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J. Wheat, N. V. Rangaswamy, R. S. Harwerth; Correlating RNFL Thickness With Perimetric Sensitivity in Glaucoma Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):491.
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© ARVO (1962-2015); The Authors (2016-present)
Prior studies of the relationship between standard automated perimetry (SAP) measures of visual sensitivity and optical coherence tomography (OCT) measures of nerve fiber layer thickness have shown poor quantitative agreement. A recent study on experimental glaucoma in macaque monkeys demonstrated a stronger relationship between OCT and SAP data when they were equated for neural populations underlying the measurements. The current study investigates the application of these techniques to clinical glaucoma patients.
Thirty glaucoma patients (ages 38 to 82 years) with early to severe visual field loss (MD 1.9 to -28.2 dB) were recruited for SAP and OCT measurements. The procedures developed for experimental glaucoma were used to derive ganglion cell densities from perimetric sensitivity values at each visual field location and grouped into ten region-specific areas corresponding to entrances into the optic nerve head. Nerve fiber layer thickness measurements taken by OCT were used to estimate the ganglion cell axon density in each of the ten corresponding regions using an age-dependent approximation of axonal density for each subject. Estimates of the total neurons were compared by sector to test agreement between measurements. The percent differences between estimates were calculated and used to assess the frequency of disagreement between the two measures.
There was a general agreement between ganglion cell estimates from OCT and SAP, with correlation coefficients ranging from 0.72 to 0.95 by sector. The mean difference between the estimates for controls is -0.16 +/- 1.48 dB and for glaucoma subjects is -1.07 +/- 1.90 dB, with the SAP predicting greater loss of ganglion cells than the OCT in general. A subset of data in the glaucoma group showed greatly reduced ganglion cell density estimates from perimetry than determined from the OCT estimates.
When OCT and SAP data were equated for neural populations underlying the measurements there was a strong structure-function relationship for the optic neuropathy caused by glaucoma. Further analysis is indicated to investigate those cases with large disagreement between the two estimates.
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