Temporal summation with age and in glaucoma

Abstract

Standard automated perimetry (SAP) serves as the cornerstone in the diagnosis andmonitoring of functional deficits associated with glaucoma. Achromatic contrastthresholds are typically measured at pre-defined locations in the visual field for circularstimuli of constant area and duration. However, the selection of SAP stimulusparameters was made with little or no regard to the ability of the visual system to sumlight energy over both space and time, and how such aspects of visual function mightvary across the visual field and in glaucoma. In recent years there has been renewedinterest in the spatial summation of perimetric stimuli, it being suggested that thesensitivity of SAP, and thus the relationship of contrast thresholds to underlying retinalganglion cell density, might be improved through a simple scaling of stimulus area. Inthis thesis we re-examined temporal summation to provide an evidence base from whichthe selection of appropriate stimulus parameters for SAP might be made. Specifically,we investigated the various factors that can influence the upper limit of completetemporal summation (critical duration) including stimulus area, rate of high-frequencyflicker, age and glaucoma. We observed that the critical duration is intrinsically linked tothe degree of spatial summation exhibited at any point in the visual field, with the resultthat temporal summation varies across the visual field when examined using a stimulusscaled to the localised area of complete spatial summation (Ricco’s area). We also foundthe critical duration to be significantly increased in glaucoma when examined using botha standard Goldmann III stimulus and a stimulus scaled to the localised Ricco’s areaunder the conditions of SAP. Based on the results of this thesis we propose the use ofstimuli modulating in area, duration and luminance to improve the sensitivity andspecificity of perimetry in the detection of glaucoma.

Date of Award	Apr 2014
Original language	English
Sponsors	Department of Employment and Learning, Northern Ireland
Supervisor	Roger Anderson (Supervisor), Margarita Vidinova (Supervisor), Tony Redmond (Supervisor) & David F. Garway-Heath (Supervisor)