Polarization Pattern Perception: Implications for the Assessment of Macular Function in Health and Disease

Abstract

The ability of humans to perceive polarized light was first documented by Haidinger in 1844, who discussed the entoptic phenomenon of what was later to be known as Haidinger’s brushes. Until recently, Haidinger’s brushes were believed to constitute the full extent of human polarization sensitivity. It is now known that the human visual system is capable of detecting visual stimuli modulated solely by light polarization (Misson et al., 2015, Temple et al., 2015). Misson and Anderson (2017) developed the technique of polarization pattern perception (PPP) and showed that human polarization sensitivity was significantly more acute and quantifiable than previously thought. Furthermore, like its related phenomenon of Haidinger’s brush, they showed that PPP is confined to the macula, and matches the spectral characteristics and distribution of the macular pigments. The known protective functions of macular pigments, and the association of its deficiency with susceptibility to macular degeneration, make a measure of PPP potentially useful as a clinical screening tool for at-risk individuals and for the early detection of macular disease. Normative polarization pattern perception values had not yet been established in humans, and the repeatability of the technique was yet to be explored. The effect of age and variations in corneal and macular characteristics on PPP are also currently unknown. The principal aim of this research project is to quantify normative monocular sensitivity values for PPP in healthy individuals and address these gaps in the field. Grating stimuli were displayed in polarization-only contrast on a delaminated LCD screen. This technique was shown to give rapid, inexpensive, quantifiable data, which, with some development, could be used to assess and monitor macular function and screen at risk individuals. PPP values across a range of ages are presented and discussed, with reference to each participant’s corneal and macular characteristics. The monocular polarization pattern sensitivity for healthy participants aged 19-59 years was 5.17, which equates to an average ability to discriminate stimuli differing by 8 degrees. This provided evidence in support of the human ability to perceive polarized light to a much higher degree than previously expected, and was similar to data from previously published pilot studies developing the technique (Misson et al., 2019, Misson and Anderson, 2017). There was no significant change in human PPP across the age range 19-59 years. Test-retest measures showed a positive correlation, but the overall repeatability of the technique would need improvement if it were to become a useful clinical measurement. A significant positive correlation between MPOD and PPP was found, which together with the lack of influence from variations in other ocular characteristics (age, refraction, central foveal thickness, central corneal thickness, corneal retardance, corneal birefringence and ocular dominance) make a measure of PPP potentially highly beneficial for macular assessment.