EyeWorld Asia-Pacific December 2013 Issue

3 EWAP December 2013 Letter from the Editor Dear Friends T he theme for this issue of EyeWorld Asia-Pacific is symmetry, or how to improve refractive outcomes with toric intraocular lenses. The articles emphasize the importance of using appropriate diagnostic tools to measure astigmatism as well as accurate marking of the selected axis. Most experts agree that a single device is probably insufficient to measure corneal astigmatism and both the amount of astigmatism and axis should be confirmed with at least one additional method of measurement. Topographic devices have proved to be useful in determining the correct axis and new biometers with an increased number of measurements on the cornea may be more accurate in determining the amount of astigmatism. New devices utilize a captured image of the cornea preoperatively and then superimpose the chosen axis in real time through an attachment to the microscope. This technology should improve our ability to align the toric lens axis correctly at the time of surgery. In addition, intraoperative aberrometers are now available that can determine both the required lens power as well as the correct axis for a toric intraocular lens (IOL) in real time. All these devices are important in optimizing outcomes with toric implants; however, there is an additional problem which is highlighted in this issue. Although Louis Emile Javal first highlighted the contribution of the posterior cornea to total ocular astigmatism, the relevance of this issue was highlighted by Doug Koch in last year’s Binkhorst Lecture. The posterior cornea contributes approximately 0.5 diopters (D) of against-the-rule astigmatism and if ignored patients with preexisting with-the-rule astigmatism will tend to be overcorrected by approximately 0.5 D and those with against-the-rule astigmatism under corrected by 0.3 D. As pointed out in this issue, most existing toric calculators ignore the contribution of the posterior cornea, which could explain the unexpected refractive outcomes after toric intraocular lenses despite careful attention to the measurement of astigmatism preoperatively and accurate axis location of the toric intraocular lens. There are therefore several strategies available to deal with this issue. Scheimpflug cameras and OCT devices are able to measure the posterior cornea, as does intraoperative aberrometry, and thus provide the true net corneal power and astigmatism. Many surgeons simply subtract an average amount from the anterior corneal astigmatism as recommended by the Baylor nomogram. I have developed a toric calculator which uses a mathematical model which takes into account the posterior cornea without requiring additional measurements. This calculator is available on the APACRS website and is a straightforward method of determining the appropriate toric lens power and axis. In a paper recently presented at ESCRS, the toric calculator proved to be more accurate than other methods of calculating toric lens power and axis. Toric lenses are increasingly becoming a standard of care. Their availability has greatly improved refractive outcomes for patients with preexisting astigmatism and reduced the need for spectacle correction for patients undergoing cataract surgery. Accurate measurements, marking and alignment are essential; however, in addition, using an appropriate toric calculator to determine the correct lens power and axis plays an important role in ensuring an optimum result. I hope you will find the improved calculator available on the APACRS website helpful in obtaining the best possible results for your patients requiring a toric intraocular lens. Warmest regards Graham Barrett Chief Medical Director EyeWorld Asia-Pacific EYEWORLD ASIA-PACIFIC EDITORIAL BOARD C HIEF MEDICAL EDITOR Graham BARRETT, Australia MEMBERS Abhay VASAVADA, India ANG Chong Lye, Singapore CHAN Wing Kwong, Singapore CHEE Soon Phaik, Singapore Choun-Ki JOO, Korea Hiroko BISSEN-MIYAJIMA, Japan ASIA-PACIFIC CHINA EDITION Editors-in-Chief ZHAO Jialiang ZHAO Kan Xing Deputy Editor HE Shouzhi Assistant Editor ZHOU Qi ASIA-PACIFIC INDIA EDITION Regional Managing Editor S. NATARAJAN ASIA-PACIFIC KOREA EDITION Regional Editor-in-Chief Hungwon TCHAH Regional Managing Editor Chul Young CHOI Hungwon TCHAH, Korea John CHANG, Hong Kong Johan HUTAURUK, Indonesia Kimiya SHIMIZU, Japan Pannet PANGPUTHIPONG, Thailand Prin ROJANAPONGPUN, Thailand Ronald YEOH, Singapore S. NATARAJAN, India YAO Ke, China Y.C. LEE, Malaysia