Assessment of linear-scale indices for perimetry in terms of progression in early glaucoma

Currently, global indices that summarize the visual field combine sensitivities on a logarithmic (decibel) scale. Recent structure–function models for glaucoma suggest that contrast sensitivity should be converted to a linear scale before averaging across visual field locations, to better relate sensitivity with the number of surviving retinal ganglion cells (RGCs). New indices designed to represent the number of RGCs already lost are described. At least one was found to be a significantly better predictor of subsequent rate of change than traditional Mean Deviation (p = 0.014) in participants with glaucomatous optic neuropathy. Issues concerning the creation of optimal global indices are discussed.

► Visual field status is predictive of subsequent rate of progression.
► Current indices of field status are based on logarithmic scaled sensitivities.
► Retinal ganglion cell counts have previously been shown to be related to linearly scaled sensitivities.
► Linearly scaled indices may offer benefits over current indices.
► Issues caused by logarithmic-scaled testing algorithms complicate this process.