Analysis of cataract surgery induced astigmatism: Two polar methods comparison

Surgically induced astigmatism (SIA) caused by the incision after cataract surgery may be calculated to improve IOL toric power calculation and achieve better visual outcome. SIA could be determined as the difference between preoperative and postoperative keratometry expressed in polar values using different equations. The objective of this study is to compare the SIA calculated with two different polar value analysis methods [Method #1: KP (90)/KP (135) developed to be used with incisions placed at 90° and Method #2: AKP/AKP (+45) developed to be used independently of the incision location].

Preoperative and one month postoperative data of 210 cataractous eyes (131 patients) undergoing uncomplicated cataract surgery were assessed. All incisions were performed at 11 o'clock (120°). No sutures were used in any patient. IOLMaster (Carl Zeiss Meditec, Dublin, Ireland) keratometry was used to polar calculation.

The average age was 66.25±12.33 years (range 22-89). SIA polar value data calculated with Method #1 were KP (90) -0.06±0.52D and KP (135) +0.05±0.91D and calculated with Method #2 were AKP -0.10±0.87D and AKP (+45) +0.02±0.02D. However, SIA value represented in traditional notation (diopters@axis in degrees) was the same value independently of the method used to calculate; +0.65@110.70°.

SIA value is independent of the polar method used to its calculation and slight variations in the incision position could be accepted without clinical relevant impact in SIA magnitude. Both methods [Method #1: KP (90)/KP (135) and Method #2: AKP/AKP (+45)] are useful to calculate SIA with superior incisions at 120°.