The exciting new technologies available to surgeons in view of correcting the various lower and higher order aberrations of the eye in recent years has been staggering. With so many options available to surgeons these days, surgeons demand IOLs with good efficacy, are user friendly and robust enough to meet the increasing demands of patients.

Figure 1: The predictability of outcomes.

One important dimension, astigmatism, has been a particular challenge due to the directional nature of its correction. The Acrysof toric (SN60TT, Alcon ) comes in three variants, namely the SN60T3, SN60T4 and SN60T5 with 1.50 D, 2.25 D and 3.00 D of cylindrical correction at the IOL plane respectively. This translates into approximately 1.03 D, 1.55 D and 2.06 D on the corneal plane respectively.

Table 1: The astigmatic measurements before and after toric IOL implantation

This retrospective observational study was part of a routine audit of post-phacoemulsification refractive outcomes. The sphero-cylindrical expected refraction was calculated using meridional analysis to select the appropriate IOL toricity in 72 eyes of 65 patients from a single surgeon. IOL spherical and toric power calculations were performed using our published meridional analysis method¹ taking into account the surgeon's surgically induced astigmatism. The mean spherical IOL implanted was +17.93±4.56 D (range +6.5 to +30.0 D). Thirty seven point five percent of eyes were implanted with the SN60T3, 33.3% with the SN60T4 and 29.2% with the SN60T5.

Figure 2: Scatter plot showing the absolute changes in astigmatism compared to the keratometric cylinder of the eye. The spectacle plane efficacy of the SN60T5 of approximately 2.55D is evident where there is little absolute change in astigmatism in eyes with greater keratometric cylinder.

Changes in astigmatism post-operatively were determined with (absolute changes) and without (simple changes) taking into account the axis of the cylinder as compared to the keratometric cylinder. A summary of the pre and post-operative cylinder is shown in Table 1. The surgeon optimized A-constant for this IOL was 118.64 with the IOLMaster and 118.40 with the RXP. The predictability of outcomes was high (Figure 1) as was the efficacy of the cylindrical correction (Figure 2 and 3).