Nasal Peripapillary Retinal Nerve Fiber Layer and Structure-Function Relationship in Glaucoma

Abstract

Purpose : Compared with inferior, superior or temporal neuroretinal rim, the nasal rim of optic disc tends to be spared until the late stage of glaucoma progression. Such characteristics may lead one to expect differences in patterns of loss between the average retinal nerve fiber layer thickness (RNFLT) and the nasal RNFLT at different stages of glaucoma. Therefore, we performed a retrospective, cross-sectional study to evaluate the structure-function relationships using the average RNFLT and the nasal RNFLT measured with spectral-domain optical coherence tomography in primary open-angle glaucoma patients.

Methods : A total of 44 normal eyes and 283 glaucomatous eyes were enrolled. The average RNFLT was defined as the mean of 360° RNFLT and the nasal RNFLT as the average of RNFLT from 1 o’clock to 5 o’clock directions. The structure-function relationships between the average or nasal RNFLT and the corresponding visual field (VF) mean deviation (MD) were assessed by regression analyses. An R package named ‘segmented’ was used to investigate whether there was a statistically significant breakpoint.

Results : The relationship between MD and average RNFLT was significant by a simple linear regression model (P<0.001, R=0.623), and was better explained by a second-order polynomial regression model than a linear model (P<0.001, adjusted-R²=0.646). The MD value of -16.29 dB (SD±1.90) was a significant breakpoint; there was no significant association between MD and the corresponding average RNFLT with MD worse than the breakpoint (P =0.147). A linear model (P<0.001, R²=0.381) fit better than a second-order polynomial model (P<0.001, adjusted-R²=0.209) with no significant breakpoint (P=0.071) for the nasal RNFLT. When the values below the breakpoint were stratified into quartiles, the nasal RNFLT showed significant differences among the four quartile groups (P=0.023).

Conclusions : The nasal RNFLT did not have a breakpoint but showed a decrease even at advanced stage of glaucoma, whereas the average RNFLT had a breakpoint over which no further decrease in RNFLT could be observed with further VF loss. These findings suggest the potential of the nasal peripapillary RNFLT as a marker to be used for monitoring progression in advanced glaucoma.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Clock-face directions of the right and left optic nerves.

 

Scatterplots showing the relationships between the MD and (A) the average RNFLT and (B) the nasal RNFLT.