the Optical Quality Analysis System: (a) 2-mm pupil, (b) 4-mm pupil, and (c) 6-mm pupil.

Figure 2

Optical quality parameters with 2-, 4-, and 6-mm pupil sizes at each diopter of astigmatism. (a) Mean modulation transfer function (MTF) cutoff frequency. (b) Mean Strehl2D ratio. Each parenthesis means values of the standard deviations. Repeated-measures analysis of variance, followed by the Dunnett post hoc test for multiple comparisons, was used to compare the differences between groups with different pupil sizes: c/deg = cycles per degree, D = diopter.

Figure 3

Bland-Altman plots represent the difference between two measurements divided by the mean of these measurements. (a) Modulation transfer function (MTF) cutoff frequency (b) Strehl2D ratio. The solid lines represent mean differences between 2 measurements of MTF cutoff frequency and Strehl2D ratio; dotted lines are the upper and lower borders of the 95% limit of agreement (mean difference ± 1.96 multiplied by standard deviation of the mean difference).