Eyeworld

EW RESIDENTS 48 February 2016 was demonstrated with the vector summation calculation of anterior and posterior astigmatisms (0.70 diopters [D], 0.60 D, 0.64 D, 0.76 D vs. 0.49 D, respectively, p<0.001). Subgroup analysis with identical comparisons of oblique (12 eyes) and with-the-rule (WTR, 62 eyes) astigmatism demonstrated similar improvement in SRA (p<0.005, and p<0.001, respectively), while against- the-rule (ATR, 41 eyes) astigmatism showed no difference (p=0.337). The study authors suggest incorporating the posterior cornea (by combin- ing its measurements with anterior corneal measurements) into calcu- lations for reducing residual astig- matism in toric IOL implantation. Potential limitations noted by the authors include the retrospective na- ture of the study, toric IOL cylinder power calculation (instead of actual measurement at the corneal plane) Review continued from page 47 View the EyeWorld CME and non-CME supplements at: cmesupplements. eyeworld.org supplements. eyeworld.org Vanderbilt Eye Institute residents, from left: Mark Breazzano, MD, Niraj Nathan, MD, and Tomas Moreno, MD Source: Vanderbilt Eye Institute based on the theoretical Holladay 1 formula, low number of eyes with oblique astigmatism, as well as induction of astigmatism by surgical incisions. Comments Integrating posterior corneal astigmatism, whether measured or estimated, into the calculation of toric IOLs has been shown to im- prove outcomes regarding refractive astigmatism. This study shows, spe- cifically, that using vector analysis to combine the measured posterior corneal astigmatism with anterior keratometry in toric IOL calculation may offer decreased overall residu- al astigmatism compared to other methods of incorporating posteri- or corneal curvature. This vector analysis was not shown to be helpful with ATR astigmatism, though, and studies with a greater number of patients may be necessary for determining its role with oblique astigmatism. Interestingly, use of the Pentacam's estimate of total corneal refractive power (TCRP) actually led to increased residual simulated refractive astigmatism compared to using anterior keratometry alone; the reason for this was unclear. However, there are some limita- tions to this study. As mentioned in the paper, the retrospective nature of the study limits the value of the results. The study assesses the simulated residual astigmatism of placing a toric IOL using the various methods of calculation, rather than assessing actual refractive outcomes of implanting the IOLs calculated by each method. While this method of calculating SRA is a very reasonable surrogate, we would be interested in seeing actual refractive outcomes

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