Structure-Function Relationships in Perimetric Glaucoma: Comparison of Minimum-Rim Width and Retinal Nerve Fiber Layer Parameters

Abstract

PurposeTo test the hypotheses that: (1) structure–function (SF) relationships between visual fields (VF) and Bruch's membrane opening-based minimum rim width (BMO-MRW) measurements are superior to those for peripapillary retinal nerve fiber layer (pRNFL) in perimetric glaucoma; (2) BMO-MRW measurements may extend the utility of structural measurement across the range of glaucoma severity; and (3) to estimate the influence of Bruch's membrane opening (BMO) size on BMO-MRW measurements.MethodsOne hundred eight perimetric glaucoma eyes (68 patients) with good quality spectral-domain optical coherence tomography images of the optic disc and pRNFL, and reliable VF within 6 months were recruited. Relationship of global and sectoral BMO-MRW and pRNFL thickness with corresponding VF parameters and the influence of normalizing BMO-MRW (on BMO circumference, nBMO-MRW) on SF relationships were investigated. Broken-stick models were used to compare the point at which pRNFL and BMO-MRW parameters reached their measurement floor.ResultsThe median (interquartile range) of VF mean deviation was −5.9 (−12.6 to −3.6) dB. Spearman correlation coefficients between pRNFL, BMO-MRW, and nBMO-MRW measures and corresponding VF cluster average deviations ranged between 0.55 to 0.80, 0.35 to 0.66, and 0.38 to 0.65, respectively. Bruch's membrane opening–MRW parameters demonstrated weaker SF relationships compared with pRNFL globally and in temporal, temporal-superior, and nasal-inferior sectors (P < 0.03). Normalization of BMO-MRW did not significantly influence SF relationships.ConclusionsStructure–function relationships were somewhat weaker with BMO-MRW parameters compared with pRNFL in eyes with perimetric glaucoma. Bruch's membrane opening–MRW normalization did not significantly change SF relationships in this group of eyes with mild departures from average BMO size.

Optical coherence tomography evaluation of the optic nerve head neuro‐retinal rim in glaucoma

“…Gardiner et al demonstrated that the minimum rim area (MRA) parameter exhibited stronger correlation to visual field sensitivity and to peripapillary retinal nerve fibre layer (RNFL) thickness than the Heidelberg Retina Tomograph‐ or OCT‐derived ‘horizontal’ measurements of rim area . Although it should be noted that the MRW parameter (rim width) correlated equally well to the visual field and RNFL thickness in that study even without adjustment for disc size . It is likely that disc size has greater impact at the extremes, that is, for very small or very large discs or discs of highly myopic eyes .…”

“…However, it is well known that optic discs with a larger diameter will have a thinner neuro‐retinal rim for the same number and calibre of axons. Therefore, measurements of rim width (that is, rim thickness) need to be adjusted for disc size in order to have the best possible diagnostic utility . Alternatively, the total cross‐sectional area of rim tissue should be directly proportional to the total number and calibre of axons in each eye and thus unrelated to disc size.…”

Longitudinal Macular Structure-Function Relationships in Glaucoma and Their Sources of Variability

“…This is consistent with findings by other investigators and our laboratory on other structural measures such as the cpRNFL and Bruch's membrane-based minimum rim width thickness. [26][27][28] Table 3 summarizes the results of the 53 segmented (broken-stick) regression analyses in this group of patients as a function of eccentricity. Overall, our assumption of stability of SF relationships FIGURE 6.…”

“…Many studies reported that the cpRNFL thickness reaches its measurement floor after about a 10-dB decrease in threshold (i.e., an average sectoral mean deviation of -10 dB). [26][27][28] Circumpapillary RNFL thickness reaches a plateau at around this level of damage beyond which the amount of change is very small to none. The magnitude of the correlation between cpRNFL thickness measurements and VF threshold sensitivity or global or sectoral mean deviation values has been quite variable in the reported studies, with a peak correlation of 0.70-0.80.…”

Diagnostic criteria for detection of retinal nerve fibre layer thickness and neuroretinal rim width abnormalities in glaucoma

“…Why does RNFLT assessment outperform BMO-MRW assessment even though both structures are essentially composed of the axons of retinal ganglion cells? The stronger association of RNFLT with axon counts, 17 as well as with visual function, 18 compared with BMO-MRW may in part explain the better discriminating ability of RNFLT to discern subtle axon loss in early glaucoma. That integrating BMO-MRW assessment to RNFLT assessment does not augment the diagnostic performance for glaucoma detection is also related to the fact that the sensitivities and specificities of RNFLT assessment alone are already high.…”