Electrophysiological studies of retinal function at low light levels in type 2 diabetes mellitus

Cumiskey, Jennifer Anne 2007. Electrophysiological studies of retinal function at low light levels in type 2 diabetes mellitus. PhD Thesis, Cardiff University.

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Abstract

Diabetic retinopathy (DR) is the major cause of registerable blindness in the working population in Western countries. It has been proposed that the retina is subject to sub-clinical levels of tissue hypoxia prior to the development of DR, and that a rod-driven hypoxia during darkness may be a significant causal factor in its development. The aim of this study was firstly to use the scotopic electroretinogram (ERG) in order to gain an objective measure of retinal function in subjects with diabetes mellitus (DM). Should there be a level of inner retinal hypoxia present this may be indirectly demonstrated by reduced oscillatory potential (OP) amplitudes, thought to arise predominantly from amacrine cells and known to be sensitive to vascular changes within the retina, and reduced b- wave amplitudes thought to arise predominantly from the bipolar cells of the inner retina. If hypoxia were present and reversable in the short term an increase in amplitude would be expected with oxygen (O2) inhalation. ERGs were recorded from subjects with Type 2 DM both with and without retinopathy before, during and following O2 inhalation and compared to age- matched control subjects. No significant difference in amplitude was observed between subjects with DM and control subjects before O2 inhalation, however both b-wave and summed OP amplitudes were significantly increased following O2 inhalation in diabetic subjects with retinopathy, and OP3 significantly increased in subjects without retinopathy, yet remained unchanged in the control group. The retinal O2 demand has been reported to halve in light conditions compared to darkness and it has therefore been proposed that patients with DM may benefit from sleeping with night-time illumination in order to reduce the level of rod activity, and thus metabolic demand on the retinal tissue, to reduce inner retinal hypoxia. The amount of light required to significantly reduce rod activity was investigated by means of a simultaneous cone-rod ERG in DM subjects with no retinopathy and control subjects. It was found that a background illumination level as little as 3.4lux was sufficient to significantly reduce rod activity in all subjects.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Medicine
Subjects:	R Medicine > RC Internal medicine
ISBN:	9781303209338
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:30
URI:	https://orca.cardiff.ac.uk/id/eprint/54593

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