Structure-function correlations using scanning laser polarimetry in primary angle-closure glaucoma and primary open-angle glaucoma

Abstract

Purpose: To assess the correlations between retinal nerve fiber layer (RNFL) thickness measured with scanning laser polarimetry and visual field (VF) sensitivity in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

Design: Prospective, comparative, observational cases series.

Methods: Fifty patients with POAG and 56 patients with PACG were examined using scanning laser polarimetry with variable corneal compensation (GDx VCC; Laser Diagnostic Technologies, Inc.) and Humphrey VF analyzer (Carl Zeiss Meditec, Inc.) between August 2005 and July 2006 at Taipei Veterans General Hospital. Correlations between RNFL thickness and VF sensitivity, expressed as mean sensitivity in both decibel and 1/Lambert scales, were estimated by the Spearman rank correlation coefficient (r(s)) and multivariate median regression models (pseudo R(2)). The correlations were determined globally and for 6 RNFL sectors and their corresponding VF regions.

Results: The correlation between RNFL thickness and mean sensitivity (in decibels) was weaker in the PACG group (r(s) = 0.38; P = .004; pseudo R(2) = 0.17) than in the POAG group (r(s) = 0.51; P < .001; pseudo R(2) = .31), but the difference in the magnitude of correlation was not significant (P = .42). With Bonferroni correction, the structure-function correlation was significant in the superotemporal (r(s) = 0.62), superonasal (r(s) = 0.56), inferonasal (r(s) = 0.53), and inferotemporal (r(s) = 0.50) sectors in the POAG group (all P < .001), whereas it was significant only in the superotemporal (r(s) = 0.53) and inferotemporal (r(s) = 0.48) sectors in the PACG group (both P < .001). The results were similar when mean sensitivity was expressed as 1/Lambert scale.

Conclusions: Both POAG and PACG eyes had moderate structure-function correlations using scanning laser polarimetry. Compared with eyes with POAG, fewer RNFL sectors have significant structure-function correlations in eyes with PACG.

Figure 1

Humphrey Field Analyzer 24-2 test pattern (left) and scanning laser polarimetry (GDx VCC) retardation map (right) for a right eye. Visual field test points and peripapillary GDx VCC measurements were grouped in six corresponding sectors as defined by Reus et al., which were based on the originally described map by Garway-Heath et al. (T: temporal, ST: superotemporal, SN: superonasal, N: nasal, IN: inferonasal, IT: inferotemporal)

Figure 2

Scatterplots of average peripapillary retinal nerve fiber layer (RNFL) thickness against VF sensitivity expressed in the decibel (dB) scale in POAG eyes and PACG eyes. (○ POAG, ● PACG, TSNIT= temporal-superior-nasal-inferior-temporal, r_s = Spearman's rank correlation coefficient)

Figure 3

Scatterplots of sectoral peripapillary retinal nerve fiber layer (RNFL) thickness against with VF sensitivity expressed in the decibel (dB) scale in POAG eyes and PACG eyes. (Top left) superotemporal, (Top right) superonasal, (Bottom left) inferotemporal, and (Bottom right) inferonasal sectors. (○ POAG, ● PACG)