Comparison of two objective methods for measuring postoperative toric intraocular lens orientation under the natural pupil

Purpose: To evaluate and compare the accuracy of iTrace and CASIA2 in measuring the postoperative orientation of toric intraocular lens (IOL) without mydriasis. Setting: Tianjin Medical University Eye Hospital, Tianjin, China. Design: Prospective cohort study. Methods: Patients with SN6AT toric IOLs implanted after cataract surgery were enrolled. 1 month after surgery, the toric IOL orientation were measured by iTrace and CASIA2 in non-mydriatic, semi-dark conditions. Then, the toric axis was directly reviewed using the slit-lamp under full mydriasis. Axis measurement differences between each of the 2 devices and the slit-lamp, described as their relative differences (RDs), were calculated and compared. The percentage of RDs within 5 degrees, within 10 degrees and greater than 30 degrees were analyzed. Results: 77 eyes of 70 patients were included. Generally, the mean toric axis measurement RDs of CASIA2 and iTrace were 9.24 +/- 10.53 degrees and 13.89 +/- 15.47 degrees respectively (P = .04). For CASIA2 (72 eyes), 54.17% (39), 72.22% (52), and 4.17% (3) of eyes had RDs within 5 degrees, within 10 degrees and greater than 30 degrees, compared with 40.00% (28), 61.43% (43) and 12.86% (9) for iTrace (70 eyes). The 95% limits of agreements of CASIA2 with slit-lamp was narrower than that of iTrace with slit-lamp. The median RD of CASIA2 was significantly smaller in eyes with pupil >= 4 mm under dark condition compared with eyes with pupil <4 mm (P = .03). Conclusions: CASIA2 demonstrates greater precision in measuring toric IOL orientation under non-mydriatic conditions compared with iTrace. Moreover, the accuracy of CASIA2 is enhanced in cases of pupil >4 mm.