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

  • Jasmine Smith

Student thesis: Doctoral ThesisDoctor of Optometry

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.
Date of Award2021
Original languageEnglish
SupervisorStephen Anderson (Supervisor) & Gary Misson (Supervisor)

Keywords

  • human polarization perception
  • polarization pattern sensitivity
  • polarization contrast
  • PPP
  • macular pigment optical density

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