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Variations in the size and shape of the eye have been observed in many species of fish. As eye size is positively related to visual acuity, larger eyes should favour foraging and detection of predators.However, few studies have examined the variation in eye morphology in relation to the complexity of lake conditions, including environmental perturbation and spatial variation in predation and competition. Such tests are especially important as the degrading of the visual climate is expected due to climate change, where browning, turbidity and variations in structural complexity should set different demands for visual acuity of foraging fish under predation risk.In this study, we tested the variation of the eye size among 667 individuals of an aquatic predator perch, Perca fluviatilis, from littoral and pelagic habitats of 14 lakes. We used Secchi depth to assess the effects of the visual climate of our lake systems, as fish foraging is highly related to visual conditions, and studied eye size variation in relation to the contribution of the pelagic resources to an individual's diet and the risk of predation.Secchi depth, the pelagic contribution to the diet and the percentage of piscivores had significant effects on eye size.These variable outcomes suggest that the lake environment in terms of visual climate, predation landscape and diet are major factors of eye size variation in this generalist predator. As many fish species trade off foraging against predation risk, future studies will show whether the complexity of intra‐ and interspecific interactions contribute to the variation in eye size in freshwater fish. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Background-objective: The eyes play an important role in communicating emotions and shape the determination of other facial attributes. Here, we explored the relationship between eye size, perceived intensity and attractiveness of facial expressions. Methods: A sample of N = 63 participants (men and women, aged 18-35) rated attractiveness and emotional intensity for images displaying emotionally expressive women's faces with digitally manipulated eye size (15% smaller, unchanged, or 15% larger). Results: The analysis of perceived intensity showed an interaction parameter between eye size and gender. Female individuals reported differences when comparing unchanged and larger eyes; male participants showed differences across all eye size comparisons (smaller-unchanged, smaller-larger, unchangedlarger). Regarding perceived attractiveness, faces with smaller eyes registered lower mean scores than both unchanged and larger. The lowest intensity level was associated with neutral faces and the highest with fearful ones. Faces displaying happiness were perceived as the most attractive. Conclusion: Larger eyes seem to make emotions more intense and attractive. We suggest that the more intense phenomenon serves an evolutive purpose, as it might encourage caretaking behavior. [ABSTRACT FROM AUTHOR]

Intraspecific variation in vertebrate eye size is well known. Ecological factors such as light availability are often correlated with shifts in relative eye size. However, experimental tests of selection on eye size are lacking. Trinidadian killifish (Anablepsoides hartii) are found in sites that differ in predation intensity. Sites that lack predators are characterized by lower light, high killifish densities, low resource availability, and intense competition for food. We previously found that killifish in sites that lack predators have evolved a larger "relative" eye size (eye size corrected for body size) than fish from sites with predators. Here, we used transplant experiments to test how selection operates on eye size when fish that are adapted to sites with predators are translocated into sites where predators are absent. We observed a significant "population × relative eye size" interaction; the relationship between relative eye size and a proxy for fitness (rates of individual growth) was positive in the transplanted fish. The trend was the opposite for resident fish. Such results provide experimental support that larger eyes enhance fitness and are favoured in environments characterized by low light and high competition. Graphical Abstract [ABSTRACT FROM AUTHOR]

Introduction: Variation in eye size is sometimes closely associated with brain morphology. Visual information, detected by the retina, is transferred to the optic tectum to coordinate eye and body movements towards stimuli and thereafter distributed into other brain regions for further processing. The telencephalon is an important visual processing region in many vertebrate species and a highly developed region in visually dependent species. Yet, the existence of a coevolutionary relationship between telencephalon size and eye size remains relatively unknown. Methods: Here, we use male and female guppies artificially selected for small- and large-relative-telencephalon-size to test if artificial selection on telencephalon size results in changes in eye size. In addition, we performed an optomotor test as a proxy for visual acuity. Results: We found no evidence that eye size changes with artificial selection on telencephalon size. Eye size was similar in both absolute and relative terms between the two selection regimes but was larger in females. This is most likely because of the larger body size in females, but it could also reflect their greater need for visual capacity due to sex-specific differences in foraging and mating behaviour. Although the optomotor response was stronger in guppies with a larger telencephalon, we found no evidence for differences in visual acuity between the selection regimes. Conclusion: Our study suggests that eye size and visual perception in guppies do not change rapidly with strong artificial selection on telencephalon size. [ABSTRACT FROM AUTHOR]

Despite vision being an essential sense for many animals, the intuitively appealing notion that the visual system has been shaped by environmental light conditions is backed by insufficient evidence. Based on a comprehensive phylogenetic comparative analysis of birds, we investigate if exposure to different light conditions might have triggered evolutionary divergence in the visual system through pressures on light sensitivity, visual acuity, and neural processing capacity. Our analyses suggest that birds that have adopted nocturnal habits evolved eyes with larger corneal diameters and, to a lesser extent, longer axial length than diurnal species. However, we found no evidence that sensing and processing organs were selected together, as observed in diurnal birds. Rather than enlarging the processing centers, we found a tendency among nocturnal species to either reduce or maintain the size of the two main brain centers involved in vision—the optic tectum and the wulst. These results suggest a mosaic pattern of evolution, wherein optimization of the eye optics for efficient light capture in nocturnal species may have compromised visual acuity and central processing capacity. [ABSTRACT FROM AUTHOR]

Background-objectiveThe eyes play an important role in communicating emotions and shape the determination of other facial attributes. Here, we explored the relationship between eye size, perceived intensity and attractiveness of facial expressions.MethodsA sample of N = 63 participants (men and women, aged 18–35) rated attractiveness and emotional intensity for images displaying emotionally expressive women’s faces with digitally manipulated eye size (15% smaller, unchanged, or 15% larger).ResultsThe analysis of perceived intensity showed an interaction parameter between eye size and gender. Female individuals reported differences when comparing unchanged and larger eyes; male participants showed differences across all eye size comparisons (smaller-unchanged, smaller-larger, unchanged-larger). Regarding perceived attractiveness, faces with smaller eyes registered lower mean scores than both unchanged and larger. The lowest intensity level was associated with neutral faces and the highest with fearful ones. Faces displaying happiness were perceived as the most attractive.ConclusionLarger eyes seem to make emotions more intense and attractive. We suggest that the more intense phenomenon serves an evolutive purpose, as it might encourage caretaking behavior.

Abstract Background Insects have evolved complex visual systems and display an astonishing range of adaptations for diverse ecological niches. Species of Drosophila melanogaster subgroup exhibit extensive intra- and interspecific differences in compound eye size. These differences provide an excellent opportunity to better understand variation in insect eye structure and the impact on vision. Here we further explored the difference in eye size between D. mauritiana and its sibling species D. simulans. Results We confirmed that D. mauritiana have rapidly evolved larger eyes as a result of more and wider ommatidia than D. simulans since they recently diverged approximately 240,000 years ago. The functional impact of eye size, and specifically ommatidia size, is often only estimated based on the rigid surface morphology of the compound eye. Therefore, we used 3D synchrotron radiation tomography to measure optical parameters in 3D, predict optical capacity, and compare the modelled vision to in vivo optomotor responses. Our optical models predicted higher contrast sensitivity for D. mauritiana, which we verified by presenting sinusoidal gratings to tethered flies in a flight arena. Similarly, we confirmed the higher spatial acuity predicted for Drosophila simulans with smaller ommatidia and found evidence for higher temporal resolution. Conclusions Our study demonstrates that even subtle differences in ommatidia size between closely related Drosophila species can impact the vision of these insects. Therefore, further comparative studies of intra- and interspecific variation in eye morphology and the consequences for vision among other Drosophila species, other dipterans and other insects are needed to better understand compound eye structure–function and how the diversification of eye size, shape, and function has helped insects to adapt to the vast range of ecological niches.

Background: Insects have evolved complex visual systems and display an astonishing range of adaptations for diverse ecological niches. Species of Drosophila melanogaster subgroup exhibit extensive intra- and interspecific differences in compound eye size. These differences provide an excellent opportunity to better understand variation in insect eye structure and the impact on vision. Here we further explored the difference in eye size between D. mauritiana and its sibling species D. simulans. Results: We confirmed that D. mauritiana have rapidly evolved larger eyes as a result of more and wider ommatidia than D. simulans since they recently diverged approximately 240,000 years ago. The functional impact of eye size, and specifically ommatidia size, is often only estimated based on the rigid surface morphology of the compound eye. Therefore, we used 3D synchrotron radiation tomography to measure optical parameters in 3D, predict optical capacity, and compare the modelled vision to in vivo optomotor responses. Our optical models predicted higher contrast sensitivity for D. mauritiana, which we verified by presenting sinusoidal gratings to tethered flies in a flight arena. Similarly, we confirmed the higher spatial acuity predicted for Drosophila simulans with smaller ommatidia and found evidence for higher temporal resolution. Conclusions: Our study demonstrates that even subtle differences in ommatidia size between closely related Drosophila species can impact the vision of these insects. Therefore, further comparative studies of intra- and interspecific variation in eye morphology and the consequences for vision among other Drosophila species, other dipterans and other insects are needed to better understand compound eye structure–function and how the diversification of eye size, shape, and function has helped insects to adapt to the vast range of ecological niches. [ABSTRACT FROM AUTHOR]

Urbanization now exposes large portions of the earth to sources of anthropogenic disturbance, driving rapid environmental change and producing novel environments. Changes in selective pressures as a result of urbanization are often associated with phenotypic divergence; however, the generality of phenotypic change remains unclear. In this study, we examined whether morphological phenotypes in two residential species (Carolina Wren [Thryothorus ludovicianus] and Northern Cardinal [Cardinalis cardinalis]) and two migratory species (Painted Bunting [Passerina ciris], and White‐eyed Vireo [Vireo griseus]), differed between urban core and edge habitats in San Antonio, Texas, USA. More specifically, we examined whether urbanization, associated sensory pollution (light and noise) and brightness (open, bright areas cause by anthropogenic land use) influenced measures of avian body (mass and frame size) and lateral eye size. We found no differences in body size between urban core and edge habitats for all species except the Painted Bunting, in which core‐urban individuals were smaller. Rather than a direct effect of urbanization, this was due to differences in age structure between habitats, with urban‐core areas consisting of higher proportions of younger buntings which are, on average, smaller than older birds. Residential birds inhabiting urban‐core areas had smaller eyes compared to their urban‐edge counterparts, resulting from a negative association between eye size and light pollution and brightness across study sites; notably, we found no such association in the two migratory species. Our findings demonstrate how urbanization may indirectly influence phenotypes by altering population demographics and highlight the importance of accounting for age when assessing factors driving phenotypic change. We also provide some of the first evidence that birds may adapt to urban environments through changes in their eye morphology, demonstrating the need for future research into relationships among eye size, ambient light microenvironment use, and disassembly of avian communities as a result of urbanization. [ABSTRACT FROM AUTHOR]

Simple Summary: Birds often exhibit differences in locomotion, foraging, and predator detection, many of which are often reflected in their eye sizes. Therefore, understanding the coevolutionary relationships between eye size and ecological factors, behaviours and brain size in birds is essential. Our results indicate that species with larger eye sizes reside in dense habitats, feed on invertebrates or vertebrates and have larger brains, suggesting that habitat openness, food type and cognition play critical roles in shaping visual sensitivity and resolution. However, we did not find any correlation between eye size and migration behaviour or foraging habitat, indicating that these factors are likely not major drivers of eye size evolution. The eye is the primary sensory organ that obtains information from the ecological environments and specifically bridges the brain with the extra environment. However, the coevolutionary relationships between eye size and ecological factors, behaviours and brain size in birds remain poorly understood. Here, we investigate whether eye size evolution is associated with ecological factors (e.g., habitat openness, food type and foraging habitat), behaviours (e.g., migration and activity pattern) and brain size among 1274 avian species using phylogenetically controlled comparative analyses. Our results indicate that avian eye size is significantly associated with habitat openness, food type and brain size. Species living in dense habitats and consuming animals exhibit larger eye sizes compared to species living in open habitats and consuming plants, respectively. Large-brained birds tend to possess larger eyes. However, migration, foraging habitat and activity pattern were not found to be significantly associated with eye size in birds, except for nocturnal birds having longer axial lengths than diurnal ones. Collectively, our results suggest that avian eye size is primarily influenced by light availability, food need and cognitive ability. [ABSTRACT FROM AUTHOR]

There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti‐predator) behaviour in Daphnia. We set‐up replicate experimental populations of Daphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50‐day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases in Daphnia density favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti‐predator behaviour. Daphnia from the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti‐predator behaviour. Such trends provide new insights into selection on eye size and behaviour. [ABSTRACT FROM AUTHOR]

Geckos feature a large range of eye sizes, but what drives this phenotypic diversity is currently unknown. Earlier studies point towards diel activity patterns (DAPs) and locomotory mode, but phylogenetic comparative studies in support of the proposed adaptive mode of eye evolution are lacking. Here, we test the hypothesis of DAPs as the driver of eye size evolution with a dataset on 99 species of gecko. Results from phylogenetic generalized least-square analysis (PGLS) and multivariate model-fitting reveal smaller eyes in diurnal geckos consistent with different phenotypic optima. However, Bayesian analyses of selective regime shifts demonstrate that only two of nine transitions from nocturnal to diurnal activity are coupled with decreases in eye size, and two other regime shifts are not associated with DAP transitions. This non-uniform evolutionary response suggests that eye size is not the only functionally relevant variable. Evolutionary adaptations may therefore include different combinations of several traits (e.g. photoreceptors), all with the same functional outcome. Our results further demonstrate that DAP only partially explains eye size diversity in geckos. As open habitats favour the evolution of large eyes while obstructed habitats favour small eyes, the degree of habitat clutter emerges as another potential axis of eye diversification.

Eyes within the marine gastropod superfamily Stromboidea range widely in size, from 0.2 to 2.3 mm - the largest eyes known in any gastropod. Despite this interesting variation, the underlying evolutionary pressures remain unknown. Here, we use the wealth of material available in museum collections to explore the evolution of stromboid eye size and structure. Our results suggest that depth is a key light-limiting factor in stromboid eye evolution; here, increasing water depth is correlated with increasing aperture width relative to lens diameter, and therefore an increasing investment in sensitivity in dim light environments. In the major clade containing all large-eyed stromboid families, species observed active during the day and the night had wider eye apertures relative to lens sizes than species observed active during the day only, thereby prioritising sensitivity over resolution. Species with no consistent diel activity pattern also had smaller body sizes than exclusively day-active species, which may suggest that smaller animals are more vulnerable to shell-crushing predators, and avoid the higher predation pressure experienced by animals active during the day. Within the same major clade, ancestral state reconstruction suggests that absolute eye size increased above 1 mm twice. The unresolved position of Varicospira, however, weakens this hypothesis and further work with additional markers is needed to confirm this result., (© The Author(s) 2024. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Links between contrasting ecological conditions and evolutionary shifts in neurosensory components, such as brain and eye size, are accumulating. Whether selection operates in a different manner on these traits between sexes is unclear. Trinidadian killifish (Anablepsoides hartii) are found in sites with and without predators. Male killifish from sites without predators have evolved larger brains and eyes than males from sites with predators. These differences in brain size are present early in life but disappear in adult size classes. Here, we evaluated female brain growth allometries to determine whether females exhibit similar size-specific differences in brain size between sites that differ in predation intensity. We also quantified brain size and structure and eye size to determine whether these structures co-evolved in a sex-specific manner. We found that female brain growth allometries did not differ across populations. Yet, female killifish from sites without predators exhibited a larger cerebellum, optic tectum and dorsal medulla early in life (before maturation), although such differences disappeared in larger size classes. Females from sites with predators exhibited similar patterns in brain growth to males in those sites; therefore, shifts in brain size and structure are driven by differences between sexes in sites without predators. We also found evidence for covariation between brain and eye size in both sexes despite different levels of variation in both structures, suggesting that these structures might covary to fluctuating degrees in sex-specific ways. We conclude that differential investment in brain tissue in sites without predators might be linked to varying reproductive and cognitive demands between the sexes. [ABSTRACT FROM AUTHOR]

Abstract Brain size, brain architecture, and eye size vary extensively in vertebrates. However, the extent to which the evolution of these components is intricately connected remains unclear. Trinidadian killifish, Anablepsoides hartii, are found in sites that differ in the presence and absence of large predatory fish. Decreased rates of predation are associated with evolutionary shifts in brain size; males from sites without predators have evolved a relatively larger brain and eye size than males from sites with predators. Here, we evaluated the extent to which the evolution of brain size, brain structure, and eye size covary in male killifish. We utilized wild‐caught and common garden‐reared specimens to determine whether specific components of the brain have evolved in response to differences in predation and to determine if there is covariation between the evolution of brain size, brain structure, and eye size. We observed consistent shifts in brain architecture in second generation common garden reared, but not wild caught preserved fish. Male killifish from sites that lack predators exhibited a significantly larger telencephalon, optic tectum, cerebellum, and dorsal medulla when compared with fish from sites with predators. We also found positive connections between the evolution of brain structure and eye size but not between overall brain size and eye size. These results provide evidence for evolutionary covariation between the components of the brain and eye size. Such results suggest that selection, directly or indirectly, acts upon specific regions of the brain, rather than overall brain size, to enhance visual capabilities.

This study was aimed to investigate the growth patterns and the relationship of the eyeball and the orbit using computed tomography (CT)-based three-dimensional (3D) techniques. A total of 175 Chinese patients who had undergone craniofacial or orbital CT scans were enrolled. This study only included data from the unaffected eye and orbit. Images were processed using 3D reconstruction to obtain the eyeball and the orbit parameters. In early postnatal years, the sizes of eyeball and orbit increased significantly with age (p < 0.001) and reached a turning point at a critical age (8.967 and 12.800 years for the eyeball and orbit volume, respectively). The orbital index and orbital depth index, showing the shape of the orbital aperture and walls, decreased significantly with age (p < 0.001). In all ages, the orbit size was correlated with eyeball size (p < 0.001). The eye-orbit index, equivalent to the ratio of eye volume to orbital volume, declined steadily with age (p < 0.001). The eyeball and orbit developed rapidly in early postnatal years, and then matured at a critical age. The eyeball size significantly contributed to the orbital growth; this contribution may be reduced as the eye-orbit index decreased with age. To the best of our knowledge, this is the first report on the growth and interrelation of the eyeball and the orbit using CT-based 3D techniques. [ABSTRACT FROM AUTHOR]

The human eye has a crystalline lens that focuses retinal images at the point of fixation. Outside this fixation region, images are distorted by optical blur, which increases light scatter and reduces the spatial resolution and contrast processed by neuronal pathways. The spectacle lenses that humans use for optical correction also minify or magnify the images, affecting neuronal surround suppression in visual processing. Because light and dark stimuli are processed with ON and OFF pathways that have different spatial resolution, contrast sensitivity and surround suppression, optical blur and image magnification should affect differently the two pathways and the perception of lights and darks. Our results provide support for this prediction in cats and humans. We demonstrate that optical blur expands ON receptive fields while shrinking OFF receptive fields, as expected from the expansion of light stimuli and shrinkage of dark stimuli with light scatter. Spectacle-induced image magnification also shrinks OFF more than ON receptive fields, as expected from the stronger surround suppression in OFF than ON pathways. Optical blur also decreases the population response of OFF more than ON pathways, consistent with the different effects of light scatter on dark and light stimuli and the ON-OFF pathway differences in contrast sensitivity. Based on these results, we conclude that optical blur and image magnification reduce the receptive field sizes and cortical responses of OFF more than ON pathways, making the ON-OFF response balance a reliable signal to optimize the size and quality of the retinal image., Competing Interests: DECLARATION OF INTEREST The authors declare no competing interests.

Researchers have suggested that infants exhibiting baby schema are considered cute. These similar studies have mainly focused on changes in overall baby schema facial features. However, whether a change in only eye size affects the perception of cuteness across different facial expressions and ages has not been explicitly evaluated until now. In the present study, a paired comparison method and 7-point scale were used to investigate the effects of eye size on perceived cuteness across facial expressions (positive, neutral, and negative) and ages (adults and infants). The results show that stimuli with large eyes were perceived to be cuter than both unmanipulated eyes and small eyes across all facial expressions and age groups. This suggests not only that the effect of baby schema on cuteness is based on changes in a set of features but also that eye size as an individual feature can affect the perception of cuteness.

Researchers have suggested that infants exhibiting baby schema are considered cute. These similar studies have mainly focused on changes in overall baby schema facial features. However, whether a change in only eye size affects the perception of cuteness across different facial expressions and ages has not been explicitly evaluated until now. In the present study, a paired comparison method and 7-point scale were used to investigate the effects of eye size on perceived cuteness across facial expressions (positive, neutral, and negative) and ages (adults and infants). The results show that stimuli with large eyes were perceived to be cuter than both unmanipulated eyes and small eyes across all facial expressions and age groups. This suggests not only that the effect of baby schema on cuteness is based on changes in a set of features but also that eye size as an individual feature can affect the perception of cuteness. [ABSTRACT FROM AUTHOR]

Motivation: Global freshwater fish biodiversity and the responses of fishes to global changes have been explored intensively using taxonomic data, whereas functional aspects remain understudied owing to the lack of knowledge for most species. To fill this gap, we compiled morphological traits related to locomotion and feeding for the world freshwater fish fauna based on pictures and scientific drawings available from the literature. Main types of variables contained: The database includes 10 morphological traits measured on 8,342 freshwater fish species, covering 48.69% of the world freshwater fish fauna. Spatial location and grain: Global. Major taxa and level of measurement: The database considers ray‐finned fishes (class Actinopterygii). Measurements were made at the species level. Software format:.csv. Main conclusion: The FISHMORPH database provides the most comprehensive database on fish morphological traits to date. It represents an essential source of information for ecologists and environmental managers seeking to consider morphological patterns of fish faunas throughout the globe, and for those interested in current and future impacts of human activities on the morphological structure of fish assemblages. Given the high threat status of freshwater environments and the biodiversity they host, we believe this database will be of great interest for future studies on freshwater ecology research and conservation. [ABSTRACT FROM AUTHOR]

Increasing artificial illumination during night has multifaceted effects on species. Moths are shown to be distracted and attracted by artificial light sources, leading to increased mortality through predation or exhaustion. Increased mortality can be expected to increase selection pressure on morphology, particularly those being functional in light detection and flight ability. We were thus interested if intraspecific traits differ between areas and times with differing light pollution values. We chose the moth Agrotis exclamationis , a common species in the Berlin-Brandenburg region, Germany, a region that offers very different levels of light pollution across space and time. We examined body length, eye size and forewing length, traits likely targeted through selection due to light pollution. We examined moths collected over the past 137 years. We predicted decreasing forewing length, body and eye size, in response to increasing light pollution and expected to see trait changes from the past to today, and from rural to urban areas, representing temporal and spatial gradients of increasing light pollution. In order to determine current levels of light pollution, we used radiance values of the years 2012 to 2019. These values were the base to extrapolate previous radiance values for all sample sites and years. We observed no trait differences along the spatial gradient, but trait and sex dependant changes along the temporal gradient. We could not confirm a direct causal link between changes in body size and female eye size. However, we revealed indirect effects of light pollution, and assume habitat fragmentation and host-plants to be the main drivers for these effects. A trend towards smaller-eyed females in 'medium' and 'high' light-polluted areas over time could be a first indication that morphological trait changes to light pollution are taking place. [ABSTRACT FROM AUTHOR]

Eye size varies markedly among taxonomic levels, and this variation is often related to the patterns shaped by phylogeny and ecological and behavioral factors. The selective pressures underlying eye size evolution are especially studied in fishes, anurans, birds, and mammals. However, selective pressures underlying the eye size evolution in anurans have inconsistent scaling rules. Here, we investigated the links between eye size and both ecological (e.g., light availability and habitat type) and behavioral factors (e.g., activity time, foraging mobility, defensive strategy, and mating system) among 252 species of anurans by using phylogenetically controlled generalized least-squared (PGLS) regression. Results show that anuran eye size scales hypo-allometrically with body size. However, eye size was not significantly influenced by ecological and behavioral factors, including habitat type, activity time, light availability, foraging mobility, defensive strategy, and mating system. Therefore, neither ecology nor behavior plays a key role in promoting eye size evolution in frogs.

A face contains crucial information for identification; moreover, face recognition is superior to other types of recognition. Notably, one's own face is recognized better than other familiar faces. However, it is unclear whether one's own face, especially one's own internal facial features, is represented more accurately than other faces. Here, we investigated how one's own internal facial features were represented. We conducted a psychological experiment in which the participants were required to adjust eye size to the real size in photos of their own or well-known celebrities' faces. To investigate why individuals' own and celebrity facial representations were different, two types of photos were prepared, with and without external features. It was found that the accuracy of eye size for one's own face was better than that for celebrities' faces in the condition without external features, in which holistic processing was less involved than in the condition with external features. This implies that the eye size of one's own face was represented more accurately than that of other familiar faces when external features were removed. Moreover, the accuracy of the eye size of one's own face in the condition with external features was worse than that in the condition without external features; the adjusted eye size in the condition with external features was larger than that in the condition without external features. In contrast, for celebrities' faces, there was no significant difference between the conditions with and without external features. The adjusted eye sizes in all conditions were overestimated compared to real eye sizes. Previous research indicated that eye size was adjusted to a larger size when evaluating as more attractive, in which the evaluation is related to holistic processing. Based on this perspective, it could be that one's own face was represented as more attractive in the condition with external features in the current study. Taken together, the results indicated that the representation of own eye size, which is an internal facial feature, was affected by the visibility of the external features.

Abstract Background Lens-induced myopization in guinea pigs has been used as model for the process of myopization in humans. It has not been explored yet whether the change in globe shape in eyes undergoing myopization is similar in experimental myopia in guinea pigs and in clinical myopia in patients. Methods The study included 70 guinea pigs (age:2–3 weeks) equally divided into a study group with lens-induced myopization for 5 weeks, and a control group wearing goggles with no refractive power. The globe diameters were measured using a microcaliper after enucleation. Results The horizontal globe diameter (9.19 ± 0.15 mm versus 9.15 ± 0.18 mm; P = 0.25) and vertical globe diameter (9.02 ± 0.11 mm versus 8.99 ± 0.14 mm; P = 0.29) did not differ significantly between the study group and control group. The sagittal diameter was significantly longer in the study group (8.96 ± 0.15 mm versus 8.84 ± 0.14 mm; P = 0.001). While the vertical and horizontal globe diameters were correlated with each other in a ratio of approximately 1:1 (non-standardized regression coefficient B:0.94;95% confidence interval (CI):0.73,1.15), the steepness of the regression lines of the associations of both diameters with the sagittal diameter were flatter (horizontal to sagittal diameter: B: 0.64; 95% CI: 0.44,0.83; vertical to sagittal diameter:B:0.55;95% CI:0.41,0.69). Correspondingly, the ratios of horizontal-to-sagittal globe diameter and of vertical-to-sagittal globe diameter decreased (P

Animals with biphasic lifecycles often inhabit different visual environments across ontogeny. Many frogs and toads (Amphibia: Anura) have free-living aquatic larvae (tadpoles) that metamorphose into adults that inhabit a range of aquatic and terrestrial environments. Ecological differences influence eye size across species, but these relationships have not yet been explored across life stages in an ontogenetic allometric context. We examined eye-body size scaling in a species with aquatic larvae and terrestrial adults, the common frog Rana temporaria, using a well-sampled developmental series. We found a shift in ontogenetic allometric trajectory near metamorphosis indicating prioritized growth in tadpole eyes. To explore the effects of different tadpole and adult ecologies on eye-body scaling, we expanded our taxonomic sampling to include developmental series of eleven additional anuran species. Intraspecific eye-body scaling was variable among species, with 8/12 species exhibiting a significant change in allometric slope between tadpoles and adults. Traits categorizing both tadpole ecology (microhabitat, eye position, mouth position) and adult ecology (habitat, activity pattern) across species had significant effects on allometric slopes among tadpoles, but only tadpole eye position had a significant effect among adults. Our study suggests that relative eye growth in the preliminary stages of biphasic anuran ontogenies is somewhat decoupled and may be shaped by both immediate ecological need (i.e. tadpole visual requirements) and what will be advantageous during later adult stages. [ABSTRACT FROM AUTHOR]

The role of light in partitioning ecological niche space remains a frontier in understanding the assembly of terrestrial vertebrate communities and their response to global change. Leveraging recent advances in biologging technology and intensive field surveys of cloud forest bird communities across an agricultural land use gradient in the Peruvian Andes, we demonstrate that eye size predicts (1) the ambient light microenvironment used by free‐ranging birds, (2) their foraging niche, and (3) species‐specific sensitivity to agricultural land use change. For 15 species carrying light sensors (N = 71 individuals), light intensity levels were best explained by eye size and foraging behavior, with larger‐eyed species using darker microenvironments. Across the cloud forest bird community (N = 240 species), hyperopic ("far‐sighted") foragers, (e.g., flycatchers), had larger eyes compared to myopic ("near‐sighted") species (e.g., gleaners and frugivores); eye size was also larger for myopic insectivores that foraged in the forest understory. Eye size strongly predicted sensitivity to brightly lit habitats across an agricultural land use gradient. Species that increased in abundance in mixed intensity agriculture, including fencerows, silvopasture, and pasture, had smaller eyes, suggesting that light acts as an environmental filter when communities disassemble in a human‐disturbed landscape. We suggest that eye size represents a novel functional trait contributing to terrestrial vertebrate community assembly and sensitivity to habitat disturbance. [ABSTRACT FROM AUTHOR]

Brain size, brain architecture, and eye size vary extensively in vertebrates. However, the extent to which the evolution of these components is intricately connected remains unclear. Trinidadian killifish, Anablepsoides hartii, are found in sites that differ in the presence and absence of large predatory fish. Decreased rates of predation are associated with evolutionary shifts in brain size; males from sites without predators have evolved a relatively larger brain and eye size than males from sites with predators. Here, we evaluated the extent to which the evolution of brain size, brain structure, and eye size covary in male killifish. We utilized wild‐caught and common garden‐reared specimens to determine whether specific components of the brain have evolved in response to differences in predation and to determine if there is covariation between the evolution of brain size, brain structure, and eye size. We observed consistent shifts in brain architecture in second generation common garden reared, but not wild caught preserved fish. Male killifish from sites that lack predators exhibited a significantly larger telencephalon, optic tectum, cerebellum, and dorsal medulla when compared with fish from sites with predators. We also found positive connections between the evolution of brain structure and eye size but not between overall brain size and eye size. These results provide evidence for evolutionary covariation between the components of the brain and eye size. Such results suggest that selection, directly or indirectly, acts upon specific regions of the brain, rather than overall brain size, to enhance visual capabilities. [ABSTRACT FROM AUTHOR]

The visual capacity of aquatic organisms is, in general, related to light penetration in the water. Therefore, aquatic environments that differ in color can potentially contribute to species polymorphism, especially in fish. In this study, we explore the relationship between light quality and intensity in water bodies and the eye and mouth size in Galaxias maculatus, one of the most widespread fish. Fish morphology was studied photographically, and the vertical attenuation coefficient of light (Kd) was measured in five aquatic systems: two humic lakes, two estuaries, and one river. Water color was also estimated as absorbance at 440 nm. In those environments with less light penetration and darker water color, we observed bigger eyes and, additionally, larger mouths. The darkness of water bodies was mainly related to water color associated with humic substances. As G. maculatus is known to be a visual predator, our results suggest that bigger eyes increase visual capacity in darker environments, which would result in improved feeding rates, also supported by larger mouth length. [ABSTRACT FROM AUTHOR]

Background: The typical imaged findings of retinoblastoma are an intraocular tumor with intratumoral calcification. Normal eye size is a supported finding of retinoblastoma. In practice, more than just a few cases had an altered eye size. Objective: To evaluate the effect of eye size in retinoblastoma. Materials and Methods: The present study included 47 patients with 54 diseased eyes. Twenty-seven patients underwent enucleation with histopathological results. The axial lengths (AL) and equatorial diameters (ED) were measured in both diseased and normal eyes. The imaging characteristics, tumor volume, and histopathological findings were recorded and analyzed. Results: The results showed no statistically significant differences between AL, ED, and calculated eye volumes (EV) between diseased and normal eyes. Anterior chamber depths were statistically shallower in retinoblastoma eyes (p<0.001). EV was weakly associated with tumor volumes. Large eye size was significantly related to choroidal invasion, massive choroidal invasion, scleral invasion, and optic nerve invasion in pathology (p=0.04, 0.03, 0.02, and 0.04, respectively). Conclusion: There were no statistically significant differences of eye size parameters in the eyes with retinoblastoma when compared to the normal eyes. Large eye size and large tumor volume are significantly related to invasive histopathological results. [ABSTRACT FROM AUTHOR]

Fish are the most diverse vertebrate group, and they have evolved equally diverse visual systems, varying in terms of eye morphology, number and distribution of spectrally distinct photoreceptor types, visual opsin genes and opsin gene expression levels.This variation is mainly due to adaptations driven by two factors: differences in the light environments and behavioural tasks. However, while the effects of large‐scale habitat differences are well described, it is less clear whether visual systems also adapt to differences in environmental light at the microhabitat level.To address this, we assessed the relationship between microhabitat use and visual system features in fishes inhabiting coral reefs, where habitat partitioning is particularly common.We suggest that differences in microhabitat use by cardinalfishes (Apogonidae) drive morphological and molecular adaptations in their visual systems. To test this, we investigated diurnal microhabitat use in 17 cardinalfish species and assessed whether this correlated with differences in visual opsin gene expression and eye morphology.We found that cardinalfishes display six types of microhabitat partitioning behaviours during the day, ranging from specialists found exclusively in the water column to species that are always hidden inside the reef matrix.Species predominantly found in exposed microhabitats had higher expression of the short‐wavelength‐sensitive violet opsin (SWS2B) and lower expression of the dim‐light active rod opsin (RH1). Species of intermediate exposure, on the other hand, expressed opsins that are mostly sensitive to the blue‐green central part of the light spectrum (SWS2As and RH2s), while fishes entirely hidden in the reef substrate had a higher expression of the long‐wavelength‐sensitive red opsin.We also found that eye size relative to body size differed between cardinalfish species, and relative eye size decreased with an increase in habitat exposure.Retinal topography did not show co‐adaptation with microhabitat use, but data suggested co‐adaptation with feeding mode.We suggest that, although most cardinalfishes are nocturnal foragers, their visual systems—and possibly those of other (reef) fishes—have also adapted to the light intensity and the light spectrum of their preferred diurnal microhabitats. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Understanding patterns and processes governing biodiversity along broad‐scale environmental gradients, such as depth or latitude, requires an assessment of not just taxonomic richness, but also morphological and functional traits of organisms. Studies of traits can help to identify major selective forces acting on morphology. Currently, little is known regarding patterns of variation in the traits of fishes at broad spatial scales.The aims of this study were (a) to identify a suite of key traits in marine fishes that would allow assessment of morphological variability across broad‐scale depth (50–1200 m) and latitudinal (29.15–50.91°S) gradients, and (b) to characterize patterns in these traits across depth and latitude for 144 species of ray‐finned fishes in New Zealand waters.Here, we describe three new morphological traits, namely fin‐base‐to‐perimeter ratio, jaw‐length‐to‐mouth‐width ratio, and pectoral‐fin‐base‐to‐body‐depth ratio. Four other morphological traits essential for locomotion and food acquisition that are commonly measured in fishes were also included in the study. Spatial ecological distributions of individual fish species were characterized in response to a standardized replicated sampling design, and morphological measurements were obtained for each species from preserved museum specimens.With increasing depth, fishes, on average, became larger and more elongate, with higher fin‐base‐to‐perimeter ratio and larger jaw‐length‐to‐mouth‐width ratio, all of which translates into a more eel‐like anguilliform morphology. Variation in mean trait values along the depth gradient was stronger at lower latitudes for fin‐base‐to‐perimeter ratio, elongation and total body length. Average eye size peaked at intermediate depths (500–700 m) and increased with increasing latitude at 700 m.These findings suggest that, in increasingly extreme environments, fish morphology shifts towards a body shape that favours an energy‐efficient undulatory swimming style and an increase in jaw‐length vs. mouth width for opportunistic feeding. Furthermore, increases in eye size with both depth and latitude indicate that changes in both the average ambient light conditions as well as seasonal variations in day‐length can act to select ecomorphological adaptations in fishes. [ABSTRACT FROM AUTHOR]

Natural variation in environmental turbidity correlates with variation in the visual sensory system of many fishes, suggesting that turbidity may act as a strong selective agent on visual systems. Since many aquatic systems experience increased turbidity due to anthropogenic perturbations, it is important to understand the degree to which fish can respond to rapid shifts in their visual environment, and whether such responses can occur within the lifetime of an individual. We examined whether developmental exposure to turbidity (clear, <5 NTU; turbid, ∼9 NTU) influenced the size of morphological structures associated with vision in the African blue-lip cichlid Pseudocrenilabrus multicolor. Parental fish were collected from two sites (clear swamp, turbid river) in western Uganda. F1 broods from each population were split and reared under clear and turbid rearing treatments until maturity. We measured morphological traits associated with the visual sensory system (eye diameter, pupil diameter, axial length, brain mass, optic tectum volume) over the course of development. Age was significant in explaining variation in visual traits even when standardized for body size, suggesting an ontogenetic shift in the relative size of eyes and brains. When age groups were analyzed separately, young fish reared in turbid water grew larger eyes than fish reared in clear conditions. Population was important in the older age category, with swamp-origin fish having relatively larger eyes and optic lobes relative to river-origin fish. Plastic responses during development may be important for coping with a more variable visual environment associated with anthropogenically induced turbidity., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Vertebrate eye size typically scales hypoallemetrically with body size—as animals grow larger their eyes get relatively smaller. Additionally, eye size is highly variable across species, and such variability often reflects functional adaptations to differences in behavior and/or ecology. The selective pressures underlying the evolution of eye size are especially well studied in birds, mammals, and fishes. However, whether similar scaling rules and selective pressures also underlie the evolution of eye size in amphibians remains enigmatic. Variation in eye size is intimately linked with variation in brain anatomy, as the retina is ontogenetically part of the brain. Eye size may therefore coevolve with brain size. Here we use phylogenetic comparative methods to study interspecific variation in eye volume across 44 species of anurans from 8 families from the Hengduan Mountains, China. We relate this variation to key factors known to impact eye size evolution in other vertebrate taxa such as body mass, habitat use, defense strategy and foraging mobility. We found that also in anurans eyes size scaled hypoallometrically with body mass. However, neither of the behavioral or ecological factors explained any variation in relative eye size in our sample. Whether this is representative for other frog species needs to be clarified. We therefore conclude that eye size in frogs is tightly linked to body mass evolution but that, at least in the species investigated here, none of our tested ecological and behavioral factors have a strong influence on eye size evolution. [ABSTRACT FROM AUTHOR]

Eye size varies notably across taxa. Much work suggests that this variation is driven by contrasting ecological selective pressures. However, evaluations of the relationship between ecological factors and shifts in eye size have largely occurred at the macroevolutionary scale. Experimental tests in nature are conspicuously absent.Trinidadian killifish, Rivulus hartii, are found across fish communities that differ in predation intensity. We recently showed that increased predation is associated with the evolution of a smaller eye. Here, we test how divergent predatory regimes alter the trajectory of eye size evolution using comparative mark–recapture experiments in multiple streams.We found that increases in eye size are associated with enhanced survival, irrespective of predation intensity. More importantly, eye size is associated with enhanced growth in communities that lack predators, while this trend is absent when predators are present.Such results argue that increased competition for food in sites that lack predators is the key driver of eye size evolution. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Proposed mechanisms for the decline of terrestrial and understory insectivorous birds in the tropics include a related subset that together has been termed the 'microclimate hypothesis'. One prediction from this hypothesis is that sensitivity to bright light environments discourages birds of the dimly lit rainforest interior from using edges, gaps, or disturbed forest. Using a hierarchical Bayesian framework and capture data across time and space, we tested this by first determining vulnerability based on differences in within‐species capture rates between disturbed and undisturbed forest for 64 bird species at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. We found that 35 species (55%) were vulnerable to anthropogenic habitat degradation, whereas only four (6%) were more commonly captured in degraded forest. To infer visual sensitivity, we then examined two different characters: eye size (maximum pupil diameter) relative to body mass and the initiation time of dawn song, which presumably reflects a species' visual capacity under low light intensities. We predicted that species with large relative eye sizes and birds with earlier dawn songs would exhibit increased vulnerability in degraded habitats with bright light. Contrary to our predictions, however, vulnerability was positively correlated with the mean start time of dawn song. This indicates that species that wait to initiate dawn song are also more vulnerable to habitat degradation. After correcting for body size, there was no effect of eye size on vulnerability. Together, our results do not provide quantitative support for the light sensitivity mechanism of the microclimate hypothesis. More sensitive experimental tests, such as behavioral assays with controlled light environments, especially in a comparative framework, are needed to rigorously evaluate the role of light sensitivity as an aspect of the microclimate hypothesis among Neotropical birds. [ABSTRACT FROM AUTHOR]

An important resource partitioning strategy allowing dung beetles to coexist in the same habitat, while utilising the same food, is species' separation of activity times. After establishing the diel activity period of three closely related, co-occurring dung beetles, we examined their eye and wing morphology. Absolute and relative eye size, and facet size were greater in the nocturnal Escarabaeus satyrus, followed by the crepuscular Scarabaeus zambesianus and then the diurnal Kheper lamarcki. The diurnal K. lamarcki had the highest wing aspect ratio (long, narrow wings), followed by the crepuscular S. zambesianus and the nocturnal E. satyrus (short, broad wings), suggesting that dim-light active species fly slower than diurnal species. In addition, the two species active in dim light had a lower wing loading than the diurnal species, indicating the need for greater manoeuvrability in the dark. Analyses of wing shape revealed that the diurnal K. lamarcki wing had a proportionally larger jugal and anal region than both dim light species. Our results show that different species of dung beetles have a combination of optical and morphological wing adaptations to support their foraging activities in diverse light conditions. [ABSTRACT FROM AUTHOR]

Increased orbit size is suggested to be an adaptation for enhanced visual acuity and sensitivity in conditions of reduced light quality. Whilst light ambience has a well established correlation with eye size in birds and primates, evidence in humans is very limited. The aim of this study was to analyse the anatomical compensations of the eye and visual cortex as a result of varying levels of light exposure. It was hypothesized that humans of higher latitudes will have an increased orbit size to improve visual sensitivity and acuity in conditions of decreased light, and thus greater cranium size due to enlarged visual cortices. Craniometric measurements of 1,209 male and 1,021 female individuals from 27 series coming from different latitudes were sourced from William W. Howells Craniometric Data Set. Mean cranial and orbit size was calculated by combining linear craniometric measurements of length, width and height for individual males and females at each latitude. Linear regressions of orbit and cranial size on latitude were created and significance was measured using Pearson’s r and P value. Partial correlations were calculated to test whether orbit size correlates with latitude independent of cranial size. Significant positive correlations were found between i) orbit and cranial size and ii) orbit size and latitude and iii) cranial size and latitude in males and females. Additionally, partial correlation values for latitude and orbit size were significant in both males and females. The relationship between visual system size and increasing latitude among humans is currently understudied. Significant relationships between visual system size and increasing latitude suggest that enlarged eyes were an evolutionary mechanism for individuals with compromised light availability. Other factors related to varying geographic location may also play a role

Acuity, the fineness with which sensory systems perceive and parse information, limits the information that organisms can extract from stimuli. Here, we focus on visual acuity (the ability to perceive static spatial detail) to discuss relationships between acuity and signal form and evolution. Research suggests that acuity varies by orders of magnitude across species, and that most animals have much lower acuity than humans. Thus, hypotheses regarding the function of spatial patterns must account for the acuity of relevant viewers. New data quantifying acuity in a range of taxa allow us to examine correlations between acuity and ecology, elucidate the selective forces that receiver acuity places on signal evolution, and examine how signals might appear to viewers with different acuities. [ABSTRACT FROM AUTHOR]

During the long migration from river habitats to the spawning ground, the Japanese eel undergoes sexual maturation. This spawning migration occurs concurrently with morphological changes, such as increases in eye size; however, the mechanisms by which sex steroids and their receptors influence these changes in peripheral tissues remain unclear. The aim of this study was to investigate changes in the eyes of female Japanese eels during sexual maturation, and our research focused on estrogen receptor (ER)α and ERβ transcripts. During ovarian development, the gonadosomatic index increased and yolk-laden oocytes developed rapidly. These changes occurred in conjunction with a steady increase in plasma levels of estradiol-17β (E2). Concomitant increases in transcript levels of ERα and ERβ in eye, brain, pituitary, and ovary were also observed. Fluorescence in-situ hybridization analyses revealed that ERα and ERβ transcripts were present in the choriocapillary layer and photoreceptor layer of the eyes, and the analysis also revealed that their signals in these layers became stronger in mature females compared to those observed in immature females, suggesting that under the influence of gonadotropins, morphological changes in the eyes are regulated by E2 through the activation of its receptors. In conclusion, E2 plays a crucial role in physiological adaptations that occur in peripheral tissues during the spawning migration.

Animals employ different sexual signal modes (e.g. visual, acoustic, chemical) in different environments and behavioural contexts. If sensory structures are costly, then evolutionary shifts in primary signal mode should be associated with changes in sensor morphology. Further, sex differences are expected if male and female signalling behaviours differ. Fireflies are known for their light displays, but many species communicate exclusively with pheromones, including species that recently lost their light signals. We performed phylogenetically controlled analyses of male eye and antenna size in 46 North American taxa, and found that light signals are associated with larger eyes and shorter antennae. In addition, following a transition from nocturnal light displays to diurnal pheromones, eye size reductions occur more rapidly than antenna size increases. In agreement with the North American taxa, across 101 worldwide firefly taxa in 32 genera, we found light displays are associated with larger eye and smaller antenna sizes in both males and females. For those taxa with both male and female data, we found sex differences in eye size and, for diurnal species, in antenna size. [ABSTRACT FROM AUTHOR]

The visual system is highly variable across species, and such variability is a key factor influencing animal behavior. Variation in the visual system, for instance, can influence the outcome of learning tasks when visual stimuli are used. We illustrate this issue in guppies ( Poecilia reticulata) artificially selected for large and small relative brain size with pronounced behavioral differences in learning experiments and mate choice tests. We performed a study of the visual system by quantifying eye size and optomotor response of large-brained and small-brained guppies. This represents the first experimental test of the link between brain size evolution and visual acuity. We found that female guppies have larger eyes than male guppies, both in absolute terms and in relation to their body size. Likewise, individuals selected for larger brains had slightly larger eyes but not better visual acuity than small-brained guppies. However, body size was positively associated with visual acuity. We discuss our findings in relation to previous macroevolutionary studies on the evolution of brain morphology, eye morphology, visual acuity, and ecological variables, while stressing the importance of accounting for sensory abilities in behavioral studies. Significance statement: Pre-existing perceptual biases can be keys for the development of specific behavioral patterns. Hence, potential differences in sensory systems need to be taken into account in the study of animal behavior. We highlight this necessity concentrating on the visual domain and using experimental data on brain size-selected guppies in which we assessed eye size and visual acuity. Behavioral differences between large-brained and small-brained guppies in learning and mate choice predominantly relied on tests using visual cues. Analyses of visual capabilities in this system are therefore necessary. Furthermore, this system offers the unprecedented opportunity to experimentally test the relationship between brain size, eye morphology, and visual capabilities. Our results show similar visual acuities between large-brained and small-brained guppies. However, the differences observed in eye area between the sexes, together with the observed positive relationship between body size and visual acuity, highlight the need to incorporate perceptive differences in the study of animal behavior. [ABSTRACT FROM AUTHOR]

Birds with larger eyes are predicted to have higher spatial resolution because of their larger retinal image. Raptors are well known for their acute vision, mediated by their deep central fovea. Because foraging strategies may demand specific visual adaptations, eye size and fovea may differ between species with different foraging ecology. We tested whether predators (actively hunting mobile prey) and carrion eaters (eating dead prey) from the order Accipitriformes differ in eye size, foveal depth, and retinal thickness using spectral domain optical coherence tomography and comparative phylogenetic methods. We found that (1) all studied predators (except one) had a central and a temporal fovea, but all carrion eaters had only the central fovea; (2) eye size scaled with body mass both in predators and carrion eaters; (3) predators had larger eyes relative to body mass and a thicker retina at the edge of the fovea than carrion eaters, but there was no difference in the depth of the central fovea between the groups. Finally, we found that (4) larger eyes generally had a deeper central fovea. These results suggest that the visual system of raptors within the order Accipitriformes may be highly adapted to the foraging strategy, except for the foveal depth, which seems mostly dependent upon the eye size. [ABSTRACT FROM AUTHOR]

Objective To (i) correlate B-mode ocular ultrasound ( US) and computed tomography ( CT) (prospective pilot study), (ii) establish a reliable method to measure the normal canine eye using CT, (iii) establish a reference guide for some dog breeds, (iv) compare eye size between different breeds and breed groups, and (v) investigate the correlation between eye dimensions and body weight, gender, and skull type (retrospective study). Procedure B-mode US and CT were performed on ten sheep cadaveric eyes. CT biometry involved 100 adult pure-bred dogs with nonocular and nonorbital disease, representing eleven breeds. Eye length, width, and height were each measured in two of three planes (horizontal, sagittal, and equatorial). Results B-mode US and CT measurements of sheep cadaveric eyes correlated well (0.70-0.71). The shape of the canine eye was found to be akin to an oblate spheroid (a flattened sphere). A reference guide was established for eleven breeds. Eyes of large breed dogs were significantly larger than those of medium and small breed dogs ( P < 0.01), and eyes of medium breed dogs were significantly larger than those of small breed dogs ( P < 0.01). Eye size correlated with body weight (0.74-0.82) but not gender or skull type. Conclusions Computed tomography is a suitable method for biometry of the canine eye, and a reference guide was established for eleven breeds. Eye size correlated with breed size and body weight. Because correlation between B-mode US and CT was shown, the obtained values can be applied in the clinical setting, for example, for the diagnosis of microphthalmos and buphthalmos. [ABSTRACT FROM AUTHOR]

Objective Ocular function is fundamental for environmental adaptation and survival capacity. Growth factors are necessary for a mature eyeball, needed for adequate vision. However, the consequences of the deficiency of circulating growth hormone (GH) and its effector insulin-like growth factor I (IGF-I) on the physical aspects of the human eye are still debated. A model of untreated isolated GH deficiency (IGHD), with low but measurable serum GH, may clarify this issue. The aim of this study was to assess the ocular aspects of adult IGHD individuals who have never received GH therapy. Design Cross sectional study. Methods Setting : University Hospital, Federal University of Sergipe, Brazil. Patients : Twenty-five adult (13 males, mean age 50.1 years, range 26 to 70 years old) IGHD subjects homozygous for a null mutation (c.57 + 1G > A) in the GHRH receptor gene, and 28 (15 males, mean age 51.1 years, range 26 to 67 years old) controls were submitted to an endocrine and ophthalmological assessment. Forty-six IGHD and 50 control eyes were studied. Main outcome measures : Visual acuity, intraocular pressure, refraction (spherical equivalent), ocular axial length (AL), anterior chamber depth (ACD), lens thickness (LT), vitreous depth (VD), mean corneal curvature (CC) and central corneal thickness (CCT). Results IGHD subjects exhibited unmeasurable serum IGF-I levels, similar visual acuity, intraocular pressure and LT, higher values of spherical equivalent and CC, and lower measures of AL, ACD, VD and CCT in comparison to controls, but within their respective normal ranges. While mean stature in IGHD group was 78% of the control group, mean head circumference was 92% and axial AL was 96%. Conclusions These observations suggest mild ocular effects in adult subjects with severe IGF-I deficiency due to non-treated IGHD. [ABSTRACT FROM AUTHOR]

The light environment of the mesopelagic realm of the ocean changes with both depth and viewer orientation, and this has probably driven the high diversity of visual adaptations found among its inhabitants. The mesopelagic ‘cockeyed’ squids of family Histioteuthidae have unusual eyes, as the left and right eyes are dimorphic in size, shape and sometimes lens pigmentation. This dimorphism may be an adaptation to the two different sources of light in the mesopelagic realm, with the large eye oriented upward to view objects silhouetted against the dim, downwelling sunlight and the small eye oriented slightly downward to view bioluminescent point sources. We used in situ video footage from remotely operated vehicles in the Monterey Submarine Canyon to observe the orientation behaviour of 152 Histioteuthis heteropsis and nine Stigmatoteuthis dofleini. We found evidence for upward orientation in the large eye and slightly downward orientation in the small eye, which was facilitated by a tail-up oblique body orientation. We also found that 65% of adult H. heteropsis (n= 69) had yellow pigmentation in the lens of the larger left eye, which may be used to break the counterillumination camouflage of their prey. Finally, we used visual modelling to show that the visual returns provided by increasing eye size are much higher for an upward-oriented eye than for a downward-oriented eye, which may explain the development of this unique visual strategy. [ABSTRACT FROM AUTHOR]