VISUAL FUNCTION AFTER PROLONGED BED RESTPolona Jaki Mekjavic1, Ola Eiken and Igor B Mekjavic2,3

Swedish Defence Research Agency, Karolinska Institutet, Stockholm, Sweden1Eye Clinic, Clinical Centre Ljubljana , Ljubljana, Slovenia

2Institute of Biomedical and Bimolecular Sciences, Department of Sports and Exercise Science, University of Portsmouth, Portsmouth , United Kingdom3Department of Automation, Biocybernetics and Robotics, Institute Jozef Stefan, Ljubljana, Slovenia

RESULTS

There were no significant changes in any of the measured indices of visual function after 35 days of horizontal bed rest.

ABSTRACT

The present study evaluated the claim of earlier reports, that of bed rest-induced alterations in visual function. Indices of visual function were studied in 10 healthy male subjects, during 35 days of horizontal bed rest. Before and after the 35 dat bed rest, both eyes of all subjects were examined for visual acuity, intraocular pressure, contrast sensitivity, stereopsis and visual field. Pre- and post-bed rest values were compared with Student’s T-test. There were no significant differences in any of the measured indices of visual function.

BACKGROUNDIn clinical practice, prolonged bed rest is normally associated with either the patient’s inability to function in an upright position due to some pathology, or as a supportive therapy of a pathological condition. Decades ago, prolonged bed rest was the primary therapy for fractured bones and retinal detachment. In contrast to clinical experiences with prolonged bed rest, which have not reported any affects of bed rest on visual function, Drozdova and Nesterenko (1969) reported that prolonged bed rest reduced visual acuity, enlarged blind spot in the visual field and reduced intraocular pressure. These observed changes persisted 20 days into recovery after the bed rest.

METHODSA total of 15 healthy male subjects participated in the study. They were assigned to either a control group (N=5) or the bed rest group (N=10). All measurements of visual function were performed on subjects in both groups. In addition to the tests described below, subjects’ optical media and fundus were examined with biomicroscopy, which is essential for appropriate interpretation of the results of the visual tests conducted.

VISUAL ACUITY - was measured for each eye separately by having subjects view standard Snellen test charts at a distance of 6 metres. The smallest line of letters, which can be resolved by the subject is noted. The test distance is then divided by this line to give a fraction.

EYE PRESSURE - was measured in each eye with a pneumotonometer (Topcon).

STEREO VISION - was measured with the Titmus test. Wearing test glasses, subjects view stereograms, and indicate the number of three-dimensional objects perceived in the stereo illustration.

CONTRAST SENSITIVITY - was measured with a computerised test, in which letters on the computer monitorare observed from a distance of one metre. The letters’ contrast progressively decreases, but not their size.

VISUAL FIELD - the visual field of each eye was tested with computerised perimetry (Octopus, G2-top program). This is an automated test, whereby subjects are requested to respond to stimuli presented at various preset locations in the visual field.

AIMThe aim of the present study was to evaluate by means of current diagnostic methods, whether prolonged bed rest influences visual function.

CONCLUSIONS• In contrast to the earlier observations of Drozdova and Nesterenko (1969), we did not observe any impairment in visual function as a consequence of 35 days of horizontal bed rest.

• A possibility for the difference between our findings and those of Drozdova and Nesterenko (1969), are that current diagnostic tools are much more sensitive and accurate.

ReferencesDrozdova N.T. and O.N. Nesterenko (1969). State of the visual analyser during hypodynamia. In: Problems of Space Biology. Prolonged limitation of motility and its influence on the human organism. Ed.: A.M. Genin and P.A. Sorokin. Moscow: Nauka, vol. 13, pp. 189-191 (NASA TT F-639, 1970).

AcknowledgementsThe authors are indebted to the personnel at the Valdoltra Orthopaedic Hospital in Ankaran (Slovenia).

Orthopaedic Hospital Valdoltra (Ankaran, Slovenia), where the bed rest study was conducted.