Understanding Disparities Among Diagnostic Technologies in Glaucoma

Abstract

Objective To investigate causes of disagreement among 3 glaucoma diagnostic techniques: standard automated achromatic perimetry (SAP), the multifocal visual evoked potential technique (mfVEP), and optical coherence tomography (OCT). Methods In a prospective cross-sectional study, 138 eyes of 69 patients with glaucomatous optic neuropathy were tested using SAP, the mfVEP, and OCT. Eyes with the worse and better mean deviations (MDs) were analyzed separately. If the results of 2 tests were consistent for the presence of an abnormality in the same topographic site, that abnormality was considered a true glaucoma defect. If a third test missed that abnormality (false-negative result), the reasons for disparity were investigated. Results Eyes with worse MD (mean [SD], −6.8 [8.0] dB) had better agreements among tests than did eyes with better MD (−2.5 [3.5] dB, P<.01). For the 94 of 138 hemi-fields with abnormalities of the more advanced eyes, the 3 tests were consistent in showing the same hemifield abnormality in 50 hemifields (53%), and at least 2 tests were abnormal in 65 of the 94 hemifields (69%). The potential explanations for the false-negative results fell into 2 general categories: inherent limitations of each technique to detect distinct features of glaucoma and individual variability and the distribution of normative values used to define statistically significant abnormalities. Conclusions All the cases of disparity could be explained by known limitations of each technique and inter-individual variability, suggesting that the agreement among diagnostic tests may be better than summary statistics suggest and that disagreements between tests do not indicate discordance in the structure-function relationship.

Detection of Glaucoma Progression with Alternation Flicker

“…As a result, individuals with a relatively thick RNFL when healthy will be more likely to reveal abnormalities of standard automated perimetry before a statistically significant RNFL abnormality is noted by OCT [6]. In instances where OCT fails to meet the cluster definition of abnormality, localized thinning can often be noted in the same regions where multifocal visual evoked potential and perimetry reveal abnormalities [7].…”

Comparing focal and global responses on multifocal electroretinogram with retinal nerve fibre layer thickness by spectral domain optical coherence tomography in glaucoma

“…Psychophysical tests detect responses from either the optic nerve or from the different components of the visual pathway 4 6 10. Though debated over many years, their role in detecting early glaucoma is still unclear 6 16.…”

“…Though debated over many years, their role in detecting early glaucoma is still unclear 6 16. The ERG components are presumed to be mass responses from photoreceptors and outer retinal layers 17 18.…”

“…Yet a linear relationship between RGC function and visual function is doubtful, which accounts for different results with techniques employing different targets for glaucomatous damage, namely RNFL, RGC or ONH function 6 7…”

Functional Testing in Glaucoma Diagnosis

“…Moreover, using interocular analysis, mfVEP can detect mild, unilateral defects with high sensitivity. However, this test can miss abnormalities when damage exists in the same location within both eyes [89,90]. Multifocal VEP and SAP have been shown to correspond in up to 81 % of early glaucomatous defects [91].…”