Evaluation of the Relationship between Incision Location and Change of Posterior Corneal Astigmatism

ABSTRACT

PURPOSE: To determine if there is a difference in surgically induced astigmatism (SIA) of the posterior corneal surface between superior and temporal incision and its effect on total corneal power in patients who underwent clear corneal incision cataract surgery. METHODS: A retrospective study of 81 patients (84 eyes) who underwent clear corneal incision phacoemulsification by one surgeon. Patients were divided into two groups according to the steep axis the temporal and superior groups. Anterior, posterior and total corneal SIA (simulated keratometry [Sm K], posterior keratometry [PK] and total corneal power [TCP] respectively) were measured using autorefractive keratometry (ARK) and dual Scheimpflug imaging before and after surgery. RESULTS: There were 61 eyes with temporal incision and 23 eyes with superior incision. The mean SIA was larger in the superior incision group than in the temporal incision group according to ARK, Sm K, PK and TCP (p < 0.05). There were no significant cylindrical changes in ARK in the temporal incision group, however, there was a significant decrease in the superior incision group before and after the operation (p < 0.05). Change in the amount and axis of PK before and after operation were not significantly different, for both incision groups. There was a significant correlation between post-operative TCP and both pre-operative ARK and Sm K for both groups. However, there was no correlation between post-operative TCP and pre-operative PK. In all patients, when pre-operative PK was more than 0.5 D, SIA-ARK, SIA-Sm K and SIA-TCP were all significantly larger than when pre-operative PK was less than 0.5 D, whereas SIA-PK was not. When pre-operative PK was more than 0.5 D, there were no significant differences in SIA-ARK, SIA-Sm K, SIA-PK or SIA-TCP in the temporal incision group. However, SIA-ARK was significantly larger in the superior incision group. CONCLUSIONS: There was no significant cylindrical change in PK before and after operation in both the temporal and superior incision groups. Therefore, when predicting post-operative TCP, it might be meaningful to consider SIA-ARK and SIA-Sm K.