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Results for “Fovea Centralis”

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At least 19 recordsLinked to original sources
PubMed1999

A note about retinal structure and visual acuity. A light microscopic study of the cones in fovea centralis.

PURPOSE: Production of reliable sections of fovea centralis of primate retina. METHODS: Rhesus monkey eyes were processed using a new technique known to minimize artefacts and cell-shrinkage in other tissues. An in vivo vascular perfusion-fixation technique with an isotonic fixative followed by a process of slow infiltration with small increments in concentrations were used. RESULTS: Tangential 1 microm thick serial-sections showed a very good morphology. An average cone-to-cone-center distance of 3.8 microm in the central part of the fovea centralis was found. A cone-to-cone-center distance of 2.2-2.6 microm is suggested in the literature. CONCLUSION: In spite of the limited study we believe that the new technique has resulted in less tissue shrinkage. Our results are discussed in relation to maximal possible resolution of the eye. Our calculations (for green light) support the idea that the structure of the fovea centralis and the refractive media of the eye are developed close to perfection.

Animals↗
PubMed1994

Association of a choroidal ganglion cell plexus with the fovea centralis.

PURPOSE: After recently demonstrating an NADPH-diaphorase-, nitric oxide synthase (NOS)-positive ganglion cell plexus in the human choroid that was absent in rabbit and rat eyes, the authors extended their comparative studies to nonhuman primates and to subprimate mammals. METHODS: The authors investigated the choroids of diurnal cynomolgus monkeys with well-developed fovea centralis and accommodative systems; diurnal tree shrews without a fovea centralis or accommodative capacity; nocturnal owl monkeys with substantial accommodative capacity but without a fovea centralis; cats with an area centralis but no fovea centralis; and pigs without an area centralis or a fovea centralis. The latter two species have moderately developed ciliary muscles. Wholemounts of the choroid of eight cynomolgus monkey, two owl monkey, four tree shrew, four cat, and four pig eyes were stained for NADPH-diaphorase. In addition, frozen sections through the cynomolgus monkey choroid were stained for NOS and vasoactive intestinal polypeptide (VIP). RESULTS: In all species, the choroidal vessels were surrounded by NADPH-diaphorase-positive nerve fibers. A ganglion cell plexus, however, was seen only in cynomolgus monkey eyes. The ganglion cells stained for NOS and VIP. CONCLUSIONS: The presence of intrachoroidal nitrergic nerve cells restricted to species with a fully developed fovea centralis may indicate a functional correlation of these structures.

Amino Acid Oxidoreductases↗
PubMed1989

The density of cones in the fovea centralis of the human dichromat.

We present estimates, based on psychophysical measurements, of the density of cones in the fovea centralis of human dichromats. The estimates for a group of three protanopes and three deuteranopes (this study) were compared to the estimates of the density of cones in a group of six color normal trichromats from previous studies (Cicerone & Nerger, 1985, 1989). The results support the conclusion that the density of cones in the fovea centralis of the dichromat is comparable to that of the color normal trichomat. These results tend not to support a model of dichromacy in which a class of cones as well as the associated pigment are lost in the dichromatic eye. Instead, dichromacy appears to involve a loss of one of the three visual pigments associated with human trichromacy, with a retention of the full numbers of cones.

Cell Count↗
PubMed1989

Discontinuities of the external limiting membrane in the fovea centralis of the primate retina.

In the center of the fovea centralis of retinas of three cynomolgus monkeys, one baboon and one male human, the external limiting membrane contains circumscribed areas in which zonulae adherentes are lacking between cone inner segments and apices of Müller cells. These discontinuities of the external limiting membrane begin about 300 microns from the foveolar center, involving only a few cones. Towards the center of the fovea the discontinuities become larger.

Animals↗
PubMed1999

Müller cell cone, an overlooked part of the anatomy of the fovea centralis: hypotheses concerning its role in the pathogenesis of macular hole and foveomacualr retinoschisis.

Poorly recognized by anatomists and pathologists is the cone-shaped zone of Müller cells that composes the central and inner part of the fovea centralis. The importance of these cells in the structural integrity of the macula, as a repository for xanthophyll, and in the pathogenesis of macular diseases, particularly regarding idiopathic macular hole and foveomacular schisis, is hypothesized.

Female↗
PubMed1989

The relative numbers of long-wavelength-sensitive to middle-wavelength-sensitive cones in the human fovea centralis.

The determination of the relative numbers of different cone types in the human retina is fundamental to our understanding of visual sensitivity and color vision; yet direct measurement which provide this basic information have not previously been made for all cone types. Here we present a model which links the detection of a test light of small dimension to the number of cones contributing to detection of the light. We selectively isolated either the long-wavelength-sensitive (L) or the middle-wavelength-sensitive (M) cones, by choosing combinations of wavelengths of adapting backgrounds and tests to favor detection by the cone class of interest. Our model was applied to the detection functions measured for six color normal observers to obtain estimates of the relative numbers of L to M cones. Our estimates ranged between 1.46 and 2.36 for our observers with a mean value near two L cones for every M cone in human fovea centralis.

Color Perception↗
PubMed1992

Position of the fovea centralis with respect to the optic nerve head.

Examination of the ocular fundus via indirect ophthalmoscopy gives the clinician an impression of foveal position relative to the nerve head. In some patients, the fovea appears to be in an unusual position (i.e., ectopic): it may appear to be higher or lower than expected, or closer to or farther from the nerve head. There is little published quantitative information on this subject. The purpose of this study was to examine foveal position in a group of normal adult eyes, so that clinicians and other researchers will be able to determine on a more objective basis whether or not a given patient shows foveal ectopia. Using ocular fundus photographs for 446 normal adult eyes, we found the foveal center to be, on average, 6.11 degrees +/- 3.32 degrees below a horizontal line bisecting the nerve head. For a smaller sample of 66 eyes, we found the average distance between the nerve head and foveal centers to be 4.93 +/- 0.33 mm (right eye) and 4.88 +/- 0.36 mm (left eye). Correlations of these data for right and left eyes are also examined. Nerve head data for the group of 66 right eyes were also analyzed to yield dimensions of a best-fitting ellipse: the mean minor axis was 1.75 +/- 0.2 mm; the mean major axis 1.95 +/- 0.2 mm. Ectopia (heterotopia) of the fovea has been found in association with chorioretinitis, fibrous traction bands, and/or colobomas of the choroid and optic nerve (including anomalous insertion of the optic nerve), microcephalus, and microphthalmia. A number of separate cases with anomalous nerve heads and/or foveal positions are discussed in this paper.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Microholes of the fovea centralis.

Foveal microholes are a possible cause of unilateral or bilateral small central visual defects in the absence of other macular pathology. In 18 eyes of 17 patients we noted the following features: small, dark-reddish holes in the centre of the fovea ranging from 50 to 150 micron in size; normal adjacent retinal pigment epithelium and neuroepithelium; unilateral in most cases; males and females are equally affected; mean age 40 years; insidious onset; no history of direct eye trauma or sungazing; non-progressive; relatively favourable visual outcome; no relationship with regular macular holes; aetiology unknown. These distinctive features justify reporting these patients as an important separate group.

Adolescent↗
PubMed1997

Nitrergic nerve cells in the primate ciliary muscle are only present in species with a fovea centralis.

Nerve cells positive for NADPH diaphorase (D)/nitric oxide synthase in the human ciliary muscle appear to be involved in relaxation of the muscle during disaccommodation. To study whether similar cells might mediate disaccommodation of the primate ciliary muscle in general, serial sections of the ciliary muscle of 5 cynomolgus monkeys (Macaca fascicularis) and 2 owl monkeys (Aotes trivirgatus) were stained for NADPH-D. Both monkey species have a ciliary muscle system and an accommodative amplitude comparable to that in humans. Positively stained cells were frequently observed in the ciliary muscle of all cynomolgus monkeys, a diurnal species with a fovea, but never in owl monkeys, a nocturnal species without a fovea. The results indicate that NADPH-D-positive and probably nitrergic ganglion cells in the ciliary muscle are not present in all primate species, but only in those with high requirements for visual acuity. They might smoothen the ciliary-ganglion-mediated contraction of the ciliary muscle or contribute to the small fluctuations or oscillations of accommodation that are observed under steady viewing conditions.

Accommodation, Ocular↗
PubMed2000

[Effect of light on choroidal blood flow in the fovea centralis].

PURPOSE: To investigate whether light and dark exposures induce a response of choroidal blood flow (ChBF) in the foveal region in humans. METHODS: In a group of healthy volunteers (age 25-60 years) ChBF was measured using a new confocal laser Doppler flowmeter (probing laser at 785 nm, power at the cornea = 90 microW). ChBF was recorded at room light, in darkness, at room light following dark adaptation, and during strong light exposure following room light. RESULTS: While ChBF was stable during room light condition, it decreased significantly by 15% (p < 0.01) during darkness. After 6 min of room light following darkness, ChBF was back to baseline. Strong diffuse, green light exposure over a field of 45 degrees had no detectable effect on ChBF. In all the experiments, no significant change of blood pressure was detected. CONCLUSIONS: Our findings did not confirm the presence of an active process of ChBF regulation in response to strong light exposure in humans. They demonstrate, however, a reversible decrease in ChBF occurring after a transition from room light to darkness.

Adaptation, Ocular↗