Ocular Test is one of eleven International Bedrest Standard Measures conducted on healthy subjects at the :envihab facility in Cologne, Germany. Ocular Tests consist of assessing Intraocular Pressure (IOP), an Ocular Ultrasound, and Optical Coherence Tomography (OCT) and A-scan. The purpose of the standard measures project is to populate a repository with data that enables high-level monitoring of countermeasure effectiveness and meaningful interpretation of health and performance outcomes. These standard measures will support future, hypothesis-driven research that enables planetary missions by providing an optimized minimal set of measures captured from subjects. These measures will be available to other studies under data sharing agreements as well as undergo analysis to understand risk posture.
Intraocular pressure is the fluid pressure of the aqueous humor inside the anterior chamber of the eye. Tonometry will be performed on the right and left eye using a commercial tonometer. The operator will stabilize the subject's head and gently tap the tonometer tip to the clear surface of the open eye directly over pupil to obtain the measurement. Each measurement consists of six successive taps. The tonometer will automatically drop the highest and lowest values and report the mean of the remaining four values. The mean constitutes one measurement. If the variability between the four taps is too high, the device reports “deviation error” and the measurement will not be recorded. Three good measurements are required, and the measurements should fall within a range of 1.5 mmHg. Measurements will be continually taken until three measurements fall within 1.5 mmHg of one another.
The diameter of the optic nerve and nerve sheath will be analyzed using a Prosolv ultrasound. Other parameters that will be derived from the ocular ultrasound scan include assessment of the optic nerve tortuosity and increased optic sheath-to-optic nerve diameter. The ultrasound scan will also be used to identify changes in the globe morphology (flattening of the posterior globe and globe axial length). Optical Coherence Tomography and A-scan:
The retinal thickness, volume, and retinal nerve fiber layer (RNFL) thickness will be measured using optical coherence tomography (OCT) and a quantitative cross-sectional analysis method. Axial samples of A-scans will be obtained in each “scan pass.” All the A-scans will be combined into one image producing an image with a resolving power of about 10 microns vertically and 20 microns horizontally. However, OCT has a high sensitivity for detecting subtle changes to the RNFL of the optic nerve head. An anterior segment module will be used to measure corneal thickness, anterior scleral thickness, and anterior chamber angles. Subjects will be seated with their chin placed on a chin rest. Subjects will focus their eyes into the machine. The machine will scan the subject's eyes and an image and report will be generated and viewed by the ophthalmologist or optometrist.
The scheduled days of collection are as follows:
The :envihab International Bedrest Standard Measures Test Battery is not a hypothesis-driven study, but rather a collection of data made available to future researchers and for trend analysis. As such, there are no specific hypotheses, outcome measures, or statistical analyses associated with the skeleton of the project. The questionnaire will capture a "snapshot" of optimized data that can be investigated by researchers in the future.
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