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Editors Selection IGR 13-4

Surgical Treatment: Effect phacoemulsification on IOP

Comment by Thomas Samuelson on:

48302 A four-year prospective study on intraocular pressure in relation to phacoemulsification cataract surgery, Falck A; Hautala N; Turunen N et al., Acta Ophthalmologica, 2011; 89: 614-616

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Falck et al. (1992) report the results of this prospective study on intraocular pressure (IOP) following phacoemulsification in otherwise normal eyes. Thirtyfive eyes were studied. Patients with glaucoma, ocular hypertension, and other comorbidities were excluded. All study eyes had open angles. Exfoliation eyes, while allowed in the initial recruitment, were later excluded because there were too few patients with exfoliation to provide a meaningful assessment. The authors found a consistent reduction in mean IOP of approximately 20% or 3.6 mmHg throughout the four-year period. The average preoperative IOP was 16.0 mmHg for the morning measurement and 16.4 mmHg for the afternoon measurement. At four years, both morning and afternoon measurements were 3.6 mmHg lower than preoperative values. These findings are consistent with work published by our group as well as several other investigators in recent years. That the authors demonstrated these findings in otherwise normal eyes is notable. In most studies the reduction in intraocular pressure following phacoemulsification is most evident in patients with elevated preoperative IOP. If an eye is normotensive, it is less likely that the lens is adversely affecting outflow and removing the lens is less likely to change aqueous humor dynamics. On the other hand, those patients with elevated pressures preoperatively have one or more mechanisms of increased IOP, potentially including a lens related mechanism. In these patients, removing the lens is more likely to have a significant effect on intraocular pressure. While speculative, it is possible that the enlarging cataractous lens causes forward movement of the iris, and ciliary-zonular complex, altering the microenvironment of the trabecular meshwork. This forward movement of the ciliary body and scleral spur could adversely affect facility of outflow.

It is possible that the enlarging cataractous lens causes forward movement of the iris, and ciliaryzonular complex, altering the microenvironment of the trabecular meshwork

Replacing the thickened (5 mm) native lens with a thinner (1 mm) intraocular lens implant allows the ciliary-zonular complex to move posteriorly. Typically, posterior movement of the ciliary body and scleral spur-TM improves outflow facility (witness the mechanism of action of pilocarpine). Much work needs to be done to further elucidate the mechanism of pressure reduction following phacoemulsification. However, glaucoma specialists can include the findings of this study to the growing body of work that suggests that cataract surgery helps lower IOP in a majority of patients.

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