The influence of surgical and medical interventions upon optic disc structure in patients with primary open angle glaucoma.

PURPOSE: To evaluate the changes of optic disc parameters in primary open angle glaucoma (POAG) patients after surgical and medical treatment, and analyze the determinants of these changes. METHODS: A total of 67 patients were enrolled in this study. Thirty nine patients (40 eyes) underwent trabeculectomy and 28 patients (32 eyes) received intra-ocular pressure (IOP) lowering medical therapy. All subjects underwent bilateral routine ocular examination and Heidelberg retina tomography (HRT) before treatment and 2 weeks, 1 month, 3 months, 6 months and 1 year after treatment. Changes in optic disc parameters in both the surgical and medical groups were analyzed, as was the influence of disease severity and IOP reduction on these changes. RESULTS: In the surgical group, the average preoperative IOP was 32.8±8.64 mmHg, which showed a significant decline at each post-operative visit. Most optic disc parameters measured by HRT were significantly improved after trabeculectomy (P=0.001~0.01), though the amount of improvement declined gradually during the post-operative period. Rim volume (RV), cup shape measure (CSM ), mean RNFL (mRNFL), RNFL cross sectional area (RNFLA) and vertical cup-to-disc ratio (C/D) still remained significantly below the pre-operative mean one year after surgery. In the medical group, the mean IOP before treatment was 24.8±4.32 mmHg and remained <21 mmHg on all subsequent post-treatment visits. However, no significant changes in optic disc parameters were found after initiation of medical treatment (F=0.52~2.21, P=0.75~0.07). In the surgical group, the extent of reduction of IOP was positively correlated with the improvement in RV, CSM and vertical C/D (r=0.41~0.58, P=0.001~0.04) at one year after trabeculectomy. The absolute value of the mean deviation on visual field testing was negatively correlated with the improvement of RV and CSM (r=-0.43~-0.62, P=0.03~0.001). CONCLUSION: Improvement in optic disc parameters occurred more commonly after surgical than medical treatment in POAG patients. The amount of reduction of IOP was correlated with the extent of this improvement, which may be more limited in more severe glaucoma.