Even a procedure as commonplace as cataract surgery poses some questions to surgeons, post-op pressure rise dynamics being one of them. “Prior studies, where they tracked what happens with the IOP immediately after cataract surgery for the first 24 hours, observed a significant increase in most of their patients who tend to return to normal on day one,” said Facundo Sanchez, MD, a post-doc research fellow of the Devers Eye Institute.¹ He presented his colleagues’ findings earlier this week at the 2021 ARVO virtual meeting. “We were interested in knowing whether some biometric parameters were associated with this increase in IOP after cataract surgery.” Dr. Sanchez pointed out that every cataract patient already undergoes a biometry scan during the preoperative visit.

“Acute IOP spikes post-cataract surgery are important [to study] because an acute IOP rise can deform the optic nerve head,” Dr. Sanchez explained.² “It’s possible that glaucoma patients are most susceptible to these kinds of acute changes. We wanted to know whether we can one day predict IOP spikes after cataract surgery.”

Using optical biometry, he and his colleagues measured the following preoperative anterior segment parameters in 42 glaucoma eyes before their cataract surgery: axial length, anterior chamber depth (i.e., distance between the posterior surface of the cornea and anterior surface of the lens), crystalline lens thickness (i.e., distance along the optical axis between the two lens surfaces) and white-to-white distance (i.e., horizontal iris width).³ They found that a shallower anterior chamber depth, shorter axial length and thicker crystalline lens were associated with an increased risk of IOP spikes the day after surgery in these patients.

The calculated change in IOP from baseline was adjusted for the number of preoperative ocular hypotensive agents. The researchers used generalized estimating equation regression to determine parameter associations with post-op day-one IOP.

They found that on post-op day one, eyes had significantly higher IOP than baseline (22.2mm Hg vs. 16.9mm Hg). Of the 42 eyes, 16 had a 5mm Hg IOP spike and six had a 10mm Hg IOP spike. They reported that patients with shallower anterior chamber depths had both a significantly higher IOP increase and a higher risk of a 10mm Hg spike. Thicker lenses resulted in higher IOP increase and were more likely to have a 5mm Hg or 10mm Hg spike, and shorter axial length indicated greater likelihood of a 10mm Hg spike. Axial length and lens thickness were significant predictors of a 5mm Hg spike.

Dr. Sanchez said there are a few theories about the mechanism of action for IOP changes. One theory centers on lens thickness. “Thicker lenses need more phaco time for removal,” he said. “Studies have shown that eyes receiving longer phaco time have a significantly greater IOP reduction, at least for up to two years, which may also suggest that a longer phaco time delivers more ultrasound energy. This ultrasound energy may activate the cytokine pathway, causing trabecular meshwork remodeling and therefore further IOP reduction.”

“In current glaucoma practice, we rely largely on surgeons’ criteria to assess the risk of IOP spikes, but it would be interesting to add biometric parameters as a more objective measure and possibly set up thresholds or formulas to help us predict changes on post-op day one for targeted prophylaxis.”