Clinical Trial of Multi-Periscopic Prism Glasses for Hemianopia

Patients with hemianopic field loss may be unaware of objects in their blind (non-seeing) hemi-field and often experience difficulties with hazards, such as walking into obstacles on the side of the field loss. Prism glasses that provide field of view expansion may be helpful in detecting hazards on the blind side. In this clinical trial, two types of high power prism glasses will be evaluated. A new design of prisms, Multi-Periscopic Prisms (MPP), will be compared to commercially-available permanent Fresnel peripheral prism (FPP) glasses. The extent to which the prismatic devices improve detection of hazards on the side of the field loss and are helpful when walking will be evaluated.

Participants will try each type of prism glasses at home for 4 weeks in counterbalanced order. Prism glasses will be fitted by Low Vision Practitioners at vision rehabilitation clinics. Participants will attend in-office study visits before and after wearing each type of prism glasses. At the in-office visits they will complete a test that involves detecting pedestrian hazards in a video simulating a walk through a busy shopping mall (virtual reality, VR, walking simulator test). In addition, they may be asked to complete questionnaires to record their experiences of using the prism glasses.

After wearing the second pair of prism glasses, participants will be asked to complete a questionnaire comparing the two types of prism glasses and to select their preferred type. A clinical decision will be made as to whether the participant should continue to use either the first or second pair of prism glasses (e.g. if a participant finds one pair of prism glasses helpful for obstacle avoidance when walking). For participants who continue with the prism glasses, telephone follow-up interviews will be conducted after about 6 and 12 months.

Inclusion criteria

• Homonymous hemianopia with or without macular sparing for at least 3 months
• Visual acuity of at least 20/50 in each eye, with correction if needed
• Refractive error in the -12D to +5D range
• Able to walk independently, using a cane or walker if needed
• Able to communicate in English sufficiently to understand the study procedures and how to use the prisms

Exclusion criteria

• Central visual field loss in the seeing hemifield of either eye (e.g. from macular degeneration, glaucoma, diabetic retinopathy or other maculopathies)
• Hemi-spatial neglect
• Significant cognitive impairment
• Dementia
• Any other physical or mental disabilities, or general health problems that could impair the ability to be independently mobile (i.e., walk ), participate in the VR walking simulator test or use the prism glasses