The Effect of Filtering Surgery on Rates of Visual Field Change in Treated Glaucoma Patients

Abstract

Purpose: : Glaucoma filtering surgery can produce greater IOP reduction and less IOP fluctuation than medical therapy. We investigated rates of VF change in medically vs. surgically-treated eyes.

Methods: : The charts of all patients seen in a glaucoma referral practice between 1999 and 2009 were reviewed. Only treated eyes with ≥8 SITA Standard 24-2 VF tests with baseline glaucomatous VF damage were included [Group A: eyes that never underwent a filtering procedure; Group B: eyes from Group A with unsatisfactory medical therapy (global rates of VF change >-0.5 dB/yr); Group C: eyes with ≥5 VF before filtering surgery; Group D: eyes with ≥5 VF after surgery (Sub-Group D-1: no glaucoma medications at last follow-up; Group D-2: ≥1 medication at last follow-up)]. Patients with other ocular conditions known to affect the VF and insufficient number of VFs to create a slope were excluded. Automated pointwise linear regression determined global rates (dB/yr) of change. Progression was defined as 2 or more adjacent test locations in the same hemifield with a threshold sensitivity decline ≥1.0 dB/yr with p<0.01. Logistic regression was used to assess variables associated with a progression outcome.

Results: : 587 eyes (587 patients; mean age 64.9±13.0 yrs; number of VF tests 11.1±3.0; follow-up time 6.4±1.7 yrs) were included (Group A=381; B=118; C=65; D=141). Mean rates of global progression for Groups A, B, C, and D were -0.3±0.6, -1.0±0.6, -0.8±0.8, and -0.5±0.9 dB/yr, respectively. Group B, used to create a subgroup of medically-treated patients similar to eyes undergoing surgery (Group C), had similar global rates of progression compared to Group C (p=0.18). Group D had a lower risk of reaching a progression endpoint compared to Group B (OR=0.40, p<0.01) and Group C (OR=0.42, p<0.01), and had slower global velocities of VF change than Groups B and C (p<0.01 and p<0.01, respectively). Group D-1 (n=67) had a lower risk of reaching a progression endpoint compared to Groups B (OR=0.37, p<0.01) and C (OR=0.38, p=0.01), as did Group D-2 (n=74; OR=0.44, p<0.01; OR=0.46, p=0.02; respectively). Group D-1 had slower global rates of progression than Group D-2 (-0.4±0.7 vs. -0.6±1.1 dB/yr), but this did not reach statistical significance (p=0.27).

Conclusions: : Filtering surgery reduces the rate of disease progression compared to medical therapy. This effect persists even if adjunctive glaucoma medical therapy is required.

Keywords: clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • visual fields • intraocular pressure