What We Can Learn from Artificial Lateral Line Sensor Arrays.

The lateral line system of fish is important for many behaviors, including spatial orientation, prey detection, intraspecific communication, and entraining. With aid of the lateral line, fish perceive minute water motions. The smallest sensory unit of the lateral line is the neuromast, which occurs freestanding on the skin and in fluid-filled canals. We have built artificial lateral line canal systems that can be used to measure spatiotemporal flow patterns. Those patterns can, for instance, be used to distinguish between different environments and upstream objects.

Perception and discrimination of movement and biological motion patterns in fish.

Vision is of primary importance for many fish species, as is the recognition of movement. With the exception of one study, assessing the influence of conspecific movement on shoaling behaviour, the perception of biological motion in fish had not been studied in a cognitive context. The aim of the present study was therefore to assess the discrimination abilities of two teleost species in regard to simple and complex movement patterns of dots and objects, including biological motion patterns using point and point-light displays (PDs and PLDs). In two-alternative forced-choice experiments, in which choosing the designated positive stimulus was food-reinforced, fish were first tested in their ability to distinguish the video of a stationary black dot on a light background from the video of a moving black dot presented at different frequencies and amplitudes. While all fish succeeded in learning the task, performance declined with decreases in either or both parameters. In subsequent tests, cichlids and damselfish distinguished successfully between the videos of two dots moving at different speeds and amplitudes, between two moving dot patterns (sinus vs. expiring sinus) and between animated videos of two moving organisms (trout vs. eel). Transfer tests following the training of the latter showed that fish were unable to identify the positive stimulus (trout) by means of its PD alone, thereby indicating that the ability of humans to spontaneously recognize an organism based on its biological motion may not be present in fish. All participating individuals successfully discriminated between two PDs and two PLDs after a short period of training, indicating that biological motions presented in form of PLDs are perceived and can be distinguished. Results were the same for the presentation of dark dots on a light background and light dots on a dark background.

Symmetry perception in bamboo sharks (Chiloscyllium griseum) and Malawi cichlids (Pseudotropheus sp.).

Several species have been shown to perceive symmetry as a measure of superior genetic quality, useful for assessing potential mates or mediating other visual activities such as the selection of food sources. The current study assessed whether Pseudotropheus sp. and Chiloscyllium griseum, two fish species from distantly related groups, possess symmetry perception. In alternative two choice experiments, individuals were tested for spontaneous preferences and trained to discriminate between abstract symmetrical and asymmetrical stimulus pairs. Pair discriminations were followed by extensive categorization experiments. Transfer tests elucidated whether bilaterally symmetrical and rotationally symmetrical stimuli could be distinguished. Sharks were also tested for the degree of dissimilarity between two symbols that could still be detected. While sharks showed both a spontaneous preference for symmetry as well as remarkable discrimination abilities by succeeding in all of the presented tasks, cichlids showed no spontaneous preference, had difficulties in discriminating between symbols and performed poorly in the categorization experiments. Sharks distinguished between bilaterally and rotationally symmetrical stimuli and easily differentiated between a four-armed cross (all arms 90° apart) and a cross where one of the arms was only 45° spaced from the one next to it. Performance did not decline when the separation was extended to 70°, but was significantly reduced at an 80° separation. Results indicate that the ability for symmetry perception varies across fish species and individuals, whereby some can detect even subtle differences in this respect.

Visual discrimination of rotated 3D objects in Malawi cichlids (Pseudotropheus sp.): a first indication for form constancy in fishes.

Fish move in a three-dimensional environment in which it is important to discriminate between stimuli varying in colour, size, and shape. It is also advantageous to be able to recognize the same structures or individuals when presented from different angles, such as back to front or front to side. This study assessed visual discrimination abilities of rotated three-dimensional objects in eight individuals of Pseudotropheus sp. using various plastic animal models. All models were displayed in two choice experiments. After successful training, fish were presented in a range of transfer tests with objects rotated in the same plane and in space by 45° and 90° to the side or to the front. In one experiment, models were additionally rotated by 180°, i.e., shown back to front. Fish showed quick associative learning and with only one exception successfully solved and finished all experimental tasks. These results provide first evidence for form constancy in this species and in fish in general. Furthermore, Pseudotropheus seemed to be able to categorize stimuli; a range of turtle and frog models were recognized independently of colour and minor shape variations. Form constancy and categorization abilities may be important for behaviours such as foraging, recognition of predators, and conspecifics as well as for orienting within habitats or territories.

Visual discrimination and object categorization in the cichlid Pseudotropheus sp.

Object categorization is an important function of the visual system, quickly providing an animal with relevant information about its surrounding and current situation, as for example during predator detection. While the ability to categorize objects has already been observed in several vertebrate and even invertebrate species, no attempt has previously been made to evaluate this function in fish, the most species-rich vertebrate group. This study assessed form discrimination abilities and object categorization skills in the African cichlid Pseudotropheus sp. Fish could discriminate between a variety of two-dimensional geometrical shapes, forms and sizes and learned to distinguish between two categories, "fish" versus "snail". Performance remained undisturbed by extensive modifications to the stimuli, as long as key features were maintained. Results indicate that fish not only memorized the features of the positive stimulus (categorized the positive stimulus), but also categorized the negative stimulus. During transfer trials involving a previously unknown object, fish were able to discriminate between both the negative and the positive stimulus and the unknown stimulus and responded accordingly.

Surface structure and frictional properties of the skin of the Amazon tree boa Corallus hortulanus (Squamata, Boidae).

The legless locomotion of snakes requires specific adaptations of their ventral scales to maintain friction force in different directions. The skin microornamentation of the snake Corallus hortulanus was studied by means of scanning electron microscopy and the friction properties of the skin were tested on substrates of different roughness. Skin samples from various parts of the body (dorsal, lateral, ventral) were compared. Dorsal and lateral scales showed similar, net-like microornamentation and similar friction coefficients. Average friction coefficients for dorsal and lateral scales on the epoxy resin surfaces were 0.331 and 0.323, respectively. In contrast, ventral scales possess ridges running parallel to the longitudinal body axis. They demonstrated a significantly lower friction coefficient compared to both dorsal and lateral scales (0.191 on average). In addition, ventral scales showed frictional anisotropy comparing longitudinal and perpendicular direction of the ridges. This study clearly demonstrates that different skin microstructure is responsible for different frictional properties in different body regions.

AlphaCor keratoprosthesis: postoperative development of six patients.

PURPOSE: AlphaCor (Argus Biomedical Pty. Ltd., Perth, Australia) is an artificial, soft, one-piece keratoprosthesis (KPro) indicated for severe corneal conditions not treatable by a donor graft. To evaluate the efficacy and visual restoring of six patients with complete corneal opacification and deep neovascularizations treated with AlphaCor. METHODS: A retrospective review of six patients with a history of corneal opacification treated with keratoprosthesis surgery. AlphaCor synthetic cornea was implanted into the corneal stroma. During the follow-up time, slit-lamp and ultrasound examinations, best corrected visual acuity (BCVA), and intraocular pressure measurements were performed. RESULTS: Six eyes with corneal scarring and vascularizations in three to four quadrants of six patients to years of age underwent a keratoprosthesis procedure. The follow-up time was 13-36 months; mean 23 months. The operation procedure was not limited by severe complications. The preoperative BCVA was hand movement to light perception. The postoperative BCVA ranged between 20/200 and 80/100. Intraocular pressure was controlled in all cases. Three patients developed a melting of the anterior corneal lamella. The keratoprosthesis had to be explanted (15-34 months after implantation) and was replaced by a donor cornea. CONCLUSIONS: Further evaluation is needed to evaluate the role of AlphaCor as a keratoprosthesis.

Peripheral and central processing of lateral line information.

The lateral line is a hydrodynamic sensory system that allows fishes and aquatic amphibians to detect the water motions caused, for instance, by conspecifics, predators or prey. Typically the peripheral lateral line of fishes consists of several hundred neuromasts spread over the head, trunk, and tail fin. Lateral line neuromasts are mechanical low-pass filters that have an operating range from <1 Hz up to about 150 Hz. Within this frequency range, neuromasts encode the duration, local direction, amplitude, frequency, and phase of a hydrodynamic stimulus. This paper reviews the peripheral and central processing of lateral line information in fishes. Special attention is given to the coding of simple and complex hydrodynamic stimuli, to parallel processing, the roles of the various brain areas that process hydrodynamic information and the centrifugal (efferent) control of lateral line information. The review argues that in order to fully comprehend peripheral and central lateral line information processing, it is imperative to do comparative studies that take into account the ecology of fishes, meaning that natural stimulus and noise conditions have to be considered.

[Cataract extraction including posterior chamber lens implantation in the treatment of acute glaucoma]. / Kataraktoperation mit Hinterkammerlinsenimplantation zur Behandlung des akuten Glaukoms.

OBJECTIVE: The aim of this study was to compare phacoemulsification in eyes with angle-closure glaucoma to the partner eyes with or without iridectomy or laser iridotomy, respectively. METHODS: Twelve eyes with an elevated intraocular pressure due to an angle closure that were treated by phacoemulsification and IOL implantation were compared with 12 partner eyes with narrow angle and iridectomy or iridotomy without intraocular pressure elevation and cataract extraction. The average follow-up period was 15.7+/-2.1 months. RESULTS: The average intraocular pressure in eyes with angle-closure glaucoma was 54.1+/-14.7 mmHg and in the partner eyes 22.4+/-8.6 mmHg preoperatively. Follow-up pressure was 19.3+/-2.0 mmHg in eyes with angle-closure glaucoma and 18.8+/-1.5 mmHg in the partner eyes. CONCLUSION: Primary cataract extraction including posterior chamber lens implantation into eyes with angle-closure glaucoma reduced intraocular pressure to normal levels, increased visual acuity, and decreased the number of antiglaucomatous drugs. Eyes with angle-closure glaucoma do not respond differently to phacoemulsification and lens implantation compared to eyes with narrow angle without pressure elevation during and after phacoemulsification.

Preliminary results after implantation of four AlphaCor artificial corneas.

PURPOSE: The purpose was to evaluate the validity of implantation of the artificial cornea (AlphaCor) in human corneas considered too high risk for penetrating keratoplasty with donor tissue. METHODS: Four keratoprostheses, made from poly(2-hydroxyethyl methacrylate) (PHEMA) with a porous skirt and a transparent optical part, were implanted into the cornea of four patients. Keratocytes invading the skirt provide a watertight fixation with the scarred corneal tissue. Deep to the clear optical part, the posterior corneal lamella was excised to a diameter of 3.5 mm before the device was implanted, and the anterior lamella was trephined similarly 3 months after AlphaCor implantation. RESULTS: The eyes selected to receive an artificial cornea had significant neovascularisation, and 0-3 previous failed grafts. Follow-up for 6 months revealed best visual acuity between 20/400 and 20/50. Factors limiting the visual acuity outcome were optic atrophy and age-related macular disease. One patient underwent an extracapsular cataract extraction after the device was implanted, as a senile cataract was then noted. One complication occurred, a central corneal stromal melt, which was managed by covering with a 9-mm donor lamella. CONCLUSION: The flexible device AlphaCor may provide a substitute for donor corneal tissue in desperate cases. Advantages include the simple implantation technique, which avoids trauma to the surrounding structures. Visual acuity results may be limited by pre-existing pathology, but it appears that a patient's visual potential can be achieved. Further follow-up to exclude long-term complications is required.

The spitting behavior of two species of spitting cobras.

Spitting cobras defend themselves by spitting their venom in the face of a harasser. Although it is common belief that spitting cobras direct their venom at the eyes of an aggressor, this has never been investigated. Here, we show that the spitting act of cobras (Naja nigricollis and N. pallida) can readily be triggered by a moving human face or by a moving real size photo of a human face. In contrast, a stationary human face (real or photo) or a moving or stationary human hand does not trigger the spitting act. If threatened, spitting cobras aim their venom, ejected either in two distinct jets (N. pallida) or in a fine spray (N. nigricollis), either between the eyes or at one eye. In both cobra species investigated, the width and height of the area hit by the venom was independent of eye distance (test range 5.5 cm and 11 cm). During the spitting act the cobras performed fast undulating head movements that lead to a larger distribution of their venom. This behavior increases the probability that at least one eye of the aggressor is hit.

Nature as a model for technical sensors.

Nature has developed a stunning diversity of sensory systems. Humans and many animals mainly rely on visual information. In addition, they may use acoustic, olfactory, and tactile cues for object detection and spatial orientation. Beyond these sensory systems a large variety of highly specialized sensors have evolved. For instance, some buprestid beetles use infrared organs for the detection of forest fires. The infrared sensors of boid and crotalid snakes are used for prey detection at night. For object detection and spatial orientation many species of nocturnal fish employ active electrolocation. This review describes certain aspects of the detection and processing of infrared and electrosensory information. We show that the study of natural exotic sensory systems can lead to discoveries that are useful for the construction of technical sensors and artificial control systems. Comparative studies of animal sensory systems have the power to uncover at least a small fraction of the gigantic untapped reservoir of natural solutions for perceptive problems.

[Removal of epikeratophakia lenticules and implantation of intraocular lenses]. / Entfernung von Epikeratophakielentikeln mit Implantation intraokularer Linsen.

Two epikeratophakia lenticules were removed from a highly myopic eye after 13 years and from an aphakic eye after 15 years, respectively. After subsequent refraction compensation, the following results were achieved. Fixation of the epikeratophakia lenticules in the corneal tissue led to a change of the K-value following the removal of the corneal transplants. The refraction compensation can be performed by an intraocular or sclera-fixated lens implantation following the complete closure of the keratotomy wounds. Neither of the two host corneas had undergone an optically relevant change so that the visual acuity was almost unchanged compared to the original data. The light microscopy examination showed a broadening of the corneal epithelium, an unclearly definable basal membrane, as well as a reduction in the number of keratocytes and plaque-shaped alteration of the unstructured matrix. Electron-microscopic examination presented many osmiophilic deposits, which were judged to be catabolic products of apoptotic keratocytes.

Effects of running water on brainstem lateral line responses in trout, Oncorhynchus mykiss, to sinusoidal wave stimuli.

We investigated how single units in the medial octavolateralis nucleus of the rainbow trout, Oncorhynchus mykiss, respond to a 50-Hz vibrating sphere in still and running water. Four types of units were distinguished. Type MI units ( N=16) were flow-sensitive; their ongoing discharge rates either increased or decreased in running water, and as a consequence, responses of these units to the vibrating sphere were masked if the fish was exposed to water flow. Type MII units ( N=7) were not flow-sensitive; their ongoing discharge rates were comparable in still and running water, and thus their responses to the vibrating sphere were not masked. Type MIII units ( N=7) were also not flow-sensitive; nevertheless, their responses to the vibrating sphere were masked in running water. Type MIV units ( N=14) were flow-sensitive, but their responses to the vibrating sphere were not masked. Our data confirm previous findings in the goldfish, Carassius auratus, indicating that the organization of the peripheral lateral line is reflected to a large degree in the medial octavolateralis nucleus. We compare data from goldfish and trout and discuss differences with respect to lateral line morphology, lifestyle and habitat of these species.

[Bioptic. A refractive surgery procedure for correction of high and extreme myopia]. / Bioptik Ein Verfahren der refraktiven Chirurgie zur Korrektur der hohen und extremen Myopie.

BACKGROUND: The complete correction of highly or extremely myopic eyes to emmetropia can only be achieved by very few procedures: The combination of implanting phacic intraocular lenses and the use of LASIK (laser in-situ keratomileusis) - Bioptic - makes it possible to achieve this goal to a great extent. PATIENTS AND METHODS: The Bioptic procedure was carried out on 17 eyes of 10 patients. Two weeks after corneal dissection with the Hansatom,an implantable phacic lens (STAAR) was introduced into the posterior chamber and 4 weeks later the residual myopia was treated with LASIK combined with the correction of astigmatic errors. The follow-up time was 10.2 (6.7) months. RESULTS: Preoperative average values of the manifest refraction were -16.22 sph (3.86) with 1.40 cyl (1.30) which changed to -3.85 sph (2.73) with -1.50 cyl (0.87) after implantation of an ICL trade mark into the posterior chamber. Visual acuity increased from uncorrected hand motion to 0.13 (0.10) and corrected from 0.53 (0.19) to 0.63 (0.19). The refraction of implanted ICLs trade mark was 14.6 dpt (1.1). Following the LASIK procedure the uncorrected visual acuity improved to 0.68 (0.16) and fully corrected to 0.79 (0.20). The final refraction measured +0.16 sph (0.67) with -0.48 cyl (0.25). The keratectomy depth was 80.63 -m (26.9) and the optical zone showed a horizontal distance of 6.28 mm (0.39). CONCLUSION: Bioptic is able to correct highly and extremely myopic eyes with the combination of phacic lenses and subsequent LASIK. A concomitant astigmatism can be corrected up to 2.5 dpt simultaneously. With the combination of both procedures,the optical zone can be enlarged. Keeping in mind that phacic lenses reveal a constant refraction after a few days and also that LASIK is refractively safe in low myopia of -4 dpt to -5 dpt, it can be expected that the refractive deviation following the Bioptic procedure is low.

Lateral line reception in still- and running water.

The lateral line of fish is composed of neuromasts used to detect water motions. Neuromasts occur as superficial neuromasts on the skin and as canal neuromasts in subepidermal canals. Fibres of the lateral line nerves innervate both. There have been extensive studies on the responses of lateral line nerve fibres to dipole stimuli applied in still water. However, despite the fact that many fish live in rivers and/or swim constantly, responses of lateral line nerve fibres to dipole stimuli presented in running water have never been recorded. We investigated how the peripheral lateral line of still water fish ( Carassius auratus) and riverine fish ( Oncorhynchus mykiss) responds to minute sinusoidal water motions while exposed to unidirectional water flow. Both goldfish and trout have two types of posterior lateral line nerve fibres: Type I fibres, which most likely innervate superficial neuromasts, were stimulated by running water (10 cm s(-1)). The responses of type I fibres to water motions generated by a vibrating sphere were masked if the fish was exposed to running water. Type II fibres, which most likely innervate canal neuromasts, were not stimulated by running water. Consequently, responses of type II fibres to a vibrating sphere were not masked under flow conditions.

Hydrodynamic trail-following in harbor seals (Phoca vitulina).

Marine mammals often forage in dark or turbid waters. Whereas dolphins use echolocation under such conditions, pinnipeds apparently lack this sensory ability. For seals hunting in the dark, one source of sensory information may consist of fish-generated water movements, which seals can detect with their highly sensitive whiskers. Water movements in the wake of fishes persist for several minutes. Here we show that blindfolded seals can use their whiskers to detect and accurately follow hydrodynamic trails generated by a miniature submarine. This shows that hydrodynamic information can be used for long-distance prey location.

[Scanning microscopy and immunohistochemical studies of an explanted phacic posterior chamber lens (ICL-M, STAAR)]. / Rasterelektronenmikroskopische und immunhistochemische Untersuchungen einer explantierten phaken Hinterkammerlinse (ICL-M, STAAR).

OBJECTIVE: This study was performed to find out if an explanted phacic collamer IOL (ICL/STAAR) showed structural or surface quality changes after an intraocular implantation. MATERIAL AND METHODS: We explanted an ICL 6 months after implantation and compared it to a new reference lens using scanning electron microscopy and immunohistochemical investigations. RESULTS: The explanted ICL showed no changes in comparison to a new ICL except for a coating with an unidentified material. Both the new and explanted ICL presented grooves on the surface and superficial holes of unknown origin measuring roughly 10 mu. Neither pigment nor macrophages could be found on the explanted lens. Although the lens material contained 0.1% collagen, the immunohistochemical staining for collagen was negative. CONCLUSIONS: The collagen content of the ICL could not be proven using immunohistochemistry. No changes were found between the new and the explanted lens, except for a coating of the explanted lens with an unidentified material.

Morphology of a thermosensitive multipolar neuron in the infrared organ of Merimna atrata (Coleoptera, Buprestidae).

Two pairs of infrared (IR) organs are situated ventrolaterally on the second and third abdominal sternites of the Australian fire beetle Merimna atrata (Buprestidae). In ventral view, each IR organ has a round IR absorbing area under which a sensory complex is attached to the epidermis. The main component of the complex is a single large multipolar neuron and its mass of highly branched dendrites. All parts of this neuron are enveloped in glial cells. The proximal primary dendrites, which arise from the soma, finally branch into several hundred tightly packed terminal dendrites, which contain many mitochondria. We term this unusual morphology of the dendritic region a terminal dendritic mass (TDM). Additionally, two chordotonal organs were found in each sensory complex. Their somata are integrated in the complex and the dendrites extend to the periphery of the absorbing area. The bauplan of the dendritic region is reminiscent of the thermosensitive trigeminal nerve fibers innervating the absorbing structures in the IR receptors in boid and crotalid snakes. Because this multipolar neuron also functions as a thermoreceptor, another example of a functional analogy between insect and vertebrate sensory systems could be demonstrated.