The Fast Component of Visual Field Decay Improves after Trabeculectomy

Abstract

Purpose: To describe changes in the visual field (VF) threshold sensitivity (decibels, dB) for the fast and slow rate components of VF decay in patients after trabeculectomy.

Methods: This was a retrospective review of the VFs of open-angle glaucoma patients who underwent trabeculectomy. All eyes had ≥ 4 reliable pre- and post-operative VFs. The last pre- and first post-operative VFs were limited to within 1.5 years of the surgery date and the minimum VF follow-up pre- and post-operatively were 2 years. With point-wise exponential regression (PER) every VF location was assigned to either fast or slow decay components. PER decay curves were fit to the sensitivities of the pre- and post−operative VF measurements separately. Delta (δ) was defined as the sensitivity difference between the first post-operative and the last pre-operative VF at each test location as estimated by the exponential curve fits. The VF mean deviation (MD) was similarly fit for the pre- and post-operative VFs with a linear regression.

Results: Seventy-one eyes (65 subjects) were followed for an average of 11.9 ± 2.9 years (5.5 ± 2.4 years pre -operatively and 5.5 ± 2.4 years post-operatively) with an average of 20.2 ± 8.1 VFs (10.7 ± 5.9 VFs pre-operatively and 9.5 ± 4.7 VFs post-operatively). Post-operatively the average sensitivity of the fast component test locations significantly increased from 20.4 ± 6.1 dB to 22.1 ± 5.4 dB (p < 0.0001), and significantly decreased for the slow component from 24.7 ± 3.7 dB to 23.9 ± 4.1 dB (p = 0.004). For the fast component locations, the sensitivity (δ) improved (1.74 ± 2.2 dB) but deteriorated (-0.79 ± 2.2 dB) for slow locations (p < 0.0001). The average MD pre-operatively (-8.4 ± 5.3) was not significantly different post-operatively (-9 ± 6.6) (p = 0.12).

Conclusions: After trabeculectomy significant differential effects on the fast and slow components of VF decay were observed. The sensitivity of the slow component of VF decay decreased slightly, consistent with progressive cataract. However, the sensitivity of the fast VF component increased significantly, suggesting that reversibility of retinal ganglion cell dysfunction after robust intraocular pressure reduction is more common than previously thought. Overall measures of VF sensitivity, such as MD, do not detect these differential changes.

Keywords: 758 visual fields • 531 ganglion cells • 642 perimetry