Change in the rate of progression after filtration surgery: incidence and characteristics.

Abstract

Purpose: To evaluate incidence and type of change in functional progression rate before and after glaucoma surgery.

Methods: The data of patients of all cases who underwent filtration surgery between 2007 and 2010 was reviewed. During this period 412 eyes with ocular hypertension or glaucoma were treated with filtration surgery and followed for a minimum 2 years preoperatively and 2 years postoperatively. From those, 33 eyes of 31 patients had visual acuity over 20/60, no other surgical procedures, absence of myopia over -5 diopters, a minimum of 5 reliable standard visual fields before surgery and another 5 or more after surgery. The rate of change in Visual Field Index (VFI) was calculated with GPA Software which applies linear regression analysis to individual VFI values overtime and probability of significant change. Main outcome variables were VFI rates before and after surgery, change in sign and value of annual VFI rate. VFI and VFI rate changes with surgery were analyzed with Wilcoxon Signed Rank test and T test respectively. The incidence of a positive clinically significant change (change from a negative to a positive rate of change and/or reduction of the rate of progression in at least 0.5%/year) in VFI rate of change with surgery was calculated.

Results: Mean (SD) intraocular pressure was 17.5 (4.1) mmHg before surgery and 12.2 (2.9) mmHg after surgery (p<0.001). Mean (SD) VFI values before surgery were 77.3 (18.2) % and were 73.8 (18.6) % at the last postop visit (p=0.004). Mean (SD) VFI preoperative rate of change was -2.7 (4.8) %/year and was -1.2 (2.0) %/year after surgery (p=0.082).Twenty three eyes (69.6%) had a negative and statistically significant (p<0.05) rate of progression before surgery and 17 eyes (51.5%) had it postoperatively. The incidence of a positive clinically significant change in the rate of progression was found in 20 eyes (60.6%). Nevertheless in 2 (6.0 %) eyes the rate of progression slowed down by less than 0.5%/year and in 11(33.3%) eyes the rate became worse after surgery was performed.

Conclusions: Filtration surgery significantly influences functional rate of change but differently among different patients. Surgery was able to slow down glaucomatous progression, measured with VFI, or even improve visual field results in 66% of patients included in the study.

Keywords: 758 visual fields • 466 clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • 462 clinical (human) or epidemiologic studies: outcomes/complications