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Glaucoma Dialogue IGR 14-2

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Comment by Paul Healey 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 reliable and standardized prospective data collection in the OHTS makes a good framework for this nested case-control study of the effect of cataract extraction on intraocular pressure. The investigators sensibly excluded subjects who had their IOP lowered by drugs, or surgery leaving a cohort of 785 ocular hypertensive subjects of whom 42 had cataract surgery. The surgery group was not the same as the control group, being older by about ten years, yet having thicker corneas (by 10 μm). IOP was averaged over three visits pre- and post-op.

Mean IOP (24 mmHg) fell 4 mmHg compared to a 0.3 mmHg in the control group. By 36 months the mean IOP of the surgery group had increased by 1.8 mmHg and the control group IOP decreased by a little over 1 mmHg (the actual amount was not reported).

Over the first three post-op visits, 16% of eyes had a fairly substantial (≥ 30%) fall in IOP whereas 11% had no change or a rise. The majority had a modest fall (10-19%). How much of this was subsequently lost by month 36 is not reported.

The major risk factor for the size of the post-op fall in IOP was the initial IOP, with eyes starting < 22 mmHg falling 10% compared with eyes > 25 mmHg which fell 22.5% over the first three post-op visits. While the IOP rises in the control and tertile groups, the correlation between fellow eyes and risk factors for IOP change (rather than absolute IOP) should have been reported, this study provides good data about post cataract surgery IOP changes in ocular hypertensive without glaucoma. About one eye in six will have a decent IOP fall, but for most only a modest fall can be expected. Furthermore about half the fall will be lost over the following three years. As a side effect of improving vision, an IOP fall after cataract surgery is certainly beneficial. As an IOP-lowering treatment for ocular hypertension however, cataract surgery is much less effective than our current standard treatments.

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