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.

This within-subject crossover pilot study involves applying a weak focused electrical current to the head, to target areas of visual processing, more specifically the primary visual cortex (V1) within the occipital pole. The purpose of this study is to investigate the efficacy of high-frequency transcranial random noise stimulation (hf-tRNS), a safe and well-established form of brain stimulation on O&M performance of individuals with constricted visual fields in both eyes due to either retinitis pigmentosa (RP), rod-cone dystrophy, or advanced glaucoma.

Participants will be recruited from university-affiliated clinics as well as local clinical practices. After obtaining full informed consent at the first visit, participants will complete clinical tests to confirm that the eligibility criteria of the study are met. These tests include measuring the participant's corrected binocular distance and near visual acuities, binocular contrast sensitivity, binocularity, as well as peripheral visual fields. Researchers will also ensure that it safe for the participant to undergo brain stimulation using a list of contraindicators for brain stimulation interventions and verify that participants are free from physical or motor impairments as well as vestibular disorders or dysfunctions that can impact the participant's walking and balancing abilities.

During the two subsequent visits, the effects of stimulation (which lasts 20 minutes) will be studied 2 and 30 minutes after stimulation. To evaluate improvement, various measures of O&M performance will be targeted as participants complete an O&M course divided into 4 sections and composed of an array of static natural and artificial (man-made) obstacles. Participants will be instructed to walk along the various sections at a comfortable pace, safely negotiating the obstacles without touching any of the obstacles. Participants will also be told in which sections obstacles will be encountered. Static natural obstacles refer to fixed/steady/stable obstacles that are either readily found in the environment (e.g., potted plants) or form part of the architecture of the building (e.g., a pole or a sealed doorway). Artificial obstacles are made of light materials such as polystyrene, rubber foam, soft cardboard, or paper. Static natural/real obstacles will be at foot level, foot to knee height, as well as shoulder and head heights, whereas artificial obstacles will be placed either above the knee, waist, at the shoulder or head height. Individuals with constricted field loss in both eyes who use a long white cane for travelling and have received O&M training (including caning skills) from an orientation and mobility professional will be asked to complete the course with their cane. However, individuals with constricted visual field in both eyes who do not use a cane can also complete the same course.

Measures of performance include the primary outcome measure percentage preferred walking speed (PPWS), that is the walking speed of the individual who is visually impaired in an environment with obstacles expressed as a percentage of their preferred walking speed in an unobstructed path. Secondary outcome measures include: the time taken to complete each of the 4 sections of the course, visual detection distance (VDD) (the distance at which an individual detects an obstacle in the travel path, even if it cannot be identified), and visual identification distance (VID) (the distance at which an individual can correctly identify an obstacle in the travel path).

Course section #1 will not consist of obstacles. The time taken to complete the course section, and preferred walking speed in an unobstructed path (obtained from the completion time and length of the straight, flat path) will be measured.

Course section #2 will consist of obstacles and will be an indoor space leading to a more opened space within the building. The time taken to complete the course section, and preferred walking speed in an obstructed path (obtained from the completion time and length of the path) will be measured. The percentage preferred walking speed (PPWS) will be calculated. PPWS is the preferred walking speed of the individual in course section #2 expressed as a percentage of the participant's preferred walking speed in course section #1.

Course sections #3 and #4 will be used for measuring VDD and VID. Each course will be a straight indoor corridor consisting of only one obstacle, and the obstacle will be different for each of the two sections. Moreover, course section #3 will be used as a training course for measuring VDD and VID. The time taken to complete the course section, visual detection distance (VDD), and visual identification distance (VID) will be measured in course sections #3 and #4.

It is important to note that for course sections with obstacles (course sections # 2 to 4), the location of the obstacles in each trial (pre, post 1, and post 2) will not be varied, but rather the location of the obstacles on each treatment day will be randomized. In addition, two researchers will always be with the participant at all times. One will be with the participant to provide instructions and record data; whilst the other will be ahead of the participant to make sure the path is clear, record the times, and confirm that the obstacles are still in place (when applicable), as well as videorecord the session once consent was obtained from the participant at the first visit. By videorecording the participant as the course task is completed, the researchers will be able to obtain more accurate measures of time.

There will be two stimulation sessions (one with active stimulation and one with placebo (the order will be randomized so that neither the participant nor the researcher will know what the subject will receive)). At the two stimulation sessions the primary and secondary outcome measures will be evaluated as the participant completes the O&M course before stimulation (O&M pretest), as well as 2 mins after stimulation (O&M post-test 1/immediately after stimulation), and 30 mins after stimulation (O&M post-test 2/30 minutes after stimulation).

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) who have little to no functional peripheral vision, any improvement noted would be attributed to be enhanced processing of visual signal in the affected periphery. The objective of this study is to improve the fundamental visual processes of individuals with constricted visual fields using hf-tRNS. From a scientific perspective, the investigators hope to discover whether brain stimulation can serve as an additional rehabilitation tool for improving the O&M skills of individuals with constricted visual fields. Investigators expect that participants will experience temporary O&M improvements, however, there will not be any lasting improvements in O&M skills from such a single session within subject study design. If the results of this study show a positive effect, the data will be used to power a larger study. All procedures will occur at the Human Visual Neuroscience Laboratory, University of Waterloo, Ontario, Canada.

Inclusion Criteria:

• 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 willing and capable of adhering to instructions and maintaining the outlined appointment schedule.

Exclusion Criteria:

• 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.
• Have been diagnosed with vestibular disorders or dysfunctions which affects one's balance and/or mobility or self-reported vestibular disorders or dysfunctions which affects one's balance and/or mobility with no formal diagnosis.
• Are unable to follow the researcher's instructions.
• Are anticipating treatment (including ocular surgery) for any eye disease within the duration of the study.
• Have any ocular pathology in addition to retinitis pigmentosa (RP), rod-cone dystrophy, or advanced glaucoma, which can diminish their visual acuity and/or their visual field, however wearing glasses or contact lenses, as well as mild cataract of grade 2 or below is acceptable.
• Have severe hearing impairment.
• Are pregnant or trying to get pregnant.
• Fit any of the typical contraindicators for brain stimulation. See contraindicator section below.

For all participants the contraindications for brain stimulation are:

• Diagnosed with epilepsy or have previously experienced an epileptic seizure.
• Implanted medication pump or implanted electronic device, including defibrillator or pacemaker.
• Any metal implants in the head (excluding tooth fillings).
• Active electric implants anywhere in the body (especially the head region).
• On psychoactive medication for any psychiatric or neurological conditions including but not limited to depression and schizophrenia.
• Areas of sensitive skin located on the face or head, or a skin condition on the face, or regularly use medication to alleviate skin irritation on the face.
• Recurring headaches.
• Previous head injury or skull fracture or head/brain surgery.
• Heart disease, neurological condition, or a history of cardiac or neurological surgery.
• Current or historical cancerous or noncancerous brain tumor, or other abnormalities in brain structure.

The IPD which underlie results in a publication will be made available after deidentification upon reasonable requests to the research team.

The IPD will be available upon publication, and no more than 9 months after the publication.

The IPD will be shared to researchers who provide a methodologically sound proposal.

Each participant will experience active brain stimulation and placebo (sham)stimulation. The participant and the researcher will be blind to which session the participant receives active brain stimulation and placebo.