Guanine and its retinal distribution in the tapetum of the bigeye tuna,thunnus obesus

The eye of the bigeye tuna (Thunnus obesus) contains a retinal tapetum composed of guanine. The total amount of the guanine in one eye of the fish (SL=120 cm) was about 88.6 mg. The mean guanine content of the tapetum was approximately 1.25 mg/cm² of the retinal surface. The highest content of guanine (2.15 mg/cm²) was observed only in the ventro-temporal part of the retina. To distinguish this area from the rest of the eye, we suggested the term ‘locus tapetalis’ for it. The visual accommodation system clearly indicated that the visual axis of the fish is upper-forward and the resulting retinal area for acute vision was suggested to be in the ventro-temporal retina. We discussed that the area centralis of the bigeye tuna may have two functions: to guarantee high visual acuity and to allow for high photo-sensitivity in dim light vision.     

Ontogenetic eye development and related behavioural changes in larvae and juveniles of barramundi Lates calcarifer (Bloch)

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the onset of the first feeding at 2 days, the shift of habitat from coastal waters to swamps at the notochord flexion stage at 7–15 days, the abrupt change in feeding behaviour from roving zooplanktivore to lurking predator at 25–30 days and a later shift of habitat from turbid swamps to open coastal or lake areas at the early juvenile stage.     

Guanine-type retinal tapetum in the eye of the Pacific pomfret <Emphasis Type="Italic">Brama japonica</Emphasis> (Perciformes: Bramidae)

The eye of Brama japonica, which exhibits eyeshine, contains a retinal tapetum composed of guanine. The total amounts of guanine in the eyes of two specimens measuring 19.5 and 51.4cm in standard length were 7.4 and 70.5mg, respectively, the respective retinal surface areas being 4.9 and 39.9cm². The mean guanine content was almost identical (1.5 and 1.8mg/cm², respectively). A locus tapetalis, with guanine values exceeding 2.5mg/cm², was developed in the ventrotemporal region of the retina, where it cooccurred with the area centralis. Evidence is presented that sound functional reasons exist for both the development of the locus tapetalis and its position in the retina. A plea is made for future examination of the retinae of additional pelagic and nonpelagic species for the presence and location of a locus tapetalis.     

Guanine-Type retinal tapetum of three species of mormyrid fishes

The eye of mormyrid fishes (Marcusenius andGnathonenius) contains a retinal tapetum composed of guanine crystals. InMarcusenius, the quantity of guanine is about 2 mg cm^?2 of the retinal surface area. The retina is duplex, and the cones and rods are grouped in bundles. Each bundle is surrounded by pigment epithelial cell processes which contain numerous guanine reflectors. Two kinds of reflector are present: brick-shaped and rodlet. Mormyrids may use their high sensitivity for nocturnal activities. The retinal features of mormyrid fishes were compared with those of other fish species belonging to the Notopteroidei such as the Hiodontidae, Notopteridae and Gymnarchidae, and related to the chemical nature of notopterid and gymnarchid tapetum.     

Low oxygen consumption in the inner retina of the visual streak of the rabbit

The oxygen requirements of different retinal layers are of interest in understanding the vulnerability of the retina to hypoxic damage in retinal diseases with an ischemic component. Here, we report the first measurements of retinal oxygen consumption in the visual streak of the rabbit retina, the region with the highest density of retinal neurons, and compare it with that in the less-specialized region of the retina underlying the vascularized portion of the rabbit retina. Oxygen-sensitive microelectrodes were used to measure oxygen tension as a function of retinal depth in anesthetized animals. Measurements were performed in the region of the retina containing overlying retinal vessels and in the center of the visual streak. Established mathematical analyses of the intraretinal oxygen distribution were used to quantify the rate of oxygen consumption in the inner and outer retina and the relative oxygen contributions from the choroidal and vitreal sides. Outer retinal oxygen consumption was higher in the visual streak than in the vascularized area (means +/- SE, 284 +/- 20 vs. 210 +/- 23 nl O2.min(-1) x cm(-2), P = 0.026, n = 10). However, inner retinal oxygen consumption in the visual streak was significantly lower than in the vascular area (57 +/- 4.3 vs. 146 +/- 12 nl O2 x min(-1) x cm(-2), P < 0.001). We conclude that despite the higher processing requirements of the inner retina in the visual streak, it has a significantly lower oxygen consumption rate than the inner retina underlying the retinal vasculature. This suggests that the oxygen uptake of the inner retina is regulated to a large degree by the available oxygen supply rather than the processing requirements of the inner retina alone.     

The tapetum lucidum in the eye of the big-eye Priacanthus arenatus Cuvier

The big-eye Priacanthus arenatus Cuvier contains a tapetum lucidum or reflector which lies in the inner region of the choroid. It extends over the entire surface of the fundus, and it consists of several layers of reflecting cells. The cells contain many layers of thin guanine crystals, and there is about 0.5 mg of guanine in a square cm of tapetum. The retina is duplex, and rods are small and very numerous. The tapetum of the big-eye is compared with those of selachians and sturgeons, which it much resembles.     

The morphology and topographic distribution of substance-P-like immunoreactive amacrine cells in the cat retina

In cat retinal wholemounts, substance-P-like immunoreactivity (SP-IR) was localized in a distinct population of amacrines whose cell bodies were normally placed in the ganglion cell layer. Although displaced amacrines accounted for 80-95% of the SP-IR amacrines in peripheral retina, this proportion decreased considerably within the area centralis, accounting for 50-80% of the labelled cells at maximum density. The SP-IR cells in both the inner nuclear and ganglion cell layers gave rise to well-defined varicose dendrites of uniform appearance that stratified around 60% depth (S3/S4) of the inner plexiform layer. In addition, sparse fine dendrites in stratum 1 (S1) could sometimes be traced to inner nuclear cells and occasionally to displaced amacrines. The combined SP-IR cell density ranged from less than 50 cells mm-2 in the far periphery to more than 500 cells mm-2 in the area centralis; the maximum density showed little individual variation despite wide differences in the proportion of displaced cells. The 39,000 SP-IR amacrines in a mapped retina had a triangular topographic distribution, with intermediate isodensity lines extending vertically in superior retina and horizontally along both arms of the visual streak. Colocalization experiments established that all SP-IR cells in cat retina showed GABA-like immunoreactivity, and that the SP-IR amacrines were quite distinct from the cholinergic amacrines identified by choline acetyltransferase immunohistochemistry.     

The formation of the area centralis of the retinal ganglion cell layer in the chick

In adult domestic chickens, the neurones in the retinal ganglion cell layer are very unevenly disposed such that there is a sixfold increase in neurone density from the retinal edge to the retinal centre. The formation of the high ganglion-cell-density area centralis was studied on chick retinal wholemounts from the 8th day of incubation (E8) to 4 weeks after hatching (4WAH). The density of viable neurones and the number and the distribution of pyknotic neurones in the ganglion cell layer were estimated across the whole retina. Between E8 and E10, the distribution of neurones in the ganglion cell layer was anisodensitic with 53,000 mm-2 in the centre compared to 34,000 mm-2 in the periphery of the retina. Thereafter, a progressively steeper gradient of neurone density developed, which decreased from 24,000 mm-2 in the retinal centre to 6000 mm-2 at the retinal periphery by 4WAH. Neuronal pyknosis in the ganglion cell layer was observed between E9 and E17. From E11 onwards, consistently more pyknotic neurones were found in the peripheral than in the central retina. It was estimated that over the period of cell death approximately twice as many neurones died per unit area in the retinal periphery than in the centre. Retinal area measurements and estimation of neurone densities in the ganglion cell layer after the period of neurone generation and neurone death indicated differential retinal expansion, with more expansion in the peripheral than in the central retina. These observations allow us to conclude that the formation of the area centralis of the chick retina involves (1) slightly higher cell generation in the retinal centre, (2) higher rate of cell loss in the retinal periphery and (3) differential retinal expansion.     

Does Nocturnality Drive Binocular Vision? Octodontine Rodents as a Case Study

Binocular vision is a visual property that allows fine discrimination of in-depth distance (stereopsis), as well as enhanced light and contrast sensitivity. In mammals enhanced binocular vision is structurally associated with a large degree of frontal binocular overlap, the presence of a corresponding retinal specialization containing a fovea or an area centralis, and well-developed ipsilateral retinal projections to the lateral thalamus (GLd). We compared these visual traits in two visually active species of the genus Octodon that exhibit contrasting visual habits: the diurnal Octodon degus, and the nocturnal Octodon lunatus. The O. lunatus visual field has a prominent 100° frontal binocular overlap, much larger than the 50° of overlap found in O. degus. Cells in the retinal ganglion cell layer were 40% fewer in O. lunatus (180,000) than in O. degus (300,000). O. lunatus has a poorly developed visual streak, but a well developed area centralis, located centrally near the optic disk (peak density of 4,352 cells/mm²). O. degus has a highly developed visual streak, and an area centralis located more temporally (peak density of 6,384 cells/mm²). The volumes of the contralateral GLd and superior colliculus (SC) are 15% larger in O. degus compared to O. lunatus. However, the ipsilateral projections to GLd and SC are 500% larger in O. lunatus than in O. degus. Other retinorecipient structures related to ocular movements and circadian activity showed no statistical differences between species. Our findings strongly suggest that nocturnal visual behavior leads to an enhancement of the structures associated with binocular vision, at least in the case of these rodents. Expansion of the binocular visual field in nocturnal species may have a beneficial effect in light and contrast sensitivity, but not necessarily in stereopsis. We discuss whether these conclusions can be extended to other mammalian and non-mammalian amniotes.     

The position of the retinal area centralis changes with age in Champsocephalus gunnari (Channichthyidae), a predatory fish from coastal Antarctic waters

Histological examinations of the topographical distribution and the area of highest density (the area centralis: AC) of presumed retinal ganglion cells found in the retina in 0- to 6-year-old Champsocephalus gunnari revealed differences between younger and older fish. Individuals of up to 2 years of age had the AC in the temporal retina, whereas in 3-, 4-, 5- and 6-year-old fish it was positioned in the ventro-temporal region of the retina. The main visual axis in the pitch plane of C. gunnari was shown to shift from facing forward to an upward-forward direction during growth, corresponding to the habitat change in this species from pelagic to benthic. Moreover, the AC in 0- to 3-year-old fish was near the retinal periphery, but displaced towards the inner retina in 4- to 6-year-old fish. This means that the visual axis in the horizontal plane of the younger fish was directed towards the frontal sector of vision, while in the older fish a slightly more lateral position was favoured. Therefore, younger fish can be expected to possess superior binocular vision when it comes to prey closely in front of them, but in older fish it seems more important to have a wider visual field to detect prey (and possibly predators) within a greater volume of water.     

Cell death and the creation of regional differences in neuronal numbers.

Regional variations in cell death are ubiquitous in the nervous system. In the retina, cell death in retinal ganglion cells is elevated in the retinal periphery and may be important in setting up the initial conditions that produce central retinal specializations such as an area centralis or visual streak. In central visual system structures, pronounced spatial and spatiotemporal inhomogeneities in cell death are seen both in layers and regions of the lateral geniculate nucleus and superior colliculus; similar indications of inhomogeneities are seen in those nonvisual structures that have been examined. Cell death in the cortex is highly nonuniform, by layer and by cortical area. A variety of possible functions for these regional losses are proposed, in the context of a uniform mechanism for cell death that allows it to assume multiple functions.     

Temporal and mosaic distribution of large ganglion cells in the retina of a daggertooth aulopiform deep-sea fish (Anotopterus pharao)

The daggertooth Anotopterus pharao (Aulopiformes: Anotopteridae) is a large, piscivorous predator that lives within the epipelagic zone at night. In this species, the distribution of retinal ganglion cells has been examined. An isodensity contour map of ganglion cells shows that the cells concentrate in a slightly ventral region of the temporal retina. The region of high ganglion cell density contains 4.07 x 10(3) cells mm(-2), and the resulting visual acuity is 3.5 cycles deg(-1). Outside the area centralis, conspicuously large ganglion cells (LGCs) are observed in the temporal margin of the retina. The LGCs are regularly arrayed, and displaced into the inner plexiform layer. Thick dendrites extend into the outer part (sublamina a) of the inner plexiform layer. In the retinal whole mount, the total number of LGCs is 1590 (90.7 cm specimen), and the mean size of the LGCs is about four times larger than that of the ordinary ganglion cells. The morphological appearance of the LGCs was similar to the off-type alpha cells of the cat retina. The function of these distinctive LGCs is discussed in relation to specific head-up feeding behaviour.     

RETINAL GANGLION CELL SIZE AND DISTRIBUTION PREDICT VISUAL CAPABILITIES OF DALL'S PORPOISE

The structure of the retina, the distribution of ganglion cells, and the extent of the tapetum lucidum were studied in Dall's porpoise ( Phocoenoides dalli ) with the aim of understanding the role vision plays in this species of cetacean. The basic organization of the retina was similar to that of other vertebrates. Average ganglion cell size was 21.5 μm. The distribution of the ganglion cells in the retina was not even and there were two high-density areas, one in the temporal and one in the rostral part of the retina. Retinal resolving power was estimated using a terrestrial animal model incorporating the density of ganglion cells and other morphological data. The resolving power in the right eyes of two individuals was 2.60 and 2.64 cycles per degree. These values were close to those of other oceanic cetaceans, but inferior to those of terrestrial mammals. On the basis of amino acid analyses, it was shown that the choroid tapetum lucidum in Dali's porpoise contained collagen. The tapetum lucidum was thick at the fundal but thin at the peripheral part of the choroid.     

Physical and morphological aspects of the eye of the manatee trichechus inunguis natterer 1883: (Sirenia: Mammalia)

The eyes and aspects of vision of the Amazonian manatee Trichechus inunguis NATTERER 1883: (Sirenia: mammalia) have been examined in five animals, in relation to previous findings for sirenians. This paper presents a review of previous findings confirming those upon gross ocular anatomy, retinal histology and ocular refraction. The confirmation of a primarily rod retina, high receptor: ganglion cell ratio and low refractive error under water were of note. A visual pigment based upon vitamin A₁ and a difference spectrum of λ max at 505 nm was in agreement with Dartnalls nomogram. The findings suggest a retina more suited to low light levels and at best, moderate visual acuity, though motion perception appears present and a low degree of binocular vision possible.     

Peculiarities of the eye morphology and the spectral sensitivity of the retinal photoreceptors of the Pacific saury <Emphasis Type="Italic">Cololabis saira</Emphasis>

This study examines some peculiarities of the eye organization and spectral properties of retinal photoreceptors of the Pacific saury Cololabis saira. The saury has relatively large eyes with a developed accomodation apparatus and an area of enhanced visual acuity (the fovea) in the retina. A specialized pigmented septum is observed in the vitreal cavity, which is supposed to function as a light-shading screen. The retina contains numerous rods and single and double cones arranged in a square mosaic pattern. Microspectrophotometric measurements indicated that their max occurs at 502 (rods), 380 (single cones), and 478/565 (double cones) nm. Such properties can provide color vision in a broad spectral range, including UV light. The peripheral visual apparatus of the Pacific saury is typical of active diurnal predatory fish that inhabit shallow and upper pelagic water layers.     

Vertebrate features revealed in the rudimentary eye of the Pacific hagfish (Eptatretus stoutii)

Hagfish eyes are markedly basic compared to the eyes of other vertebrates, lacking a pigmented epithelium, a lens and a retinal architecture built of three cell layers: the photoreceptors, interneurons and ganglion cells. Concomitant with hagfish belonging to the earliest-branching vertebrate group (the jawless Agnathans), this lack of derived characters has prompted competing interpretations that hagfish eyes represent either a transitional form in the early evolution of vertebrate vision, or a regression from a previously elaborate organ. Here, we show the hagfish retina is not extensively degenerating during its ontogeny, but instead grows throughout life via a recognizable PAX6+ ciliary marginal zone. The retina has a distinct layer of photoreceptor cells that appear to homogeneously express a single opsin of the RH1 rod opsin class. The epithelium that encompasses these photoreceptors is striking because it lacks the melanin pigment that is universally associated with animal vision; notwithstanding, we suggest this epithelium is a homologue of gnathosome retinal pigment epithelium (RPE) based on its robust expression of RPE65 and its engulfment of photoreceptor outer segments. We infer that the hagfish retina is not entirely rudimentary in its wiring, despite lacking a morphologically distinct layer of interneurons: multiple populations of cells exist in the hagfish inner retina and subsets of these express markers of vertebrate retinal interneurons. Overall, these data clarify Agnathan retinal homologies, reveal characters that now appear to be ubiquitous across the eyes of vertebrates, and refine interpretations of early vertebrate visual system evolution.     

The relationship of ocular morphology to feeding modes and activity periods in shallow marine teleosts from New Zealand

Synopsis Thirty one species of shallow water teleosts were captured from the NE coast of New Zealand. Ocular morphology was assessed in terms of eye size, pupil shape, theoretical sensitivity and acuity based on retinal morphology, and regional distribution of photoreceptors within the retina. Eye size was relatively or absolutely larger in carnivores than herbivores. Diurnal planktivores and nocturnal species of small body size maximise vision by having relatively large eyes. Anterior aphakic spaces were present in most of the species examined, and 25% of the species also had posterior aphakic spaces. Theoretical sensitivity was generally higher among nocturnal than diurnal species, however, a number of benthic and pelagic carnivores showed retinal specialization for enhanced sensitivity. Diurnal species displayed high spatial acuity, with maximum acuity occurring in carnivorous species. Crepuscular species had either high or low acuity, whereas that of nocturnal species was generally lower than in diurnal species. Ten species displayed regional variation in rod density, with crepuscular and nocturnal species showing streaks of high rod density in the retina. Eleven species of carnivores displayed regional variation in cone density, with highest density usually occurring in the caudal part of the retina. In most of the species with areas of high cone density, there was a forward visual axis that coincided with the location of the aphakic space, suggestive of accomodation along that axis.     

正常有色素家兔眼的视网膜功能研究

目的通过分析正常有色素家兔的mfERG的特征,了解其视网膜的功能特性。方法对9只兔18眼正常有色素家兔同时检测mfERG,并与正常成人的18只眼的检测结果对照分析。结果正常有色素家兔mfERG的P1波振幅密度三维地形图特点,可见黄斑区高峰,但较人黄斑区高峰为低,其他部分呈颞侧高鼻侧低的斜坡状,象限野mfERG颞侧半可见P1波振幅密度、P1波振幅、N1波振幅比鼻侧增高;也高于正常成人眼的颞侧值。五个环形野mfERG,P1波振幅密度,第1环最大,由1环到5环依次递减,P1和N1波振幅以4环和5环最大;与人相比环1的P1波振幅密度和振幅降低,环4和环5增高。结论兔眼颞侧视网膜功能高于鼻侧。兔眼视网膜存在类人黄斑区,但其黄斑中心视功能不如人眼,中心外视功能高于人眼。     

玻璃体视网膜手术治疗先天性视网膜劈裂及其并发症的临床疗效

目的:评价玻璃体视网膜手术治疗先天性视网膜劈裂及其并发症的临床疗效。方法:选择2009年1月-2012年1月于我院进行玻璃体视网膜手术的先天性视网膜劈裂患者30例(42只眼),患者均接受了闭合式睫状体经扁平部三切口入路保留晶状体的玻璃体切割手术,并分析其术前及术后情况。结果:先天性视网膜劈裂患者中发生孔源性视网膜脱离19眼,牵拉性视网膜脱离8眼,玻璃体积血10眼,同时伴有视网膜脱离和玻璃体积血有5眼;在末次随访时视力提高者有36只眼,占85.71%,无提高者有6只眼,占14.29%;术前平均视力为(0.15±0.09),末次随访时平均视力提高至(0.31±0.16),两者平均视力差异具有统计学意义(t=5.649,P0.001);42只眼视网膜解剖结构复位良好,视网膜平伏;OCT检查结果显示,末次随访时黄斑劈裂平均面积(0.22±0.18)mm2,与术前黄斑劈裂平均面积(1.07±0.52)mm2比较,差异有统计学意义(t=10.011,P0.001),黄斑微囊样改变有改善;随访期间5只眼出现并发症,占11.90%,其中2眼术后发生PVR且伴牵拉性视网膜脱离,2只眼发生白内障,1只眼出现玻璃体积血,术后视网膜解剖均复位良好。结论:玻璃体视网膜手术可以帮助患者进行视网膜解剖复位及提高其先天性视网膜劈裂患者视功能,具有良好的临床疗效。     

Parallel processing of binocular disparity in the cat's retinogeniculocortical pathways

In the cat, parallel streams of information processing have been traced from X-, Y- and W-type retinal ganglion cells to visual cortical areas 17 (X-, Y- and W-type), 18 (Y-type) and 19 (W-type). In the present study we have examined, in the anaesthetized and paralysed adult cat, the role played by X-, Y- and W-subsystems, projecting to areas 17 and 19, in the processing of binocular retinal disparity. The tapetal reflection technique was used to monitor residual eye movements and to provide a map, for each eye, of the retinal blood vessels which could later be compared with retinal wholemounts stained with cresyl violet to reveal the area centralis. The receptive-field disparities of cells recorded from areas 17 and 19 were compared with each other and with reference to the visual axes defined by the area centralis of each eye. Cells of area 19 (receiving W-type input) had horizontal receptive-field disparities that were significantly more divergent than those of the cells in area 17 and 17-18 'border region'. Referred to the area centralis, the mean horizontal receptive-field disparity in area 19 was -0.5 degrees (+/- 0.8 degrees). The mean horizontal receptive-field disparity of area 17 (receiving X-, Y- and W-type input) was convergent with respect to the visual axis at +2 degrees (+/- 0.5 degrees). Finally, the mean horizontal receptive-field disparity of the cells in the 17-18 border region (which receive mainly Y-type input) was even more convergent (2.6 degrees +/- 1.5 degrees) than that of area 17. Binocular interactions of cortical neurons were tested with the Risley biprism technique. Area 19 cells had maximal responses to binocular stimulation when the receptive-field disparities were either close to zero or slightly divergent. In contrast, area 17 cells tended to respond optimally to disparities that were either slightly or strongly convergent. At the level of the lateral geniculate nucleus there were significant differences between the receptive-field disparities inferred from the comparison of receptive-field positions of adjacent neurons recorded on either side of the border between the A and A1 geniculate laminae and those inferred from a similar comparison at the C1-C2 border. The mean horizontal disparities inferred from the interlaminar comparison at the A-A1 border were +2.1 degrees (+/- 0.3 degrees); those inferred from the interlaminar comparison at the C1-C2 border -0.2 (+/- 0.2 degrees) were more divergent.(ABSTRACT TRUNCATED AT 400 WORDS)