EyeWorld India September 2020 Issue

CATARACT EWAP SEPTEMBER 2020 29 N egative dysphotopsias are now an increasingly well-established phenomenon in uncomplicated cataract surgery. Patients typically describe an arc or crescent-like shadow or dark region in the temporal visual field of the eye in question. While this occurs in up to 19% of patients following uncomplicated cataract surgery, many of these patients note spontaneous resolution by postoperative year 1. However, 3.2% of these patients have persistent complaints of this phenomenon after the first year. 1 Given the aging population and expected increase in the number of cataract surgeries, the number of patients with negative dysphotopsias (NDs) can also be expected to increase. There have been several theories describing how this process occurs including increased (and decreased) axial distance between the iris and intraocular lens (IOL), corneal edema, IOL edge design, smaller pupil size, large positive angle kappa, and anterior capsule overlying the optic. 1,2 These studies have limited clinical anatomical data supporting these theories. Additionally, there have been other studies analyzing surgical and medical management of this phenomenon with varying levels of success. 3–5 Most notably, inducing reverse optic capture seems to relieve many of the symptoms described in patients with NDs. 4 In this paper, the authors have performed novel analyses with both clinical imaging data and ray-tracing simulations to better pinpoint specific anatomical factors that could explain NDs in these patients. The authors of this paper prospectively enrolled 30 pseudophakic controls and 27 pseudophakic patients with NDs (referred by outside ophthalmologists following uncomplicated cataract surgery). Initially, the diagnosis of NDs was confirmed, no evident explanation for this visual phenomenon was identified, and the IOL was found to be in normal position without significant anomalies. Imaging analysis of these patients and controls was performed with anterior segment tomography, using the Pentacam (Oculus), and biometry, using the LENSTAR LS900 (Haag-Streit). Anterior chamber depth, horizontal decentration of the pupil, and pupil diameter were obtained from tomography. Pupil decentration, pupil diameter, keratometry, and axial length were measured from biometry. Iris tilt was calculated by manipulating iris tomography data through a custom written program. Subsequently, peripheral and central ocular aberrations in the horizontal meridian were obtained using the VPR peripheral aberrometer (Voptica). Finally, the OpticStudio (Zemax) was used to create ray-tracing simulations detailing the spherical equivalent shifts seen in eccentric lateral gaze up to 30 degrees on modified and accepted ocular schematic models. The authors found that corneal wavefront, anterior chamber depth, and central ocular aberrometry did not show statistical differences between the NDs group and pseudophakic controls. The NDs group had significantly more temporally tilted irides, temporally decentered pupils, smaller diameter pupils, and increased difference in relative spherical equivalent (SE) of nasal eccentricities compared with pseudophakic controls. Ray-tracing models showed more negative SEs 1) in nasal eccentricities of temporally decentered IOLs, 2) with temporal tilt of the iris and IOL, and 3) while inducing positive angle kappa. Additionally, increasing the axial distance between iris and IOL resulted in a 1 D increase in SE. The novel use of anterior segment imaging targeting specific anatomical differences between patients with NDs and pseudophakic controls strengthens the conclusions in this paper. While the exact pathophysiology behind NDs is not yet definitive, Holladay and Simpson 2 believe the phenomenon occurs due to the temporal retinal field angle gap in light rays that are refracted by the IOL and light rays missing the edge of the optic. However, this conclusion was based solely on ray-tracing simulations. Given the currently available evidence, the relative Review of ‘Distinct differences in anterior chamber configuration and peripheral aberrations in negative dysphotopsia’ by Ravi Shah, MD, Brandon Wong, MD, Charles Flowers, MD Contact information Flowers: Charles.Flowers@med.usc.edu Wong: Brandon.Wong@med.usc.edu This article originally appeared in the June/July 2020 issue of EyeWorld . It has been slightly modified and appears here with permission from the ASCRS Ophthalmic Services Corp. Charles Flowers, MD Residency program director USC Roski Eye Institute Keck School of Medicine of USC University of Southern California Los Angeles, California Brandon Wong, MD Associate residency program director USC Roski Eye Institute Ravi Shah, MD Chief resident USC Roski Eye Institute