{
    "age": {
        "Description": "age of the participant",
        "Units": "years"
    },
    "sex": {
        "Description": "sex of the participant as reported by the participant",
        "Levels": {
            "M": "male",
            "F": "female"
        }
    },
    "group": {
        "Description": "clinical description of visual field loss",
        "Levels": {
            "hemianopia": "participants with homonymous hemianopia as determined by perimetry",
            "quadrantanopia": "participants with homonymous quadrantanopia as determined by perimetry"
        }
    }
}