[Corneal astigmatism before cataract surgery]

To investigate the distribution of corneal astigmatism, and the relationship of astigmatism to the patients' age in a large number of pre-cataract surgery patients.

We retrospectively examined 12428 eyes of 7187 patients (5396 eyes of men, 7032 eyes of women) who underwent cataract surgery at Kitasato University Hospital from April, 2002 to September, 2009. The mean patients' age at the time of surgery was 69.9 +/- 12.1 years. We determined corneal astigmatism using an Auto Refract Keratometer ARK-700A, a RKT-7700 (Nidek), a RK-F1 (Canon) and a Retinomax K-plus2(Righton). We carried out these measurements at least three times for each patient, and the average values were used for analysis.

The mean corneal astigmatism was 1.02 +/- 0.81 D (0 to 14.75 D). The percentage of 1 D or less of corneal astigmatism was 63.6%, that of more than 1 D and 1.5 D or less was 20.9%, that of more than 1.5 D and 2 D or less was 7.4%, that of more than 2 D and 2.5 D or less was 3.8% and that of more than 2.5 D and 3 D or less was 1.8%. Neither significant laterality nor age difference in corneal astigmatism were found. The prevalence of with-the-rule astigmatism (WTR) was common in young population, whereas the prevalence of against-the-rule astigmatism(ATR) increased in the older population, whereas the prevalence of oblique astigmatism remains unchanged.

Approximately two thirds of the preoperative patients had 1 D or less corneal astigmatism, and the remaining one third had over 1 D corneal astigmatism. The frequency of WTR was greater at a younger age, and that of ATR, at an older age.