Lamina Cribrosa Reversal after Trabeculectomy and the Rate of Progressive Retinal Nerve Fiber Layer Thinning

PurposeTo determine whether the reversal of lamina cribrosa (LC) displacement observed after trabeculectomy is associated with the rate of progressive retinal nerve fiber layer (RNFL) thinning in primary open-angle glaucoma (POAG).DesignObservational case series.ParticipantsThirty-four patients with POAG who underwent trabeculectomy and were followed up for at least 2.5 years, during which the RNFL thickness was measured by serial spectral-domain (SD) optical coherence tomography (OCT).MethodsThe participants underwent enhanced depth imaging scanning of the optic nerve using SD OCT before surgery (PREOP), at a 6-month postoperative follow-up (FU1), and at a subsequent follow-up that was performed at least 2.5 years postoperatively (FU2), and serial RNFL thickness was measured at least 5 times during the study period. Preoperative and postoperative LC depths (LCDs) as determined on 7 selected B-scan images from each eye were averaged to produce the mean LCD. The rate of RNFL thinning was determined by linear regression of serial OCT RNFL thickness measurements over time.Main Outcome MeasuresFactors associated with the rate of OCT RNFL thinning.ResultsThe intraocular pressure (IOP) decreased from 23.8±7.9 mmHg (mean ± standard deviation) to 11.0±4.4 mmHg at FU1 (P < 0.001) and subsequently increased to 13.1±5.2 mmHg at an overall follow-up of 3.5±0.8 years (P = 0.003). The LCD was reduced from 589.90±148.32 to 508.57±136.28 μm at FU1 (P < 0.001). A subsequent slight but nonsignificant increase in the LCD was noted at FU2 (516.48±145.87 μm; P = 0.410). A faster rate of RNFL thinning was associated with a shorter follow-up period (P = 0.032), higher IOP at PREOP (P = 0.011) and FU2 (P = 0.014), and a larger increase in LCD from FU1 to FU2 (P < 0.001). The changes in LCD between PREOP and FU1 and between PREOP and FU2 were not associated with the rate of RNFL thinning.ConclusionsEyes with sustained LCD reduction over a long period had a slow rate of progressive RNFL thinning after trabeculectomy. A large LCD reduction in the early postoperative period was not associated with the long-term rate of progression if it was not maintained during subsequent follow-up.