Rational and design of the REMOTE trial: An exploratory, pilot study to analyze REtinal MicrOcirculaTion in wEightlessness

BACKGROUND

"Spaceflight associated neuro-ocular syndrome" (SANS) represents a challenging health condition in modern space medicine. Forty-eight percent of astronauts are diagnosed with SANS after long-term space missions. The pathophysiological mechanism seems to be multifactorial, and yet remains unknown. In this proof-of-concept study we plan to investigate retinal microcirculatory changes in weightlessness and aim to identify their role in the development of SANS.

METHODS AND DESIGN

Healthy individuals will take part in a parabolic flight campaign, which recreates fractioned total weightlessness periods. The airplane is specifically equipped, and designed for the execution of parabolic flight maneuvers and scientific research in microgravity. Retinal microcirculation will be assessed with a modified fundus camera, which allows dynamic vessel analysis. We will additionally measure intra-ocular pressure and hemodynamic changes during each phase of the flight. Blood samples will be analyzed at baseline, one hour and 24 hours after exposure to weightlessness.

CONCLUSIONS

This pilot study aims to investigate the feasibility of retinal microcirculation assessment during varying gravity. Results of this study may generate insights whether venous stasis in the eye, surrogated by the dilatation of retinal vessels and increase in intraocular pressure as signs of venous insufficiency, may potentially contribute to the development of SANS.

The effect of hypoxia on intra-ocular, mean arterial, retinal venous and ocular perfusion pressures

INTRODUCTION

High altitude hypoxia is linked to decreased blood oxygen saturation with a related increase of Endothelin-1 (ET-1) blood plasma levels. As a consequence of such elevated ET-1 levels, alterations of retinal venous and ocular perfusion pressures are suspected.

PURPOSE

To measure the effect of hypoxia on intra-ocular pressure, mean arterial pressure, retinal venous pressure and to calculate ocular perfusion pressure.

METHOD

An experimental, prospective cohort study with 33 healthy subjects was conducted in which the subjects were confronted with long-term (days) environmental hypoxia at high altitudes. Mean arterial pressure, arterial blood oxygen saturation, intra-ocular pressure, retinal venous and ocular perfusion pressure were measured at 300 m/1'000 ft (baseline), 4200 m/13'800 ft and 6000 m/19'700 ft above sea level.

RESULTS

Arterial oxygen saturation (-13.06% ± 4.69, p = < 0.001; -23.46% ± 5.7,p = < 0.001), retinal venous pressure (+7.16 m Hg±8.2, p = < 0.001;+9.9 mm Hg±8.5, p = < 0.001) and ocular perfusion pressure (-8.49 mm Hg±10.6, p = < 0.001; -6.02 mm hg±11.2, p = 0.006) changed significantly from baseline at both high altitude of 4200 and 6000 m. Intra-ocular pressure did not change significantly at all altitudes (+1.16 mm Hg±4.5, p = 0.227; +0.84 mm Hg±4.8, p = 0.286) and mean arterial pressure changed significantly only at an altitude of 6000 m (+3,8 mm Hg±21.1, p = 0.005) from baseline.

CONCLUSION

As hypoxia increases with higher altitude, arterial oxygen saturation and ocular perfusion pressure decreased, retinal venous pressure increased, intra-ocular pressure remains stable and mean arterial pressure was elevated only at 6000 m.

Patients with diabetic retinopathy have high retinal venous pressure

Background

The introduction of ophthalmodynamometric measurement of retinal venous pressure (RVP) now permits the quantification, or at least an approximation, of the real pressure in the retinal veins.

Methods

We measured the RVP of healthy control subjects, patients with diabetes without diabetic retinopathy (nonDR) and patients with diabetes and diabetic retinopathy (DR).

Results

The mean ± SD RVP for the control, nonDR and DR groups were 23.4 ± 7.33, 22.5 ± 5.78 and 37.7 ± 10.1 mmHg, respectively. In the diabetes patients with DR, the RVP was markedly and significantly increased, and this result was significantly age dependent. RVP was not increased in the group of diabetes patients without DR. In our tested population, diabetes had a minor influence on intraocular pressure.

Conclusion

Regardless of the cause, a marked increase in RVP in diabetes patients with DR is clinically relevant, as it reduces perfusion pressure and increases transmural pressure. The reduced perfusion pressure contributes to hypoxia, and the increased transmural pressure can facilitate retinal edema.

Diabetes is an increasing burden, and DR is one of its most severe complications. Strategies to recognize the risk for DR and to develop personalized prevention and therapy therefore have major implications.

Trial registration

ClinicalTrials.gov ID: NCT01771835.

[Neurological diseases and suicide: from neurobiology to hopelessness]

Neurologic diseases expose at a high risk of suicidal behaviors and they constitute a privileged domain for exploring the heterogeneity of underlying mechanisms. They are in fact characterized by strictly biological injuries that may be involved in cerebral systems considered at the basis of neurobiological vulnerability for suicide. At the same time, they oblige a numberof existential topics to emerge, as the hopelessness in respect of several particularly severe conditions without an etiologic treatment. A clinical approach reserving an unconditional listening can prevent a suicidal attempt. Furthermore, it can illustrate the role of the liaison's psychiatrist, who tries to transform a hopelessness situation into a patient's personal questioning and try to be present when therapeutic action is not longer possible.

The effect of flammer-syndrome on retinal venous pressure

BACKGROUND

The purpose of the study was to measure the retinal venous pressure (RVP) in the eyes of primary open-angle glaucoma (POAG) patients and healthy subjects with and without a Flammer-Syndrome (FS).

METHODS

RVP was measured in the following four groups of patients and age- and sex-matched healthy controls: (a) 15 patients with a POAG and a FS (POAG/FS+); (b) 15 patients with a POAG but without a FS (POAG/FS-); (c) 14 healthy subjects with a FS (healthy/FS+) and (d) 16 healthy subjects without a FS (healthy/FS-). RVP was measured in all participants bilaterally by means of contact lens ophthalmodynamometry. Ophthalmodynamometry is done by applying increasing pressure on the eye via a contact lens. The minimum force required to induce a venous pulsation is called ophthalmodynamometric force (ODF). The RVP is defined and calculated as the sum of ODF and intraocular pressure (IOP) [RVP = ODF + IOP].

RESULTS

The participants with a FS (whether patients with POAG or healthy subjects), had a significantly higher RVP compared to subjects without a FS (p = 0.0103). Patients with a POAG and FS (POAG/FS+) had a significantly higher RVP compared to patients without a FS (POAG/FS-) (p = 0.0301). There was a notable trend for a higher RVP in the healthy/FS + group compared to the healthy/FS - group, which did not reach statistical significance (p = 0.0898).

CONCLUSIONS

RVP is higher in subjects with a FS, particularly in glaucoma patients. The causal relationship needs to be further evaluated.

Correction of high amounts of astigmatism through orthokeratology. A case report

The purpose of this case report is to introduce a method for a successful treatment of high astigmatism with a new orthokeratology design, called FOKX (Falco Kontaktlinsen, Switzerland). This novel toric orthokeratology contact lens design, the fitting approach and the performance of FOKX lenses will be illustrated in the form of a case report. Correcting astigmatism with orthokeratology offers a new perspective for all patients suffering astigmatism.