DEC 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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Page 48 of 72

46 EW RESIDENTS December 2012 Review continued from page 45 benefit more from Scheimpflug analysis prior to astigmatic surgical interventions? For example: Do eyes with long axial lengths have a greater propensity to have a high degree of posterior corneal astigmatism? Does race or gender make any difference? When considering the importance of an analysis that many ophthalmologists can not presently obtain in their own office, we think it will be important to attempt to tease out which patients would benefit most from Scheimpflug analysis. One posterior corneal astigmatism magnitude sub-analysis undertaken by the authors was that of the relationship between anterior corneal astigmatism and posterior corneal astigmatism. Even though they found moderate correlation between the two when the steep anterior corneal meridian was aligned vertically, we agree with the authors��� stated conclusion that one cannot confidently predict the amount of posterior astigmatism from anterior corneal measurements alone. With each type of anterior corneal astigmatism (WTR, ATR, or oblique), there were a number of corneas with posterior astigmatism >0.5 D. If the type of anterior corneal astigmatism isn���t predictive of these outliers, what factors might be? Symposium & Congress 0jW April 19���23, 2013 W ? ����F��!������j����+�� ~��? ��V����������������r����^���������� �� �� �� �� �� �� �� Follow @ASCRStweets on Twitter. #ASCRSASOA2013 avings mum S Now for Maxi soa.org Register or www.a scrs.org www.a Perhaps the most enthusiastic portion of our resident journal club centered on the authors��� conclusion drawn from their measured simulated keratometry anterior corneal astigmatism estimation error. They found on average that determining corneal astigmatism by anterior corneal measurements alone produced an estimation error of 0.22 @ 180 when compared to measurements produced by the Scheimpflug analyzer. While statistically significant, we wondered if this error will prove to be clinically significant. For what percentage of patients will it be significant? Will this justify increased costs for new equipment? Given the inherent errors associated with current toric IOL implantation techniques and limbal relaxing incisions, our group felt that such a small average gain in accuracy must be considered carefully when determining the significance of using posterior corneal measurements to determine total astigmatic corneal power. That being said, incremental improvements in accuracy coupled with ever-evolving intraocular lens technology and surgical technique is certainly a path we support traveling down. Future clinical trials comparing refractive outcomes in patients undergoing astigmatic surgical interventions with and without prior Scheimpflug analysis should be helpful in determining the significance of Scheimpflug corneal analysis. In summary, we applaud the authors��� well-designed and analyzed study. We find this study by Dr. Koch and his colleagues to be an excellent stepping stone toward improved understanding of corneal astigmatism and hopefully improved astigmatic surgical intervention outcomes. The study suggests that posterior corneal astigmatism plays an important role in overall astigmatism in a significant number of corneas, is not yet easy to predict without direct measurement, and may become another important measurement when considering work-up of astigmatic surgical interventions. We look forward to the authors��� reporting on their continued investigation of this important topic. EW Reference SanFrancisco2013 American Society of Cataract and Refractive Surgery American Society of Ophthalmic Administrators 1. Ho J-D, Tsai C-Y, Liou S-W. Accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement. Am J Ophthalmol 2009; 147:788-798. Contact information Denny: kjdenny1@aol.com

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