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Editors Selection IGR 7-2

Surgical treatment: Cataract extraction and IOP

Comment by Winifred Nolan & Tec Kuan Paul Chew on:

12421 A novel index for predicting intraocular pressure reduction following cataract surgery, Issa SA; Pacheco J; Mahmood U et al., British Journal of Ophthalmology, 2005; 89: 543-546

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In this study Issa et al. (710) measure central anterior chamber depth (ACD), lens thickness and axial length in 103 non-glaucomatous eyes pre and post-cataract surgery and try to correlate these measures with the change in intraocular pressure (IOP). The most notable finding was the extent of reduction in IOP following surgery was inversely related to the pre-operative ACD. Extent of IOP reduction was also directly related to pre-operative IOP measurement. Based on these findings the authors then devised a ratio of pre-op IOP/ pre-op ACD which they found could predict the extent of IOP reduction i.e. the greater the ratio of the pre-operative measurements (and the shallower the pre-operative ACD) the more extensive the IOP reduction following surgery.

These findings are interesting because they support previously reported data looking at IOP and biometric changes following cataract surgery in eyes with POAG and PACG (Hayeshi K et al. Ophthalmology 2000; 107: 698-703). In that paper ACD and angle width (using Scheimpflug imaging) were found to increase following cataract surgery in tandem with a decrease in IOP.

The extent of IOP reduction following surgery was inversely related to the pre-operative ACD and was also directly related to pre-operative IOP measurement

The assumption can be made that it is a widening of the angle that is responsible for the relationship between shallow pre-operative anterior chamber and a subsequent decrease in IOP. Gonioscopic or UBM measurements would have lend more support to this theory. Even if the angle is not closed in eyes with a shallow anterior chamber there may be compromise of aqueous outflow due to relative crowding of the angle by a large lens (or a normal sized lens in a small eye). It remains to be seen if this effect remains in eyes with PACG and established trabecular dysfunction, where widening of the angle may not be associated with an increase in outflow.

These findings lead us to a discussion of the role of lens extraction in glaucoma. In particular is it possible to achieve IOP control in eyes with PACG by removing the lens and avoiding filtering surgery? There are probably a number of other factors such as degree of synechial angle-closure and level of IOP, which would influence clinicians when deciding whether to do phaco alone or combine it with trabeculectomy for PACG patients, but there is no evidence from randomized controlled trials on the effectiveness of these surgical options. In the case of POAG with co-existing cataract maybe we should be considering cataract surgery alone in patients with a shallow ACD. The data from this paper should be applied to POAG and advanced PACG patients with caution given that compromised trabecular meshwork function is likely to play a greater role in the pathogenesis of raised IOP than angle width.

Is it worth measuring the ACD in POAG cases to determine whether cataract surgery alone may be adequate for reducing IOP to desired levels? The problem is especially relevant to populations in East Asia where many patients with POAG with raised IOP are also found to have a shallow anterior chamber. There is a place for work in this area to further investigate the described effect in both POAG and PACG.

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