Before cataract surgery consults with patients who have open-angle glaucoma (OAG), it is, of course, highly useful to be familiar with the relative risks associated with various individual patient factors — and yet causes of intraocular pressure (IOP) changes may be interconnected, according to an investigation into the relationships between anterior segment structures after cataract removal. The prospective study was published in Scientific Reports.
Forty participants received uncomplicated phacoemulsification and intraocular lens (IOL) implantation at the Lithuanian University of Health Sciences, in Kaunas, Lithuania. The two cohorts included 15 eyes with OAG and 25 nonglaucomatous eyes. Before the surgery and 6 months postoperatively, investigators evaluated axial length (AL), central corneal thickness (CCT), IOL thickness, and anterior chamber depth, as well as anterior chamber angle (ACA) and related parameters such as angle opening distance (AOD) and trabecular-iris space area. All of the OAG group patients received the same medical glaucoma treatment before and after cataract surgery.
Unexpectedly, no correlation was found between preoperative ACA width and postoperative IOP reduction in either cohort. “Nonglaucomatous cataract patients and OAG cataract patients had similar biometrical and ACA characteristics preoperatively, but the postoperative structural dynamics differed, suggesting different postoperative ocular tissue adaptation,” the researchers explained. Although patients with OAG had a higher preoperative mean IOP — possibly influencing overall results — a ROC analysis showed participants with OAG were more likely to have a drop in IOP of less than 3.0 mm Hg compared with the control group.
In the OAG cohort, mean pre-op IOP was 17.1 mm Hg, dropping to 12.5 mm Hg at 6 months post-op. For patients without OAG, baseline IOP of 14.9 mm Hg fell to 13.1 mm Hg during this period. Mean IOP reduction significantly differed based on cohort (P <.001, Mann-Whitney U Test). Further, at 6 months, anterior chamber depth significantly increased both for patients with OAG (P =.001) and patients in the control group (P <.001), but the difference between groups was not significant — and this change was also not connected to lower IOP in either set.
Postoperatively, 26.6% of participants with OAG experienced AL shortening of ≥0.1 mm (P =.257), compared with 92.0% of control individuals who had this decrease in length (P <.001). Further, mean CCT was significantly thinner in the OAG cohort pre- and post-op, but corneal thickness remained relatively stable in both groups from before surgery to 6 months afterwards.
Previous studies have focused on closed-angle glaucoma, and most lacked a control set. The authors of the current investigation suggest that longitudinal evaluation of larger samples may be needed to explore long-term stability of IOP change. Choroidal thickness and trabecular meshwork were not assessed, a limitation of this study. Conversely, thorough ocular biometry and AS-OCT comprehensively examined relationships between anterior chamber structures and IOP change.
Participants’ AOD was measured at 500 μm from the scleral spur, and those in both cohorts who experienced the greatest decreases in IOP did not have narrow angles below 200 μm. “This suggests another mechanism alongside the ACA opening after phacoemulsification and IOL implantation,” the investigators explain. “One such factor could be trabecular meshwork remodeling and ciliary body fibrosis after cataract surgery.”
Pakuliene G, Kuzmiene L, Siesky B, Harris A, Januleviciene I. Changes in ocular morphology after cataract surgery in open angle glaucoma patients. Sci Rep. Published online June 9, 2021. doi:10.1038/s41598-021-91740-z