Nature and Risk Factors of Initial Glaucomatous Visual Field Defect Threatening Fixation

Abstract

Purpose: : To assess risk factors for an initial glaucomatous visual field defect threatening fixation (VFDTF) compared to an initial nasal step (NS) and its perimetric characteristics.

Methods: : Based on at least two reliable, consistent 24-2 Humphrey perimetry results, 2 groups of glaucoma patients were retrospectively and consecutively enrolled: those with only VFDTF in 1 hemifield (≥3 adjacent points with P<5% within 10° of fixation, ≥2 point with P<1%, and any 1 of these lying at the innermost points) [Group A] and those with only NS in 1 hemifield (≥3 adjacent points with P<5% in the nasal periphery outside 10° of fixation, ≥2 point with P<1%, any 1 of these lying in the nasal-most point [Group B]. Demographic and ocular variables were compared between groups. VFDTF was further analyzed using 10-2 perimetry.

Results: : A total of 44 and 51 eyes (patients) were included in Group A and B, respectively. The maximum untreated intraocular pressure (IOP) was significantly lower in Group A than in B (20.3±3.4 vs 26.7±8.5 mmHg, P<0.001). Mean deviation (MD) was not significantly different between the 2 groups (-3.02±2.06 vs -2.85±1.58 dB; Group A vs B, P=0.643), but pattern standard deviation (PSD) was significantly greater in Group A than in B (5.24±2.23 vs 3.73±1.51 dB, P=0.001). Mean age (63 vs 65 years), proportion of women (66 vs 71%), disc area by HRT (2.00 vs 1.87 mm²), spherical equivalent (-1.3 vs -1.8 D), central corneal thickness (535 vs 537 µm), and foveal threshold (34.5 vs 34.4 dB) showed no significant differences between the 2 groups (Group A vs B, all P>0.1). In Group A, 24-2 PSD had a stronger significant correlation with 10-2 MD (R: 0.65 vs 0.46) or 10-2 PSD (R: 0.70 vs 0.37), compared to 24-2 MD (P<0.001). At least 1 point with P<1% was present within 2° of fixation on 10-2 perimetry in 27/44 (61.4%) patients of Group A. MD, PSD, and worst sensitivity among and mean sensitivity of the innermost points on 24-2 in Group A had no significant correlation with the mean sensitivity within 2° of fixation on 10-2 (all P>0.06).

Conclusions: : Initial VFDTF tended to occur in glaucoma patients with low IOP, and had deeper local defects, with 24-2 PSD being a better parameter representing the sensitivity within 10° of fixation than 24-2 MD. Patients with initial VFDTF on 24-2 perimetry quite often had a field defect within 2° of fixation, but 24-2 parameters had poor correlation with the sensitivity within 2° of fixation, requiring 10-2 perimetry.

Keywords: visual fields