Are there mechanisms of which we can take advantage for patients with a high degree of astigmatism including residual, post-surgical astigmatism? Alan N. Carlson, M.D., Professor of Ophthalmology and Chief of the Corneal and Refractive Surgery Service at the Duke Eye Center in Durham, NC has observed that the astigmatic patient becomes particularly symptomatic under poorly lit conditions. An example of this would include the “drop off” in quality of vision while driving at night under poorly lit conditions. This might also include added eye strain with prolonged reading or computer usage. This latter group of patients may benefit from increasing the illumination in the room to reduce pupil size and increase the effective depth of focus and reduce eye strain. The following article seems to support this recommendation even though it is not specifically mentioned:
|Pupil Size and Uncorrected VA in Astigmatic Eyes
In Japan, investigators examined 20 normal eyes of 20 healthy volunteers (age 26.7 ± 4.9 years [mean ± SD]; 8 men, 12 women) to determine the effects of pupil size on uncorrected visual acuity (UCVA) in astigmatic eyes.
After fully correcting cycloplegic refraction, they created with-the-rule (WTR) and against-the-rule (ATR) astigmatism of 1, 2 and 3 D in each eye, and then assessed UCVA using artificial pupils (1 to 5 mm) in these astigmatic eyes. They then performed measurements three times and used the mean value for statistical analysis.
In eyes with WTR astigmatism of 1, 2 and 3D, logMAR UCVA was 0.04±0.08, 0.09±0.09 and 0.16±0.16 for 1 mm pupils, –0.01±0.09, 0.12±0.15 and 0.33±0.24 for 2 mm pupils, 0.02±0.09, 0.20±0.19 and 0.46±0.30 for 3 mm pupils, 0.02±0.08, 0.24±0.20 and 0.48±0.21 for 4 mm pupils, and 0.08±0.10, 0.33±0.18 and 0.53±0.22 for 5 mm pupils, respectively. The investigators reported that the variance of the data was statistically significant (p=0.03 for 1 D, p<0.001 for 2 D, p<0.001 for 3 D, analysis of variance). Similar results were obtained in eyes with against-the-rule astigmatism. To conclude, both the amount of astigmatism and the pupil size can affect UCVA in astigmatic eyes. It is suggested that not only the amount of astigmatism but also the pupil size should be taken into consideration for acquiring better visual performance in astigmatic eyes.
|SOURCE: Kamiya K, Kobashi H, Shimizu K, et al. Effect of pupil size on uncorrected visual acuity in astigmatic eyes. Br J Ophthlmol. 2012;96(2):267–270.|