Glaucoma Rehabilitation Using ElectricAI Transcranial Stimulation (GREAT) - Randomized Controlled Trial Using Combined Perceptual Learning and Transcranial Electrical Stimulation for Vision Enhancement

Visual field test is measured monocularly using the 24-2 Swedish interactive threshold algorithm (SITA) standard tests by Humphrey Visual Field Analyzer (HFA, Carl Zeiss Meditec Inc., California). The mean deviation (MD), pattern standard deviation (PSD), and visual field index (VFI) are recorded and the MD of 24-2 visual field test is used as primary outcome of intervention effectiveness.

The current HRP is a valid and reliable computer-based visual field assessment based upon a previously well-established program. The revised HRP uses circular geometry instead of a rectangle to present stimuli, while maintaining its high-resolution advantage. During the HRP test, suprathreshold stimuli are presented in a radial pattern within 20 degrees, with a step size of 3 degrees. These stimuli are presented monocularly at a total of 98 positions, with the order of presentation randomized. To ensure a stable result and accurate assessment of participants' responses, the HRP test is repeated five times. Throughout the HRP test, fixation is monitored by an infrared eye tracker (SR Research, Eyelink Portable Duo).

64-channel electroencephalography(EEG) recordings from Neuroscan will be used to understand the electrophysiological changes in the intervention. A standard visual evoked potential task (VEP) and a specific designed SSVEP task will be used to assess the functional integrity of central vision and peripheral function. Besides, resting-state EEG will be recorded to measure the functional connectivity at different timepoints. ERP components (such as P100, N1 and N2) in VEP, tagging frequency response in SSVEP, and the power correlation in resting state will be analyzed as physiological indicators.

All participants will be asked to walk along a 7-m walkway at their normal pace. Two disturbing factors will be introduced while walking: visual searching task and obstacle crossing. For trials with visual search, visual stimuli will be presented on the monitor (located at the end of the walkway) when the participant crosses the obstacle. For trials with obstacle crossing, an obstacle with two different colors (grey for low contrast and yellow for high contrast obstacle) of two different heights (2.5x60x5 cm or 2.5x60x15 cm) are positioned at the middle of the walkway. Participants' gait parameters including hip flexion/extension (degree), knee Min/Max (degree), ankle flexion/extension (degree), head flexion/extension (degree), walking speed (mm/s), step width (mm), and toe clearance(mm) will be measured and analyzed for each condition.

Balance function will be evaluated for the following two conditions:

• Static Balance: Participants will be asked to stand on a force place with a foam while performing visual searching. Parameters including maximum antero-posterior amplitude (mm), maximum medio-lateral amplitude (mm), total sway path (mm), and root mean square sway (mm/s) will be analyzed.
• Perturbed Balance: Participants will be asked to stand on a force place which will translate forward or backward while performing visual searching. Parameters including latency (ms) reacting to the perturbation, maximum antero-posterior amplitude (mm), maximum medio-lateral amplitude (mm), total sway path (mm), and root mean square sway (mm/s) will be analyzed.

National Eye Institute Visual Function Questionnaire 25 (NEI-VFQ 25) and Low Vision Quality of Life (LVQoL) will be used to evaluate the patient-perceived outcome of the intervention on daily living. In NEI-VFQ 25, more positive person measures indicates greater visual ability, and more negative person measures have less visual ability. In the LVQoL, the completion results in a summed score between 0 (a low quality of life) and 125 (a high quality of life).

Magnetic resonance spectroscopy (MRS) is a non-invasive imaging technique that can be used to study the chemical composition of tissues, including the brain. Changes in GABAergic and Glutamatergic concentrations within the MRS voxels will be used to evaluate the mechanistic changes in the brain. To study the mechanism of glaucoma, we plan to use MEGA-PRESS in primary visual cortex(V1) of the brain to understand the neural and metabolic mechanisms.

Serum BDNF concentration will be measured using an enzyme-linked immunoassay (ELISA) kit and liquid chromatography-mass spectrometry(LCMS). DNA will be extracted from the leucocytes for the determination of BDNF Val66Met polymorphism (rs6265G>A) using a method based on polymerase chain reaction (PCR).

Collection of tear sample by capillary tube (10 ul) or Schirmer Strip in labelled eppendorf tube and keep them frozen immediately. Tear BDNF concentration will be measured using an enzyme-linked immunoassay (ELISA) kit and liquid chromatography-mass spectrometry.

Cortisol concentration will be measured using an enzyme-linked immunoassay (ELISA) kit and liquid chromatography-mass spectrometry(LCMS).

Collection of tear sample by capillary tube (10 ul) or Schirmer Strip in labelled eppendorf tube and keep them frozen immediately. Tear Cortisol concentration will be measured using an enzyme-linked immunoassay (ELISA) kit and liquid chromatography-mass spectrometry.

Perceived Stress Scale (PSS-10) and Patient Health Questionnaire - 9 (PHQ9) will be used to evaluated the stress and depression severity of the outcome of the intervention of participant. Individual scores on the PSS-10 can range from 0 to 40 with higher scores indicating higher perceived stress. In PHQ9, the completion results in a summed score between 0 (none minimal) to 27 (severe).

Falling is a significant concern for glaucoma patients, with the fear of falling being a major contributing factor to the incidence of falls. Moreover, fear of falling is associated with a decreased physical and social activity. The Chinese version of the Falls Efficacy Scale- International (FES-I) is a validated and reliable questionnaire used to assess fear of falling in everyday life. This questionnaire includes sixteen items that are related to common daily activities, each graded on a scale of from 1 (not at all concerned) to 4 (very concerned). Higher scores indicate a greater concern about falling, which may indicate a poorer balance ability.

The kinetic test is highly sensitive in detecting changes in the far peripheral visual field, which significantly correlates with balance function and gait performance. The binocular kinetic visual field is measured using Octopus 900 perimetry (Haag-Streit AG, Switzerland). Tests are done in the kinetic mode using the standard protocol (sixteen vectors), with a stimulus size of III4e moving at a speed of 5 degrees/sec to map the hill of vision. Any changes in the area of the isopter over time would indicate the effect of training on the kinetic visual field.