Glaucoma drug efficacy may be underestimated after refractive surgery: study

The effect of hypotensive drugs on IOP readings after refractive surgery may be underestimated because of changes in corneal thickness or corneal curvature, a study found. Physicians should consider using a nomogram to correct IOP measurements in glaucoma patients after refractive corneal surgery, a group of Italian researchers advised.

Ciro Tamburelli and colleagues at Catholic University in Rome randomly selected 24 eyes of 24 patients who were undergoing photorefractive keratectomy for myopia in which to evaluate this phenomenon. Before photorefractive keratectomy and again at 6 months postop, they measured central corneal thickness (CCT), corneal curvature and IOP before and after instillation of one drop of latanoprost.

The mean CCT was 544.6 µm and the anterior radius of corneal curvature was 7.73 mm before PRK. Postoperatively, the mean CCT was 463.2 µm and the mean radius of curvature was 8.33 mm.

Mean IOP preop was 15.8 mm Hg before latanoprost administration and 12.54 mm Hg after administration. Postop, the mean IOP was measured as 12.23 mm Hg before latanoprost administration and 10.19 mm Hg after.

After a recalculation using a correction factor for CCT and curvature, the pre- and postop IOP readings were compared. The pre- and postop IOP reductions significantly differed, but not the “true,” adjusted IOP reductions.

The study is published in the March issue of Investigative Ophthalmology & Visual Science.