The investigators will develop and test different configurations of high-power prisms to expand the field of vision of patients with visual field loss to assist them with obstacle detection when walking. The study will involve multiple visits (typically four) to Schepens Eye Research Institute for fitting and testing with the prism glasses. The overall objective is to determine best designs and fitting parameters for implementation in prism devices for future clinical trials.

Inclusion Criteria:

• Visual field loss, either peripheral field loss or hemianopic field loss
• Visual acuity of at least 20/50 in the better eye
• In sufficiently good health to be able to complete sessions lasting 2-4 hours
• Able to independently walk short distances
• Able to give voluntary, informed consent
• Able to speak English

Exclusion Criteria:

• Any physical or mental impairments, including cognitive dysfunction, balance problems or other deficits that could impair the ability to walk or use the prism spectacles
• A history of seizures in the last 6 months
• Hemispatial neglect (subjects with hemianopic field loss only)