Progression of visual field defects and visual loss in trabeculectomized eyes

To evaluate progression of visual field (VF) defects and development of visual impairment (low vision and blindness) after trabeculectomy.

We evaluated retrospectively 138 eyes of 138 consecutive patients over 40 years of age with primary open-angle glaucoma (POAG) or exfoliation glaucoma (EG) operated on by trabeculectomy without antimetabolites. The mean follow-up period was 3.5 years (range 2-5). In 83 eyes, pre- and postoperative VF measured by the same technique were compared to detect progression. Visual acuities (VA) were recorded as Snellen decimal notations. VA of <0.3 to 0.05 was defined as low vision and VA of <0.05 or VF constricted to less than 20 degrees in diameter as blindness.

In 34 (41%) of 83 eyes with comparable fields, VF defects progressed because of glaucoma. In logistic regression analysis, severity of preoperative VF loss (P=0.0047) and use of preoperative oral anti-glaucomatous medication (P=0.047) correlated significantly with VF progression. In univariate analysis, also initial intraocular pressure (IOP) reduction after surgery (P=0.023) and IOP reduction from preoperative to last postoperative examination (P=0.036) were significantly smaller in eyes with VF progression. Defect progression did not, however, correlate significantly with the last IOP (P=0.58). Six eyes (4.3%) were blind due to glaucoma preoperatively and 14 eyes (10.1%) at the last follow-up. Visual impairment correlated with the severity of initial VF loss (P=0.008).

Progression of VF defects and development of visual impairment due to glaucoma was fairly common despite trabeculectomy. Both were associated with severity of initial VF defect. In this series, no significant correlation appeared between defect progression and the last IOP, but association between stability of VF and the amount of IOP reduction after surgery indicate that a lower target IOP level particularly in eyes with initially severe VF defect would, however, be needed.