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Editors Selection IGR 23-2

Surgical Treatment: Cataract Surgery is Beneficial for Glaucoma

Comment by Angelo Tanna on:

98129 Cataract Surgery Lowers Intraocular Pressure and Medication Use in the Medication Group of the Ocular Hypertension Treatment Study, Mansberger SL; Gardiner SK; Gordon M et al., American Journal of Ophthalmology, 2022; 236: 53-62

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The landmark post-hoc analysis of data from the observation arm of the Ocular Hypertension Treatment Study (OHTS) provided strong evidence that cataract surgery lowers IOP in eyes with untreated OHT.¹ That study, published in 2012, found a mean reduction in IOP after cataract surgery of 4.1 mmHg from a baseline of 23.9 mmHg, with a gradual loss of effect over time. The importance of the body of knowledge regarding the effects of cataract surgery on IOP has grown with the advent of various minimally invasive glaucoma surgeries. In evaluating the efficacy of such procedures when combined with cataract surgery in clinical studies and even in our own clinical practices, we must be cognizant of the IOP lowering effect of cataract surgery alone.

The latest report from OHTS on this topic adds important new information about the effects of cataract surgery on IOP by focusing on the OHTS subjects who were randomized to treatment to achieve a 20% reduction in IOP.² Among 1612 eyes of 806 OHTS subjects randomized to treatment, this study included a subset of eyes for which at least two study visits occurred prior to and after cataract surgery. As in their prior report on the effect of cataract surgery among eyes in the observation arm of OHTS, the study visit at which subjects reported they had undergone cataract surgery was defined as the 'split date' ‐ the first post-cataract surgery study visit. Because treatment strategies evolved during the course of the clinical trial, particularly as a result of the approval of latanoprost, it was important to compare temporally matched IOP data from the control group that did not undergo cataract surgery. The investigators attempt to do this by defining the matching split date for the control group as the 15^th study visit such that the median number of study visits prior to the split date was the same for both groups. The investigators analyzed 149 eyes of 92 subjects that underwent cataract surgery and 1004 eyes of 531 control subjects, all from the treatment arm.

Subjects in the cataract surgery group were significantly older and had slightly worse mean deviation and pattern standard deviation values. Interestingly, the control group had significantly larger vertical and horizontal cup-disc ratios. The only other notable difference between groups prior to the split date was a higher IOP in the cataract surgery arm, 18.9 vs 18.2 mmHg (p = 0.053).

Cataract surgery resulted in a mean IOP change ranging from -2.2 to -1.3 mmHg through 48 months after the split date (p < 0.001), compared to the group's own baseline. Contemporaneously, there was a significant and persistent (72 months after the split date) reduction in the mean number of medications ranging from -0.5 to -0.3 classes (p < 0.001), with 13.8 to 23.5% of eyes that were medication-free. There was also a slight but statistically significant decrease in the IOP in the control group, ranging from -0.1 to -0.7 mmHg (p < 0.01); however, there was no change in the number of medications.

An important question is whether undergoing cataract surgery reduced the risk of the subsequent conversion to POAG. First, it is noteworthy that the presence of a developing, visually significant cataract, did not appear to influence the likelihood of conversion to a POAG endpoint prior to cataract surgery, i.e., the eyes that underwent cataract surgery were not more likely to have already converted to POAG prior to surgery. After cataract surgery, the hazard ratio for conversion by either visual field or optic disc criteria was 0.7 (95% CI: 0.32-1.55, p = 0.38). There was a lower risk of conversion to POAG in the cataract surgery group based on optic disc criteria alone (HR 0.22; 95% CI: 0.05-0.95; p = 0.042, but not significant after adjustment for multiple comparisons). Since OHTS required a protocol-driven target IOP, there was no significant difference in IOP between groups by 12 months after the split date, possibly accounting for the lack of a clear protective effect against conversion to POAG. Moreover, since only ten eyes in the cataract surgery group converted to POAG, there may not have been sufficient statistical power to detect a difference in the risk of conversion should one have existed.

We already knew cataract surgery lowers IOP and reduces the need for medications in medically treated POAG and OHT eyes from the many MIGS clinical trials that have been published. Many of those studies provided additional information based on IOP assessment after medication washout. This study, however, provides more reliable evidence about the magnitude of IOP reduction because it is relatively free of the confounding effect of regression to the mean since the decision to intervene with cataract surgery was independent of the IOP prior to surgery.

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