EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/129516
58 EW RESIDENTS May 2013 Review continued from page 57 Pictured from left to right. Back row: David Salvay, Ian Pitha (chief resident), Aaron Lee, Manik Goel, Daniel Hammer, Sarah Jacobs, Bradley Shoss. Front row: Linda Tsai (faculty supervisor), Ling Bei, Smith-Ann Chisolm, Courtney Kraus, Kimberly Hsu, Gokul Kumar, and Arsham Sheybani (chief resident). Not pictured: Tahira Mathen, Benjamin Currie, Kisha Piggott One surgeon performed all cases using a standard phacoemulsification technique, thereby removing surgical approach and instruments as variables. Patients were randomly assigned to either the one-piece AcrySof SA60AT (Alcon, Fort Worth, Texas) with 0-degree haptic angulation or the three-piece Sensar AR40e (Abbott Medical Optics, Santa Ana, Calif.) with 5-degree haptic angulation. Follow-up examinations were performed 5-7 years after cataract surgery. Fifty-six of the 80 patients completed the follow-up visit. Measurement of corrected distance visual acuity (CDVA) with standard, 100%, and 2.5% contrast charts were performed. To evaluate PCO, retroilluminated slit lamp images of the IOL were obtained. Computerized image analysis was then used to quantify the average area of opacification, from which a severity rating of mild, moderate, or severe was generated. Quantification of the PCO using retroillumination photography did not reveal any significant difference between the two lens types. 22% of the Sensar IOL group and 10% of the AcrySof group required Nd:YAG capsulotomy, but the difference was not significant (p>0.05). Furthermore, centration of the capsulorhexis on the IOL did not affect PCO rates (p>0.05). Glistenings were rated by an ophthalmologist's exam at the slit lamp on a scale of 0 to 3. Scheimpflug Pentacam (Oculus, Arlington, Wash.) images were used to calculate the light scattering within the IOL as an indirect representation of glistenings, with analysis at three levels: full thickness of the IOL, deep glistenings, and very deep glistenings. Slit lamp rating correlated well with Scheimpflug findings. Significantly more glistenings were seen in the AcrySof than in the Sensar lens. Correlation between glistenings and contrast sensitivity was evaluated by calculating the difference in logMAR CDVA at 2.5% vs. 100% contrast sensitivity. There was no significant correlation between glistenings and contrast sensitivity. Design strengths and concerns Major strengths of this study are its design as a prospective, randomized trial with a single surgeon and surgical technique, as well as its relatively long follow-up time. This study evaluated two lenses made of the same material (hydrophobic acrylic), whereas other studies have compared silicone vs. acrylic vs. PMMA.5 However, it is unclear why the authors chose to compare a one-piece and three-piece IOL manufactured by two different companies. Using two different lens designs and manufacturers leaves other variables unaccounted for. Further data involving one-piece and three- piece lenses from both Alcon and Abbott Medical Optics could be useful. The authors should be commended for their use of quantitative methods cross-checked with subjective observations. Grading PCO on two separate occasions by a single examiner helped establish the reliability of the grading, and use of quantitative image analysis gave objective results. The accuracy of using Scheimpflug light scattering as a proxy for glistenings has been criticized elsewhere in the literature.6 Furthermore, one recent study found that acrylic IOLs have higher light scattering, but still provide better corrected visual acuity at 10 years than silicone or PMMA lenses.7 In this study, slit lamp rating of glistenings was performed and shown to correlate well with the Scheimpflug findings. Measuring light scattering in the very deep part of the IOL helped improve the likelihood that scatter was due to glistenings rather than other impurities on the surface of the lens. One drawback to the study is that the examiner grading PCO and glistening would clearly be able to tell whether the patient had a onepiece or three-piece IOL and was therefore not blinded to which group the patient was in. Another limitation is that patients had undergone interventions outside the scope of the study between the time of surgery and the time of follow-up, with three patients having YAG capsulotomy prior to the study visit. All three patients were noted to be in the three-piece IOL group (not statistically significant), but criteria for performing the capsulotomy was not specified. Another point noted as a weakness in the study was that the statistical analysis did not include a correction for multiple comparisons. Because the p-values reported were robust enough to withstand a multiple comparisons correction (e.g., Bonferroni test) this did not affect the outcomes. However, caution must be exercised interpreting statistical significance of more than one variable from the same clinical sample. Finally, the authors concluded that there is no correlation between glistenings and visual acuity or contrast sensitivity. Since most patients had only grade 0 or 1 glistenings, subgroup analysis would be useful to determine whether patients with higher-grade glistening may actually have a reduction in VA or contrast sensitivity, as suggested by the trend seen in other papers on the subject.4 Clinical relevance This study gives us several interesting points to consider. First, there was no significant difference in rates of PCO between the AcrySof SA60AT and the Sensar AR40e IOL with 5-7 years of follow up. This adds to the evidence in the literature that onepiece vs. three-piece does not seem to affect PCO rates.8 It also indirectly suggests that a lens's propensity for developing glistenings does not affect its likelihood of PCO formation. Thus, concern for higher rates of PCO should not affect choice of one of the studied lenses over the other. Second, significantly more glistenings were found in patients who had the AcrySof SA60AT IOL compared with the Sensar AR40e, but in this study these did not affect CDVA or contrast sensitivity. This adds data for the debate over whether glistenings are visually relevant. While this study provides useful information on the two IOLs that were compared, larger studies with a variety of IOLs are needed to determine which lenses are more prone to glistenings and whether their impact on visual function becomes significant as the severity of the glistenings increases. Finally, it is noteworthy that the 5-7 year follow-up in this study places it among the longer-duration continued on page 60