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Retinal image light distributions in a standard optical model of a diffraction-limited eye with round pupils are presented for several patterns of amplitude and phase modulation of the light admitted into the eye. Of special interest are circularly symmetrical configurations of truncated Bessel amplitude transmission functions, and of light subjected to axicon deviation. It is shown by several examples that this kind of beam shaping allows generation of retinal imagery, which can be more robust to defocus while maintaining minimal image degradation, and it points to situations of two separate zones simultaneously in sharp focus, several diopters apart.

Strasburger et al.'s welcome translation of Hering's seminal paper, and reminder of what Hering actually said about eye movements and spatial averaging in vernier acuity, is supplemented by references to further trends on how the subject has evolved to the present state of knowledge.

The oblique effect-poorer performance when contours are in oblique meridians-is here extended from the discrimination of line-orientation to the tilt illusion and to the detection and contextual induction of curvature. The distinction is made between a contour's susceptibility to contextual perturbation and its capacity to induce such perturbation, for which the oblique effect is only about one half. That the cardinal/oblique superiority is retained for the orientation of illusory borders and for the implicit orientation of shapes lacking explicit rectilinear delineation has implications for its neural substrate. To the extent that a geometrical-visual illusion, such as Poggendorff's or Hering's, depends on interaction in the domain of contour orientation, it manifests a corresponding orientational anisotropy. On the other hand, visual functions that govern whether and how well a boundary is visible are invariant with orientation.

Thomas Reid (1720–1796) claims to have learned of Idomenians, “an order of beings” in “sublunary regions” whose visual system is very much like ours except that they could detect only the direction of rays reaching their eyes, not the distance of origin. The properties of Idomenian vision are here examined in the light of the physiological optics of Reid’s time and of the scientific developments that have since augmented our knowledge of the discipline.

BackgroundVisual acuity is measured by diminishing letter size till recognition threshold is reached, letters varying in legibility. In this experiment, size reduction was compared with other means of handicapping letter legibility.MethodsIn five normal observers, discrimination thresholds for 13 sans-serif capital letters in a 5 × 4 format were obtained by a staircase procedure for size reduction, as well as for 20 minutes of arc (logMAR = 0.6) letters subjected to four kinds of image degradation: reducing contrast, convolving with blurring spread, embedding in noise and perturbing contour smoothness.ResultsThreshold correlation and distribution of response errors show prominent differences and indicate the degree to which the visual processing of the various modes of image degradation is distinct.ConclusionsThe validation of four other ways of impairing the recognition of optotypes in addition to size diminution reveals their potential in the differential diagnosis of defects in pattern detection, in evaluating therapeutic regimens and in developing concepts of form perception.

A narrative starting with the author's entering the Optometry program at the Sydney Technical College in 1940, taking him through his days as an optometry and science student, an optometrist in private practice, and participant in organized optometry in Sydney. It described his steps to become an optometric scientist and his service as faculty member in three optometry schools in the United States. Finally, it follows him into a long career in vision science and neurophysiology at Berkeley.

The law of equal innervation of the two eyes, positing that conjugacy of movement of our two eyes is basic and innate, was enunciated in Hering's 1868 persuasively argued monograph. It has prevailed over Helmholtz's contrary view that conjugacy is learned. Yet 100 years earlier, Thomas Reid (1710-1796), Scottish clergyman and professor of philosophy, advanced exactly the same view as Hering, using almost identical arguments. Reid also considered whether the eyes' parallelism might have its origin in "custom" or "habit" rather than "nature" and reached the now accepted conclusion that it is innate.

Tests of target recognition under blur mostly fail to separate factors of resolution and contrast from the influences of pure blur, i.e., shallow luminance edge gradients. In experiments designed to single out blur, patterns of fixed size were convolved with a Gaussian spread function whose parameter was the variable. In addition, contrast invariance was ensured. The spread parameter was varied to measure form discrimination thresholds for simple geometrical shapes. Following determination of baseline values, observers trained for 7days, 1000 form discrimination responses with error feedback per day in a staircase procedure of the blur parameter. For four observers, thresholds improved an average of 5% (range -11% to +14%) equally for trained and untrained patterns and remained stable during subsequent training with the same targets in a related form discrimination task not involving blur. Because it transferred across target sets, the very slight improvement was indeed in the perceptual capacity to compensate for optical image degradation and not in form discrimination, but its defocus equivalent was quite minor, well less than ¼ diopter. Previous claims for blur adaptation must therefore rest on more complex factors that are not fully excluded in clinical settings.

Principles of the design and administration of clinical stereopsis tests are outlined. Once the presence of the distinct sense of the third dimension by binocular vision alone and without help from monocular cues has been established in a patient, the examination can proceed to the measurement of stereoscopic acuity. Best results are obtained with high-contrast, sharp, well-articulated and uncrowded elements from easily-recognized target sets, displayed with no time constraints. Polarization is the preferred method of right/left eye separation; time-sharing at a minimum of 60 Hz on computer displays with counterphase occluding goggles is a feasible procedure. Random-dot stereograms are problematic because not all observers can disentangle the coherent global disparity on a first view.

The clear distinction between an object and its illusory percept implies the question whether the transformstion can be investigated in terms of differential geometry and metrical properties.

Vision scientists long ago pointed to black and white as separate sensations and saw confirmation in the fact that in the absence of light, one perceives the visual field as gray against which the negative after-image of a bright light appeared blacker. The first recordings from optic nerve fibers in vertebrates revealed ON and OFF signals, later associated with separate streams, arising already at the synapse between receptors and bipolar cells. These can be identified anatomically and physiologically and remain distinct all the way to the lateral geniculate nucleus, whose fibers form the input to the primary visual cortex. The dichotomy has been probed by electroretinography and analyzed by means of pharmacological agents and dysfunction due to genetic causes. The bi- rather than a unidirectional nature of the retinal output has advantages in allowing small signals to remain prominent over a greater dynamic range. The two streams innervate cortical neurons in a push-pull manner, generating receptive fields with spatial sensitivity profiles featuring ON and OFF subregions. Manifestations of the dichotomy appear in a variety of simple visual discriminations where there are often profound threshold differences in patterns with same polarity as compared with mixed contrast-polarity components. But even at levels in which the spatial, contrast and color attributes have already been securely established and black and white elements participate equally, a categorical difference between blackness and whiteness of a percept persists. It is an opponency, akin to the ones in the color domain, derived from the original ON and OFF signals and subsequently bound with the other attributes to yield a feature's unitary percept. (C) 2007 Elsevier Ltd. All rights reserved.

A review covering the trends that led to the current state of knowledge in the areas of: (a) schematic models of the eye, and the definition of the retinal image in terms of first-order optics; (b) the description of the actual image on the retina and methods for accessing and characterizing it; (c) available procedures for controlling the quality of the retinal image in defined situations; and (d) intra-receptoral optical effects that cause differences between the light distribution on the retinal surface and at the level of interaction with photopigment molecules.

Vernier acuity for short horizontal, vertical and oblique target lines was measured in many locations in the periphery of the visual field in normal human observers. In the 10 deg periphery the average alignment threshold with oblique vernier lines in eight locations for three observers was 2.29 times higher than that with vertical and horizontal target lines. This oblique effect was found everywhere in the visual field. Similar conclusions are drawn for configurations in which the lines were replaced by just their distal endpoints, but here, additionally, performance was distinctly better when the dot pair was collinear with the fixation point, i.e. oriented radially, than when it was oriented tangentially. Both for vernier lines and for dot pairs, in all observers horizontal configurations showed somewhat better thresholds than vertical ones. These results suggest an inherent pattern of connectivity throughout the visual field favoring processing in the cardinal orientations over the obliques, the radial over the tangential and, to a limited extent, the horizontal over the vertical.

Mach and Hering had early advanced a model of spatial visual processing featuring an antagonistic interaction between adjoining areas in the visual field. Spatial opponency was one of the first findings when single-unit studies of the retina were begun. Not long afterwards psychophysical experiments revealed a center-surround organization closely matching that found in the mammalian retina. It hinged on the demonstration of reduction of sensitivity in a small patch of the visual field when its surround was changed from dark to bright. Because such patterns inevitably produce borders, well-known phenomena of border interaction could be seen as providing alternative explanations, whose substrate would most likely be in the visual cortex. These competing viewpoints are discussed especially as they pertain to the recent demonstration of spatial differences in the center/surround organization between the normal and affected eyes of amblyopes. To the extent that most findings favor a retinal site for the psychophysically measured antaaonism, and that evidence is accumulating for a direct effect on the mammalian retina of stimulus manipulation during visual development, the difference in spatial parameters of center/surround antagonism in amblyopia Suggests that the dysfunction in amblyopia begins already in the retina. (C) 2004 Elsevier Ltd. All rights reserved.

That myopic defocus, even if restricted to the peripheral retina, inhibits eye growth in young monkey eyes has motivated the therapy of myopia control through multifocal contact lens wear in children. To understand how eye-length regulating mechanisms are triggered by light requires knowledge of retinal light spread. That is largely lacking for the multifocal contact lenses used in the therapy because empirical methods identifying just the defocus in dioptres are inadequate. "Through-focus" diffraction computations in contact lens/eye models with typical normal eye parameters, including polychromatic light, the chromatic aberrations and an M-cone phototransduction layer, offer estimates of retinal image spread for a range of viewing distances. Point- and edge-spread distributions of activation of phototransduction in the central retina show that the addition of multifocal zones produces some veiling for in-focus viewing and substantial improvement of image quality for near targets in the unaccommodated eye. These effects are much reduced in the retinal periphery. Whatever therapeutic value there is in prescribing multifocal contact lenses for myopia control, it is not particularly dependent on the precise configuration of the multifocal zones, nor can it be ascribed to changes in image quality specific to the retinal periphery; its origin is more likely less blur for near targets, reducing the stimulus to accommodation. [ABSTRACT FROM AUTHOR]