This pilot clinical trial evaluates whether non-invasive brain stimulation improves the orientation and mobility (O\&M) skills of individuals with constricted visual fields in both eyes. The study is composed of three visits. The first visit is meant to confirm eligibility by performing a few clinical tests. Eligible participants will then complete two additional visits, one in which the participants receive active stimulation, and one in which the participants receive placebo (sham) stimulation. Stimulation will be administered in a randomized, double-blind order. To evaluate improvement, various measures of O\&M performance will be assessed on a standardized obstacle course featuring static natural and artificial obstacles at defined intervals after the intervention. We hypothesize that the application of hf-tRNS to V1 will improve the orientation and mobility skills of individuals with constricted visual fields immediately following stimulation as a results of enhanced periphery through modulation of the mechanisms responsible for crowding, thereby reducing crowding effects and improving contrast for individuals with rod-cone dystrophy and RP (genetic conditions), whereas for individuals with glaucoma (a neurogenerative condition), any improvement noted would be attributed to be enhanced processing of visual signal in the affected periphery. The results will inform the design of a future, larger-scale study.
Are healthy, capacitated adults with binocular constricted visual field loss (due to either retinitis pigmentosa (RP), rod-cone dystrophy, or advanced glaucoma) resulting in functional vision losses. These individuals with visual impairments can be those who have been previously trained by an Orientation and Mobility (O&M) specialist to independently travel with the long white cane daily (since the length of the white cane and tip at the base are based on personal preference, they should be willing to use their own white cane for the study), and those who do not necessarily use a cane for travelling.
Have binocular visual acuity or best corrected binocular visual acuity no worse than 6/12 or 20/40 or +0.30 logMAR (inclusive) with no eccentric viewing and binocular visual fields no better than 50 degrees in total in each eye as given by the Humphrey Field analyzer and no better than 50 degrees binocularly as given by arc perimeter test. The Humphrey Field Analyzer measures static visual field test, whereas the Arc perimeter test measures kinetic visual field test. Measuring kinetic and static visual field would promote a greater understanding of the individual's daily performance.
Are over the age of 18 (inclusive) and has full legal capacity to provide informed consent.
Have read and fully comprehends the information in the consent letter.
Are involved in other recent eye-related studies, either clinical or research-related. To be eligible they would have to wait at least one week for studies not involving brain stimulation, and four weeks for studies in which they receive brain stimulation before they could participate in this study.
Have been diagnosed with dementia or self-reported dementia with no formal diagnosis.
Have been diagnosed with a cognitive impairment or self-reported cognitive impairment with no formal diagnosis.
Have been diagnosed with physical or motor impairments resulting in walking and/or balancing issues or self-reported physical or motor impairments resulting in walking and/or balancing issues with no formal diagnosis.
Crossover
Active hf-tRNS.
DeviceActive hf-tRNS: A weak alternating electric current is applied to the head through two electrodes to affect the cortical excitability of the targeted cells in the brain. Stimulation instrument: neuroConn DC Stimulator Plus 2019 (Direct current stimulator Model number 0021, power: 1.2 W, charger: 2.9 V (maximum 160 mA)) (neurocaregroup.com), or neuroConn DC Stimulator MC 2016 (Multi-channel stimulator Model number 0028, power: 24 W, rating: 12 V (maximum 2 A)) (neurocaregroup.com).
Placebo/sham hf-tRNS
DevicePlacebo/sham hf-tRNS: The tRNS machine will be used as in active stimulation, except the electrical current will not be applied. Stimulation instrument: neuroConn DC Stimulator Plus 2019 (Direct current stimulator Model number 0021, power: 1.2 W, charger: 2.9 V (maximum 160 mA)) (neurocaregroup.com), or neuroConn DC Stimulator MC 2016 (Multi-channel stimulator Model number 0028, power: 24 W, rating: 12 V (maximum 2 A)) (neurocaregroup.com).
Percentage preferred walking speed (PPWS)
* Change in Percentage preferred walking speed (PPWS (%)) before and right after (2 mins) active stimulation. * Change in Percentage preferred walking speed (PPWS (%)) before and 30-minutes after active stimulation. * Change in Percentage preferred walking speed (PPWS (%)) before and right after (2 mins) placebo/sham stimulation. * Change in Percentage preferred walking speed (PPWS (%)) before and 30-minutes after placebo/sham stimulation. * Behavioural Measure: The participant will first complete section #1, which is obstacle free. The time taken to complete the section and preferred walking speed in an unobstructed path (obtained from the completion time and length of the straight, flat path) will be measured. They will then proceed to complete section #2, which has obstacles. The time taken to complete the section, and preferred walking speed in an obstructed path will be measured. PPWS= (preferred walking speed course 1/ preferred walking speed course 2)\*100.
Visual detection distance (VDD)
* Change in Visual detection distance (VDD (m)) before and right after (2 mins) active stimulation. * Change in Visual detection distance (VDD (m)) before and 30-minutes after active stimulation. * Change in Visual detection distance (VDD (m)) before and right after (2 mins) placebo/sham stimulation. * Change in Visual detection distance (VDD (m)) before and 30-minutes after placebo/sham stimulation. * Behavioural Measure: Participants will be instructed to walk along the various sections at a comfortable pace, safely negotiating the obstacle without touching any of them. The participant will complete sections #3 and #4. Each section will be a straight indoor corridor consisting of only one obstacle. Moreover, section #3 will be used as a training course, whereas section #4 is meant to collect data. The time it takes to first detect the obstacle and the distance from the participant to the obstacle, the moment it is first detected will be measured. This distance is VDD.
Visual identification distance (VID)
* Change in Visual identification distance (VID (m)) before and right after (2 mins) active stimulation. * Change in Visual identification distance (VID (m)) before and 30-minutes after active stimulation. * Change in Visual identification distance (VID (m)) before and right after (2 mins) placebo/sham stimulation. * Change in Visual identification distance (VID (m)) before and 30-minutes after placebo/sham stimulation. * Behavioural Measure: Participants will be instructed to walk along the various sections at a comfortable pace, safely negotiating the obstacle without touching any of them. The participant will complete sections #3 and #4. Each section will be a straight indoor corridor consisting of one obstacle. Section #3 will be used for training, whereas section #4 is meant to collect data. The time it takes to correctly identify the obstacle just detected, and the distance from the participant to the obstacle, the moment they first identify it will be measured (VID).
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University of Waterloo
Lead sponsor
University of Waterloo School of Optometry and Vision Science
Collaborator
The Hong Kong Polytechnic University
Collaborator
