Eyeworld

EW RESIDENTS 158 April 2016 by Ingrid Chang, MD, Marc Comaratta, MD, Jason Kam, MD, Narae Ko, MD, and Mark Prendes, MD P ostoperative changes in anterior segment anatomy after phacoemulsification with intraocular lens (IOL) implantation remain an impediment to achieving universally consistent and precise refractive out- comes. After cataract extraction, it is well-established that anterior cham- ber depth (ACD) and the anterior chamber angle increase significant- ly. 1–4 This has obvious implications for the postoperative effective lens position (ELP). Preoperative estima- tion of the postoperative ELP has been shown to contribute as much as 35% of postoperative refractive error in eyes of average dimensions. 5 The amount of error in this predic- tion has been shown to be greatest in eyes of shorter and longer axial lengths. 6,7 Some IOL calculation formu- las, such as the Holladay, SRK, and SRK/T formulas, only use measured axial length and keratometry values, while the Haigis formula also uses the measured ACD to predict the postoperative refractive outcome and ELP. Other formulas, such as the Holladay 2, Olsen, and Barrett Universal II, use several other fac- tors, such as ACD and crystalline lens thickness, to calculate ELP. Despite the use of these increasingly sophisticated IOL calculation formu- las, postoperative refractive surprises still occur. 8,9 For this reason, postop- erative information is important to understand preoperative variables and their effect on ELP. Customized ocular coherence tomography (OCT) systems have been used to investi- gate pre- and postoperative ocular anatomy and have been shown to improve calculation of the ELP. 10,11 The successful application of such technology could be useful in eyes with long and short axial length, in which accurate IOL power calcula- tion is less consistent. In "Anterior chamber depth, iris and lens position before and after phacoemulsification in eyes with short and long axial length," Muzyka-Wozniak et al. performed a prospective, consecutive study com- paring ACD, iris, and lens position before and after phacoemulsification with intraocular lens placement. The study evaluated a total of 61 eyes of 61 consecutive cataract patients, which included 20 short eyes (<22 mm), 22 normal eyes (22.5–25 mm), and 19 long eyes (>25 mm). Patients with glaucoma, pseudoexfoliation syndrome, and zonular instability were excluded. All patients under- went cataract extraction by one surgeon using the same technique on every patient, and none ex- perienced intra- or postoperative complications. All patients received Review of "Anterior chamber depth, iris phacoemulsification in eyes with short Parisa Taravati, MD, residency program director, Department of Ophthalmology, University of Washington Effective lens position is the nagging variable that still confounds our accuracy with IOL power calculations. Can we better predict it? I invited the University of Washington residents to review this paper that appears in this month's JCRS issue. –David F. Chang, MD, EyeWorld journal club editor University of Washington ophthalmology residents. Back row, from left: Adam Sweeney, MD, Christine Petersen, MD, Alex Lin, MD, Mark Prendes, MD, Ingrid Chang, MD, Alex Foster, MD, Erika Brewer, MD, and Thao Le, MD. Front row, from left: Ariel Trying, MD, Emily Zepeda, MD, Narae Ko, MD, Marc Comaratta, MD, Jason Kam, MD, Yungtai Kung, MD, and Thomas Chia, MD Source: University of Washington an SA60AT IOL (Alcon, Fort Worth, Texas) placed in the capsular bag. Parameters that were measured included axial length (AL), ACD, anterior chamber angle, distance from the corneal epithelium to the anterior iris, distance from the ante- rior surface of the iris to the anterior surface of the crystalline lens, and distance from the anterior surface of the iris to the intraocular lens implant. The AL and ACD were mea- sured by the IOLMaster 500 (Carl Zeiss Meditec, Jena, Germany). The Visante OCT (Carl Zeiss Meditec) was used to measure ACD, as well as the other measurements of iris and lens position. Each of these measure- ments was performed before surgery and 4–6 weeks after surgery without pupil dilation. It is noteworthy that the ACD measurement utilized the corneal epithelium as the anterior point of measurement as opposed to the corneal endothelium. This likely introduces an unnecessary degree of error based on the variability of central corneal thickness among pa- tients. A simple solution would have been to use the corneal endothelium for ACD measurements and for the distance between the cornea and the iris. The authors reported that all parameters in all eyes significantly changed after surgery. The group found a significant opening of the anterior chamber angle in all eyes after surgery. The iris was found to move posteriorly in all groups after cataract surgery, with the largest change occurring in the eyes with the shortest axial length. After surgery, the iris in short eyes moved 0.93 mm, in normal eyes moved 0.7 mm, and in long eyes moved 0.43 mm. These differences were found to be statistically significant. The change in distance between the iris and lens was greater in patients with longer eyes. The absolute changes in ACD as measured by Visante were not significantly different among the groups, with 1.46 mm in short eyes, 1.37 mm in normal eyes, and 1.49 mm in long eyes. When con- verted to relative change, based on the preoperative ACD, a statistically significant difference was found (57% for the short eyes, 44% in normal eyes, and 42% for the long eyes). This is not surprising due to the expected trend toward a shal- lower anterior chamber in hyperopic patients. EyeWorld journal club

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