Corneal Biomechanics May Help Predict Degree of Post-injection IOP Change

Clinicians may reasonably be concerned that, after intravitreal injections, patients’ intraocular pressures (IOP) can rise sharply for approximately 30 minutes, occasionally longer. A comprehensive study finds that swifter recovery of post-injection IOP is associated with higher corneal hysteresis (CH) and corneal resistance factor (CRF), according to the research published in Journal of Glaucoma. The study examined 100 patients who received bevacizumab therapy at the Henkind Eye Institute at Montefiore Medical Center in the Bronx, New York, from November 2018 to March 2020.

Participants in the prospective analysis were 34 to 89 years of age — 49% men, 51% women — who visited the clinic for conditions such as diabetic macular edema (DME), vaso occlusive disease, and macular degeneration. Of the total, 32% exhibited, or were suspect for, glaucoma. In the 2 hours before injection, patients underwent Goldmann applanation tonometry (GAT); 3 ocular biomechanical tests with an Ocular Response Analyzer® (ORA, Reichert, Inc.); and optical biometry, if axial length (AL) was not on file. Post-injection IOP was measured 5 minutes or sooner after injection, then every 10 minutes until IOP reached ≤150% of baseline, and at 30 minutes, if indicated. 

In mean values, baseline IOP of 18.3 mm Hg increased to 47.4 mm Hg after injection, with a difference of 29.14 mm Hg (P <.001), while baseline CH decreased from 9.5 mm Hg to 5.5 mm Hg, a change of -4.07 mm Hg (P <.001). Higher IOP immediately after injection was associated with higher preinjection IOP (P =.014), and higher CRF (P =.026). Using GAT data specifically, the “overall accuracy of the low (<15.5 mm Hg), middle (15.5 to 18.5 mm Hg), and high (>18.5 mm Hg) baseline IOP ranges to predict minor, moderate, and severe IOP increase was 43%.” No association was found between AL and a spike in pressure.

In a statistical model evaluating the effect of CH on return to ≤150% of baseline IOP — adjusted for clinically-relevant variables — higher CH (P =.002), higher preinjection IOP (P <.001), and lower immediate postinjection IOP (P <.001) were each connected with quicker recovery. Using data comparing CRF with recovery, higher CRF (P =.046), higher preinjection IOP (P =.004), and lower immediate post injection pressure (P <.001) were each linked to swifter IOP return.

This research also compared Goldmann applanation-measured IOP with measurements by ORA, finding that IOP higher than 30 mm Hg was significantly associated with reduced waveform quality of ORA biomechanical metrics.

Results of this study may be limited for generalizability to a population without diabetes, as 81% of the participants were diagnosed with DME. Another limitation relates to individuals taking prostaglandin analogue who displayed faster IOP recovery from enhanced aqueous outflow. However, this is the first investigation that evaluates the effect of CH and CRF on postinjection IOP elevation related to increased ocular volume.

Overall, CH value was better than CRF for predicting an extended post-injection IOP elevation. For clinicians, “both pretreatment IOP measurements and measurements of corneal biomechanics may add complementary information in predicting the magnitude and duration of pressure elevations after intravitreal injections and may be clinically useful to prevent acute pressure-related visual loss in susceptible patients,” the study explains.

Reference

Dackowski EK, Moon J-Y, Wang J, et al. The relationship between corneal biomechanics and intraocular pressure dynamics in patients undergoing intravitreal injection. J Glaucoma. May 2021;30(5):451-458. doi:10.1097/IJG.0000000000001833