[Contrast sensitivity and visual acuity in animals]. / Kontrastempfindlichkeit und Sehschärfe bei Tieren.

BACKGROUND: Fundamental spatial vision capabilities of visual systems can be characterized by their contrast sensitivity and visual acuity. OBJECTIVE: Comparison of contrast sensitivity and visual acuity in humans and other animals. MATERIAL AND METHODS: An analysis of known contrast sensitivity functions and maximum visual acuity across selected taxa was carried out, with consideration of measurement principles, viewing conditions and allometry. RESULTS: Comparing across all analyzed species, contrast sensitivity functions have inverted U­shape characteristics, with key differences in both position and absolute sensitivity within the spectrum of spatial frequencies. Humans, for example, have a maximum sensitivity at 5 cycles/degree and mice at approximately 0.1 cycles/degree. Body and eye size generally correlate well with maximum visual acuity. Across eye types, lens eyes have the highest optical and visual resolution, all other things being equal. Diurnal species typically outperform crepuscular or nocturnal species. Humans generally excel at both maximum contrast sensitivity as well as visual acuity. CONCLUSION: Despite great differences in optical, anatomical and neurophysiological structures between humans and animals, spatial vision capabilities are generally comparable across taxa. This favors the hypothesis that spatial vision in animals develops primarily towards meeting similar evolutionary needs within the limits of biophysical and optical laws.

[Potential of Adaptive Optics for the Diagnostic Evaluation of Hereditary Retinal Diseases]. / Adaptive Optiken ­ Möglichkeiten für die Diagnostik hereditärer Netzhauterkrankungen.

The use of adaptive optics in ophthalmoscopy is a breakthrough technological achievement. With AO ophthalmoscopes, the microscopic retinal structure can be visualised non-invasively and on a cellular level, allowing for cellular scale imaging of the retinal nerve fibre layer, the smallest retinal capillaries, rod and cone photoreceptors, and the retinal pigment epithelium mosaic in the living subject. Regarding the diagnostic evaluation of retinal diseases, the current research focuses on monogenetic retinal diseases, which - when better understood - may allow for conclusions to be drawn about other multifactorial diseases and their underlying mechanisms (model disease). For disease monitoring and current and future pharmacological intervention (e.g. gene therapy), they will help to better establish novel and reliable clinical endpoints. New AO imaging devices have just become commercially available, and the number of retinal pathologies visualised with AO is increasing. Recently, an AO-based microstimulation technique has been introduced, which offers the possibility to directly correlate retinal structure with visual function on a cellular level.

[Technical principles of adaptive optics in ophthalmology]. / Technische Grundlagen adaptiver Optiken in der Ophthalmologie.

During the last 25 years ophthalmic imaging has undergone a revolution. This review gives an overview of the possibilities of adaptive optics (AO) for ophthalmic imaging technologies and their development and illustrates that the role of ophthalmic imaging changed from the documentation of obvious abnormalities to the detection of microscopic yet significant conspicuities. This enables earlier and more precise diagnoses. The implementation of AO for imaging systems like fundus cameras, scanning laser ophthalmoscopy and optical coherence tomography has gained in importance. In recent years a couple of companies started developing commercially available AO systems, thus, indicating a future use in clinical routine.

[Optical coherence tomography angiography (OCT­A) in rats]. / Optische-Kohärenztomographie-Angiographie (OCT­A) bei Ratten.

PURPOSE: Optical coherence tomography angiography (OCT­A) allows for the non-invasive, three-dimensional visualization of retinal and chorioidal vascular structures. In this study, this new imaging modality was evaluated in rats. METHODS: In vivo imaging in Dark Agouti rats was performed using confocal scanning laser ophthalmoscopy (cSLO) and OCT­A (Spectralis prototype, Heidelberg Engineering) after adjusting the length of the reference arm. The OCT­A en-face images were compared to conventional fluorescein angiography cSLO images. The histological examination allowed for correlation of retinal and chorioidal plexus. RESULTS: While the diagnostic device was developed for use in humans, OCT­A and cSLO imaging can be applied in rodents after only minor hardware modifications. High-resolution and contrast-enhanced images enable a depth-selective visualization of the three retinal plexus and the inner and outer chorioidal vascular networks. In comparison to fluorescein angiography (FA), OCT­A is characterized by higher resolution and more accurate three-dimensional localization of vascular structures, particularly in deep layers. A current limitation includes the relatively small area imaged by OCT­A. DISCUSSION: The recently developed OCT­A imaging technology also allows for three-dimensional detection of retinal and chorioidal vascular changes in vivo without dye injection in rodents. OCT may potentially replace invasive FA for specific questions and will be useful in animal models for research of retinal and chorioidal angiogenic processes physiologically and during pharmacological interventions.

[Histology of the living eye : Noninvasive microscopic structure and functional analysis of the retina with adaptive optics]. / Histologie im lebenden Auge : Nichtinvasive mikroskopische Struktur- und Funktionsanalyse der Netzhaut mit adaptiven Optiken.

Equipping an ophthalmoscope with adaptive optics (AO) offers access to the living human retina with unprecedented spatial resolution. With AO, cellular structures such as the nerve fiber layer, the microvasculature of the smallest retinal capillaries, rod and cone photoreceptors and the mosaic of the retinal pigment epithelium are directly observable. A large number of studies in the normal and diseased retina have already shown that this level of detail offers new insights into disease mechanisms and progression, and promises to identify early disease markers. In conjunction with functional testing of single photoreceptors that is possible with AO microstimulation, a structure-function relationship on the cellular scale is within reach. These technological advances offer new avenues for clinical ophthalmology, interventional efforts, and basic research of the function and dysfunction of vision.

[Technical principles of OCT angiography]. / Technische Grundlagen der OCT-Angiographie.

BACKGROUND: Optical coherence tomography angiography (OCT-A) is a new diagnostic non-invasive method by which the vascular structures of the retina and choroid can be visualized three-dimensionally without need for using fluorescence dyes. The technology of OCT-A is an advancement of the OCT. By means of more powerful software and hardware used for OCT-A not only morphological but also retinal and choroidal vascular perfusion analyses can be performed. In this article, the principles and applications of OCT-A are discussed and compared to other non-invasive diagnostic devices for visualization of the retinal and choroidal blood circulation. METHODS: This article is based on a selective literature review and analyses of own data. RESULTS: The advantages of OCT-A include easy application without the need for mydriasis or intravenous injection of fluorescence dyes and also the exact three-dimensional localization of vascular changes. In the case of retinal pathologies there is a considerable difference between software-assisted automatic segmentation and the real architecture of the retina, which must be taken into consideration in the clinical interpretation. CONCLUSION: Of all noninvasive devices for visualization of the retinal and choroidal circulation, OCT-A is the only one which can already be implemented into the clinical routine. With this novel imaging device retinal and choroidal alterations can be visualized in a depth- selective manner and without masking affects, such as pooling or staining phenomena.

Evaluation of two minimally invasive techniques for electroencephalogram recording in wild or freely behaving animals.

Insight into the function of sleep may be gained by studying animals in the ecological context in which sleep evolved. Until recently, technological constraints prevented electroencephalogram (EEG) studies of animals sleeping in the wild. However, the recent development of a small recorder (Neurologger 2) that animals can carry on their head permitted the first recordings of sleep in nature. To facilitate sleep studies in the field and to improve the welfare of experimental animals, herein, we test the feasibility of using minimally invasive surface and subcutaneous electrodes to record the EEG in barn owls. The EEG and behaviour of four adult owls in captivity and of four chicks in a nest box in the field were recorded. We scored a 24-h period for each adult bird for wakefulness, slow-wave sleep (SWS), and rapid-eye movement (REM) sleep using 4 s epochs. Although the quality and stability of the EEG signals recorded via subcutaneous electrodes were higher when compared to surface electrodes, the owls' state was readily identifiable using either electrode type. On average, the four adult owls spent 13.28 h awake, 9.64 h in SWS, and 1.05 h in REM sleep. We demonstrate that minimally invasive methods can be used to measure EEG-defined wakefulness, SWS, and REM sleep in owls and probably other animals.