Evaluation of a new method of assessing suppression in amblyopia and the effect of light source variability.

Tidbury, L, O'Connor, ORCID: 0000-0002-0376-9670 and Newsham, ORCID: 0000-0002-7013-7008 (2017) Evaluation of a new method of assessing suppression in amblyopia and the effect of light source variability. In: SOE2017, 2017-6-3 - 2017-6-6, Barcelona.

Slideshow EP-PED483-LTidbury Handout.pptx - Author Accepted Manuscript Download (6MB)

Abstract

Purpose A concern with the treatment of amblyopia in those with strabismus is the risk of intractable diplopia; where suppression is reduced in parallel to amblyopic suppression. The usual method of assessing suppression is to reduce the amount of light being transmitted to the non-amblyopic eyes retina. The commonly used Sbisa bar, is known to produce variable responses, therefore we aim to assess a new method of measuring the density of suppression, to determine if a more consistent response is possible, in comparison to the Sbisa and Bagolini bars. We also evaluate the stability of luminance of various light sources, to determine if changes in filter density exceed luminance variability. Methods The new device comprises of two linear polarisers that can vary in angle from parallel to perpendicular, thus varying the amount of light transmitted according to Malus’ law, using 5o changes in angle. The experiment measured the amount of light passing through the different devices as the filter opacity increased using a spectroradiometer (SpectroCAL MKII). Two different light sources were used for comparison: a standard tungsten photography light source and a specialist high end stable light source (GTI GLE-m5/32). Results The correlation (Spearman’s) between filter density and luminance for the different methods is as follows: Polarisers: r=-0.98, Sbisa: r=-0.99, Bagolini: r=-1.0, all significant with p<0.01. The variation in light source luminance over eight minutes was 9% for the tungsten and 2% for the stable light source. This means that each filter must effect a change of greater than the light source variability. We also show that the difference between filters is non-linear on traditional bars. Conclusions All three methods tested show a significant, strong negative correlation; as the filter strength increases, the transmission of light reduces. A change of filter number may not necessarily represent a change in density of suppression however, as variations in the light source stability may affect the light transmitted. Malus’ law demonstrates that crossed polarisers provide near perfect linear steps between 10o and 80o crossing.

Item Type:	Conference or Workshop Item (Unspecified)
Depositing User:	Symplectic Admin
Date Deposited:	28 Jun 2017 15:12
Last Modified:	19 Jan 2023 07:02
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3008149