COMMENTARY

Cataract Surgery for Ocular Hypertension?

Shuchi B. Patel, MD

Disclosures

March 01, 2013

Reduction in Intraocular Pressure After Cataract Extraction: the Ocular Hypertension Treatment Study

Mansberger SL, Gordon MO, Jampel H, et al; Ocular Hypertension Treatment Study Group
Ophthalmology. 2012;119:1826-1831

Study Summary

Many studies have looked at the effect of cataract extraction on intraocular pressure (IOP). Similarly, this study sought to determine the effect of cataract extraction on IOP specifically in patients with ocular hypertension.

This study was a comparative case series from the Ocular Hypertension Treatment Study Group, which analyzed IOP after cataract extraction in the observation group. The cataract surgery group consisted of 42 participants (63 eyes) who underwent cataract surgery in at least 1 eye during the study. The control group of 743 participants (743 eyes) did not undergo cataract surgery.

Preoperative IOP was defined as the mean IOP of up to 3 visits before the "split date," which was defined as the first study visit date at which cataract surgery was reported in the cataract surgery group. A corresponding split date was given to the control group. Postoperative IOP was the mean IOP of up to 3 visits, including the split date.

The differences in preoperative and postoperative IOP were compared in the cataract surgery and control groups. In the control group, the mean IOP for visits corresponding to pre- and postoperative visits were 23.8 ± 3.6 mm Hg and 23.4 ± 3.9 mm Hg, respectively. In the cataract surgery group, postoperative IOP was significantly lower than preoperative IOP (19.8 ± 3.2 mm Hg vs 23.9 ± 3.2 mm Hg; P < .001), and the average percent decrease from preoperative IOP was 16.5%.

Decrease in IOP was also analyzed in subgroups according to preoperative IOP. The 63 eyes were stratified into tertiles, with approximately 21 eyes in each group. In the tertile with the lowest preoperative IOP (< 22.3 mm Hg), the mean percent change in postoperative IOP was -11.0% ± 13.1%. The second tertile (preoperative IOP, 22.3-25.0 mm Hg) had a mean percent change in postoperative IOP of -16.2% ± 11.9%, and the change in the third tertile (IOP > 25 mm Hg) was -22.5% ± 12.7%.

On the basis of this study, it appears that cataract surgery results in a persistent reduction in IOP in patients with ocular hypertension, with a greater reduction in postoperative IOP occurring in eyes with the highest preoperative IOP.

Viewpoint

Although previous studies have analyzed the effect of cataract surgery on IOP, this study had some unique findings. Other studies have varied in the reduction in IOP shown, but most have agreed that some reduction occurs postoperatively.

The reported duration of this effect is variable. Reviews as recent as 2002 have not addressed the issue of persistence of decreased IOP.[1] Other studies have compared the reduction in IOP in different conditions as well, such as narrow angles or chronic angle closure.[2,3] This particular study is distinctive in that all patients had ocular hypertension with open angles and no other ocular conditions.

In addition, other studies were not designed to minimize regression to the mean or differential bias due to IOP lowering from ocular hypotensive medications.[4,5,6] This study protocol, however, took precautions to prevent regression to the mean and measurement bias. Also, this study followed accepted protocols for IOP measurement, such as using the Goldmann tonometer, averaging at least 2 IOP readings per visit, and finding the mean by taking at least 3 readings separated by at least 2 days. Therefore, the data from this study, although retrospective, had few confounding variables and followed patients up to 36 months postsurgically.

All patients had an IOP of 24-32 mm Hg in one eye and 21-32 mm Hg in the other eye, with no evidence of glaucomatous structural or functional damage and a best-corrected visual acuity of at least 20/40 in both eyes. For patients who had bilateral cataract surgery, only 1 eye was included, and the demographic and ocular characteristics of the control and surgery groups were compared. The cataract surgery group was older and had greater central corneal thickness, but all other factors, such as race, gender, horizontal and vertical cup-to-disc ratio, and preoperative IOP, were not statistically significant.

In conclusion, although this study provides confirmation of what may already be generally accepted in terms of reduction of IOP with cataract surgery, it provides more solid evidence that corroborates previous studies. The reduction of variables provides reliable data, although they are still derived from a specific cohort.

As the authors pointed out, caution must be used when extrapolating the findings to eyes with lower IOP, higher IOP, or preexisting glaucoma. Therefore, the data still need to be considered carefully when applying them to clinical management. Similar data from a larger cohort would help with clinical management and should be a goal of future studies. Also, the rates at which patients with and without cataract extraction develop glaucoma should be studied to determine whether the degree of IOP reduction is clinically significant in reducing the rate of glaucoma in patients with ocular hypertension.

Abstract

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