The effect of intraocular pressure on visual field after trabeculectomy in patients with primary open angle glaucoma.

ABSTRACT

PURPOSE: To compare the mean intraocular pressure (IOP), peak IOP and percentage reduction in IOP in the first five years following trabeculectomy between the patients with progressed visual field loss and the patients with stable visual fields. MATERIAL AND METHODS: Thirty-six eyes of 36 patients were followed for five years after their first trabeculectomy with tonometry and automated perimetry (Octopus 500EZ, program G1). The rate of change of the visual field was measured by linear regression analysis of the mean sensitivity value (dB) of each field test versus time (month). Based on the statistical significance of the slope of the regression line (Spearman p value of the correlation coefficient less than 0.05), patients were divided into two groups with significant negative slope of the regression line (group with progressed visual field loss) and with non-significant slope of the regression line (group with stable visual field). The mean IOP values and percentage of IOP reduction at the end of each of the first five years after surgery were compared between the group with progressed field loss and group with stable fields by using Mann-Whitney U test. RESULTS: Patients with progressed visual field loss had higher mean IOP, higher peak IOP and less reduction in pressure after the operation than patients with stable visual field. The mean IOP at end of the two year postoperative period was significantly higher in patients with progressed visual field loss (21.98 +/- 3.38 mmHg) than in those with stable fields (17.48 +/- 4.80 mmHg). The mean percentage reduction in IOP at the end of two year postoperative period was significantly less in patients that showed progression of field loss (21.84%) than in those with stable fields (41.0%). CONCLUSION: Prognosis for further field loss seems to be better if postoperative pressure is at lower levels and greater percent reduction of IOP is obtained after surgery. The data that predict better prognosis is the mean postoperative IOP value of approximately 18 mmHg or less resulting from at least 35% of IOP reduction.