Eyeworld

EW RESIDENTS 70 June 2016 by Susie Drake, MD, Robert Hyde, MD, Shilpa Gulati, MD, Alex Pleet, MD, Mei Zhou, MD, Kai Kang, MD, and Siya Huo, MD, Illinois Eye and Ear Infirmary, University of Illinois at Chicago C ataract surgery is the most commonly performed surgery worldwide, with a predicted 32 million total cataract operations performed in the world by 2020 by the World Health Organization. 1 An aging population and a developing technological society have created demands for efficient strategies for precise surgical outcomes. Many people in the baby boomer gen- eration have had prior refractive surgery, so more precise IOL power calculations and toric IOL alignment are essential to obtain excellent post-refractive visual acuity. Traditional methods of IOL power calculations rely on either ultrasound or non-contact optical methods to measure axial length and central corneal power. Immer- sion A-scan or B-scan ultrasonogra- phy remains the gold standard for measuring axial length and may achieve a resolution of 0.10 to 0.12 mm. Central corneal power is calcu- lated via manual or automated ker- atometry. Although these traditional methods of biometry and IOL power calculations are generally accurate for cataract surgery using monofo- cal IOLs in eyes with average axial ket for use during cataract surgery. ORA uniquely uses Talbot-Moiré in- terferometry, a technology in which the optical wavefront from the device passes through a pair of grat- ings; its diffraction produces a fringe pattern and the analysis results in an estimation of IOL power. Given its efficiency and small size, this tech- nology can be used intraoperatively at the operating microscope. 1,2 Various clinical studies have looked at the utility of the ORA system in cataract surgery. Donnenfeld and colleagues found a strong correlation in the sphere, cylinder and axis between the wavefront measurements using the first generation ORA system intraop- eratively and 1 month after surgery. 3 Another study evaluating intraoper- ative wavefront aberrometry for use in limbal relaxing incisions and toric IOLs found that eyes with wavefront aberrometer-assisted surgery had sig- nificantly better uncorrected visual acuity and lower mean astigmatism compared to controls. 4 Others have reported that in patients with prior histories of laser keratorefractive sur- gery, 85.7% achieved a final refrac- tive goal of +/–0.50 D of the target refraction compared to 68.6% using standard calculation methods. 5,6 The ORA system was also found to improve refractive outcomes in post- LASIK eyes that underwent cataract surgery with Crystalens accommoda- tive IOLs (Bausch + Lomb, Bridgewa- ter, New Jersey). 7 More recently, studies with larg- er numbers of eyes revealed some deficiencies in the intraoperative aberrometry system. For example, Huelle and colleagues performed a clinical trial investigating the quality and reproducibility of aberrome- try-based intraoperative refraction during cataract surgery. 8 This group investigated 74 eyes and found that most successful readings were achieved in aphakia with viscoelas- tic and worse outcomes were found in pseudophakia with viscoelastic. 8 They concluded that more efforts are required to improve the preci- sion of measurement before this strategy can be used to guide cat- aract surgery. Fram and colleagues further compared the accuracy of established methods (Haigis-L and Masket) and newer methods, including intraoperative aberrom- etry (ORA) and a Fourier-domain OCT-based IOL formula (Optovue, Fremont, California) for IOL power Review of "Intraoperative aberrometry vs. for bilateral toric IOL implantation with a University of Illinois at Chicago residents Source: University of Illinois at Chicago William Mieler, MD, residency program director, Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago Does intraoperative wavefront aberrom- etry improve outcomes enough to justify the expense and time that it adds to refractive cataract surgery? I asked the University of Illinois at Chicago residents to review this month's JCRS study that looks at toric IOL outcomes with and without this technology in paired fellow eyes. –David F. Chang, MD, EyeWorld journal club editor EyeWorld journal club lengths, all current formulas have inherent flaws when the axial length is on the extremes of the normal range. Patients with prior refractive surgery also tend to demand a per- fect postoperative visual outcome, but these methods may underesti- mate IOL power and potentially lead to hyperopic surprise and dissatisfied patients. Misalignment of toric IOLs can also lead to postoperative prob- lems. The commonly implemented 3-step ink marker procedure for toric IOL orientation can result in an average error of 5 degrees, which may lead to reduction in astigmatic correction and hyperopic spherical surprise. Intraoperative aphakic autore- fraction using wavefront analysis and manifest refraction have been applied to cataract surgery to im- prove estimation of post-surgical refractive error. Wavefront analysis can be used to detect irregular astig- matism and higher-order aberration and thus can guide IOL selection to optimize postoperative visual out- come. The Optiwave Refractive Analysis (ORA) intraoperative wavefront aberrometer (Alcon, Fort Worth, Texas) is the first intraopera- tive aberrometry system on the mar-

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