Geometrical optics of a galatheid compound eye

The eyes of galatheid squat lobsters (Munida rugosa) are shown to be of the reflecting superposition type. In the dark-adapted state corneal lenses focus light at the level of the rhabdoms and light from more than 1000 facets is redirected to the superposition focus by the reflecting surfaces of the crystalline cones. When the eye is light adapted, apposition optics are used. In this state paraxial light is focused by the corneal lens and the parabolic proximal end of the cone onto the distal end of a rhabdomeric lightguide. The latter transmits light across the clear zone to the rhabdom layer. In the dorsal part of the eye the individual ommatidia become progressively shorter until the cones and rhabdoms are no longer separated by a clear zone. Although formerly considered to be developing ommatidia, they are shown to be retained specifically for scanning the downwelling irradiance.Abbreviations RI refractive index - SEM scanning electron microscope     

Superposition optics and the time of flight in onitine dung beetles

Dung beetles fly to fresh dung, with vision essential for flight navigation. The daily period of flight varies among different species: some beetles fly only in sunlight, others only when ambient light levels change rapidly during dusk or dawn and others in the constant dark of night. Measurements of the optical properties of the lenses, eye geometry and photoreceptor dimensions were used in a computer ray-tracing model to determine the optical performance of the superposition eyes of nine species of onitine dung beetles. Eye sensitivity to light is determined mainly by body size, by the refractive-index parameters and size of the crystalline cones, and by the photoreceptor dimensions. Based on the optics of the ommatidial lenses and absorption of light in the retina, the most sensitive eyes, found in the crepuscular-nocturnal beetles, are 85 times or nearly two log units more sensitive than the eyes of the diurnal beetles. Three possible criteria are considered to determine the best position for the retina: maximum amount of light absorbed in the target rhabdom; maximum amount of light falling on the target rhabdom (best focus); and maximum resolution. The structure and physiological optics of the superposition compound eyes of an onitine dung beetle are matched to the range of light intensities at which it flies. Accepted: 4 February 1998     

The ultrastructure of the compound eye of Munida rugosa (Crustacea: Anomura) and pigment migration during light and dark adaptation

The galatheid squat lobster, Munida rugosa, has compound eyes of the reflecting superposition type in which a distal cone cell layer and a proximal rhabdom layer are separated by an extensive clear zone. The eye is shown to have certain unique features. In all other reflecting superposition eyes, the clear zone is traversed by crystalline tracts formed by the cone cells. In M. rugosa a thin distal rhabdom thread, formed by the eighth retinula cell, connects the cones to the proximal fusiform rhabdoms. The cytoplasm of the other retinula cells also crosses the clear zone in a complex pattern. Fully light-adapted ommatidia are optically isolated by limited migrations of distal shielding pigments. A reflecting pigment multilayer lines each cone to facilitate the formation of a superposition image. This also shows a light-induced change which may limit the acceptance angle of the eye during light adaptation.     

北京萤火虫复眼的光学成像*

本文利用光学成像方法,研究了不同适应状态下的北京萤火虫phrococelia Pekininsis复眼所成的光学重叠像以及复眼的视场角。不同适应状态的晶体柱都能在距离复眼表面300-350μm之处形成光学重叠像。经过暗适应的晶体柱可以对不同物距的目标形成清晰的正重叠像,像的大小随物距的增大而减小;经明适应的晶体柱,成像物距范围变小,重叠像的像面亮度降低;经过漂白处理的晶体柱只能对一定的物距成像,像面亮度最低。 不同数目的晶体柱都能形成一重叠像,并随着其数目的增加,像面亮度也逐渐增强。根据对局部复眼视场范围的观察和其结构特征的了解,认为萤火虫单个复眼的视场角大于180度。     

Interspecific variations in the morphology and ultrastructure of the rhabdoms of oplophorid shrimps

Interspecific variations in rhabdom structure between various oplophorid shrimps are described and the differences are related to the light environment at different depths within the mesopelagic zone. The ultrastructure of the distal rhabdom in these species is described for the first time. Quantitative measurements show that the proportion of the rhabdom layer occupied by the distal rhabdom varies from 3.5-25% in the dorsoventral plane of the eye of Systellaspis debilis. The distal rhabdom occupies less than 1% of the rhabdoms in the eye of Acanthephyra pelagica, where it can only be seen by using the electron microscope. It is suggested that the rhabdoms of those species that remain within the photic zone (such as S. debilis) are adapted to maximize contrast, whereas in those whose depth ranges extend into the aphotic zone (such as A. pelagica) they are adapted for maximum sensitivity.     

Structure of the dorsal eye region of the moth,Adoxophyes reticulana Hb. (Lepidoptera : Tortricidae)

Ommatidia of the eucon compound eye of Adoxophyes reticulana (Lepidoptera : Tortricidae) were investigated elect ronmicroscopically. The dorsofrontal part and the dorsal rim region were examined in serial sections. Seven radially arranged retinula cells RC₁₋₇ form the rhabdom from distal to proximal region (Fig. 1). The 8th retinula cell RC₈ joins the first 7 at their bases; this cell enlarges proximally (Fig. 1C, D). In the dorsofrontal region, 2 types of rhabdoms are distinguished; Type II (Figs. 1B₂;3b) outnumbers Type I (Figs. 1B₁;3a by a ratio of 4 : l. In the dorsal rim area, the first 2 rows are occupied exclusively by Type 11-rhabdoms; beyond this, the rhabdom of the dorsal rim area is characterized by the fact that its middle and proximal parts are considerably larger in diameter than in the dorsofrontal part; in this region, the microvilli of the horizontally oriented rhabdomeres are also parallel to the ;,-axis of the eye (Figs. 1B₃;3d). Thus, this small eye region meets the structural requirements for the detection of polarized light. The eye is interpreted as an intermediate between apposition and superposition eyes, because the rhabdom begins at the tip of the crystalline tract and the retinula cells are pigmented like those of an apposition eye. On the other hand, the structure of the dioptric apparatus and the tracheal system corresponds to those of superposition eyes. Parallels with the Ephestia eye in basic structural features are discussed in regard to the possible function of this eye and to the systematic position of A. reticulana.     

棉铃虫蛾复眼的微细结构及其区域性差异

用电子显微镜观察棉铃虫蛾复眼的微细结构及其区域性差异。此复眼具有小网膜细胞柱的透明带。每个小眼包括一个外凸内平的角膜,一个晶锥,四个形成晶锥、晶束的晶锥细胞和两个围绕着晶锥的主虹膜细胞,六至八个小网膜细胞和一个基细胞。晶锥末端有一短小固定的晶束。小网膜细胞柱远侧中央有似微绒毛结构的视杆束。每个小眼被六个附色素细胞围绕。 微细结构的区域性差异:1.背方小眼视杆中段横切面近似矩形,主要由六个微绒毛平行排列的三角形视小杯组成,整个视杆包含两个互相垂直的微绒毛轴;腹方、前方、后方和侧方区域的小眼视杆中段横切面为风扇形,“V”字形视小杆内微绒毛排列不平行;2.前方区域小眼视杆中段的横切面要比后方大;3.前方、腹方区域内,有的相邻小眼的小网膜细胞柱互相连结,背方、后方区域未观察到这一现象。     

Retina and dioptric apparatus of the dung beetle Euoniticellus africanus

Retinal fine structure and optics of the eye of the dung beetle Euoniticellus africanus have been studied and compared with those of three other scarabaeid beetles: Repsimus manicatus, Anoplognathus pallidicollis and Sericesthis geminata. The eye of Euoniticellus, in common with that of the other three species, possesses a dioptric system in which light first passes through a thick optically homogeneous cornea, and then enters a non-homogeneous crystalline cone. The lens cylinder properties of the latter cause the light rays to become partially focused across the clear-zone upon the rhabdom layer. Rays traced through a large scale drawing of the eye, with refractive indices measured for each component, predict an acceptance angle of approximately 26°. Since no significant aperture changes, lengthening of crystalline thread, cell or pigment migrations appear to be associated with dark/light adaptation, the eye may be assumed to be permanently poorly focused. In optomotor experiments the beetles did not show their characteristic antennal following response to black and white stripes when the latter had repeat periods of <30°. Structurally the eye of Euoniticellus differs markedly from that of other scarabaeids. It is totally divided into dorsal and ventral eye which are of a different size (the dorsal eye is smaller), but whose structural organization is basically the same. Principal pigment cells (they do not fully surround the cone) as well as accessory pigment cells (they accompany the retinula cells in an extraordinarily regular fashion as far as to the basement membrane) exhibit some unusual features. On the proximal side of the clear-zone, at a level where all retinula cell membranes form complex meanders and convolutions, cell 1 is the first to possess a rhabdomere. In it, all microvilli run parallel. This rhabdomere becomes part of the rectangular proximal rhabdom over the upper 20% of its length. Below this level the rhabdom consists of 6 rhabdomeres, but throughout its length microvilli are oriented in 2 orthogonal directions. It is thought that polarization sensitivity in dung beetles generally is related to the rhabdom organization described for Euoniticellus. An eighth (basal) cell is present in each ommatidium, but it lacks a rhabdomere. A tracheal tapetum is not developed. Finally, the point is made not to regard all different eye structures in insects as perfect adaptations to a particular environment or way of living, for specializations of photoreceptors may either follow, parallel or precede any ecological adaptation.     

灰茶尺蠖成虫复眼的超微结构及其明暗适应中的变化

【目的】明确灰茶尺蠖Ectropis grisescens成虫复眼的超微结构及其明暗适应中的变化,探究其调光机制。【方法】采用超景深显微镜测定了灰茶尺蠖成虫复眼的小眼数量、间角、直径和曲率半径等外部参数,并通过组织切片、光学显微镜和透射电子显微镜等技术观察了复眼的内部超微结构;通过光学显微镜观察了灰茶尺蠖成虫复眼在明暗环境中分别适应2 h后晶锥结构及色素颗粒的位置变化。【结果】灰茶尺蠖成虫复眼呈半球形,雌、雄虫单个复眼分别有2 502±105和3 123±78个小眼。小眼自远端至近端由角膜、晶锥、透明区构成的屈光层和由15个视网膜细胞构成的感光层组成。2个初级色素细胞包裹着晶锥,自角膜近端延伸至视网膜细胞核区的远端;每个小眼外围由6个次级色素细胞围绕,自角膜近端延伸至基膜;在透明区内14个视网膜细胞聚集成束(非感杆束),远端与晶锥束末端连接,在感光层内形成闭合型感杆束,延伸至第15个视网膜细胞(基部视网膜细胞)。在明暗适应时,灰茶尺蠖复眼的晶锥细胞间出现开闭,色素颗粒进行纵向位移,以适应外界的光强度的变化。【结论】灰茶尺蠖成虫复眼属于重叠像眼,感杆束为“14+1”模式;屏蔽色素颗粒的移...     

Optics of the butterfly eye

The afocal apposition optics of butterfly eyes was examined from both a geometrical optics and a wave optics point of view. We used several different species of butterfly but put special emphasis on a common Australian nymphalid,Heteronympha merope. From the anatomy of the retina, the optics of isolated components of the eye and the ophthalmoscopy of the intact living eye we derived the following.

Screening pigment,aperture and sensitivity in the dung beetle superposition eye

Summary Sensitivity to light was investigated in the refracting superposition eye of the dung beetle Onitis alexis using electrophysiological measurements and optical modelling. Intracellular recordings were made from single retinula cells over 24-h periods, with cells light and dark adapted, in order to measure the response/intensity (V-LogI) functions. The combined effects of a circadian rhythm and light adaptation allow the determination of the relative contributions of screening-pigment migration and transduction gain to changes in sensitivity in the eye. Between the extremes of dark adaptation at night and light adaptation during the day, the maximum sensitivity change possible is at least 4 log units, of which approximately 2 log units can be accounted for by changes in the transduction gain and at least 2 log units by screening-pigment migration. The role of the superposition aperture (the number of facets that contribute light to one rhabdom) in 3 species of dung beetle was investigated with an optical ray-tracing model of the eye. The facets of the superposition aperture do not contribute light equally to the target rhabdom; except in one species, the greatest contribution comes from facets located away from both the centre and periphery of the aperture. Light adaptation increases the optical density of the superposition aperture and decreases its size.     

亲土苔蛾成虫复眼超微结构

【目的】重叠型眼在昆虫复眼演化中起着重要作用。本研究旨在阐明夜出型亲土苔蛾Manulea affineola复眼类型及结构特征,以期填补灯蛾亚科昆虫复眼研究的空白,扩充夜出型昆虫复眼的特征数据,为探讨重叠型眼的变异趋势及复眼演化提供依据。【方法】运用光学和透射电子显微技术观察亲土苔蛾成虫复眼的超微结构。【结果】亲土苔蛾成虫复眼具有一个透明区,由6个次级色素细胞的透明胞质构成。小眼具8个视网膜细胞,其中1个视网膜细胞较短,仅位于小眼基部。在透明区内,7个视网膜细胞聚集成一束,其远端与晶体束末端相接,但并不形成视杆。在透明区下方,这7个视网膜细胞形成一个中心融合的视杆。在复眼背缘区的小眼的视杆具有近似矩形的横截面,而其余小眼的视杆具多分支状截面。【结论】亲土苔蛾成虫复眼属于重叠型眼;复眼背缘区的矩形视杆很可能与昆虫的偏振敏感性有关。     

Larval and adult eye of the Western Rock Lobster (Panulirus longipes)

A number of differences exists between the compound eyes of larval and adult rock lobsters, Panulirus longipes. The larval eye more closely resembles the apposition type of compound eye, in which retinula cells and rhabdom lie immediately below the cone cells. The adult eye, on the other hand, is a typical clear-zone photoreceptor in which cones and retinula cell layers are separated by a wide transparent region. The rhabdom of the larval eye, if cut longitudinally, exhibits a "banded" structure over its entire length; in the adult the banded part is confined to the distal end, and the rhabdom is tiered. Both eyes have in common an eighth, distally-located retinula cell, which possesses orthogonally-oriented microvilli, and a peculiar lens-shaped "crystal", which appears to focus light onto the narrow column of the distal rhabdom. Migration of screening pigment on dark-light adaptation is accompanied by changes in sensitivity and resolution of the eye. Retinula cells belonging to one ommatidium do not arrange into one single bundle of axons, but interweave with axons of four neighbouring facets in an extraordinarily regular fashion.     

Structural specializations of the cornea and retina at the dorsal rim of the compound eye in hymenopteran insects

Summary Structurally specialized ommatidia at the dorsal rim of the compound eyes of honey bees have been shown to be indispensable for polarized skylight navigation. In this study numerous other hymenopteran genera belonging to various superfamilies are shown to exhibit similar specializations in this part of the eye: (1) The cornea is penetrated by pore canals, which affect the optics of the ommatidia by scattering the light falling into the eye. In Andrena and Ammophila the cornea contains extensive cavities. (2) Each retinula contains 9 long receptor cells as opposed to 8 long ones in the adjacent dorsal area, and the rhabdom area is increased by a factor of up to 2. In all ant species examined there are no corneal but only retinal specializations at the dorsal rim of the eye. They include a specially shaped rhabdom as in Cataglyphis, in which polarization vision has also been demonstrated.     

A crustacean compound eye adapted for low light intensities (Isopoda)

Summary The optical performance of the apposition compound eye of the marine isopodCirolana borealis Lilljeborg (Crustacea) was investigated. The ommatidia comprise large lenses (diam. ca. 150 m), spherical crystalline cones and hypertrophied rhabdoms. The 7 rhabdomeres are fused distally and open proximally. We have designated this rhabdom type as semifused. Distal pigment cells screen neighbouring ommatidia, and a well developed reflecting pigment layer surrounds the rhabdom. The focal length was determined in situ and refractive index measurements, raytracings, and eye mappings were made. The focus was found to lie well below the distal rhabdom tip. A theoretical acceptance function was constructed and a 50% acceptance angle of 45 ° was estimated. The eye parameter (p, according to Snyder 1977) of different ommatidia was between 44 and 14. This together with the anatomy demonstrate an optimation to extremely low light intensities. TheCirolana eye provides an example where acuity is sacrificed for the eye to be able to see at the low light intensities of the inhabitat.The investigation has been supported by a grant from the Swedish Natural Science Research Council (grant no. 2760-103). Our thanks are due to the staff of the marine biological station in Espegrend (Norway). The skilled technical assistance of Miss Inger Norling, Mrs. Rita Wallen, and Miss Maria Walles is gratefully acknowledged. And finally, we would like to express our deep appreciation to Professor Rolf Elofsson for constructive discussions and for his interest and encouragement throughout the investigation.     

The eye of the soldier beetle Chauliognathus pulchellus (Cantharidae).

The soldier beetle eye is unusual in having large optically isotropic corneal cones which project inwards from a thick isotropic cornea. Refraction is mainly at the corneal surface. Calculation shows that the first focal plane is near the tip of the cone, from which the optical pathway continues as a crystalline tract. At the distal end of the crystalline tract, 3 micrometer in diameter, the four cone cells enclose the proximal tip of the corneal cone; at the proximal end they enclose the distal tip of a long fused rhabdom rod. The eye is remarkable in that there are two classes of retinula cells; four cells contribute to the long thin axial rhabdom, 2 micrometer in diameter and 120 micrometer long, and the other four cells form two rounded rhabdoms, 10 x 4 micrometer in cross-section and 20 micrometer deep, which lie to one side of the optical axis. The physiological properties of individual retinula cells were measured by intracellular recording. The retinula cells are of three spectral types with peaks near 360, 450 and 520--530 nm. Except by the criterion of spectral sensitivity, the retinula cells sampled could not be sorted into more than one class. The measured value of the acceptance angle, near 3 degrees in the dark-adapted state, is consistent with the hypothesis that all sampled cells were of the anatomical type that participate in the central rhabdom rod. A calculation of the theoretical field size of individual retinula cells from measurments of refractive index and lens dimensions predicts that cells which participate in the central rhabdom will have acceptance angles near 3 degrees. The conclusion, therefore, is that only one anatomical type of cell has so far been sampled.     

Maturation of optics and resolution in adult dung beetle superposition eyes

Summary The maturation of the morphology and refractive-index gradients of the crystalline cones and cornea of the superposition compound eye of the nocturnal dung beetle Onitis aygulus was traced as a function of age following adult ecdysis. Intracellular recordings from retinula cells were also made to trace the maturation of angular sensitivity, thereby determining the resolution of the eye at each age. Maturation proceeded quickly during the first 3 days following ecdysis, and then more slowly, with full maturation attained by the end of the second week. The main experimental results obtained during the first 2 weeks after ecdysis were: (1) the mean length of the crystalline cones increases from 67 m to 79 m; (2) the mean thickness of the cornea increases from 36 m to 50 m; (3) the mean refractive index along the axis of the crystalline cones increases from 1.459 to 1.511 in the distal cone region, from 1.434 to 1.501 in the waist region and from 1.425 to 1.486 in the proximal region; (4) the shape of the refractive-index gradient becomes more parabolic; (5) the mean rhabdom cross-sectional area increases from 190 m² to 230 m²; (6) the angular-sensitivity function narrows, with the acceptance angle decreasing from 22 ° to 4 °. An optical ray tracing model predicts an image quality limited only by the immaturity of the optics, a prediction confirmed by the electrophysiological results. The results are compared to optical maturation in day-active moths and skipper butterflies (which mature very quickly) and discussed in relation to ecological efficiency.     

Sexual dimorphism in the compound eye of the moth Operophtera brumata (Lepidoptera, Geometridae)

Abstract. Brachyptery in female moths is a common phenomenon. This article examines the eyes of the moth Operophtera brumata , in which only the males have wings. Both sexes possess eyes of the superposition type, have facets with corneal nipples, and exhibit eyeglow, but the eye of the male has 2174 facets, measures 725 μm in diameter, and has a clear zone of 112-μm width. That of the female has 1352 facets, measures 557 μm across, and has a 77-μm-wide clear zone. There were no significant differences in rhabdom diameters (10 μm) and tracheal sheath development, but male rhabdoms were significantly longer (85 vs. 65 μm). Dark/light adaptational changes manifested themselves in the positions of the distal screening pigment granules: between the cones during darkness and into the clear zone during light adaptation. The combination of a larger radius of curvature, wider clear zone, and longer rhabdoms gives the males a sensitivity at least twice that of the female. The narrower interommatidial angles of the male (2.8° vs. 3.2°) together with the well-developed tracheal rhabdom sheaths, furthermore, provide the eyes of the males with better resolution. Finally, eye-glow intensity in males diminishes considerably faster in light than it does in females. The differences between males and females appear to reflect their different roles: males begin to search after sunset in and around stands of trees for the pheromone-emitting females, which sit on the trunk of the tree under which they had emerged from their pupal case. Flying males encounter rapid light intensity changes and have to evade obstacles and enemies. The females are considerably more sedentary, but once mated, still seek suitable oviposition sites long after the males have ceased searching for them. During this activity, the females also need visual sensitivity and acuity, but less than the actively flying males.     

Challenging limits: Ultrastructure and size‐related functional constraints of the compound eye of Stigmella microtheriella (Lepidoptera: Nepticulidae)

With a body length of only 2 mm, the nepticulid Stigmella microtheriella (Stainton, 1854) is one of the smallest moths known to date. We investigated the optical design of its lemon‐shaped compound eyes, which measure 83.60 μm in anterior–posterior and 119.77 μm in dorso‐ventral direction. The eyes consist of about 123 facets, each of the latter just 9.9 μm in diameter. Transmission electron microscopy reveals an optical design with features intermediate between apposition and superposition optics similar to that known from two other small species of moths (one Nepticulid and one Gracillarid). Size‐related evolutionary adaptations of the ommatidial organization include (1) the involvement of only five rhabdomeres in the formation of the distal rhabdom (2) the complete absence of a rhabdomere of the eighth (= basal) retinula cell, (3) the “hourglass” shape of the rhabdom with a characteristic narrow waist separating distal from proximal portion, and (4) the reduction to one single layer of tracheoles as an adaptation to the overall restricted space available in this minute eye. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

An exceptionally well-preserved Eocene dolichopodid fly eye: function and evolutionary significance

The exceptionally preserved eyes of an Eocene dolichopodid fly contained in Baltic amber show remarkable detail, including features at micrometre and submicrometre levels. Based on this material, we establish that it is likely that the neural superposition compound eye existed as far back as 45 Ma. The ommatidia have an open rhabdom with a trapezoidal arrangement of seven rhabdomeres. Such a structure is uniquely characteristic of the neural superposition compound eye of present-day flies. Optical analysis reveals that the fossil eyes had a sophisticated and efficient optical system.