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Editors Selection IGR 12-4

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Comment by Keith Barton on:

50418 Reduction in Intraocular Pressure after Cataract Extraction: The Ocular Hypertension Treatment Study, Mansberger SL; Gordon MO; Jampel H et al., Ophthalmology, 2012; 119: 1826-1831

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The effect of cataract surgery on IOP is widely quoted and frequently exaggerated as is common with issues where hard evidence is lacking. Previous studies have examined the effect of cataract surgery on IOP, but the closest we might come to the answer could be in this manuscript by Mansbergeret al. The Ocular Hypertension Treatment Trial investigators considered all participants in the observation arm of OHTS who underwent cataract surgery, providing there was no use of ocular hypotensive medication beforehand, no laser iridotomy in the preceding 12 months, or prior trabeculectomy. A split date was defined as the first follow-up at which cataract surgery was reported. To be eligible, participants must have attended at least one visit before and after this date. Sixty-three eyes (42 subjects) were included in the surgery group. Control subjects were phakic participants in the observation arm who did not undergo cataract surgery, and who otherwise fulfilled the same eligibility criteria. Seven hundred forty-three control eyes were derived by random selection of eyes after stratification according to follow-up, so that the distribution of follow-up visits of the control eyes corresponded to the split dates in the cataract surgery group.

Overall, cataract surgery reduced the IOP by around 16% for up to 36 months. The greatest percentage and magnitude reduction was observed in those with the highest starting IOP. Other preoperative factors were not associated with the percentage IOP drop.

… cataract surgery reduced the IOP by around 16% for up to 36 months

It is possible that the long-term IOP levels might be skewed by censorship of those initiating medication, though the numbers censored were greater in the control group, implying that the IOP lowering in the cataract surgery group might otherwise have been greater. It is surprising that the authors included two eyes of some patients, as these are not independent, presumably because the study numbers would otherwise be small. Despite these criticisms,a positive aspect of this study is its IOP measurement methodology (two observers), consistent measurement time windows, and low likelihood of regression toward the mean.

Overall, these data are cleaner than previously reported results and likely give a truer reflection of the IOP reduction induced by cataract surgery. With a 16% reduction, cataract surgery certainly lowers IOP and even cures (for 36 months) some mild ocular hypertensives, but as the authors correctly state, this is not evidence of a reduction in the risk of developing glaucoma in ocular hypertension.

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