Relationship between preoperative high intraocular pressure and retinal nerve fibre layer thinning after glaucoma surgery

Abstract

Recent reports show varying results regarding peripapillary retinal nerve fibre layer (RNFL) thickness after intraocular pressure (IOP)-lowering glaucoma surgery. We hypothesised that different levels of the preoperative IOP influence RNFL thickness. A total of 60 patients (60 eyes) with glaucoma, who underwent glaucoma surgery and had a stable postoperative mean IOP < 22 mmHg, were enrolled. The RNFL thickness was measured using spectral domain optical coherence tomography, before and at 3-6 months after surgery. The preoperative peak IOP, 37.4 ± 10.8 mmHg, decreased to a postoperative mean IOP of 14.8 ± 3.5 mmHg (p < 0.001). The average RNFL thickness was significantly reduced from 75.6 ± 17.7 μm to 70.2 ± 15.8 μm (p < 0.001). In subgroup analyses, only patients with a preoperative peak IOP ≥ median value (37 mmHg) exhibited significant RNFL thinning (9.7 ± 6.6 μm, p < 0.001) associated with a higher preoperative peak IOP (r = 0.475, p = 0.008). The RNFL thinning was evident for a few months after glaucoma surgery in patients with a higher preoperative peak IOP, although the postoperative IOP was stable.

Figure 1

Correlation between the preoperative peak intraocular pressure (IOP) and postoperative thinning of the retinal nerve fibre layer (RNFL). In patients with IOP ≥ 37 mmHg (median value), postoperative RNFL thinning was significantly associated with preoperative peak IOP (r = 0.475, p = 0.008). In patients with IOP < 37 mmHg, there was not a significant correlation between postoperative RNFL thinning and preoperative peak IOP (r = 0.175, p = 0.354).

Figure 2

A representative patient. He was 72 years old and had primary open-angle glaucoma in both his eyes. Although the usual intraocular pressure in the left eye was uncontrolled, ranging 25~30 mmHg despite IOP lowering medical therapy, he wanted to delay surgical treatment. However, he eventually underwent trabeculectomy because of the more increased IOP in his left eye. His preoperative peak IOP was 57 mmHg and the average RNFL thickness was 99 µm (it was 16 µm thicker than the average RNFL thickness of 83 µm measured 4 months previously). Five months after the trabeculectomy, his average RNFL thickness decreased by 22 µm. During the same period, the preoperative average GCIPL thickness decreased by only 2 µm. RNFL = retinal nerve fibre layer, GCIPL = ganglion cell plus inner plexiform layer, T = temporal, S = superior, N = nasal, and I = inferior.

Figure 3

Correlation between preoperative peak IOP and postoperative thinning of the RNFL in patients with primary open-angle glaucoma (POAG, n = 29) and with glaucoma other than POAG (n = 31). In patients with POAG, postoperative RNFL thinning was significantly associated with the preoperative peak IOP (r = 0.500, p = 0.006). In patients with glaucoma other than POAG, postoperative RNFL thinning was also significantly associated with the preoperative peak IOP (r = 0.716, p < 0.001).