Residual Refractive Astigmatism following Toric Intraocular Lens Implantation without Consideration of Posterior Corneal Astigmatism during Cataract Surgery with Low Anterior Keratometric Astigmatism upto 2.5 Dioptres.

Purpose: To determine the refractive astigmatism following toric intraocular lens (tIOL) implantation without consideration of posterior keratometric astigmatism with a conventional tIOL calculator for eyes with low keratometric astigmatism (0.75D to 2.5D) and to theoretically compare the outcomes with predicted refractive astigmatism using a calculator with Barrett's formula.Methods: 34 eyes (34 patients) were assessed with Scheimpflug imaging and underwent tIOL implantation employing conventional tIOL calculator. Eyes were grouped on preoperative keratometric astigmatism as against-the-rule (ATR), with-the-rule (WTR), and oblique (OB). The refractive astigmatism was assessed at 1, 3, 6 and 12 months postoperatively and was classified as ATR, WTR, and OB. Theoretical refractive astigmatism calculations were performed for the same eyes using Barrett's formula.Results: Preoperatively keratometric astigamtism was ATR, WTR, and OB in 32%, 53% and 15% of eyes. At 12 months, in ATR, WTR and OB groups, 45.5%, 16.7% and 60% had ATR refractive astigmatism; 16.7%, 0%, and 20% had WTR refractive astigmatism; 55.6%, 54.5% and 20% were emmetropic (no sphere and cylinder) respectively. There was a significant difference between the theoretical predicted postoperative refractive astigmatism using conventional tIOL calculator and Barrett's formula (P < .05). Postoperative refractive astigmatism was not significantly different from the theoretical predicted refractive astigmatism with Barrett's formula but it was significantly higher than that with a conventional tIOL calculator.Conclusions: At 12 months, with a conventional tIOL calculator, postoperative emmetropia is achieved in half, two third and one-fifth of eyes with preoperatively ATR, WTR, and OB keratometric astigamtism respectively. Around 1/4th WTR keratometric astigamtism eyes preoperatively were overcorrected to ATR refractive astigmatism whereas ½ATR remained undercorrected at 12 months Outcomes achieved were dissimilar to predicted outcomes with a conventional tIOL calculator but similar to those with Barrett's formula.