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Editor,—We read with interest the article by Kee and Moon1 who provided interesting data on the effect of cataract removal on outflow facility and intraocular pressure (IOP). We have been interested for some time in the effect of ocular surgery upon measured IOP.2 Previous studies have shown a reduction in IOP after cataract surgery34and have suggested implications for combined cataract and filtering surgery.
To assess change in outflow facility Kee and Moon utilised pneumotonometry. However, this technique has been shown to give low reproducibility5 as a tonography method. Indeed, Shiotz tonography may have been more accurate.5 The investigators may have had technical reasons for their choice of instrument; however, no justification was provided, nor was diurnal variation in IOP accounted for in this study.
The authors' extrapolated ciliary muscle response to pilocarpine from measurements of the outflow facility before and 1 hour after 2% pilocarpine instillation. To specifically investigate the effect of the lens on ciliary muscle contractility the authors repeated the measurement 2 months after phacoemulsification surgery. Interestingly, these latter assessments may not have allowed sufficient time for IOP and outflow facility to stabilise and the hypertensive effect of topical corticosteroids to wane. In general, published 1 year follow up studies demonstrate mixed results in relation to IOP reduction and altered outflow facility.346
We have carried out a prospective observational study of phacoemusification (phaco) surgery performed at a major teaching hospital. In 393 consecutive small incision (3.2 mm) phaco procedures performed over a 5 month period we also demonstrated a significant (Student's t test p<0.001) drop of measured IOP comparing preoperative and 4 weeks post-phaco IOP (1.28 (SD 3.10) mm Hg). Furthermore, analysis of the data revealed the drop in IOP was significant for both clear corneal incision (n=318) and scleral tunnel incision (n=75) phaco techniques, being 1.5 (3.16) mm Hg (p<0.001) and 0.9 (2.9) mm Hg (p=0.015), respectively. However, when those with a history of glaucoma (n=39) were analysed separately, a non-significant (p=0.28) reduction of IOP (0.69 (3.47) mm Hg) was demonstrated. We believe to adequately define the effects of cataract surgery on IOP in a glaucomatous population, a larger group prospectively studied over a period longer than 2 months and preferably more than 1 year is required and a reproducible accurate assessment of outflow facility would be of added value.
The authors of this recent article elegantly address the important issue of IOP changes after intraocular surgery but standard investigative techniques that are practical, accurate, and reproducible in the clinical setting need to be developed.
The authors have no proprietary or commercial interest in the findings presented.