Eyeworld

EW RESIDENTS 70 June 2017 by Erin Boese, MD, Dong-Wouk Park, MD, Bryce Radmall, MD, Hillary Stiefel, MD, Fran Wu, MD, MPH, Afshan Nanji, MD, MPH, and Thomas Hwang, MD it remains to be seen whether an average of a 1.5-degree difference in toric alignment would indeed lead to a statistically and, most impor- tantly, clinically significant improve- ment in visual acuity in subsequent groups of patients with higher corneal astigmatism. Furthermore, the study may have failed to show a significant clinical benefit because it was performed by experienced surgeons. A digital guided system may be especially advantageous for novice surgeons with less experience using toric lenses. This study only compares the VERION to one method of manual marking, though there are numerous other manual marking techniques that have been described, includ- ing several demonstrating better accuracy. Methods of preoperative manual toric marking techniques include a three-step ink marker procedure described by Visser et al., 5 pendula ink marking evaluated by Popp et al., 7 the Cha et al. conjunc- tival blood vessel reference method, 6 and a four-point manual marking procedure described by Carey et. al. 8 Of these, the manual marking done with the pendula toric marker had the least misalignment at 1.8±2.2 degrees, 4 while the three-step marker procedure had the most misalign- ment at 4.9±2.1 degrees. 3 Given the expense and additional time involved in the VERION method, it difference between the desired toric IOL axis and the achieved axis at 1 hour postoperatively. Rotation was defined as the difference between the implanted toric IOL axis 1 hour postoperatively and the toric IOL axis at consecutive follow-up visits. The authors demonstrated that using the novel digital marking technique, compared to tradition- al manual marking, resulted in a smaller mean toric misalignment at 1 hour (1.3±1.6 degrees vs. 2.8±1.8 degrees, p=0.02) and 3 months post- operatively (1.7±1.5 degrees vs. 3.1± 2.1 degrees, p<0.05). Despite the improved alignment of the toric IOLs, the authors did not find a significant difference in uncorrected distance visual acuity (0.03±0.10 logMAR vs. 0.04±0.09 logMAR, p=0.74) or mean residual refractive cylinder (–0.36±0.32 D vs. –0.47±0.28 D, p>0.05) between the VERION group and the manual group at 3 months. The authors suggest that the statistically significant reduction in toric misalignment in the VERION group did not lead to a significantly better visual acuity due to the rela- tively low mean preop corneal astig- matism in the study subjects. They hypothesize that the more accurate alignment might become clinically relevant in patients with a higher level of pre-existing astigmatism. While this makes theoretical sense, features, to create a digital overlay between the preoperative image and live surgery image. It then projects the desired implantation axis of the toric IOL into the right ocular of the surgeon's microscope while using eye-tracking navigation to account for cyclotorsion and eye movement. The VERION can therefore theoret- ically eliminate multiple sources of error from manual alignment. In "A randomized controlled trial of an image-guided system versus manual marking in the alignment of toric intraocular lenses in cataract surgery" 4 Webers and colleagues compare the accuracy of toric IOL alignment using the VERI- ON Image Guided System versus a conventional manual ink marking procedure. This single-center trial from Maastricht University Medical Center in the Netherlands included 36 eyes from 24 patients with reg- ular corneal astigmatism of at least 1.25 D undergoing cataract surgery with toric IOL implantation (Acry- Sof SN6AT3-9, Alcon). Eyes were randomly assigned to either the VERION group or the manual ink marking group. The two groups were not significantly different in their preoperative characteristics. The manual marking method utilized a Nuijts/Lane corneal marker to create three preoperative marks at 0 de- grees, 180 degrees, and 270 degrees on the peripheral cornea. Intraop- erative marking of the target axis was accomplished with a Mendez ring and a Nuijts toric axis marker. All surgeries were performed by two experienced surgeons using the same standardized technique. The primary outcome was alignment of the toric IOL, and secondary outcome mea- sures included residual astigmatism, uncorrected distance visual acuity, and complication profile. Preoperative images of the desired axis relative to anatomic reference points were obtained on all patients using the VERION mea- surement unit, and dilated slit lamp photography was performed at all postoperative visits (1 hour, 1 week, and at 1 and 3 months). An overlay of reference spots on the conjunc- tiva and limbus in the preoperative and postoperative images allowed the toric IOL axis to be determined. Misalignment was defined as the T oric intraocular lenses (IOLs) are commonly used in patients with regular corneal astigmatism who wish to achieve freedom from spectacles following cataract surgery. IOL position and alignment are critical to refractive success; for every degree of misalignment, there is a reduction of 3% of the astigma- tism correction. 1 Currently, manual corneal marking systems are the standard in guiding intraoperative toric IOL position. However, manual marking methods introduce mul- tiple potential sources of error that can cause the final toric position to be misaligned. Potential sources of error include patient head tilt caus- ing cyclotorsion of the eye, washout or smearing of preoperative marks, and incorrect spacing of the marks. Various techniques and technologies have been developed to reduce po- tential misalignment from a manual marking technique. 2 Here, we pres- ent a review of a study evaluating a digital image-guided system that utilizes anatomic reference points to accurately identify the target axis and guide the surgeon through the operating microscope. Alcon (Fort Worth, Texas) developed a toric alignment tech- nology, the VERION Image Guided System, that claims to "minimize data transcription errors, improve clinical efficiency, increase toric and multifocal IOL confidence, ensure surgical consistency, and optimize visual outcomes." 3 The VERION system takes a color photograph of the patient's eye preoperatively, a step that can be incorporated at the time of biometry. During surgery, it uses multiple reference points on the conjunctiva and limbus, such as scleral vessels, limbal vessels, and iris Toric lens alignment: A review of a digital image- guided system versus traditional manual marking Markerless digital alignment systems represent the latest advancement for intraoperative toric IOL positioning. I asked the Casey Eye Institute residents to review this study assessing the efficacy of one such technology from the June issue of JCRS. –David F. Chang, MD, EyeWorld journal club editor Afshan Nanji, MD, Erin Boese, MD, Dong-Wouk Park, MD, Bryce Radmall, MD, Hillary Stiefel, MD, Fran Wu, MD, and Thomas Hwang, MD, residency program director, Casey Eye Institute Source: Casey Eye Institute EyeWorld journal club

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