Changes In Eye Size Research Articles

Eye Size Does Not Change with Artificial Selection on Relative Telencephalon Size in Guppies (Poecilia reticulata)

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.

Optimized Signal Flow through Photoreceptors Supports the High-Acuity Vision of Primates

The fovea is a neural specialization that endows humans and other primates with the sharpest vision among mammals. This performance originates in the foveal cones, which are extremely narrow and long to form a high-resolution pixel array. Puzzlingly, this form is predicted to impede electrical conduction to an extent that appears incompatible with vision. We observe the opposite: signal flow through even the longest cones (0.4-mm axons) is essentially lossless. Unlike in most neurons, amplification and impulse generation by voltage-gated channels are dispensable. Rather, sparse channel activity preserves intracellular current, which flows as if unobstructed by organelles. Despite these optimizations, signaling would degrade if cones were lengthier. Because cellular packing requires that cone elongation accompanies foveal expansion, this degradation helps explain why the fovea is a constant, miniscule size despite multiplicative changes in eye size through evolution. These observations reveal how biophysical mechanisms tailor form-function relationships for primate behavioral performance.

The poverty of adult morphology: Bioacoustics, genetics, and internal tadpole morphology reveal a new species of glassfrog (Anura: Centrolenidae: Ikakogi) from the Sierra Nevada de Santa Marta, Colombia.

Ikakogi is a behaviorally and morphologically intriguing genus of glassfrog. Using tadpole morphology, vocalizations, and DNA, a new species is described from the Sierra Nevada de Santa Marta (SNSM), an isolated mountain range in northern Colombia. The new taxon is the second known species of the genus Ikakogi and is morphologically identical to I. tayrona (except for some larval characters) but differs by its genetic distance (14.8% in mitochondrial encoded cytochrome b MT-CYB; ca. 371 bp) and by the dominant frequency of its advertisement call (2928–3273 Hz in contrast to 2650–2870 Hz in I. tayrona). They also differ in the number of lateral buccal floor papillae, and the position of the buccal roof arena papillae. Additionally, the new species is differentiated from all other species of Centrolenidae by the following traits: tympanum visible, vomerine teeth absent, humeral spines present in adult males, bones in life white with pale green in epiphyses, minute punctuations present on green skin dorsum, and flanks with lateral row of small, enameled dots that extend from below eye to just posterior to arm insertion. We describe the external and internal larval morphology of the new species and we redescribe the larval morphology of Ikakogi tayrona on the basis of field collected specimens representing several stages of development from early to late metamorphosis. We discuss the relevance of larval morphology for the taxonomy and systematics of Ikakogi and other centrolenid genera. Finally, we document intraspecific larval variation in meristic characters and ontogenetic changes in eye size, coloration, and labial tooth-rows formulas, and compare tadpoles of related species. Ikakogi tayrona has been proposed as the sister taxon of all other Centrolenidae; our observations and new species description offers insights about the ancestral character-states of adults, egg clutches, and larval features in this lineage of frogs.

A scalable and deformable stylized model of the adult human eye for radiation dose assessment

With recent changes in the recommended annual limit on eye lens exposures to ionizing radiation, there is considerable interest in predictive computational dosimetry models of the human eye and its various ocular structures including the crystalline lens, ciliary body, cornea, retina, optic nerve, and central retinal artery. Computational eye models to date have been constructed as stylized models, high-resolution voxel models, and polygon mesh models. Their common feature, however, is that they are typically constructed of nominal size and of a roughly spherical shape associated with the emmetropic eye. In this study, we present a geometric eye model that is both scalable (allowing for changes in eye size) and deformable (allowing for changes in eye shape), and that is suitable for use in radiation transport studies of ocular exposures and radiation treatments of eye disease. The model allows continuous and variable changes in eye size (axial lengths from 20 to 26 mm) and eye shape (diopters from −12 to +6). As an explanatory example of its use, five models (emmetropic eyes of small, average, and large size, as well as average size eyes of −12D and +6D) were constructed and subjected to normally incident beams of monoenergetic electrons and photons, with resultant energy-dependent dose coefficients presented for both anterior and posterior eye structures. Electron dose coefficients were found to vary with changes to both eye size and shape for the posterior eye structures, while their values for the crystalline lens were found to be sensitive to changes in only eye size. No dependence upon eye size or eye shape was found for photon dose coefficients at energies below 2 MeV. Future applications of the model can include more extensive tabulations of dose coefficients to all ocular structures (not only the lens) as a function of eye size and shape, as well as the assessment of x-ray therapies for ocular disease for patients with non-emmetropic eyes.

Sex-biased response in activity to light sources with different spectral composition in geometrid moths with flightless females (Lepidoptera: Geometridae)

Geometrid moths occurring in late autumn and early spring in temperate forest habitats are often harmful defoliators of deciduous stands. Their populations can cause locally cyclic outbreaks and thus preventive monitoring actions have been developed, mainly based on pheromone attraction of males. Females are mostly flightless with reduced or lost wings and reduced senses associated with flying. Males are standard flyers with well-developed eyes and must be able to deal with rapidly changing light conditions during their activity. Although such differences indicate sex-biased differences in reactions to light, this has been insufficiently tested. In conditions of an experimental arena and using light-emitting diodes, we tested the different reactions of the sexes for nine species to precisely defined short segments of the electromagnetic spectrum in the range 360-660 nm. Across all species, males preferred shorter wavelengths up to 500 nm, while females were nonselective and generally less active. The sexes differed by eye size and body mass, with males having significantly larger eyes and lower body mass. Between brachypterous and apterous females, the former had larger eye size, while body mass differences were statistically insignificant. There were differences between the sexes in move-to-light reactions and changes in eye size and body mass in line with wing reduction. While males preferred a relatively distinct range of shorter wavelengths, a method of attraction to lights with distinct narrow spectra could be used markedly to enhance the established methods of forest pest monitoring, either alone or in combination with chemical male attraction.

Selection on incremental variation of eye size in a wild population of Daphnia.

Several studies of eye morphology have analysed macroevolutionary patterns in the diversity of eyes, and although these studies are often linked to environment or behaviour, they provide only indirect evidence of selection. Specific data to show the microevolutionary potential for adaptation by natural selection in eye morphology have been lacking. We document directional selection on eye size, an important determinant of visual capabilities, in a wild population of the freshwater microcrustacean Daphnia. We show that even slight changes in eye size may have major consequences for fitness. An increase in eye diameter of 19.9μm - slightly more than one standard deviation - is associated with an increase in clutch size of one egg, or an increase of nearly 20% of the mean clutch size. Furthermore, relative eye size is genetically variable and thus could evolve in response to the observed selective pressure. We conclude that selection on incremental variation in eye size may have led to differences observed on broader taxonomic scales.

Changes in Body Weight and Eye Size in Female European Eel Kept in Fresh and Salt Water

The eel is a catadromous fish which spends most of its life in freshwater and adults swim to the Sargasso Sea region to spawn. While preparing for the reproductive process, eels undergo a metamorphosis to become what is called silver eel; a process involving changes in the colour and weight of the body and an increase in the eye size. These are indicators of fish maturity and they facilitate the selection of fish for reproduction under controlled conditions. During this study, changes in the body weight (BW) and eye size in female European eel were observed while being given weekly hormonal injections of 20 mg kg–1 carp pituitary homogenate and kept in 15°C freshwater and in 15°C saltwater with a salinity of 32-33‰. Fish kept in saltwater but not subjected to hormonal stimulation were used as a control group. Furthermore, after the experiment was finished, females in the control group were kept for next 5 months, with the same environmental parameters maintained. Differences between the treated groups were observed as early as week 4 of the experiment. An increase in fish BW was observed in fish kept both in salt and freshwater which were subjected to hormonal stimulation. On the other hand, changes in eye size were observed in the fish kept in saltwater, both in those hormonally stimulated and otherwise. The eye diameter in the fish kept in fresh after hormonal stimulation did not change significantly.

Genetic and developmental analysis of differences in eye and face morphology between Drosophila simulans and Drosophila mauritiana

Eye and head morphology vary considerably among insects and even between closely related species of Drosophila. Species of the D. melanogaster subgroup, and other Drosophila species, exhibit a negative correlation between eye size and face width (FW); for example, D. mauritiana generally has bigger eyes composed of larger ommatidia and conversely a narrower face than its sibling species. To better understand the evolution of eye and head morphology, we investigated the genetic and developmental basis of differences in eye size and FW between male D. mauritiana and D. simulans. QTL mapping of eye size and FW showed that the major loci responsible for the interspecific variation in these traits are localized to different genomic regions. Introgression of the largest effect QTL underlying the difference in eye size resulted in flies with larger eyes but no significant difference in FW. Moreover, introgression of a QTL region on the third chromosome that contributes to the FW difference between these species affected FW, but not eye size. We also observed that this difference in FW is detectable earlier in the development of the eye-antennal disc than the difference in the size of the retinal field. Our results suggest that different loci that act at different developmental stages underlie changes in eye size and FW. Therefore, while there is a negative correlation between these traits in Drosophila, we show genetically that they also have the potential to evolve independently and this may help to explain the evolution of these traits in other insects.

The choroid as a sclera growth regulator

Emmetropization is a vision dependent mechanism that attempts to minimize refractive error through coordinated growth of the cornea, lens and sclera such that the axial length matches the focal length of the eye. It is generally accepted that this visually guided eye growth is controlled via a cascade of locally generated chemical events that are initiated in the retina and ultimately cause changes in scleral extracellular matrix (ECM) remodeling which lead to changes in eye size and refraction. Of much interest, therefore, are the molecular mechanisms that underpin emmetropization and visually guided ocular growth. The choroid, a highly vascularized layer located between the retina and the sclera is uniquely situated to relay retina-derived signals to the sclera to effect changes in ECM synthesis and ocular size. Studies initiated by Josh Wallman clearly demonstrate that the choroid plays an active role in emmetropization, both by modulation of its thickness to adjust the retina to the focal plane of the eye (choroidal accommodation), and well as through the release of growth factors that have the potential to regulate scleral extracellular matrix remodeling. His discoveries prompted numerous investigations on the molecular composition of the choroid and changes in gene expression associated with visually guided ocular growth. This article will review molecular and functional studies of the choroid to provide support for the hypothesis that the choroid is a source of sclera growth regulators that effect changes in ocular growth in response to visual stimuli.

Observations on the ultrastructure of equatorial scleral collagen fibrils in sheep eyes

To investigate collagen fibrils of the equatorial sclera in relation to the age-related changes in eye size in sheep. Lambs and outbred ewes. Sheep eyes (three lamb and three from adult outbred ewes), presumed disease-free, were processed for transmission electron microscopy (TEM) immediately postmortem. Tissue blocks from the equatorial region were sectioned across fibril bundles orientated along the equator. Micrographs including at least 500 fibrils were projected at 22,000× magnification for measures of fibril diameters (FDs). Lamb eyes were smaller than those of adult ewes but equatorial scleral thickness was only marginally less at 0.232±0.013 vs. 0.254±0.012 mm (P value not significant). Scleral tissue was composed of compacted bundles of collagen fibers that tended to be rounder in outer compared to being flatter in inner regions. In typical (normal) appearing regions, FDs were distinctly larger (68-410 nm) in outer sclera compared to inner sclera (63-281 nm). Outer sclera FDs were bimodal averaging 192±58 nm, compared to unimodal distributions at inner locations averaging 156±48 nm (P<0.001). Some atypical regions, especially at outer-mid sclera locations, were also noted where the FD distribution was bimodal but also included numerous microfibrils (<50 nm diameter), with similar appearances being found for both lamb and adult ewe eyes. The equatorial sclera is a mixture of rounder versus flatter collagen fiber bundles, the former being more likely to be made up of a mixture of both smaller and larger fibrils, as compared to slightly smaller fibrils.

Postnatal Elongation of Eye Size in DBA/2J Mice Compared with C57BL/6J Mice: In Vivo Analysis with Whole-Eye OCT

To characterize postnatal changes in eye size in glaucomatous DBA/2J (D2) mice and in nonglaucomatous C57BL/6J mice (B6) in vivo by means of whole-eye optical coherence tomography (OCT). D2 (n = 32) and B6 (n = 36) mice were tested between 2 and 20 months of age in eight age bins. A custom time-domain OCT system with a center wavelength of 825 nm and an axial scan length of 7.1 mm produced axial A-scan interferograms at a rate of 20 A-lines/s with a resolution of 8 μm. Axial length (AL), corneal thickness (CT), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and retinal thickness (RT) were measured in the optical axis and adjusted with corresponding refractive indices. Corneal curvature (CC) and IOP were also measured. AL increased (P < 0.001) more in the D2 (21%) than in the B6 (9%) mice. There was an interaction effect (two-way ANOVA, P < 0.001) between age and strain for AL, CT, ACD, and VCD. In the D2 mice, the lens became dislocated posteriorly. Multiple regression analysis in the D2 mice revealed an independent effect of age and IOP (P ≤ 0.01) on axial length. CC steepened in the older D2 mice, whereas it flattened in the B6 mice. In D2 mice, postnatal elongation of AL is larger than that in B6 mice and is associated with a greater increase in ACD and IOP, which seems to be a causal factor. The ease of use, short acquisition time, and noninvasiveness of whole-eye OCT make it suitable for routine use in longitudinal studies of mouse models.

Change in Embryonic Eye Size and Retinal Cell Proliferation following Intravitreal Injection of Glycosaminoglycans

The vitreous body (VB) is a transparent, extracellular matrix structure that fills the vitreous cavity of the eye. Major constituents of the VB are hyaluronic acid (HA) and glycosaminoglycans (GAGs), both of which are highly charged, linear carbohydrate polymers. The present experiments investigate a possible role of HA and GAGs in regulating eye size during development and investigate whether changes in eye size are synchronized with cell proliferation in the retina. Chondroitin sulfate (CS), heparan sulfate (HS), heparin (Hep), dextran sulfate (DexS), and HA were injected into the vitreous cavity of embryonic day 5 chick embryos. Eye size was assessed 1 to 5 days after the injections. Cell counts and BrdU labeling established whether changes in eye size were paralleled by an increase or a decrease in retinal cell proliferation. Injection of CS and HS led to an increase in eye size that was accompanied by a similar increase in retinal cell numbers. Hep and DexS injections led to a decrease in eye size that had no impact on cell proliferation in the retina. HA application had no effect on eye size. The changes in eye size after intravitreal application of GAGs demonstrate that the composition of the VB can play an important role in the regulation of eye size during embryogenesis. The fact that retinal cell proliferation is elevated after an increase in eye size indicates a regulatory role of eye size for retinal cell numbers.

Evolution of eye size and shape in primates

Strepsirrhine and haplorhine primates exhibit highly derived features of the visual system that distinguish them from most other mammals. Comparative data link the evolution of these visual specializations to the sequential acquisition of nocturnal visual predation in the primate stem lineage and diurnal visual predation in the anthropoid stem lineage. However, it is unclear to what extent these shifts in primate visual ecology were accompanied by changes in eye size and shape. Here we investigate the evolution of primate eye morphology using a comparative study of a large sample of mammalian eyes. Our analysis shows that primates differ from other mammals in having large eyes relative to body size and that anthropoids exhibit unusually small corneas relative to eye size and body size. The large eyes of basal primates probably evolved to improve visual acuity while maintaining high sensitivity in a nocturnal context. The reduced corneal sizes of anthropoids reflect reductions in the size of the dioptric apparatus as a means of increasing posterior nodal distance to improve visual acuity. These data support the conclusion that the origin of anthropoids was associated with a change in eye shape to improve visual acuity in the context of a diurnal predatory habitus.

Effects of activity pattern on eye size and orbital aperture size in primates

Among primates, nocturnal species exhibit relatively larger orbital apertures than diurnal species. Most researchers have considered this disparity in orbital aperture size to reflect differences in eye size, with nocturnal primates having relatively large eyes in order to maximize visual sensitivity. Presumed changes in eye size due to shifts in activity pattern are an integral part of theoretical explanations for many derived features of anthropoids, including highly convergent orbits and a postorbital septum. Here I show that despite clear differences in relative orbital aperture size, many diurnal and nocturnal primates do not differ in relative eye size. Among nocturnal primates, relative eye size is influenced by diet. Nocturnal visual predators (e.g., Tarsius, Loris, and Galago moholi) tend to have larger relative eye sizes than diurnal primates. By contrast, nocturnal frugivores (e.g., Perodicticus, Nycticebus, and Cheirogaleus) have relative eye sizes that are comparable to those of diurnal primates. Although some variation in orbital aperture size can be attributed to variation in eye size, both cornea size and orbit orientation also exert a strong influence on orbital aperture size. These findings argue for caution in the use of relative orbital aperture size as an indicator of activity pattern in fossil primates. These findings further suggest that existing scenarios for the evolution of unique orbital morphologies in anthropoids must be modified to reflect the importance of ecological variables other than activity pattern.

The role of visual information in the control of scleral matrix biology in myopia

Changes in eye size during the development of refractive error are accompanied by alterations in scleral biochemistry in both humans and animal models of myopia. This review discusses more recent data on scleral changes in mammalian models of myopia and considers the role of visual information in the control of scleral matrix biology. These visually-driven changes in scleral biochemistry are placed in the context of both the emmetropisation process and the abnormal enlargement of the eye that is characteristic of human high myopia.

Connexin α1 and Cell Proliferation in the Developing Chick Retina

During the formation of the eye, high levels of connexin α1 (connexin 43) are expressed within the tissues of the cornea, lens, and neural retina. In order to determine whether connexin α1 plays a role in the regulation of cell proliferation we have used a novel antisense technique to reduce its expression early in development (embryonic days 2–4). Application of Pluronic gel, containing antisense oligodeoxynucleotides (ODNs) to connexin α1, to one eye of early chick embryos results in a rapid and significant reduction of α1 protein which lasts for 24–48 h. Embryos grown for 48 h, after ODN application to one eye, showed a marked reduction in the diameter of the treated, compared to that of the contralateral untreated, eye. Sections cut from the treated eyes showed that the retina was also reduced in size. TUNEL labeling and staining with propidium iodide showed that apoptosis within the retinae of both treated and untreated eyes was rare and thus that the reduction in the area of the retina brought about by antisense ODNs directed at connexin α1 was unlikely to be the result of increased cell death. However, the number of mitotic figures in the ventricular zone of the antisense-treated retinae revealed by propidium iodide staining was significantly reduced (P<0.0001) to 53 ± 3.5% (n=5) of that in the contralateral untreated control eyes. Embryos in which one eye was sham operated, treated with pluronic gel, or treated with sense ODN showed no significant changes in eye size or in the number of mitotic figures within the neural retina. These results point to a role for connexin α1-mediated gap-junctional communication in controlling the early wave of neurogenesis in the chick retina.

Ophthalmic changes from age of 10 to 18 years. A longitudinal study of sequels to low birth weight. IV. Ultrasound oculometry of vitreous and axial length.

The present report on vitreous and axial length completes an analysis of changes in eye size during adolescence. The sample is divided into 70 with low birth weight (less than 2000 g) and 67 full-term controls (FT). 1) Contrary to classical statements regarding early arrest of eye growth, a basic 'pubertal' axial growth of about 0.4-0.5 mm is found in refractively static eyes. Eyes with progressive myopia elongate even more, due mainly to vitreous elongation. 2) The previously reported 10-year LBW ocular size deficit remains an adult feature, even in seemingly normal eyes. There is a parallel permanent lack of catching-up also regarding height, head circumference, and some other anthropometric parameters. 3) Two classical rules of thumb are discussed: a) 1 mm axial length change coincides with 3 D refractive change, and b) that of 24 mm as the emmetropic eye length. Although tenacious, bot statements have to be modified--according to biological variation and the weak correlation between most refractive parameters.