Effect of Trabeculectomy on OCT Measurements of the Optic Nerve Head Neuroretinal Rim Tissue.

PURPOSE

Ophthalmologists commonly perform glaucoma surgery to treat progressive glaucoma. Few studies have examined the stability of OCT neuroretinal rim parameters after glaucoma surgery for ongoing detection of glaucoma progression.

DESIGN

Longitudinal cohort study.

PARTICIPANTS

20 eyes (16 subjects) with primary open angle glaucoma who had undergone a trabeculectomy.

METHODS

We calculated the change in OCT parameters (minimum rim area (MRA), minimum rim width (MRW), Bruch's membrane opening (BMO) area, mean cup depth (MCD), anterior lamina cribrosa surface depth (ALCSD), prelaminar tissue thickness (PLTT), retinal nerve fiber layer thickness (RFNLT) during an interval from the visit before the surgery to the visit after the surgery, a span of approximately 6-months. We also calculated changes in the same eyes over two separate 6-month intervals that did not contain trabeculectomy to serve as control. We compared these intervals using a generalized linear model (with compound symmetry correlation structure), accounting for the correlation between time intervals for the same eye.

MAIN OUTCOMES MEASURES

MRW, MRA, angle above the reference plane for MRW and MRA, BMO area, MCD, mean ALCSD, PLTT, RNFLT and visual field parameters (mean deviation (MD), pattern standard deviation (PSD), and visual field index (VFI)).

RESULTS

The intervals containing trabeculectomy showed a significant decrease in intraocular pressure (-9.2 mmHg, p<.001) when compared to control intervals. Likewise, the following neuroretinal rim parameters showed significant changes with trabeculectomy: increased MRW (+6.04μm, p=.001), increased MRA (+0.014mm, p=.024), increased angle above reference plane of MRW (+2.64°, p<.001), decreased MCD (-11.6μm, p=.007), and decreased mean ALCSD (-18.91μm, p=.006). This is consistent with an increase in rim tissue thickness and a more anterior position of the ILM and ALCS relative to the BMO plane. Conversely, RNFLT change was not significantly different between trabeculectomy and control intervals (p=.37).

CONCLUSION

Trabeculectomy resulted in anatomical changes to the ONH rim associated with reduced glaucomatous cupping. The RNFL thickness may be a more stable measure of disease progression that clinicians can use to monitor across time intervals containing glaucoma surgery.