June 2022
Volume 63, Issue 7
Open Access
ARVO Annual Meeting Abstract  |   June 2022
Geometrical-optics approach to the Stiles-Crawford effect of the first and second kind
Author Affiliations & Notes
  • Brian Vohnsen
    Physics, University College Dublin, Dublin, Ireland
  • Qi Qi Kennedy
    Physics, University College Dublin, Dublin, Ireland
  • Najnin Sharmin
    Physics, University College Dublin, Dublin, Ireland
  • Footnotes
    Commercial Relationships   Brian Vohnsen None; Qi Qi Kennedy None; Najnin Sharmin None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science June 2022, Vol.63, 2231 – F0439. doi:
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      Brian Vohnsen, Qi Qi Kennedy, Najnin Sharmin; Geometrical-optics approach to the Stiles-Crawford effect of the first and second kind. Invest. Ophthalmol. Vis. Sci. 2022;63(7):2231 – F0439.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose : The photopic Stiles-Crawford effect of the first kind (SCE-I) is typically described by waveguiding whereas the Stiles-Crawford of the second kind (SCE-II) is attributed to self-screening by visual pigments. Here, both effects are analyzed experimentally and compared to a geometrical-optics absorption model. This will show whether both effects are caused by light leakage rather than waveguiding.

Methods : Light absorption and optical path length in foveal outer segments is simulated for a hexagonal packing foveal cones across a retinal patch of up to 37 cones: 2 S-cones (5%), 11 M-cones (30%) and 24 L-cones (65%), respectively using ComsolTM. Excess light is absorbed by the retinal pigment epithelium layer RPE. Absorption data are fitted to a Gaussian SCE-I and an Airy function representative of the collective light-capture efficiency for stacked visual pigments (Vohnsen, BOE 2014). The SCE-I directionality is evaluated and compared to psychophysical results obtained for two emmetropic subjects using a uniaxial digital micromirror device (DMD) flicker system (Carmichael Martins and Vohnsen, OPO 2018) and a liquid crystal bandpass filter for spectral tuning. Power-weighted absorption in adjacent outer segments is used to calculate an effective SCE-II hue shift as a function of wavelength for oblique light.

Results : Outer segment data in combination with ray optics and absorption can explain the typical Gaussian SCE-I visibility function with directionality parameters in the range of 0.03/mm2 – 0.10/mm2. In turn, if all outer segments contain the same class of visual pigment, such as rhodopsin in rods, the directionality becomes negligible confirming the absence of the SCE-I in scotopic conditions. The SCE-II hue shift matches psychophysical observations with no on-axis hue shift but a parabolic hue shift at for oblique incidence. The SCE-II distribution is fully contained within the spectral data of the SCE-I.

Conclusions : The study shows that leakage of light in outer segments can fully explain the SCE-I and crosstalk the related SCE-II without enforcing waveguiding. This shows the visual importance of the retina and photoreceptor optics on par with the optics of the anterior eye and the need for their careful consideration both in Maxwellian and normal Newtonian view. Ultimately, such knowledge may be applied in the development of new ophthalmic optics.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.


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