Abstract
PurposeTo evaluate photopic negative response (PhNR) discrimination ability between healthy and glaucomatous patients. MethodsNinety eyes of 50 patients with primary open angle glaucoma (POAG) and 45 eyes of 23 healthy age- and sex-matched controls were investigated. Based on European Glaucoma Society criteria, POAG patients were divided into three groups: early, moderate and advanced glaucoma. Following measurements were analysed: mean defect (MD) from Humphrey Visual Field Analyzer, SITA standard 24-2 white on white perimetry; nerve fibre index (NFI) obtained from scanning laser polarimetry; and GDx and PhNR amplitude and PhNR/b-wave ratio. PhNR was elicited by red stimuli with flash strength of 1.6 cd s/m2 on blue background of 25 cd/m2. Correlations between retinal ganglion cells function (PhNR), retinal sensitivity (MD) and structure (NFI) were calculated. Sensitivity and specificity of PhNR parameters were calculated with standard formulas. Receiver operating characteristic (ROC) curves were used to determine optimal cut-off values. The area under the curve (AUC) was used to compare the ROC curves results between PhNR amplitude and ratio.ResultsPhNR amplitude and ratio were significantly reduced in early, moderate and advanced glaucoma groups compared to controls. The sensitivity and specificity to detect glaucoma in early POAG were equal to 53.3 and 90.0 % for PhNR amplitude and 60.0 and 70.0 % for PhNR ratio; in moderate POAG 63.3 and 80.0 % for PhNR amplitude and 60.0 and 86.7 % for PhNR ratio; and in advanced POAG 76.6 and 80.0 % for PhNR amplitude, 90.0 and 73.3 % for PhNR ratio. There were no significant differences between AUC for PhNR amplitude (0.76–0.86) and PhNR ratio (0.78–0.86), p > 0.05. PhNR amplitudes and ratios correlated significantly with MD measured by SAP and NFI obtained from GDx (p < 0.05). PhNR amplitude significantly decreases with advancement of visual field defects in glaucoma patients.ConclusionsPhNR reveals dysfunction of RGCs in early, moderate and advanced stage of POAG. PhNR has good discrimination ability in detecting glaucomatous patients. PhNR might be a useful test in glaucoma diagnosis.
Highlights
According to the World Health Organization, glaucoma is the second leading cause of preventable blindness globally [1]
photopic negative response (PhNR) amplitudes and ratios correlated significantly with mean defect (MD) measured by SAP and nerve fibre index (NFI) obtained from GDx (p \ 0.05)
When glaucomatous groups were compared between each other, no differences between means of PhNR amplitude and ratio in the early and moderate glaucoma groups (p [ 0.05), as well as between moderate and advanced glaucoma groups (p [ 0.05), were found
Summary
According to the World Health Organization, glaucoma is the second leading cause of preventable blindness globally [1]. Glaucoma diagnosis is still based on fundus examination, intraocular pressure (IOP) measurements and visual field testing. Visual field losses become detectable after a substantial number of RGCs has been lost [2, 3]. Previous studies have reported [3, 4] that repeatable defects in static visual field perimetry results occurred when at least 25–50 % of RGC had been lost. Damage of the RGCs is assessed with the use of imaging technologies. Optical coherent tomography (OCT) and GDx (scanning laser polarimetry) measure retinal nerve fibre layer (RNFL) thickness and can capture early morphological changes [5,6,7]
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