Interferometric resolution determinations in the fovea and parafovea

Enoch, Jay M.; Hope, G. M.

doi:10.1007/bf00151803

Cited by 32 publications

(33 citation statements)

References 7 publications

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“…The initial contrasts for each staircase were determined by a method of descending limits. A maximum-likelihood procedure, QUEST,1 5 determined the fringe contrast presented on each trial. A single run ended when 25 trials had been presented for each condition.…”

Section: Methodsmentioning

confidence: 99%

Cone spacing and the visual resolution limit

1987

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It is commonly assumed that the visual resolution limit must be equal to or less than the Nyquist frequency of the cone mosaic. However, under some conditions, observers can see fine patterns at the correct orientation when viewing interference fringes with spatial frequencies that are as much as about 1.5 times higher than the nominal Nyquist frequency of the underlying cone mosaic. The existence of this visual ability demands a closer scrutiny of the sampling effects of the cone mosaic and the information that is sufficient for an observer to resolve a sinusoidal grating. The Nyquist frequency specifies which images can be reconstructed without aliasing by an imaging system that samples discretely. However, it is not a theoretical upper bound for psychophysical measures of visual resolution because the observer's criteria for resolving sinusoidal gratings are less stringent than the criteria specified by the sampling theorem for perfect, alias-free image reconstruction.There are at least two reasons to measure the visual resolution limit. First, the visual resolution limit is one of many benchmarks that specify the limits of human visual performance. A more interesting reason is that such measurements might allow us to draw inferences about the underlying architecture of the visual system. In this paper we address difficulties that arise in comparing visual resolution with the theoretical resolution limit of the cone mosaic. The theoretical tool often invoked for this purpose is the sampling theorem.1 ' 2 It states that a band-limited signal that is sampled at regular intervals can be completely recovered from the sample values without aliasing if the highest frequency in the signal does not exceed 1/2s, where s is the spacing between samples. This critical frequency is commonly called the Nyquist limit of the sampling array. Attempts to relate visual acuity to the anatomical spacing of photoreceptors have treated the Nyquist frequency of the cone mosaic as a theoretical upper bound on the visual resolution of the entire visual system. 3 -5 Coletta and Williams 6 introduced a psychophysical technique for estimating cone spacing outside the fovea, complementing another technique for measuring cone spacing in the living fovea.7 ' 8 These techniques make possible a comparison of cone spacing with measurements of visual resolution in the same retinal locations of the same observers. Such a comparison could disentangle the limitations imposed by the cone mosaic and postreceptoral mechanisms across the retina. In order to determine whether the cone mosaic can determine the resolution limit of the visual system as a whole, one must employ a psychophysical technique that pushes the cone mosaic to its own theoretical limits. Under many conditions of ordinary viewing, the spacing of cones does not limit resolution. Vision at low light levels or with improper refraction are familiar examples. The use of interference fringe stimuli minimizes optical blurring, and the use of high intensities reduces quantum and neural l...

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Section: Methodsmentioning

confidence: 99%

Cone spacing and the visual resolution limit

1987

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“…Variables affecting the Stiles-Crawford effect include luminance [11][12][13], wavelength [11,14], and retinal eccentricity [15][16][17]. Choi et al [17] reported that emmetropes have greater directionality than myopes between 10 nasal and 15 temporal retina.…”

Section: Introductionmentioning

confidence: 99%

Influences of accommodation and myopia on the foveal Stiles–Crawford effect

Singh

Atchison

Kasthurirangan

et al. 2009

Journal of Modern Optics

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We determined the foveal Stiles-Crawford effect (SCE) as a function of up to 8D accommodation stimulus in six young emmetropes and six young myopes using a psychophysical two-channel Maxwellian system in which the threshold luminance increment of a 1 mm spot entering through variable positions in the pupil was determined against a background formed by a 4 mm spot entering the pupil centrally. The SCE became steeper in both groups with increasing accommodation stimulus, but with no systematic shift of the peak. Combining the data of both groups gave significant increases in directionality of 15-20% in horizontal and vertical pupil meridians with 6D of accommodation. However, additional experiments indicated that much of this was an artefact of higher order aberrations and accommodative lag. Thus, there appears to be little changes in orientation or directionality in the SCE with accommodation stimulus levels up to 6 D, but it is possible that changes may occur at very high accommodation levels.

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“…Thus, uncertainties in the values of the refractive indices may affect significantly the calculated results as well as the conclusions reached from the waveguide model [5]. An error estimation of Dn ¼ 1 Â 10 À4 corresponds to an error value of the directionality factor of D ¼ 7 Â 10 À3 mm À2 [7], which is an error of about 5-10% as commonly reported in SCE studies [1,12].…”

Section: The Waveguide Modelmentioning

confidence: 97%

Single- and multimode characteristics of the foveal cones: the super-Gaussian function

Rátiva

Vohnsen

2011

Journal of Modern Optics

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A Super-Gaussian (SG) function has been introduced to describe the Stiles-Crawford effect and to match apodization changes caused by single-and multimode characteristics of the cone photoreceptors. The SG function has been validated by fitting it to the apodization at the pupil predicted by waveguide models and experimentally using a liquid-filled crystal fibre simulating the retina structure. Experiments of the Stiles-Crawford effect were performed for the author's eyes to examine the variation with wavelength throughout the visible spectral region of its characteristic directionality parameter and the visibility dependence on pupil point. The SG function describes a multimodal characteristic of the foveal cones at short wavelengths.

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Interferometric resolution determinations in the fovea and parafovea

Cited by 32 publications

References 7 publications

Cone spacing and the visual resolution limit

Cone spacing and the visual resolution limit

Influences of accommodation and myopia on the foveal Stiles–Crawford effect

Single- and multimode characteristics of the foveal cones: the super-Gaussian function

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