Changes in lamina cribrosa and prelaminar tissue after deep sclerectomy

Abstract

Aim: To determine the response of the lamina cribrosa (LC) and prelaminar tissue to a reduction of intraocular pressure (IOP) after nonpenetrating deep sclerectomy (NPDS) using enhanced depth imaging (EDI) spectral domain optical coherence tomography (SD-OCT).

Methods: A total of 28 eyes from 28 patients presenting with primary open angle glaucoma who underwent NPDS were studied. SD-OCT scans using EDI technology were obtained before surgery and 1 week, 1 month, and 3 months postoperatively. The OCT device was set to image a 15 × 10° vertical rectangle centred on the optic disc. The scan closest to the optic nerve head (ONH) centre was selected for analysis. The vertical distances from three equidistant points on the reference line (Bruch's membrane opening) to the anterior prelaminar tissue surface and the anterior and posterior surfaces of the LC were measured.

Results: The IOP decreased from 18.7 ± 4.3 to 9.1 ± 4.0 at the first week, 11.4 ± 3.7 at 1 month, and 13.1 ± 3.6 mm Hg at 3 months postoperatively (P<0.001). There was a significant reduction of the ONH cupping at 1 week (22.3%, P<0.001), 1 month (13.7%, P<0.001), and 3 months (9.8%, P=0.001) after surgery. Anterior displacement of the LC was slight but statistically significant at 1 week (4.5%, P=0.003), 1 month (3.8%, P=0.014), and 3 months postoperatively (3.3%, P=0.010). IOP reduction was significantly correlated with a reduction of ONH cupping and anterior displacement of LC at the first week and first month (P<0.05).

Conclusions: Cupping reversal after NPDS is mainly due to changes in prelaminar tissue thickness, whereas the LC changes in position are less pronounced.

Figure 1

Images obtained preoperatively (a1, a2), and at 1 week (b1, b2), 1 month (c1, c2), and 3 months (d1, d2) postoperatively. The IOP decreased from 18 to 6 mm Hg at 1 week, 13 mm Hg at 1 month, and 14 mm Hg at 3 months after surgery. a reference line connecting the termination of bruch's membrane was set (horizontal lines). Three vertical lines connecting points from the reference line to cup surface (a1, b1, c1, d1) and to the anterior surface of the Lc (a2, b2, c2, d2) were measured (vertical lines). Thickening of the prelaminar tissue (red arrow) and cupping reversal are noticeable in b1, but laminar displacement is mild (b2). Prelaminar thickness and cup excavation decreased at 1 month (c1, c2) and 3 months postoperatively (d1, d2).