Torsten Strasser

The clinical phenotype of CNGA3-related achromatopsia: Pretreatment characterization in preparation of a gene replacement therapy trial

Purpose The purpose of this study was to clinically characterize patients with CNGA3-linked achromatopsia (CNGA3-ACHM) in preparation of a gene therapy trial. Methods Thirty-six patients (age 7-56 years) with complete (cACHM) or incomplete (iACHM) CNGA3-ACHM were examined, including detailed psychophysical tests, extended electrophysiology, and assessment of morphology by fundus autofluorescence and spectral-domain optical coherence tomography (SD-OCT). Results Mean best-corrected visual acuity was 0.78 ± 0.14 logMAR. Color vision tests were consistent with a rod-dominated function in every cACHM patient. Microperimetry indicated an overall lowered retinal sensitivity within 20° of visual field. In electroretinography (ERG), photopic responses were nondetectable in cACHM patients, but residual cone responses were observed in the iACHM patients. Scotopic responses were altered referring to anomalies of photoreceptor and postreceptor signaling, whereas in voltage versus intensity functions, Vmax was significantly below normal values (P < 0.05). In contrast, slope (n) and semisaturation intensity (K) were found to be within normal limits. Spectral-domain OCT examination showed no specific changes in 14.7%, disruption of the ellipsoid zone (EZ) at the fovea in 38.2%, absent EZ in 17.7%, a hyporeflective zone in 20.5%, and outer retinal atrophy in 8.9% of all cases and foveal hypoplasia in 29 patients (85%). No correlation of retinal morphology with visual function or with a specific genotype was found. The severity of morphologic and functional changes lacked a robust association with age. Conclusions Our extended investigations prove that even among such a genetically homogenous group of patients, no specific correlations regarding function and morphology severity and age can be observed. Therefore, the therapeutic window seems to be wider than previously indicated.

An integrated domain specific language for post-processing and visualizing electrophysiological signals in Java

Electrophysiology of vision - especially the electroretinogram (ERG) - is used as a non-invasive way for functional testing of the visual system. The ERG is a combined electrical response generated by neural and non-neuronal cells in the retina in response to light stimulation. This response can be recorded and used for diagnosis of numerous disorders. For both clinical practice and clinical trials it is important to process those signals in an accurate and fast way and to provide the results as structured, consistent reports. Therefore, we developed a freely available and open-source framework in Java (http://www.eye.uni-tuebingen.de/project/idsI4sigproc). The framework is focused on an easy integration with existing applications. By leveraging well-established software patterns like pipes-and-filters and fluent interfaces as well as by designing the application programming interfaces (API) as an integrated domain specific language (DSL) the overall framework provides a smooth learning curve. Additionally, it already contains several processing methods and visualization features and can be extended easily by implementing the provided interfaces. In this way, not only can new processing methods be added but the framework can also be adopted for other areas of signal processing. This article describes in detail the structure and implementation of the framework and demonstrate its application through the software package used in clinical practice and clinical trials at the University Eye Hospital Tuebingen one of the largest departments in the field of visual electrophysiology in Europe.

Combination of cGMP analogue and drug delivery system provides functional protection in hereditary retinal degeneration

Significance Development of treatments for hereditary degeneration of the retina (RD) is hampered by the vast genetic heterogeneity of this group of diseases and by the delivery of the drug to an organ protected by the blood–retina barrier. Here, we present an approach for the treatment of different types of RD, combining an innovative drug therapy with a liposomal system that facilitates drug delivery into the retina. Using different animal models of RD we show that this pharmacological treatment preserved both the viability of cells in the retina as well as retinal function. Thus, our study provides an avenue for the development of therapies for hereditary diseases which cause blindness, an unmet medical need. Inherited retinal degeneration (RD) is a devastating and currently untreatable neurodegenerative condition that leads to loss of photoreceptor cells and blindness. The vast genetic heterogeneity of RD, the lack of “druggable” targets, and the access-limiting blood–retinal barrier (BRB) present major hurdles toward effective therapy development. Here, we address these challenges (i) by targeting cGMP (cyclic guanosine- 3′,5′-monophosphate) signaling, a disease driver common to different types of RD, and (ii) by combining inhibitory cGMP analogs with a nanosized liposomal drug delivery system designed to facilitate transport across the BRB. Based on a screen of several cGMP analogs we identified an inhibitory cGMP analog that interferes with activation of photoreceptor cell death pathways. Moreover, we found liposomal encapsulation of the analog to achieve efficient drug targeting to the neuroretina. This pharmacological treatment markedly preserved in vivo retinal function and counteracted photoreceptor degeneration in three different in vivo RD models. Taken together, we show that a defined class of compounds for RD treatment in combination with an innovative drug delivery method may enable a single type of treatment to address genetically divergent RD-type diseases.

Analysis of retinal function using chromatic pupillography in retinitis pigmentosa and the relationship to electrically evoked phosphene thresholds

To analyse pupil responses to specific chromatic stimuli in patients with advanced retinitis pigmentosa (RP) to ascertain whether chromatic pupillography can be used as an objective marker for residual retinal function. To examine correlations between parameters of the pupil response and the perception threshold of electrically evoked phosphenes.

Pupillographic campimetry: an objective method to measure the visual field

Abstract Pupillographic campimetry allows measuring the visual field objectively by analyzing the pupil response to perimetric stimuli. One of the drawbacks of this technique, similar to static perimetry, is the need of reliable fixation of the subject. By using stimulus sizes comparable to static perimetry and applying gaze tracking, we enable a retinotopic visual field examination regardless of fixation problems and with an increased stability and improved spatial resolution. Here, we present the results of applying the method in eight normal sighted subjects as well as in three patients suffering from diseases usually diagnosed by perimetry. The results in normal sighted subjects show a reduction in the amplitude of the pupil response with increasing eccentricity as expected. We also demonstrate that gaze-controlled campimetry is able to detect organic visual field defects objectively in a patient group and classify the visual field defects without an organic background. Moreover, we show that our method is able to evaluate the visual field sensitivity loss beyond classical perimetry in patients with late-stage retinitis pigmentosa. Thus, gaze-controlled pupil campimetry can be used in addition to classical perimetry, allowing for an objective monitoring of disease progression, rendering it as a biomarker for novel treatments.

Color Pupillography in Dorsal Midbrain Syndrome

Objective: The purpose of this study was to evaluate the pupil response to chromatic stimuli in patients with lesions in the dorsal midbrain and possibly gain new insights into the afferent pupillary pathways. Methods: Color pupillography was performed in 5 patients with dorsal midbrain syndrome (DMS), and their results were compared with those of 20 healthy control subjects. We used full-field red stimuli (605 nm) that primarily address the rod/cone system and blue stimuli (420 nm) that preferentially activate intrinsically photosensitive retinal ganglion cells (ipRGCs) directly, with a duration of 4 seconds and a stimulus intensity of 28 lx corneal illumination under mesopic conditions. One eye was stimulated, and the consensual pupil response was recorded and analyzed. Results: The pupillary light reflex in patients with DMS was reduced, differed in shape, and showed a prolonged latency time compared to normal subjects. The blue response was less affected than the red response: the mean maximal relative amplitude (M) was 15.8% (SD = 7.8) in patients with DMS compared with 43.0% (SD = 5.5) in normal subjects for red stimulation, and M = 40.8%, SD = 8.4 (DMS) with M = 58.3%, SD = 4.8 (normals) for blue stimulation. The reduction was 63% for red stimulation but only 30% for blue stimulation in patients with DMS. Moreover, there was a preserved postillumination pupil response to blue stimulation in DMS patients. Conclusions: In DMS, the melanopsin-mediated ipRGC pathway appeared relatively preserved.

Phosphene perception and pupillary responses to sinusoidal electrostimulation - For an objective measurement of retinal function

&NA; The purpose was to evaluate retinal function by measuring pupillary responses to sinusoidal transcorneal electrostimulation in healthy young human subjects. This work also translates data from analogous in vitro experiments and connects it to the pupillary responses obtained in human experiments. 14 healthy human subjects participated (4 males, 10 females); for the in vitro experiments, two male healthy mouse retinas (adult wild‐type C57B/6J) were used. Pupillary responses to sinusoidal transcorneal electrostimulation of varying stimulus carrier frequencies (10, 20 Hz; envelope frequency constantly kept at 1.2 Hz) and intensities (10, 20, 50 &mgr;A) were recorded and compared with those obtained with light stimulation (1.2 Hz sinusoidal blue, red light). A strong correlation between the sinusoidal stimulation (electrical as well as light) and the pupillary sinusoidal response was found. The difference between the lag of electrical and light stimulation allowed the estimation of an intensity threshold for pupillary responses to transcorneal electrostimulation (mean ± SD: 30 ± 10 &mgr;A (10 Hz); 38 ± 10 &mgr;A (20 Hz)). A comparison between the results of the two stimulation frequencies showed a not statistically significant smaller lag for 10 Hz (10 Hz: 633 ± 90 ms; 20 Hz: 725 ± 178 ms; 50 &mgr;A intensity). Analogous in vitro experiments on murine retinas indicated a selective stimulation of photoreceptors and bipolar cells (lower frequencies) and retinal ganglion cells (higher frequencies) and lower stimulation thresholds for the retinal network with sinusoidal compared to pulsatile stimulation – emphasizing that sinusoidal waveforms are well‐suited to our purposes. We demonstrate that pupillary responses to sinusoidal transcorneal electrostimulation are measurable as an objective marker in healthy young subjects, even at very low stimulus intensities. By using this unique approach, we unveil the potential for an estimation of the individual intensity threshold and a selective activation of different retinal cell types in humans by varying the stimulation frequency. This technique may have broad clinical utility as well as specific relevance in the monitoring of patients with hereditary retinal disorders, especially as implemented in study protocols for novel therapies, e.g. retinal prostheses or gene therapies. HighlightsFunctional evaluation of the retina in humans based on pupillary responses.New paradigm for transcorneal sinusoidal electrical stimulation.Method for an easy estimation of individual thresholds for pupillary responses.Possibility for a selective activation of different retinal cell types.Verification of sinusoidal stimulation in animal in vitro model.

ElVisML: an open data format for the exchange and storage of electrophysiological data in ophthalmology

PurposeThe ISCEV standards and recommendations for electrophysiological recordings in ophthalmology define a set of protocols with stimulus parameters, acquisition settings, and recording conditions, to unify the data and enable comparability of results across centers. Up to now, however, there are no standards to define the storage and exchange of such electrophysiological recordings. The aim of this study was to develop an open standard data format for the exchange and storage of visual electrophysiological data (ElVisML).MethodsWe first surveyed existing data formats for biomedical signals and examined their suitability for electrophysiological data in ophthalmology. We then compared the suitability of text-based and binary formats, as well as encoding in Extensible Markup Language (XML) and character/comma-separated values.ResultsThe results of the methodological consideration led to the development of ElVisML with an XML-encoded text-based format. This allows referential integrity, extensibility, the storing of accompanying units, as well as ensuring confidentiality and integrity of the data. A visualization of ElVisML documents (ElVisWeb) has additionally been developed, which facilitates the exchange of recordings on mailing lists and allows open access to data along with published articles.ConclusionsThe open data format ElVisML ensures the quality, validity, and integrity of electrophysiological data transmission and storage as well as providing manufacturer-independent access and long-term archiving in a future-proof format. Standardization of the format of such neurophysiology data would promote the development of new techniques and open software for the use of neurophysiological data in both clinic and research.

Development of a Chromatic Pupillography Protocol for the First Gene Therapy Trial in Patients With CNGA3-Linked Achromatopsia

Purpose To establish a feasible and sensitive pupillographic protocol to assess outer and inner retinal function for the first gene therapy trial in achromatopsia patients (ACHM) with mutations in CNGA3. Methods Twenty-seven CNGA3-ACHM patients and 22 age-matched control subjects were tested using chromatic pupillography. Three different protocols were established to assess the pupillary light reflex parameters and to create the final protocol. In the individual protocols, various stimulus parameters (i.e., intensity, duration, wavelength, adaptation states) were applied to evaluate the impact of these stimuli on the pupillary response in untreated ACHM patients. Results In the light-adapted conditions, CNGA3-ACHM patients showed significantly reduced maximal amplitudes compared with the control group when using a 1-second high intensity (28-lux corneal illumination) blue or red stimulus (P < 0.005). In the dark-adapted conditions, CNGA3-ACHM patients unexpectedly revealed significantly increased maximal amplitudes when stimulating with red (1 second) or blue (4 ms and 1 second) stimuli of low intensity (0.01-lux corneal illumination; P < 0.05). Pupil responses of CNGA3-ACHM patients after high intensity (28 lux) red and blue 1-second stimuli were within the normal range. Conclusions Chromatic pupillography demonstrated significant reduced pupil responses to stimuli addressing primarily cone function, an increased sensitivity to rod-favoring stimuli and evidence for disinhibition of intrinsically photosensitive retinal ganglion cells in CNGA3-ACHM patients. A final protocol was established based on these findings. These conclusions may be useful for the objective assessment of efficacy gained by gene therapy or other innovative interventions in this hereditary retinal disorder.