FEB 07, 2012
This prospective study found that not only the amount of astigmatism but also the pupil size can affect UCVA in astigmatic eyes.
The authors examined 20 eyes of 20 healthy volunteers (mean age, 26.7 ± 4.9 years). After fully correcting cycloplegic refraction, they created with-the-rule and against-the-rule astigmatism of 1, 2, and 3 D in each eye, and then used artificial pupils (1 to 5 mm) to assess UCVA. They used the mean value of three measurements for statistical analysis.
UCVA was better in eyes with smaller pupil sizes and less astigmatism. The authors say smaller pupil size may have some advantages in image formation, such as an increasing depth of focus, a decrease in HOAs, and a decrease in light scatter, all of which may offset the deleterious effects of reduced luminance and diffraction and thereby moderate the impact of astigmatic defocus.
The authors note that in eyes with 1 D of astigmatism, UCVA was highest in 2 mm-pupils, while in eyes with 2 and 3 D of astigmatism, it was highest in 1 mm-pupils. They posit that the pupil-dependent effect of increasing depth of focus and a decrease in HOAs and light scatter on UCVA may be larger than the counteractive effect of diffraction and reduced luminance for a 1 mm-pupil in eyes with high but not low astigmatism.
They conclude that both amount of astigmatism and pupil size need to be considered to acquire better visual performance in eyes with astigmatism. It may be necessary to correct pre-existing astigmatism to acquire excellent visual outcomes, especially in eyes with larger pupils.