EyeWorld Asia-Pacific March 2019 Issue

3 EWAP EDITORIAL March 2019 EYEWORLD ASIA-PACIFIC EDITORIAL BOARD C HIEF MEDICAL EDITOR Graham BARRETT, Australia MEMBERS Abhay VASAVADA, India CHAN Wing Kwong, Singapore CHEE Soon Phaik, Singapore Hiroko BISSEN-MIYAJIMA, Japan Hungwon TCHAH, South Korea ASIA-PACIFIC CHINA EDITION Regional Managing Editor YAO Ke Deputy Regional Editors HE Shouzhi ZHAO Jialiang Assistant Editors SHENTU Xing-chao ZHOU Qi ASIA-PACIFIC INDIA EDITION Regional Managing Editor S. NATARAJAN Deputy Regional Editor Abhay VASAVADA ASIA-PACIFIC KOREA EDITION Regional Managing Editor Hungwon TCHAH Deputy Regional Editor Chul Young CHOI John CHANG, Hong Kong Johan HUTAURUK, Indonesia Kimiya SHIMIZU, Japan Pannet PANGPUTHIPONG, Thailand Ronald YEOH, Singapore S. NATARAJAN, India Sri GANESH, India YAO Ke, China Y.C. LEE, Malaysia Eliminating astigmatism Graham Barrett Chief Medical Editor EyeWorld Asia-Pacific T he focus of this month’s edition of EyeWorld Asia- Pacific is a reevaluation of the management of preexisting astigmatism in patients undergoing cataract surgery. Personally, there are few innovations that have had as significant an impact as the introduction of toric intraocular lenses. When I first began using toric intraocular lenses in 2006, the threshold for considering a toric intraocular lens (IOL) was considerably higher than today. The ability to accurately predict astigmatic outcomes has improved but the most dramatic change when I look back is the increased usage of toric IOLs. In my own practice these lenses are used in approximately 80% of cases and I target less than a 0.5 D of residual astigmatism in all patients. It is a myth that residual astigmatism is of optical benefit and it has been clearly demonstrated that astigmatism affects contrast and reading speed. Any benefit in terms of depth of focus depends on a myopic spherical outcome and the latter without residual astigmatism is more effective than the equivalent amount of myopic defocus associated with astigmatism. There is nothing special about astigmatic defocus and indeed the impact on quality of vision is greater than the equivalent spherical myopic defocus. The error in predicting residual astigmatism is similar to that of predicting spherical errors. The absolute error is approximately 0.3 D with a standard deviation of 0.19 D. Achieving an astigmatic outcome less than 0.5 D therefore demands a target close to zero, as we are accustomed to in targeting spherical defocus. It seems to me that there is little sense in focusing on perfect spherical outcomes if similar attention is not applied to astigmatism. A target of less than 0.5 D residual astigmatism in all patients requires accurate alignment and an understanding of the impact of surgically induced astigmatism. One of the unique features of the Barrett toric calculator on the APACRS website is the integrated K calculator. This simplifies the interpretation of utilizing multiple instruments. Up to three different devices can be entered and the K calculator will provide a median vector considering both the axis and meridian of the astigmatism measured by different devices. Data analysis shows this offers significant improvement and I utilize this method in all my cases. Accurate alignment is facilitated by image-guided systems but similar accuracy can be achieved with the inexpensive toric cam app and dual axis marker. Surgical incisions in the cornea have an unpredictable impact on astigmatism. Even the impact of a relatively small corneal limbal incision is unpredictable. Although the mean or median magnitude of the induced astigmatism may be in the order of 0.3 to 0.4 D, the direction or meridian is quite variable. The centroid value which encompasses both the magnitude and direction of the vector of surgically induced astigmatism is typically in the range of 0.1 D and should be utilized in toric calculators for optimum prediction. I would recommend a toric calculator be used in all patients undergoing cataract surgery. If one is not accustomed to using this protocol the number of patients requiring a toric lens will be significantly underestimated. The most frequently used toric lens in my practice is a low-diopter T2 with a 1-D cylinder power. These low powers are not available in all regions, particularly the U.S. Although astigmatic keratotomy is used as an alternative, several studies have shown this is less predictable and effective than using low toric cylinder powers. The use of toric lenses in the U.S. is significantly lower than in countries such as Australia and I suspect there will be an exponential growth when low dioptric implants become available. Leaving a patient with significant astigmatism may have been acceptable in an era when extracapsular cataract surgery was widely practiced but today with small incision cataract surgery and phacoemulsification I would suggest that an attempt to achieve a target of less than 0.5 D in all patients is preferable and may become a standard of care. EWAP I t is a myth that residual astigmatism is of optical benefit and it has been clearly demonstrated that astigmatism affects contrast and reading speed… There is nothing special about astigmatic defocus and indeed the impact on quality of vision is greater than the equivalent spherical myopic defocus.