EyeWorld Asia-Pacific September 2020 Issue

CATARACT 30 EWAP SEPTEMBER 2020 temporal scotoma in NDs likely occurs due to differences in reflected and refracted light rays at the IOL edge. Anatomical conditions that exploit those differences can characterize the types of patients most likely to experience NDs following uncomplicated cataract surgery. A temporally decentered pupil, a small pupil, a tilted iris/IOL complex, or a positive angle kappa all change the types of light ray interactions with the IOL at the nasal edge. 2-4 There were several limitations to this study, some of which were addressed in the paper. First, a prospective cohort study with a more even IOL distribution would have been ideal. While all the IOLs seen in pseudophakic controls were also present in the NDs group, there was a wider variety of IOL types in the NDs group, and a more in-depth discussion on various IOL edge designs would be clinically useful. In fact, the initial reports of NDs began in the early 2000s when square-edge IOLs were taking off, as a means of reducing the incidence of posterior capsular opacification. 6,7 The baseline characteristics between the two groups show almost twice the percentage of females and smaller axial lengths in the NDs group compared with pseudophakic controls, both statistically significant differences. These two specific factors may themselves be related and could help explain nasal light ray pathways in patients with persistent NDs. Much larger population studies are needed to make such a conclusion, however. Moreover, it is not entirely clear how decreased SEs in nasal eccentricities correlate to the symptoms of NDs including temporal shadows or dark spots. As seen in peripheral ocular aberrometry and ray- tracing simulations, there is a large myopic shift in nasal eccentricities. It may be that in eccentric gaze even beyond 30 degrees, the increasing myopic blur is perceived as a relative scotoma as light is split and bent away from this retinal field angle. Finally, the method of determining iris tilt using an individually coded program in Python has not yet been validated to the authors’ knowledge. While this method of analysis may provide accurate data, it has not yet been shown to effectively model the eye in the manner it was used in this study. The resulting data from this methodology, however, is quite promising and recapitulates some of the previous work on NDs. In summary, this paper provides exciting clinical and anatomical support to previously posited theories on the etiology of negative dysphotopsias after uncomplicated cataract surgery. Small pupils, temporally decentered pupils, and positive angle kappa are anatomical factors that increase the risk of NDs. Screening patients preoperatively for these factors can better help us manage patient expectations and potentially elucidate definitive postoperative remedies. Residents of USC Roski Eye Institute.