City Research Online

Abstract

Aim.
To investigate the retinal origins of the linear and nonlinear components of the human multifocal electroretinogram.

Method.
Linear and nonlinear multifocal electroretinograms of human subjects were recorded with the VERIS system. Normal subjects (n=34) with an age range of 26-76 years were studied, and subjects with glaucoma (n=23). The temporal and spatial characteristics of VERIS responses were analysed. Comparisons were formed between VERIS responses and published data on retinal neurone densities. The affects of ageing and of primary open angle glaucoma on VERIS responses were studied.

Results.
a-Wave amplitude (linear response) shows close similarity with cone densities in the central retina, but not above 3 degrees. Temporal analysis of second order kernel slices reveals that three corneal positive components and one corneal negative component contribute to the nonlinear response. A close approximation of the nonlinear response can be achieved using Gaussian functions modelled on these four components. A further component of the nonlinear response may be extracted using the method of Sutter and Bearse (1995, 1999). The amplitude of the a- and b-waves are unaffected by ageing (P>0.05), except in the central retina (<1.55 degrees). The latency of the a- and b-waves increase with ageing at every eccentricity at between 0.05 and 0.10 ms/year (P<0.05). The amplitude of the nonlinear response is unaffected by ageing, but above 6.5 degrees the latency decreases at 0.05- 0.06 ms/year. Glaucoma causes a reduction in the amplitude of a positive component of the nonlinear response (P<0.05) in scotomatous areas of retina only, whilst the linear response is everywhere unchanged. ROC curves indicate that VERIS is as efficient as the PERG at discriminating between scotomatous and normal retina.

Conclusions.
The a-wave contains a significant cone response, but at eccentricities>3 degrees other responses intrude. Cone function in ageing may be reduced due to impaired phagocytotic reactions. Age related changes in the nonlinear response may be associated with an achromatic component that is only present in peripheral responses and has an enhanced susceptibility to degeneration. Alterations to the outer retina in glaucoma do not register in the linear response. The nonlinear response contains a component rooted in inner retinal neurone function, but VERIS may not be capable of detecting neurone loss in glaucoma that is hidden using standard perimetric methods.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RA Public aspects of medicine > RA0421 Public health. Hygiene. Preventive Medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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