Mobility testing will be videotaped at each study visit at which it is conducted. Independent reviewers may grade subjects' mobility videos. Graders will use a defined combination of speed and accuracy to grade each course attempt at a given light intensity. The course will be re-configured between each attempt, using twelve standardized templates, to reduce the impact of a potential learning effect. Each subject will be tested, using both eyes, under at least two and sometimes three different (specified) lighting conditions. The levels of light, selected to span lighting conditions that individuals encounter in daily life, range from a studio with floodlights (400 lux) or a brightly lit office (250 lux) down to a poorly lit sidewalk at night (1 lux).

FST testing measures the light sensitivity of the entire visual field by recording the luminance at which a subject reports seeing the dimmest flash. The test is carried out on subjects with dilated eyes in a dark-adapted state; subjects are seated in front of a Ganzfeld dome in which the light flashes are generated. The light sensitivity of each eye is measured separately by patching one eye (and then the other). A sound is generated and the subject presses one button when they see a flash or a second button if they do not see a flash. Flashes of varying luminance (in a range spanning ~80 dB) are presented in a randomized order with no flashes, except that the series starts with dim flashes. From this data, an algorithm calculates the minimum luminance (for each eye) at which the subject perceives light.

Visual field parameters will evaluate alterations in function of different regions of the retina; kinetic fields will be measured with Goldmann perimetry and static fields with Humphrey computerized testing.