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Cataract surgery and IOP
  1. S Fraser,
  2. P S Phelan
  1. Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR4 9HP, UK
  1. Correspondence to: MrScott Fraser Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR4 9HP, UK;

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We would like to congratulate Issa et al1 on their excellent and, we believe, important paper regarding cataract surgery and intraocular pressure drop.

It has become increasingly obvious to us, in our practice, that many patients do indeed get a significant drop in intraocular pressure (IOP) after phacoemulsification. We now have a substantial number of patients with both acute and chronic angle closure who, following cataract surgery, have been able to come off all antihypertensive medications. We would now goes as far as to say that in these patients it is now the operation of choice (when medical therapy has deemed to have failed) and this is supported by a number of studies.2–5 There is also the added benefit of a reduction in the incidence of aqueous misdirection.

It is interesting that Issa et al used “normal” patients in their study and still found a significant reduction in IOP. We have thought for sometime that a number of glaucoma patients who, on gonioscopy, are seen to have “open angles” but on closer inspection have some (usually central) anterior chamber shallowing, often seem to have profound drops in their IOP following cataract surgery. Although many of these patients have degrees of hypermetropia, this is not always the case. Indeed with increasing nuclear sclerosis some may be myopic at presentation.

The authors rightly state that their study needs to be repeated by others to confirm their results. We think that lens thickness has more of a role than this study suggests. There is an important flaw—acknowledged by the authors—regarding the lack of data on corneal thickness. Any future studies need to correct for this, not only to allow a more accurate assessment of the IOP, but because the cornea itself is part of the anterior structure of the eye and may not necessarily be an independent variable.

Finally we speculate that there is likely to be a measurable relation between IOP, volume of the anterior segment, lens size, and possibly corneal thickness. Once we have quantified this it may then allow us not only to be able to assess the likely magnitude of IOP drop after phacoemulsification, but will give an essential insight into some of the underlying mechanisms of raised IOP.