Eyeworld

EW RESIDENTS 110 October 2016 the results that both uncorrected and corrected distance visual acuity, as well as contrast sensitivity and wavefront aberrations, did not significantly differ among eyes with different categories of preoperative astigmatism. Further emphasis on such functional tests and additional standardized evaluation of patients' subjective satisfaction with their final postoperative outcomes might shed light on the practical relevance of relatively small differences in errors in predicted postoperative astigmatism. The Ninomiya et al. study is appropriately designed to answer the questions that the authors pose, although the generalizability of their findings is limited by the specific surgical technique (superior sclero- corneal incision) employed, type of toric IOL used, and exclusion of eyes with high preoperative astigmatism. It could also be helpful to include a statistical adjustment for the bias introduced from including both eyes from some patients. Another limitation, while not specific to this study, is the somewhat artificial divi- sion of different axes of astigmatism into the discrete categories of WTR, ATR, and oblique—it may be worth treating axis of astigmatism more as a continuous variable in future analyses. Ninomiya et al. demonstrate promising outcomes from toric IOL implantation, while also confirming the need for differential treatment of eyes with different preoperative axes of astigmatism that Goggin et al. seek to address in their work. Among the challenges that remain in opti- mizing toric IOL outcomes are: (1) establishment of a gold standard for accurate determination of preopera- tive astigmatism, (2) establishment of a gold standard and clinically practical method for direct mea- surement of posterior and/or total corneal astigmatism, (3) improved understanding of and development of models that accurately capture the relationship between posterior corneal astigmatism and refractive outcomes, and (4) refinement of all steps to toric IOL selection in corneas that are irregular, diseased, and/or have previously undergone surgery. 24 The work from Goggin et al. and Ninomiya et al. featured in the October issue of the Journal of Cataract & Refractive Surgery are valuable additions to the expand- ing literature on management and outcomes of preoperative corneal astigmatism in cataract surgery, and their results invite confirmation and exploration in future research. EW References 1. Miyake T, et al. Distribution of posterior cor- neal astigmatism according to axis orientation of anterior corneal astigmatism. PLoS One. 2015;10:e0117194. 2. Davison JA, et al. Refractive cylinder out- comes after calculating toric intraocular lens cylinder power using total corneal refractive power. Clin Ophthalmol. 2015;9:1511–1517. 3. Eom Y, et al. Toric intraocular lens calcu- lations using ratio of anterior to posterior corneal cylinder power. Am J Ophthalmol. 2015;160:717–724.e2. 4. Ho JD, et al. Accuracy of corneal astigma- tism estimation by neglecting the posterior corneal surface measurement. Am J Ophthal- mol. 2009;147:788–795, 795.e1–2. 5. Zheng T, et al. Influence factors of estima- tion errors for total corneal astigmatism using keratometric astigmatism in patients before cataract surgery. J Cataract Refract Surg. 2016;42:84–94. 6. Bissen-Miyajima H, et al. Microincision hydrophobic acrylic aspheric toric intraocular lens for astigmatism and cataract correction. J Refract Surg. 2015;31:358–364. 7. Goggin M, et al. Adjustment of anterior corneal astigmatism values to incorporate the likely effect of posterior corneal curvature for toric intraocular lens calculation. J Refract Surg. 2015;31:98–102. 8. Koch DD, et al. Contribution of posterior cor- neal astigmatism to total corneal astigmatism. J Cataract Refract Surg. 2012;38:2080–2087. 9. Savini G, et al. An analysis of the factors influencing the residual refractive astig- matism after cataract surgery with toric intraocular lenses. Invest Ophthalmol Vis Sci. 2015;56:827–835. 10. Zhang L, et al. Effect of posterior corneal astigmatism on refractive outcomes after toric intraocular lens implantation. J Cataract Refract Surg. 2015;41:84–89. 11. Ho JD, et al. Effects of aging on anterior and posterior corneal astigmatism. Cornea. 2010;29:632–637. 12. Ueno Y, et al. Corneal thickness profile and posterior corneal astigmatism in normal cor- neas. Ophthalmology. 2015;122:1072–1078. 13. Reitblat O, et al. Effect of posterior corneal astigmatism on power calculation and align- ment of toric intraocular lenses: Comparison of methodologies. J Cataract Refract Surg. 2016;42:217–225. 14. Aramberri J, et al. Dual versus single Scheimpflug camera for anterior segment analysis: Precision and agreement. J Cataract Refract Surg. 2012;38:1934–1949. 15. Kim EJ, et al. Repeatability of posterior and total corneal curvature measurements with a dual Scheimpflug-Placido tomographer. J Cataract Refract Surg. 2015;41:2731–2738. 16. Koch DD, et al. Correcting astigmatism with toric intraocular lenses: effect of posterior corneal astigmatism. J Cataract Refract Surg. 2013;39:1803–1809. 17. Mi H, et al. Comparison of anterior and posterior topographic analysis between 3 imaging systems. J Cataract Refract Surg. 2015;41:2533–2545. 18. Abulafia A, et al. Prediction of refractive outcomes with toric intraocular lens implan- tation. J Cataract Refract Surg. 2015;41:936– 944. 19. Abulafia A, et al. Comparison of meth- ods to predict residual astigmatism after intraocular lens implantation. J Refract Surg. 2015;31:699–707. 20. Abulafia A, et al. New regression formula for toric intraocular lens calculations. J Cata- ract Refract Surg. 2016;42:663–671. 21. Hoffmann EM, et al. Distribution of central corneal thickness and its association with ocular parameters in a large central European cohort: the Gutenberg health study. PLoS One. 2013;8:e66158. 22. Pan CW, et al. Ethnic variations in central corneal thickness in a rural population in China: the Yunnan minority eye studies. PLoS One. 2015;10:e0135913. 23. Sng C, et al. Central corneal thickness and its associations with ocular and systemic factors in an urban west African population. Am J Ophthalmol. 2016;169:268–275. 24. Koch DD. The enigmatic cornea and in- traocular lens calculations. Am J Ophthalmol. 2016 Aug 22. [Epub ahead of print] Contact information Boland: boland@jhu.edu The role continued from page 109

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