Reversible Increase of Central Choroidal Thickness During High-Altitude Exposure

PURPOSE

This study aimed to quantify the impact of high altitude on choroidal thickness and relate changes of altered choroidal blood flow to clinical parameters and acute mountain sickness (AMS). This work is related to the Tübingen High Altitude Ophthalmology (THAO) study.

METHODS

Enhanced depth imaging spectral-domain optical coherence tomography was used to quantify macular choroidal layer thickness. Peripheral oxygen saturation, heart rate, and AMS scores were assessed in eight healthy subjects at baseline (altitude, 341 m) and at altitude (4559 m) for respective correlations.

RESULTS

Longitudinal analysis revealed a significant (P = 0.011, ANOVA) increase in central choroidal thickness (CCT) during altitude exposure (CCT baseline = 271 ± 9 μm; CCT altitude = 288 ± 9 μm) due to an increased choroidal blood flow. Incidence of AMS at altitude was 50%, peripheral oxygen saturation decreased by 25%, and heart rate increased by 39%. All changes were completely reversible after descent to low altitudes.

CONCLUSIONS

A small but significant increase in choroidal thickness was observed upon acute altitude exposure to 4559 m. This increase in choroidal blood flow was not related to AMS and was fully reversible after return to low altitude.

[The role of the vitreous body in diseases of neighboring structures]

BACKGROUND

The vitreoretinal interface is not merely the space between the vitreous body and the retina but it is also a site for highly complex pathologies with the vitreous body exerting an influence on all the neighbouring structures.

METHODS

A literature search was performed in Pubmed and current book articles

RESULTS

This review article highlights the role of the vitreous body in vitreomacular adhesion and traction, in the development of macular holes and epiretinal membranes as well as its role in age-related macular degeneration. In the retinal periphery the vitreous structures play a pivotal role in retinal tears and detachment as well as in diabetic and other proliferative vitreoretinopathies. The role of the vitreous bodyin the emergence of various forms of cataract is often underestimated.

DISCUSSION

Vitreo-etinal surgeons should thoroughly understand the pathophysiological relationship between the vitreous body and the neighboring structures, especially in the era of medical vitreolysis.

Oculomotor behavior of blind patients seeing with a subretinal visual implant

Electronic implants are able to restore some visual function in blind patients with hereditary retinal degenerations. Subretinal visual implants, such as the CE-approved Retina Implant Alpha IMS (Retina Implant AG, Reutlingen, Germany), sense light through the eye's optics and subsequently stimulate retinal bipolar cells via ∼1500 independent pixels to project visual signals to the brain. Because these devices are directly implanted beneath the fovea, they potentially harness the full benefit of eye movements to scan scenes and fixate objects. However, so far, the oculomotor behavior of patients using subretinal implants has not been characterized. Here, we tracked eye movements in two blind patients seeing with a subretinal implant, and we compared them to those of three healthy controls. We presented bright geometric shapes on a dark background, and we asked the patients to report seeing them or not. We found that once the patients visually localized the shapes, they fixated well and exhibited classic oculomotor fixational patterns, including the generation of microsaccades and ocular drifts. Further, we found that a reduced frequency of saccades and microsaccades was correlated with loss of visibility. Last, but not least, gaze location corresponded to the location of the stimulus, and shape and size aspects of the viewed stimulus were reflected by the direction and size of saccades. Our results pave the way for future use of eye tracking in subretinal implant patients, not only to understand their oculomotor behavior, but also to design oculomotor training strategies that can help improve their quality of life.

Subretinal Visual Implant Alpha IMS--Clinical trial interim report

A subretinal visual implant (Alpha IMS, Retina Implant AG, Reutlingen, Germany) was implanted in 29 blind participants with outer retinal degeneration in an international multicenter clinical trial. Primary efficacy endpoints of the study protocol were a significant improvement of activities of daily living and mobility to be assessed by activities of daily living tasks, recognition tasks, mobility, or a combination thereof. Secondary efficacy endpoints were a significant improvement of visual acuity/light perception and/or object recognition (clinicaltrials.gov, NCT01024803). During up to 12 months observation time twenty-one participants (72%) reached the primary endpoints, of which thirteen participants (45%) reported restoration of visual function which they use in daily life. Additionally, detection, localization, and identification of objects were significantly better with the implant power switched on in the first 3 months. Twenty-five participants (86%) reached the secondary endpoints. Measurable grating acuity was up to 3.3 cycles per degree, visual acuities using standardized Landolt C-rings were 20/2000, 20/2000, 20/606 and 20/546. Maximal correct motion perception ranged from 3 to 35 degrees per second. These results show that subretinal implants can restore very-low-vision or low vision in blind (light perception or less) patients with end-stage hereditary retinal degenerations.

In vivo biocompatibility of a new cyanine dye for ILM peeling

PURPOSE

To investigate the biocompatibility of the new cyanine dye: 3,3'-Di-(4-sulfobutyl)-1,1,1',1'-tetramethyl-di-1H-benz[e]indocarbocyanine (DSS) as a vital dye for intraocular application in an in vivo rat model and to evaluate the effects of this dye on retinal structure and function.

METHODS

DSS at a concentration of 0.5% was applied via intravitreal injections to adult Brown Norway rats with BSS serving as a control. Retinal toxicity was assessed 7 days later by means of retinal ganglion cell (RGC) counts, light microscopy, optical coherence tomography (OCT), and electroretinography (ERG).

RESULTS

No significant decrease in RGC numbers was observed. No structural changes of the central retina were observed either in vivo (OCT) or under light microscopy. ERGs detected a temporary reduction of retinal function 7 days after injection; this was no longer evident 14 days after injection.

CONCLUSIONS

DSS showed good biocompatibility in a well-established experimental in vivo setting and may be usable for intraocular surgery as an alternative to other cyanine dyes. In contrast to indocyanine green, it additionally offers fluorescence in the visual spectrum. Further studies with other animal models are needed before translation into clinical application.

Safety evaluation of "retina implant alpha IMS"--a prospective clinical trial

BACKGROUND

To restore vision in patients with retinitis pigmentosa, several types of electronic devices have been developed to stimulate neurons at different levels along the visual pathway. Subretinal stimulation of the retina with the Retina Implant Alpha IMS (Retina Implant AG, Reutlingen, Germany) has been demonstrated to provide useful vision in daily life. Here we evaluated the safety of this device.

METHODS

An interventional, prospective, multi-center, single-arm study was conducted in patients with retinitis pigmentosa with the Retina Implant Alpha IMS. The results from the first nine patients of a single center regarding safety of the device are reported. Any untoward medical occurrence related or unrelated to the tested device was documented and evaluated.

RESULTS

Nine adult subjects were included in the study at the Tübingen site. Seventy-five adverse events occurred in total, and 53 affected the eye and its adnexa. Thirty-one ocular adverse events had a relationship to the implant that was classified as "certain" while 19 had a probable or possible relationship; three had no relationship to the implant. Thirty-nine ocular adverse events resolved without sequelae, two resolved with sequelae, 11 remained unresolved, and in one the status was unknown. The intensity of ocular adverse events was mild in the majority of cases (n = 45), while six were of moderate and two of severe intensity. There was no non-ocular adverse event with certain relationship to the device. One subject lost light perception (without light localization) in her study eye.

CONCLUSIONS

In conclusion, this prospective study, "Safety and Efficacy of Subretinal Implants for Partial Restoration of Vision in Blind Patients," shows that the Retina Implant Alpha IMS is an option for restoring vision using a subretinal stimulation device with a clinically acceptable safety profile.

Pupillary light reaction during high altitude exposure

PURPOSE

This study aimed to quantify the pupillary light reaction during high altitude exposure using the state of the art Compact Integrated Pupillograph (CIP) and to investigate a potential correlation of altered pupil reaction with severity of acute mountain sickness (AMS). This work is related to the Tübingen High Altitude Ophthalmology (THAO) study.

METHODS

Parameters of pupil dynamics (initial diameter, amplitude, relative amplitude, latency, constriction velocity) were quantified in 14 healthy volunteers at baseline (341 m) and high altitude (4559 m) over several days using the CIP. Scores of AMS, peripheral oxygen saturation and heart rate were assessed for respective correlations with pupil dynamics. For statistical analysis JMP was used and data are shown in terms of intra-individual normalized values (value during exposure/value at baseline) and the 95% confidence interval for each time point.

RESULTS

During high altitude exposure the initial diameter size was significantly reduced (p<0.05). In contrast, the amplitude, the relative amplitude and the contraction velocity of the light reaction were significantly increased (p<0.05) on all days measured at high altitude. The latency did not show any significant differences at high altitude compared to baseline recordings. Changes in pupil parameters did not correlate with scores of AMS.

CONCLUSIONS

Key parameters of the pupillary light reaction are significantly altered at high altitude. We hypothesize that high altitude hypoxia itself as well as known side effects of high altitude exposure such as fatigue or exhaustion after ascent may account for an altered pupillogram. Interestingly, none of these changes are related to AMS.

Functional outcome in subretinal electronic implants depends on foveal eccentricity

PURPOSE

An active microelectronic subretinal implant, developed to replace the photoreceptive function in hereditary degenerations of the outer retina, has been applied in a pilot and clinical study in patients with end-stage retinal degeneration.

METHODS

The study population comprised 20 blind patients, all of whom lost vision as result of a hereditary retinal disease. An active visual implant was placed surgically within the subretinal space of each patient: subfoveal placement in eight patients (group 1) and parafoveal placement in 12 (group 2). Standardized low-vision tests, including light perception, light localization, movement detection, grating acuity, and visual acuity by Landolt C-rings, were used under masked, randomized implant-OFF and implant-ON conditions. For the chip-mediated vision functional results of both subject groups were compared.

RESULTS

Three of 20 patients were excluded from analysis because of surgical or technical implant issues. Among patients with nonfoveal placement of the implant, 80% could perceive light, 10% recognized location, and 10% correctly distinguished stripe patterns up to a resolution of 0.33 cycles/degree. No nonfoveal placement patient passed the motion or Landolt C-ring tests. When the implant was placed subfoveally, 100% of patients could perceive light and determine light localization, 75% could resolve motion up to 35°/s, 88% correctly distinguished stripe patterns up to a resolution of 3.3 cycles/degree, and 38% passed a Landolt C-ring test with a decimal visual acuity of up to 20/546 (logMAR 1.43).

CONCLUSIONS

Subfoveal placement of active subretinal visual implants allows superior measurable outcomes compared to para- or nonfoveal placement locations. (ClinicalTrials.gov numbers, NCT01024803, NCT00515814.).

Missing correlation of retinal vessel diameter with high-altitude headache

The most common altitude-related symptom, high-altitude headache (HAH), has recently been suggested to originate from restricted cerebral venous drainage in the presence of increased inflow caused by hypoxia. In support of this novel hypothesis, retinal venous distension was shown to correlate with the degree of HAH. We quantified for the first time retinal vessel diameter changes at 4559 m using infrared fundus images obtained from a state of the art Spectralis™ HRA+OCT with a semiautomatic VesselMap 1® software. High-altitude exposure resulted in altered arterial and venous diameter changes at high altitude, however, independent of headache burden.

Electroretinographic assessment of retinal function during acute exposure to normobaric hypoxia

BACKGROUND

The current study aimed to investigate retinal function during exposure to normobaric hypoxia.

METHODS

Standard Ganzfeld ERG equipment (Diagnosys LLC, Cambridge, UK) using an extended ISCEV protocol was applied to explore intensity-response relationship in dark- and light- adapted conditions in 13 healthy volunteers (mean age 25 ± 3 years). Baseline examinations were performed under atmospheric air conditions at 341 meters above sea level (FIO2 of 21 %), and were compared to hypoxia (FIO2 of 13.2 %) by breathing a nitrogen-enriched gas mixture for 45 min. All subjects were monitored using infrared oximetry and blood gas analysis.

RESULTS

The levels of PaCO2 changed from 38.4 ± 2.7 mmHg to 36.4 ± 3.0 mmHg, PaO2 from 95.5 ± 1.9 mmHg to 83.7 ± 4.6 mmHg, and SpO2 from 100 ± 0 % to 87 ± 4 %, from baseline to hypoxia respectively. A significant decrease (p < 0.05) was found for saturation amplitude of the dark-adapted b-wave intensity-response function (Vmax), dark-adapted a- and b-wave amplitudes of combined rod and cone responses (3 and 10 cd.s/m(2)), light-adapted b-wave amplitudes of single flash (3 and 10 cd.s/m(2)), and flicker responses (5-45 Hz) during hypoxia compared to baseline, without changes in implicit times. The a-wave slope of combined rod and cone responses (3 and 10 cd.s/m(2)) and the oscillatory potentials were significantly lower during hypoxia (p < 0.05). A isolated light-adapted ON response (250 ms flash) showed a reduction of amplitudes at hypoxia (p < 0.05), but no changes were observed for the OFF response.

CONCLUSIONS

The results show significant impairment of retinal function during simulated normobaric short-term hypoxia affecting specific retinal cells of rod and cone pathways.

Identification of a novel mutation in the PRCD gene causing autosomal recessive retinitis pigmentosa in a Turkish family

PURPOSE

Progressive rod-cone degeneration (PRCD) is a canine form of autosomal recessive photoreceptor degeneration and serves as an animal model for human retinitis pigmentosa (RP). To date, only two RP-causing mutations of the PRCD gene have been reported in humans. We found a novel mutation in PRCD (c.52C>T, p.R18X) in three siblings affected by RP and present detailed morphologic and functional parameters.

METHODS

A complete ophthalmological examination was performed including psychophysical tests (best-corrected visual acuity, Lanthony Panel D-15 color vision test, and visual field) and electrophysiology (ganzfeld and multifocal electroretinogram). Additionally, color and infrared fundus photography, autofluorescence, and spectral domain optical coherence tomography recordings were performed. Genomic DNA of the three affected individuals was analyzed with high-throughput sequencing for all RP-related genes in a diagnostic set-up.

RESULTS

We identified a novel homozygous mutation in PRCD (c.52C>T, p.R18X) with diagnostic high-throughput panel sequencing. All three patients showed an advanced stage of retinitis pigmentosa with reduced visual acuity (mean: 20/80), small residual visual fields (mean for target III4e: 1134.35 deg²), and non-detectable electrophysiological responses. Myopia, posterior subcapsular cataract, bone spicule-like pigmentation, and attenuated arterioles were typical findings. Interestingly, bull's eye maculopathy due to patchy retinal pigment epithelium atrophy was also present in all patients. The mean central retinal thickness observed in optical coherence tomography was 148 µm.

CONCLUSIONS

The identification of a third mutation in PRCD confirms its role in the pathogenesis of RP. Clinical findings were in line with the morphological changes observed in previous studies. Bull's eye maculopathy seems to be a hallmark of RP due to mutations in the PRCD gene.

Electroretinographic assessment of retinal function at high altitude

Although hypoxia plays a key role in the pathophysiology of many common and well studied retinal diseases, little is known about the effects of high-altitude hypoxia on retinal function. The aim of the present study was to assess retinal function during exposure to high-altitude hypoxia using electroretinography (ERG). This work is related to the Tübingen High Altitude Ophthalmology (THAO) study. Electroretinography was performed in 14 subjects in Tübingen, Germany (341 m) and at high altitude at La Capanna Regina Margherita, Italy (4,559 m) using an extended protocol to assess functional integrity of various retinal layers. To place findings in the context of acute mountain sickness, correlations between ERG measurements and oxygen saturation, heart rate, and scores of acute mountain sickness (AMS) were calculated. At high altitude, the maximum response of the scotopic sensitivity function, the implicit times of the a- and b-wave of the combined rod-cone responses, and the implicit times of the photopic negative responses (PhNR) were significantly altered. A-wave slopes and i-waves were significantly decreased at high altitude. The strongest correlation was found for PhNR and O2 saturation (r = 0.68; P < 0.05). Of all tested correlations, only the photopic b-wave implicit time (10 cd·s/m(2)) was significantly correlated with severity of AMS (r = 0.57; P < 0.05). ERG data show that retinal function of inner, outer, and ganglion cell layer is altered at high-altitude hypoxia. Interestingly, the most affected ERG parameters are related to combined rod-cone responses, which indicate that phototransduction and visual processing, especially under conditions of rod-cone interaction, are primarily affected at high altitude.

[Therapeutic approaches for retinitis pigmentosa]

BACKGROUND

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of hereditary retinal disorders, which lead to progressive loss of vision and finally blindness. Yet there is no approved therapy. Advances in unravelling underlying genetic disorders and pathophysiological mechanisms offer new therapeutic approaches of which some are summarised in this review.

METHODS

We performed a systematic literature research for defined key words in PubMed.

RESULTS

New approaches to therapy for RP include: gene therapy, pharmacological treatment, neuroprotection, electrical stimulation, retinal prostheses, retinal transplantation and optogenetic therapy.

CONCLUSIONS

Recently there have been advances in new approaches for therapy of dystrophic retinal diseases. Advances in the different approaches are being made at different rates. Although there is no approved therapy yet, the future for treating RP at least in some patients looks promising.

Artificial vision with wirelessly powered subretinal electronic implant alpha-IMS

This study aims at substituting the essential functions of photoreceptors in patients who are blind owing to untreatable forms of hereditary retinal degenerations. A microelectronic neuroprosthetic device, powered via transdermal inductive transmission, carrying 1500 independent microphotodiode-amplifier-electrode elements on a 9 mm² chip, was subretinally implanted in nine blind patients. Light perception (8/9), light localization (7/9), motion detection (5/9, angular speed up to 35 deg s⁻¹), grating acuity measurement (6/9, up to 3.3 cycles per degree) and visual acuity measurement with Landolt C-rings (2/9) up to Snellen visual acuity of 20/546 (corresponding to decimal 0.037 or corresponding to 1.43 logMAR (minimum angle of resolution)) were restored via the subretinal implant. Additionally, the identification, localization and discrimination of objects improved significantly (n = 8; p < 0.05 for each subtest) in repeated tests over a nine-month period. Three subjects were able to read letters spontaneously and one subject was able to read letters after training in an alternative-force choice test. Five subjects reported implant-mediated visual perceptions in daily life within a field of 15° of visual angle. Control tests were performed each time with the implant's power source switched off. These data show that subretinal implants can restore visual functions that are useful for daily life.

Transcorneal electrical stimulation in patients with retinal artery occlusion: a prospective, randomized, sham-controlled pilot study

Introduction

The purpose of this study was to investigate the safety and efficacy of transcorneal electrical stimulation (TES) in patients suffering from retinal artery occlusion (RAO).

Methods

Twelve patients with central and one patient with branch RAO (age 25–84 years, median 74 years) were enrolled in this prospective, randomized, sham-controlled study. RAO was diagnosed 10 days to 17 months prior to study participation. Patients were treated with TES (5 ms positive followed by 5 ms negative biphasic pulses at 20 Hz; applied with DTL electrodes) for 30 min once a week for 6 consecutive weeks. Patients were randomly assigned to TES with 0 mA (sham, n = 3), 66% (n = 5) or 150% (n = 5) of the patient’s individual electrical phosphene threshold (EPT) at 20 Hz. Best corrected visual acuity, ophthalmology examination and EPT (at 3, 6, 9, 20, 40, 60, and 80 Hz) were determined at baseline and at eight follow-up visits over 17 weeks. During four visits (week 1, 5, 9, and 17) kinetic and static visual fields as well as full-field and multifocal electroretinography were measured. The method of restricted maximum likelihood (P < 0.05, Tukey–Kramer) was used to estimate the development of parameters under treatment.

Results

TES was tolerated well; no ocular or systemic adverse events were observed except for foreign-body sensation after TES (n = 3). During the study period the slopes of the scotopic a-wave increased significantly (high-intensity flash white 10 cd.s/m²; P = 0.03) in the 150% treatment group. All other parameters in all other groups remained statistically unchanged.

Conclusions

Although TES was tolerated well, statistically significant improvements were found only for specific a-wave slopes. This is in contradiction to previous smaller, uncontrolled reports. Further studies with larger sample sizes and longer duration might, however, show additional significant effects.

Safety and efficacy of subretinal visual implants in humans: methodological aspects

BACKGROUND

Replacing the function of visual pathway neurons by electronic implants is a novel approach presently explored by various groups in basic research and clinical trials. The novelty raises unexplored methodological aspects of clinical trial design that may require adaptation and validation.

METHODS

We present procedures of efficacy and safety testing for subretinal visual implants in humans, as developed during our pilot trial 2005 to 2009 and multi-centre clinical trial since 2010.

RESULTS

Planning such a trial requires appropriate inclusion and exclusion criteria. For subretinal electronic visual implants, patients with photoreceptor degeneration are the target patient group, whereas presence of additional diseases affecting clear optic media or the visual pathway must be excluded. Because sham surgery is not possible, a masked study design with implant power ON versus OFF is necessary. Prior to the efficacy testing by psychophysical tests, the implant's technical characteristics have to be controlled via electroretinography (ERG). Moreover the testing methods require adaptation to the particular technology. We recommend standardised tasks first to determine the light perception thresholds, light localisation and movement detection, followed by grating acuity and vision acuity test via Landolt C rings. A laboratory setup for assessing essential activities of daily living is presented. Subjective visual experiences with the implant in a natural environment, as well as questionnaires and psychological counselling are further important aspects.

CONCLUSIONS

A clinical trial protocol for artificial vision in humans, which leads a patient from blindness to the state of very low vision is a challenge and cannot be defined completely prior to the study. Available tests of visual function may not be sufficiently suited for efficacy testing of artificial vision devices. A protocol based on experience with subretinal visual implants in 22 patients is presented that has been found adequate to monitor safety and efficacy.