Directional sensitivity of the retina: 75 years of Stiles-Crawford effect - PubMed (original) (raw)

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Directional sensitivity of the retina: 75 years of Stiles-Crawford effect

Gerald Westheimer. Proc Biol Sci. 2008.

Abstract

The reduction of the brightness when a light beam's entry into the eye is shifted from the centre to the edge of the pupil has from the outset been shown to be due to a change in luminous efficiency of radiation when it is incident obliquely on the retina. The phenomenon is most prominent in photopic vision and this has concentrated attention on the properties of retinal cones, where responsibility has yet to be assigned to factors such as differences in shape, fine structure and configuration, and membrane anchoring of photopigment molecules. Geometrical optics and waveguide formulations have been applied to the question of how light is guided in receptors, but details of their geometry and optical parameters even if they become available will make calculations complex and of only moderate generality. In practice, the diminution of oblique light helps visual performance by reducing deleterious influence of ocular aberrations and of glare caused by light scattering when the pupil is wide. Receptor orientation can come into play in ocular conditions due to mechanical disturbance and has been shown to have potentiality as a tool for clinical diagnosis. Currently, open questions include microanatomical and molecular differences between rods and cones, the coupling of the optical image of the eye with the transducing apparatus in the photoreceptors, possible phototropism and more convincing methods of estimating the actual spatial distribution of photon events as it affects visual resolution.

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Figures

Figure 1

Figure 1

Schematic eye with a wide pupil showing two identical bundles of rays from a distant object focused on the retina that enter through different pupillary regions: A, the centre, and B, near the edge. Stiles & Crawford (1933) discovered that, in photopic vision, the oblique incidence of beam B causes a prominent diminution of luminous efficiency, since called the Stiles–Crawford effect.

Figure 2

Figure 2

Relative luminance efficiency for narrow bundles, as a function of pupil location of the entering beam. Data for two sets of measurements three months apart in the left eye of W. S. Stiles (Stiles & Crawford 1933).

Figure 3

Figure 3

Microscopic view of a (a) mammalian cone and (b) rod, somewhat schematized, illustrating that morphology could account for the difference in acceptance of obliquely incident light. For cones, the width of inner segments and the width, length and taper of outer segments can vary several-fold depending on the location. Foveal cones have a rod-like appearance; in the retinal periphery, wide, stubby cones are intermixed with rods. Phototransduction takes place in the outer segment. Adapted with permission from Borwein (1981).

Figure 4

Figure 4

Nineteenth-century drawing (Greeff 1874) of cones in three locations in the human retina. (a) In extreme periphery; (b) in 30° periphery; (c) in fovea.

Figure 5

Figure 5

Schematic of high-magnification histological sections of mammalian (a) rod and (b) cone outer segments showing the membraneous invaginations of cones (a detailed view in the inset) and the intracellular stacked discs of rods in which the photopigment molecules are embedded. Adapted from Oyster (1999).

Figure 6

Figure 6

A model of a cone receptor used for geometrical ray tracing and for computation of waveguide modes. The dimension of the diameters _d_i and _d_o and of the lengths of the inner and outer segments and the taper of the ellipsoid are taken from anatomical measurements. The refractive index values of the intra-receptor regions and the extracellular space are estimates from mammalian biological preparations. Apart from the schematized geometrical shape, the important feature of the model is that light is accepted only at one aperture and is guided from there into the interior space of the receptor.

Figure 7

Figure 7

A photomicrograph of a small section of the parafoveal mixed rod–cone retina in a macaque, especially prepared to preserve as best as possible the in vivo orientation of the receptors. Reprinted with permission from Laties (1969).

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References

    1. Applegate R.A, Bonds A.B. Induced movement of receptor alignment towards a new pupillary aperture. Invest. Ophthalmol. Vis. Sci. 1981;21:869–873. - PubMed
    1. Barer R. Refractometry and interferometry of living cells. J. Opt. Soc. Am. 1957;47:545–556. - PubMed
    1. Birch D.G, Sandberg M.A, Berson E.L. The Stiles–Crawford effect in retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 1982;22:157–164. - PubMed
    1. Blank K, Provine R.R, Enoch J.M. Shift in the peak of the photopic Stiles–Crawford function with marked accommodation. Vision Res. 1975;15:499–507. doi:10.1016/0042-6989(75)90027-9 - DOI - PubMed
    1. Borwein B. The retinal receptor: a description. In: Enoch J.M, Tobey F.L, editors. Vertebrate photoreceptor optics. Springer; Berlin, Germany: 1981. pp. 11–81.

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