Why Does the Human Retina Possess a Fovea?

Ra, Weale

doi:10.1038/212255a0

Cited by 44 publications

(15 citation statements)

References 6 publications

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“…And, in foveate, Halporrhine primates (tarsiers, monkeys and apes) the central retinal vascular specialization has evolved further such that the fovea is located within an FAZ (Figure 1). The significance of the relationship of the FAZ to acuity functions of the fovea has been discussed previously (Rodieck, 1988; Weale, 1966). …”

Section: Anatomy Of Retinal Specializationsmentioning

confidence: 82%

Adaptation of the central retina for high acuity vision: Cones, the fovea and the avascular zone

Provis

Dubis

Maddess

et al. 2013

Progress in Retinal and Eye Research

245

227

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Presence of a fovea centralis is directly linked to molecular specification of an avascular area in central retina, before the fovea (or `pit') begins to form. Modeling suggests that mechanical forces, generated within the eye, initiate formation of a pit within the avascular area, and its later remodeling in the postnatal period. Within the avascular area the retina is dominated by `midget' circuitry, in which signals are transferred from a single cone to a single bipolar cell, then a single ganglion cell. Thus in inner, central retina there are relatively few lateral connections between neurons. This renders the region adaptable to tangential forces, that translocate of ganglion cells laterally / centrifugally, to form the fovea. Optical coherence tomography enables live imaging of the retina, and shows that there is greater variation in the morphology of foveae in humans than previously thought. This variation is associated with differences in size of the avascular area and appears to be genetically based, but can be modified by environmental factors, including prematurity. Even when the fovea is absent (foveal hypoplasia), cones in central retina adopt an elongated and narrow morphology, enabling them to pack more densely to increase the sampling rate, and to act as more effective waveguides. Given these findings, what then is the adaptive advantage of a fovea? We suggest that the advantages of having a pit in central retina are relatively few, and minor, but together work to enhance acuity.

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Section: Anatomy Of Retinal Specializationsmentioning

confidence: 82%

Adaptation of the central retina for high acuity vision: Cones, the fovea and the avascular zone

Provis

Dubis

Maddess

et al. 2013

Progress in Retinal and Eye Research

245

227

View full text Add to dashboard Cite

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“…In addition, we found that the ratio between foveal depth and retinal thickness was higher in Harris's hawks than in black kites. As the scattering of light making up the retinal image by the neuronal layers of the inner retina may reduce the contrast of the image, a relatively deep fovea in which superficial neuronal layers are displaced could increase spatial resolution (Weale, 1966). A detailed understanding of the link between visual acuity and foveal characteristics has not been developed to date, as very few studies have explored foveal shape and visual acuity in raptors (but see Sillman, 1973).…”

Section: Foveal Characteristicsmentioning

confidence: 99%

Visual abilities in two raptors with different ecology

Potier

Bonadonna

Kelber

et al. 2016

Journal of Experimental Biology

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Differences in visual capabilities are known to reflect differences in foraging behaviour even among closely related species. Among birds, the foraging of diurnal raptors is assumed to be guided mainly by vision but their foraging tactics include both scavenging upon immobile prey and the aerial pursuit of highly mobile prey. We studied how visual capabilities differ between two diurnal raptor species of similar size: Harris's hawks, Parabuteo unicinctus, which take mobile prey, and black kites, Milvus migrans, which are primarily carrion eaters. We measured visual acuity, foveal characteristics and visual fields in both species. Visual acuity was determined using a behavioural training technique; foveal characteristics were determined using ultra-high resolution spectraldomain optical coherence tomography (OCT); and visual field parameters were determined using an ophthalmoscopic reflex technique. We found that these two raptors differ in their visual capacities. Harris's hawks have a visual acuity slightly higher than that of black kites. Among the five Harris's hawks tested, individuals with higher estimated visual acuity made more horizontal head movements before making a decision. This may reflect an increase in the use of monocular vision. Harris's hawks have two foveas (one central and one temporal), while black kites have only one central fovea and a temporal area. Black kites have a wider visual field than Harris's hawks. This may facilitate the detection of conspecifics when they are scavenging. These differences in the visual capabilities of these two raptors may reflect differences in the perceptual demands of their foraging behaviours.

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“…It is aligned with the visual axis of the eye and contains a disproportionately high density of photoreceptors. The optics of foveae are an enduring interest (Walls, 1937; Weale, 1966; Locket, 1992; Ross, 2004) because the fovea has greater spatial resolving power than other retinal specialization (Inzunza et al, 1989; Moore et al, 2012). A fovea is therefore the site of maximal visual acuity among vertebrates (Walls, 1942; Polyak, 1957; Provis et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Niche convergence suggests functionality of the nocturnal fovea

Moritz

Melin

et al. 2014

Front. Integr. Neurosci.

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The fovea is a declivity of the retinal surface associated with maximum visual acuity. Foveae are widespread across vertebrates, but among mammals they are restricted to haplorhine primates (tarsiers, monkeys, apes, and humans), which are primarily diurnal. Thus primates have long contributed to the view that foveae are functional adaptations to diurnality. The foveae of tarsiers, which are nocturnal, are widely interpreted as vestigial traits and therefore evidence of a diurnal ancestry. This enduring premise is central to adaptive hypotheses on the origins of anthropoid primates; however, the question of whether tarsier foveae are functionless anachronisms or nocturnal adaptations remains open. To explore this question, we compared the diets of tarsiers (Tarsius) and scops owls (Otus), taxa united by numerous anatomical homoplasies, including foveate vision. A functional interpretation of these homoplasies predicts dietary convergence. We tested this prediction by analyzing stable isotope ratios that integrate dietary information. In Borneo and the Philippines, the stable carbon isotope compositions of Tarsius and Otus were indistinguishable, whereas the stable nitrogen isotope composition of Otus was marginally higher than that of Tarsius. Our results indicate that species in both genera consumed mainly ground-dwelling prey. Taken together, our findings support a functional interpretation of the many homoplasies shared by tarsiers and scops owls, including a retinal fovea. We suggest that the fovea might function similarly in tarsiers and scops owls by calibrating the auditory localization pathway. The integration of auditory localization and visual fixation during prey detection and acquisition might be critical at low light levels.

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Why Does the Human Retina Possess a Fovea?

Cited by 44 publications

References 6 publications

Adaptation of the central retina for high acuity vision: Cones, the fovea and the avascular zone

Adaptation of the central retina for high acuity vision: Cones, the fovea and the avascular zone

Visual abilities in two raptors with different ecology

Niche convergence suggests functionality of the nocturnal fovea

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