Combined Non-Invasive Brain and Visual Stimulation for Vision Improvement

Evaluation of Combined Non-invasive Brain Stimulation (NIBS) and Visual Tetanic Stimulation (VTS) for Vision Enhancement: A Randomized, Single-blind, Cross-over Trial

Glaucoma is a complex disease that can result in progressive vision loss. It is the second leading cause of blindness, accounting for 23% of permanent blindness in Hong Kong. There are no treatments that restore vision lost to glaucoma. This study will examine the effect of transcranial direct current stimulation (NIBS) on improving quality of life, visual function and functional performance in patients with peripheral field loss due to glaucoma.

This study uses a prospective, single-masked, randomized, cross-over, placebo-controlled training RCT design.

The eligible participants will be randomly allocated into 4 groups:

(A) Transcranial direct current stimulation; (B) Visual Tetanic Stimulation; (C) Transcranial direct current stimulation+ Visual Tetanic Stimulation; (D) Sham. All participants will underwent all the 4 types of intervention with a 14 days washing out period between intervention types:

All participants will complete twenty-six study visits:

Visit 1: Eligibility assessment (refer to the recruitment criteria); Visit 2: Outcome measures (Pre-intervention/ baseline); Visit 3-7: 5 sessions intervention (1st intervention block); Visit 8: Post 1 outcome measures; Visit 9-13: 5 sessions intervention (2nd intervention block); Visit 14: Post 2 outcome measures; Visit 15-19: 5 sessions intervention (3rd intervention block); Visit 20: Post 3 outcome measures; Visit 21-25: 5 sessions intervention (4th intervention block); Visit 26: Post 4 outcome measures

Eight sessions of assessment will be conducted: (1) Baseline-1; (2) Post-1 (after 5-sessions training); (3) Baseline-2; (4) Post-2 (after 5-sessions training); (5) Baseline-3; (6) Post-3 (after 5-sessions training); (7) Baseline-4; and (8) Post-4 (after 5-sessions training).

Inclusion Criteria:

• Age range from 18 to 80 years;
• Diagnosis of primary open angle or normal tension glaucoma with relative scotoma in both eyes;
• A relative scotoma defined as a Humphrey Field Analyser (HFA) threshold perimetry loss (mean deviation of -6dB) within the central 24 degree of the visual field for at least one eye;
• Best-corrected distance visual acuity of 6/12 or better (equivalent to 0.3 logMAR acuity or better to confirm that participant's central vision is preserved).
• Stable vision and visual field loss for at least 3 months;
• With a cognitive functional score of 22 or above in the Montreal Cognitive Assessment - Hong Kong version (HK-MoCA) (to confirm participant's intact cognitive function).

Exclusion Criteria:

• Ocular diseases other than glaucoma (e.g. age-related macular degeneration, diabetic retinopathy, moderate to severe cataract) or severe hearing impairment (to ensure that participant can hear the instructions clearly during assessments and training);
• Severe medical problems (e.g. stroke, Parkinson's disease) or self-reported neurological (e.g. brain surgery, brain tumor, peripheral neuropathy), or cognitive disorders (e.g. diagnosed dementia or cognitive impairment);
• Self-reported vestibular or cerebellar dysfunction, history of vertigo;
• Using any medications for any neurological conditions or psychiatric drugs (e.g. sedative, hypnotic) that might interfere motor control;
• Contraindications for non-invasive brain stimulation.