Variability of flashes and background luminances of clinical electroretinography stimuli across 14 UK centres

Abstract

Three different flash strengths (dim, 0.01 cd s m⁻²; strong, 3 cd s m⁻²; strongest, 10 or 30 cd s m⁻²) and one adapting field luminance (30 cd m⁻²) are used for clinical electroretinograms (ERGs). To quantify their variability for local, LED-flash protocols, and for an ISCEV-specified, xenon-flash protocol, photometric measurements were made at 14 ERG centres across the UK. For local protocols, flashes were within a median of 0.01 log units of nominal, target levels and six, nine, eight and eight of 14 centres were within ISCEV tolerance (±0.05 log units) for dim, strong, strongest flashes and backgrounds, respectively. For the ISCEV-specified protocol, flashes were within a median of 0.02, 0.001 and 0.01 log units of ISCEV target dim, strong and strongest flashes, and fewer (5/12, 7/13, 3/13 and 11/13) centres were within ISCEV tolerance for dim, strong and strongest flashes and backgrounds, respectively. Paired LED–xenon comparison for a subset of centres showed close agreement. Variability of flashes was less for LED than xenon flashtube sources for strong and strongest flashes; for the strongest flash, LED flashes were closer to target values than xenon flashes. These data support a recommendation of LED use for clinical electroretinography.

Keywords:

• photometry
• flash
• clinical electroretinography
• ISCEV standard

Acknowledgements

The assistance of the following is gratefully acknowledged: ISCEV small grants for laboratory visits; Professor Tony Fisher for donating electrodes; Mrs Mary Broadberry, Dr Paul Spry, Professor Daphne McCulloch, Dr Richard Hagan, Dr Neil Parry, Mr Chris Hogg, Mrs Karen Bradshaw, Mrs Beverley Holland, Dr Charles Cottrial and Dr Gillian Ruddock.