Study Shows How Cataract Surgery Lowers IOP in Different Glaucoma Subtypes

Doctor performing eye surgery in modern clinic
A new study evaluates the precise magnitude of IOP reduction following cataract surgery across glaucoma subtypes.

Surgeons expect to see a reduction in intraocular pressure (IOP) after phacoemulsification, but a new study evaluates the precise magnitude of that change, and how that change differs between diagnoses and other patient factors. The California-based research team identified a lower association of IOP reduction following cataract surgery with phacoemulsification than in past referral-based studies, but confirmed that surgeons are likely to see IOPs lowered by approximately 1 mm Hg to 2 mm Hg after phacoemulsification in patients with preoperative IOPs lower than 20 mm Hg.

The investigators conducted a community-based retrospective cohort study to evaluate change in IOP after simple phacoemulsification in patients with glaucoma, ocular hypertension, narrow angles, and in glaucoma suspects. They also showed the differences between those who underwent surgery with phacoemulsification and those who did not receive surgery. 

Non-surgical patients had an increase in IOP over the 3-year follow-up period, regardless of glaucoma subtype. Those who underwent cataract surgery experienced a decrease in IOP, regardless of subtype. The decrease was greatest for patients with ocular hypertension, anatomic narrow angle, and primary angle closure glaucoma, and for those whose baseline IOP was most elevated.

The researchers identified the “difference-in-difference” (the average difference in the change in IOP between the surgical and non-surgical patients) amongst the different subtypes of glaucoma. This metric was greatest for patients with ocular hypertension (2.00 mm Hg) and for patients with preoperative IOP greater than or equal to 20 mm Hg (2.46 mm Hg). Researchers recorded difference-in-difference IOP reductions of 1.78 mm Hg for patients with anatomic narrow angle and 1.55 mm Hg for pseudoexfoliation glaucoma. Normal tension glaucoma saw the least reduction at 0.65 mm Hg. Glaucoma suspects saw a reduction of 1.29 mm Hg. 

It’s widely accepted throughout the academic literature that cataract surgery can lower intraocular pressure. By way of example, nearly half of American Glaucoma Society members surveyed in 2017 said that they would treat a patient with primary open angle glaucoma and visually significant cataract using phacoemulsification alone.2 However, this research is unique in that it provides a large controlled study of more than 16,000 subjects.

Investigators say this research can assist in surgical decisions about whether minimally invasive glaucoma surgery or conventional glaucoma procedures will be necessary at the time of cataract surgery to achieve IOP targets.1 


  1. Carolan J, Liu L, Alexeeff S, Amsden L, Shorstein N, Herrinton L. Intraocular pressure reduction after phacoemulsification: a matched cohort study. Ophthalmology Glaucoma. Published online October 10, 2020. doi: 10.1016/j.ogla.2020.10.002
  2. Vinod K, Gedde SJ, Feuer WJ, et al. Practice preferences for glaucoma surgery: a survey of the american glaucoma society. J Glaucoma. 2017;26:687-693. doi: 10.1097/IJG.0000000000000720