Flow and diffusion of indocyanine green and fluorescein dyes in the fovea centralis.
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Adult↗
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Results for “Fovea Centralis”
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[Morphometry and histology of the eye of Callimico goeldii (Thomas 1904, callimiconidae primates) (author's transl)].
The histologic anatomy of the eye of Callimico goeldii is described and histometric data are communicated. The retina is treated with special attention. The eye of Callimico features all characteristics of a visual organ adapted to diurnal activity as is known from many higher primates and man. The well-differentiated Fovea centralis and the numerical relations of the three retinal neurons, which are clearly reduced from the periphery towards the center of the retina, indicate a particularly high degree of centralization ("Zentralisationsstufe" sensu Rohen). Similar numerical relations are found in the taxonomically related families Cebidae and Callithrichidae. A high degree of centralization is understood to facilitate a good visual resolution. The eyelid apparatus is differentiated like in other higher primates. The eye muscles contain extraordinarily many nervous-muscular entities that are interpreted to serve as nervous regulatory functions. The histologic results relate well with certain behavioral phenomena of this species.
Animals↗
Development of the zebrafish foveal analogue: a quantitative atlas of high-acuity zone growth and retinal regionalisation.
The vertebrate retina contains specialised regions for high-acuity vision, exemplified by the human fovea and its zebrafish analogue, the high-acuity zone (HAZ). Despite the widespread use of zebrafish to model retinal disease, a stage-resolved quantitative reference describing normal eye, photoreceptor layer (PRL) and lens growth has been lacking. Here, we apply contrast-enhanced micro-computed tomography (micro-CT) to construct the first three-dimensional micro-CT normative atlas of wild-type zebrafish eye development across five larval stages [3, 5, 7, 10 and 18 days post-fertilisation (dpf)], mapping circumferential PRL thickness, eye and lens morphology, and compartment growth rates. Regional PRL thickening within the temporo-ventral region of the expected HAZ emerged by 5 dpf and was sustained by a localised redistribution of growth, persisting and extending towards the optic nerve through 18 dpf. The PRL, lens and eye grew through four phases, alternating between disproportionate PRL expansion and coordinated growth, while the eye remodelled from a nasal-dominant to a temporo-ventral-dominant form. This regional specialisation was protracted relative to gross ocular growth and could proceed independently of it, paralleling the extended postnatal maturation of the human fovea. This atlas provides a quantitative baseline for distinguishing disease-induced changes from normal variation, supporting zebrafish models of foveal hypoplasia and related disorders.
Animals↗
Amblyopia occurs in retinal ganglion cells in cats reared with convergent squint without alternating fixation.
The spatial resolving power, contrast sensitivity, and receptive field properties of retinal ganglion cells were studied in cats reared with either convergent or divergent squint in one eye. Sustained-X cells in the area centralis of the squinting eye of the cats with esotropia without alternating fixation showed significantly poorer spatial resolution, and reduced contrast sensitivity compared with cells in the area centralis of the normal eye. These amblyopic sustained-X cells in the area centralis of the squinting eye had receptive field characteristics similar to those found in immature cells of young kittens. They had a shallow sensitivity gradient within a relatively widespread centre zone and a weak and widespread inhibitory surround. In contrast, the sustained cells in the area centralis of the normal eye revealed a typical, well defined, small centre zone with its sensitivity gradient extremely steep and its inhibitory surround strong and confined. A minor degree of amblyopia was also found in transient Y-cells in the area centralis of the squinting eye of these cats. However, no loss of resolving power was found in the cells in the area centralis of the squinting eye of the cats with esotropia or exotropia which showed alternating fixation. Thus, amblyopia occurs in those eyes which have lost the use of the area centralis as the normal visual axis during early postnatal development, and its organic lesion is already apparent in the retinal ganglion cells--the third order neurone in the afferent visual system. It is suggested that the loss of the ability to fixate results in inadequate stimulation of the central retinal ganglion cells due to the habitual presence of blurred images at the area centralis which prevents their full development during the critical period.
Accommodation, Ocular↗
Familial foveal retinoschisis.
Three young women, offspring of a nonconsanguineous marriage of normal parents, manifested mild visual loss associated with a bilateral foveal dystrophy that resembled the macular involvement in juvenile sex-linked retinoschisis. Electrophysiologic and psychophysiologic tests showed less severe involvement than the gonosomal equivalent. An autosomal recessive inheritance is proposed.
Adolescent↗
Foveal sparing. New anatomical evidence for bilateral representation of the central retina.
The pattern of retinal ganglion cell projections to the dorsal lateral geniculate nuclei has been demonstrated with horseradish peroxidase neuronography. A 1 degree-wide strip centered on the vertical meridian has been found in which ipsilaterally and contralaterally projecting ganglion cells intermingle. This strip expands to a width of 3 degrees at the fovea, since mixing of horseradish peroxidase-labeled and unlabeled ganglion cells was found in a band approximately 0.5 degrees wide along both the nasal and temporal rims of the foveola. These labeled ganglion cells rimming the foveal pit in its entirety represent a possible anatomical basis for "foveal sparing".
Animals↗
Foveal lesions seen in retinitis pigmentosa.
A total of 110 patients with retinitis pigmentosa were prospectively and consecutively evaluated for the presence of foveal lesions. Of these 69 (63 percent) patients showed one of two types of separate and distinct bilateral foveal lesions. Forty-seven (43 percent) patients had atrophic-appearing lesions of the retinal pigment epithelium within the fovea of both eyes, and an additional 22 (20 percent) patients showed bitalteral foveal cysts or partial-thickness holes. Of the 22 patients in this last group, 16 showed cystoid macular edema evident on fluorescein angiography.
Aged↗
Whiplash maculopathy.
Maculopathy in three patients, caused by whiphash injury demonstrated three features that are characteristic of this subtle disturbance of the macula: a history of flexion-extension, head and neck trauma; a history of immediate mild reduction of central visual acuity in one or both eyes; and grayish swelling of the foveal zone accompanied by a small (50 to 100-mu) pit or depression in the fovea. In patients with this disturbance, the retinal opacification and the visual disturbance are transient, but the tiny depression in the retina with its whitish border is permanent.
Accidents, Traffic↗
X-linked ocular albinism in Blacks. Ocular albinism cum pigmento.
X-linked ocular albinism can be an unsuspected cause of congenital nystagmus in blacks. In this study, eight of ten black ocular albinos from two kindreds had nonalbinotic, moderately pigmented fundi and no transillumination of the iris. We refer to this paradoxical condition as "ocular albinism cum pigmento." The only constant ophthalmoscopic feature was a foveal hypoplasia. Biopsy of clinically normal skin to demonstrate giant pigment granules is the most accurate means of diagnosis.
Adolescent↗
Whiplash injury as one cause of the foveolar splinter and macular wisps.
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Aged↗
Demonstration of bilateral projection of the central retina of the monkey with horseradish peroxidase neuronography.
In the primate, ganglion cells of the temporal retina project ipsilaterally and those of the nasal retina, contralaterally into the optic tract. The vertical meridian passing through the fovea defines the border between these two populations of ganglion cells and has been demonstrated in four Macaque monkeys after unilateral injection of horseradish peroxidase into the dorsal lateral geniculate nucleus and examination of the pattern of retrograde labeling of those ganglion cells projecting to the injected side. A median 1 degree vertical strip in which ipsi- and contralaterally projecting ganglion cells intermingle was found, confirming the report by Stone et al. ('73). In addition, occasional extrafoveal labeled ganglion cells were found as far as 2 degrees from the vertical midline in the otherwise unlabeled hemiretinae. These ganglion cells were not numerous and had somata of all sizes, suggesting that they do not constitute a separate class of ganglion cells as found in the temporal retina of the cat. In contrast to the description by Stone et al. ('73), the strip of vertical overlap did not show a constant width through the fovea, since mixing of labeled and unlabeled ganglion cells was found in a band approximately 1/2 degree wide along both the nasal and temporal rims of the foveal pit which is 500 mum (2 degrees) in diameter. Beyond these 1/2 degree arcs, the appropriate hemiretina was either completely unlabeled, or contained virtually every ganglion cell labeled on the side projecting to the injected dorsal lateral geniculate nucleus. The scattered labeled ganglion cells rimming an otherwise unlabeled hemifovea represent a possible anatomical basis for the phenomenon of "macular" or "foveal sparing" in which unilateral damage to the occipital cortex produces homonymous hemianopsia with sparing of a small island of centralmost vision extending about 1 degree from the foveal center. From this study, it is not possible to define the receptive fields or specific photoreceptor connections of the ganglion cells labeled with horseradish peroxidase, so that at the present time quantitative correlations cannot be made between the numbers of ganglion cells remaining on the affected side of the fovea and the extent of preservation of visual function in the spared zone. The presence of labeled ganglion cells rimming the fovea in its entirety is compatible with the sequence of foveal development in late prenatal life. After lateral displacement both nasally and temporally of ganglion cells which initially lay in the median vertical overlap strip of 1 degree, in the adult retina a strip approximately 1/2 degree wide around the perimeter of the foveola should contain a mixture of ipsi- and contralaterally projecting ganglion cells. The total population of ganglion cells beyond this 1/2 degree band should be completely ipsi- or contralateral in their projection patterns, as is observed...
Animals↗
Development of the compound eyes of dragonflies (Odonata). II. Development of the larval compound eyes.
The development of the compound eye was analyzed by marking individual ommatidia and by studying naturally occurring pigment band patterns. New ommatidia are added to the eye along its anterior margin. This changes the directions of view of the older ommatidia with the greatest change occurring in the fovea. New ommatidia are added to the fovea medially, and old ones are removed laterally as their interommatidial angles and directions of view in the visual field change. Over one-third of the aeshnid ommatidia are foveal during at least one of the early larval instars, and are then used for peripheral vision later in development. The design of each ommatidium is a compromise so that it is adapted for all stages of development, but sometimes better adapted for one instar than for others. Factors which are balanced for best vision are lens diameter, facet admission function, interommatidial angle, and inclination of the optic axis to the eye surface. Ommatidia are described in terms of these factors throughout their life history, from initial differentiation anteriorly, through passage through the fovea, to their final relatively posterior location.
Animals↗
The retinal pigment epithelium and photoreceptor cells. Light- and electron microscopic studies on monkey eyes.
In the perifoveal retina of the monkey, Cercopithecus aethiops, the melanin granules are accumulated in apical cytoplasmatic protrusions of the pigment epithelial cells, facing the end of the cones. The rods are inserted deeper into the pigment epithelium than the cones; they reach the bottom of the infoldings of the apical surface membrane of the pigment epithelial cells. No melanin granules or other inclusions are situated at the end of the rods. The outer extremity of the rods is considerably inclined and in sections often appears as groups of rod discs which are incompletely or completely separated from the main part of the outer segments. This separation is regarded as an artifact caused by the inclination of the rods, and it is therefore not considered to represent phagocytosis of the outer segments by the pigment epithelium. The inclusions of the pigment epithelial cells are classified in five categories which seem to be related to each other owing to their shared structural characteristics. It is suggested that melanin granules are produced, modified and destroyed by the pigment epithelial cells of the adult. Because of the relations between the photoreceptors and the melanin granules it is suggested that light scattered by the melanin granules may pass backwards through the outer segments of the cones, but not of the rods.
Animals↗
Loss of spatial resolution of lateral geniculate nucleus neurones in kittens raised with convergent squint produced at different stages in development.
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Aging↗
Apparent movements induced by stroboscopic illumination of stabilized images.
Stroboscopic illumination of stabilized images causes habituation effects and illusory phenomena which, at low stimulation frequencies, show up as brighter patches. When a line is used as a stimulus, these patches are observed as brighter spots in the line surrounded by dimmer patches in the background. These locally brighter parts function as sources from which brightness spreads in the direction of the line at light-on and as sinks to which the brightness retracts again after light-off. This spread and retraction of the brightness induces the perception of movements. Higher stimulation frequencies or a diminished stimulus-background contrast enables the brightness to spread also in the direction perpendicular to the line contour, i.e., into the background. Again a perception of movement is induced, local displacements of a part of the field are observed as a result of the brightness spread. Tiny pinpoints of light, the smallest foveal perceptive elements, visible in lines narrower than 10 min arc (Gerrits, 1978), are also observed when these lines are illuminated with stroboscopic light. These tiny elements do not spread their brightnesses and so also no movement is induced. The results are discussed in relation to the properties of the perceptive elements and the cells activating them (habituation, barriers, filling-in).
Afterimage↗
Differences in peripheral and foveal effects observed in stabilized vision.
Foveal images fade much faster than peripheral images, at light-on as well as at light-off. An opposite result can be obtained, however, in case of unsatisfactory stabilization. The amount and extension of the brightness spreading before the fading depend on the stimulus brightness and its location on the retina. The intensity threshold and the maximal obtainable sharpness of the image decrease towards the periphery, the image becomes wider and sharper on increasing the stimulus intensity. In the foveal area brightness or darkness can be observed (even from stimuli below the foveal threshold) by a filling-in from the periphery, which has a lower threshold. On increasing the stimulus intensity very small pinpoints of light, tiny dots are observable in the foveal area. Each dot measures less than 1 min arc in diameter and is visible for a few hundred milliseconds only. The final sharply contoured foveal percept of a narrow line, observed at higher intensities, is made up of a crowding of these tiny dots. When lines wider than about 10 min arc are used as stimuli these small foveal dots are only seen along the inside contours but not on the (diffuse) interior of the line. In the periphery no tiny dots but only spots of larger size can be observed. At each location of the visual field the final percept seems to be built up from the co-operation of a number of perceptive elements of different sizes. Small elements fade faster, have higher thresholds, habituate more easily on repeated stimulation and become easier activated by small-amplitude stimulus displacements than larger elements. The results described, contradicting some literature date, depend heavily on the quality of the stabilization.
Color Perception↗
Reduction of the human detective quantum efficiency due to lateral neural interactions.
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Fovea Centralis↗
A mathematical model of the optokinetic reflex.
The role of the optokinetic reflex (OKR) is that of cooperating with the vestibulo-ocular reflex (VOR) in the task of image stabilization on the retina during head rotations in a stationary visual surround. Since the dynamics of VOR was already well established, it has been possible to make a broad estimation of what the dynamics of OKR should be in order to obtain the performances observed in normal subjects. A mathematical model of OKR has been presented, and the experimental results obtained by Raphan et al. (1977) in the monkey and by Collins et al. (1970) in man were used to validate the model and to obtain a precise estimation of its parameters.
Animals↗