Correlating nerve fibre layer defects spatially with functional loss

Abstract

The ultimate aim of clinical glaucoma research is to maintain visual function in the patient. Visual field (VF) loss can be determined more effectively by considering the related structural damage (ie retinal nerve fibre layer (RNFL) defect, optic disc notching, and splinter haemorrhages). A stack of individually digitized RNFL traces, which are superimposed by appropriate rotation and zoom procedures, allows for characterizing so-called trajectories defining the average course of retinal nerve fibres. Individual test point density in perimetry can be increased in regions of interest, that is in areas, or at the edges of, already detected VF defects (VFD) using SCotoma-Oriented Perimetry (SCOPE) or can be tailored (locally condensed) in an evidence-based manner by considering the local morphological damage using fundus-oriented perimetry (FOP). Focusing on areas most likely to be damaged makes conventional perimetry more efficient by locally enhancing spatial resolution. This technique requires a mathematical model that provides age-related normative values of differential luminance sensitivity for any location of the VF. Automated static perimetry with enhancement of spatial resolution in regions of interest has indeed a higher sensitivity than standard automated perimetry using a conventional rectangular (6 Â 61) grid. The new method can also be used for followup purposes: both scotoma depth and area, as well as their changes with time, need to be considered. The clinician has to be aware of the fact that any kind of perimetry is a rather exhausting and artificial examination procedure. It is rather inadequate for predicting per se patients' quality of life and daily functionality as it does not consider compensation for VFD, for example by gaze and head movements.