A model for assessment of cone directionality

Gorrand, Jean-Marie; Delori, François C.

doi:10.1080/095003497153879

Cited by 9 publications

(24 citation statements)

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“…We did not determine ρ values inside the outer segment (which would be of interest to do) as these reflections were at least an order of magnitude dimmer than those from the IS/OS and PTOS in the averaged A-scans, making their contribution to the optical SCE likely inconsequential. The second model bases the optical SCE on reflections from the posterior tips of the outer segment and possibly from melanin granules in the RPE [21][22][23]. While we found the PTOS reflection to be strongly waveguided, the IS/OS was equally strong and almost no waveguiding was observed for the RPE.…”

Section: Directionality Of the Retinal Layers Measured With Sd-octmentioning

confidence: 69%

“…Two leading views are that the waveguided light originates from (1) reflections across the entire axial length of the outer segment due to refractive index variations induced by the stack of photopigment carrying discs [20] and (2) reflections from the posterior tips of the photoreceptor outer segments (PTOS) and possibly from melanin granules of the RPE [21][22][23]. A third view has been suggested recently in that light reflecting from layers further behind the photoreceptors is also waveguided, especially at longer wavelengths [24].…”

Section: Introductionmentioning

confidence: 99%

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Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

Gao¹,

Cense²,

Zhang³

et al. 2008

Opt. Express

121

113

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The directional component of the retinal reflection, i.e., the optical Stiles-Crawford effect (SCE), is well established to result from the waveguiding property of photoreceptors. Considerable uncertainty, however, remains as to which retinal reflections are waveguided and thus contribute. To this end we have developed a retina camera based on spectral-domain optical coherence tomography (SD-OCT) that axially resolves (~5 μm) these reflections and permits a direct investigation of the SCE origin at near infrared wavelengths. Reflections from the photoreceptor inner/outer segments junction (IS/ OS) and near the posterior tip of the outer segments (PTOS) were found highly sensitive to beam entry position in the pupil with a considerable decrease in brightness occurring with an increase in aperture eccentricity. Reflections from the retinal pigment epithelium (RPE) were largely insensitive. The average directionality (ρ oct value) at 2 degree eccentricity across the four subjects for the IS/OS, PTOS, and RPE were 0.120, 0.270, and 0.016 mm −2 , respectively. The directionality for the IS/OS approached typical psychophysical SCE measurements, while that for the PTOS approached conventional optical SCE measurements. Precise measurement of the optical SCE was found to require significant A-scan averaging.

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Section: Directionality Of the Retinal Layers Measured With Sd-octmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

Gao¹,

Cense²,

Zhang³

et al. 2008

Opt. Express

121

113

View full text Add to dashboard Cite

show abstract

“…Several causes are pointed to in that study to explain the narrowing of the single-entry reflectometric measurements 14 . Gorrand and Delori 21 proposed a model that explained the differences between psychophysical and reflectometric measurements, that suggested that some modes guided within the photoreceptors are poorly excited backwards, giving rise to a narrowing of the reflected distribution. While in some animals it is possible to image waveguides in vivo 22 , in humans it has not been possible; so although a very plausible explanation, this hypothesis is not proven.…”

Section: Reflectometric Measurements and The Stiles-crawford Effectmentioning

confidence: 99%

Cone spacing and waveguide properties from cone directionality measurements

Marcos

Burns

1999

J. Opt. Soc. Am. A

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Reflectometric techniques estimate the directionality of the retinal cones, by measuring the distribution of light at the pupil plane of light reflected off the bleached retina. The waveguidescattering model [ Marcos et al. (1998) , J. Opt. Soc. Am A] predicts that the shape of this intensity distribution is determined by both the waveguide properties of the cone photoreceptors and by the topography of the cone mosaic (cone spacing). We have performed two types of cone directionality measurements. In the first type, cone directionality estimates are obtained by measuring the spatial distribution of light returning from the retina with a single entry pupil position (single-entry measurements). In the second type, estimates are obtained by measuring the total amount of light guided back through the pupil as a function of entry pupil position (multipleentry measurements). As predicted by the model, single-entry measurements provide narrower distributions than the multiple-entry measurements, since the former are affected by both waveguides and scattering and the latter primarily by waveguides. Measurements at different retinal eccentricities and at two different wavelengths are consistent with the model. We show that the broader multiple-entry measurements are not accounted for by cone disarray. Results of multiple-entry measurements are closer to results from measurements of the psychophysical Stiles-Crawford effect (although still narrower), and the variation with retinal eccentricity and wavelength is similar. By combining single-and multiple-entry measurements we can estimate cone spacing. The estimates at 0 and 2 deg retinal eccentricities are in good agreement with published anatomical data.

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“…Diffraction sets a minimum limit for the angular extent. Waveguide models 18,14 approximate the angular extent into which a cone radiates light by a Gaussian function (with a shape factor that we denote by wg ). There are two major implications when we combine waveguide properties and cone directionality in our model:…”

Section: Unified Waveguide-scattering Modelmentioning

confidence: 99%

“…12 shows our predictions for from the waveguide model: increases from approximately 0.05 to 0.08 when moving from 0 to 3 deg. If we assume that there is no significant photoreceptor disarray at these eccentricities 14,42 and ignore effects such as cross talk and self-screening, we can compare the angular tuning of a single cone with the psychophysical Stiles-Crawford function. Measurements 43,44 indicate that the StilesCrawford directionality ( factor) increases from ϳ0.05 on average at the center of the fovea to 0.08 at 3 deg, in good agreement with the predictions from the waveguide model.…”

mentioning

confidence: 99%

Model for cone directionality reflectometric measurements based on scattering

Marcos

Burns

1998

J. Opt. Soc. Am. A

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Reflectrometric measurements provide an objective assessment of the directionality of the photoreceptors in the human retina. Measurements are obtained by imaging the distribution at the pupil plane of light reflected off the human fundus in a bleached condition. We propose that scattering as well as waveguides must be included in a model of the intensity distribution at the pupil plane. For scattering, the cone-photoreceptor array is treated as a random rough surface, characterized by the correlation length T (related to the distance between scatterers, i.e., mean cone spacing) and the roughness standard deviation (assuming random length variations of the cone outer-segment lengths that produce random phase differences). For realistic values of T and we can use the Kirchhoff approximation for computing the scattering distribution. The scattered component of the distribution can be fitted to a Gaussian function whose width depends only on T and . Actual measurements vary with experimental conditions (exposure time, retinal eccentricity, and ) in a manner consistent with the scattering model. However, photoreceptor directionality must be included in the model to explain the actual location of the peak of the intensity distribution in the pupil plane and the total angular spread of light.

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A model for assessment of cone directionality

Cited by 9 publications

References 0 publications

Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

Cone spacing and waveguide properties from cone directionality measurements

Model for cone directionality reflectometric measurements based on scattering

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