Clinical Trial of Peripheral Prism Glasses for Hemianopia

The purpose of this study is to evaluate the functional utility for general mobility (walking) of new high power permanent peripheral prism glasses, which provide visual field expansion device for patients with homonymous hemianopia (the complete loss of half the field of vision on the same side in both eyes). The efficacy of real peripheral prism glasses will be assessed relative to sham peripheral prism glasses.

Patients with hemianopic field loss are unaware of objects in their blind (non-seeing) hemi-field and often experience difficulties with mobility and navigation, such as walking into obstacles on the side of the field loss. In 2000, Peli (2000) described a new peripheral-prism design of prismatic correction for hemianopia, which addresses many of the inadequacies of existing designs of hemianopic visual aids, and produces true field expansion (i.e. the simultaneously seen field is larger with the device than without). In collaboration with the Schepens Eye Research Institute (Boston, MA), Chadwick Optical Inc (White River Junction, VT) has developed a permanent form of Fresnel prism segments, which are made from an acrylic material and can be embedded in a plastic spectacle lens. These permanent prisms offer better cosmesis, optical quality and durability than the temporary 40 prism-diopter press-on Fresnel prism segments used in previous evaluations of the peripheral prism system. In this study we will evaluate new high-power (57 prism diopter) permanent peripheral prism glasses. The study will employ a crossover design in which each participant will wear a pair of real prism glasses (high-power, 57 prism diopter) and a pair sham prism glasses (low-power, 5 prism diopters, that provide little field expansion) in counterbalanced order. The efficacy of the real prism glasses relative to the sham prism glasses will be assessed for general mobility (walking). We expect that participants will prefer the real prism glasses over the sham prism glasses as the former will be more helpful for obstacle detection when walking. Prism glasses will be fitted by Low Vision Practitioners at community-based Vision Rehabilitation Clinics. After wearing the first pair of glasses for 4 weeks, participants will return for an in-office follow up visit, at which a questionnaire will be administered to record their experiences of wearing the glasses. The second pair of prism glasses will then be fitted. Another questionnaire will be administered 4 weeks later to record the experiences of wearing the second set of glasses. At the end of the period of wearing the second pair of prism glasses, a clinical decision will be made as to whether the participant should continue to use the real prism glasses (e.g. if a participant finds the prism glasses helpful for obstacle avoidance when walking). For participants who continue with the prism glasses, a final telephone follow-up interview will be conducted after about 6 months.

Participants in this arm will receive high power (57 prism diopter) peripheral prism glasses in the first period of the crossover and low power sham peripheral prism glasses in the second period

Participants in this arm will receive low power sham peripheral prism glasses in the first period of the crossover and high power (57 prism diopter) peripheral prism glasses in the second period

All patients will wear two pairs of prism glasses in a crossover design: the high power peripheral prism glasses and sham peripheral prism glasses. Each pair of prism glasses will be worn for four weeks

Low power (5 prism dioptre) prism glasses that provide only about 2 degrees of visual field expansion.

At the end of each crossover period, participants were asked a yes/no question: "If the study were to end today, would you want to continue with these prism glasses (i.e. the prism glasses worn in that period)?" The primary outcome was the overall difference, across the two periods of the crossover, between the proportion of participants saying "yes" to real prism glasses and the proportion saying "yes" to sham prism glasses.

Perceived difficulties with mobility were quantified using a 5-point rating scale (no difficulty to extreme difficulty) for 7 situations (items) relevant to people with hemianopia, including at home, in stores, outdoors, in unfamiliar areas, in familiar areas, in crowded areas, and noticing objects off to the side when walking. The questionnaire was administered at baseline (without prisms) and after each period of the crossover. Interval scale measures of perceived difficulty with overall mobility for each participant were estimated using Rasch analysis of the responses to all seven items (Winsteps software, version 3.70.0.226). Rasch measures were expressed as logits (log odds ratios). Mobility change scores for real and sham prisms were defined as the difference in perceived difficulty relative to baseline (in logits).

Perceived difficulties with mobility were quantified using a 5-point rating scale (no difficulty to extreme difficulty) for 7 situations (items) relevant to people with hemianopia, including at home, in stores, outdoors, in unfamiliar areas, in familiar areas, in crowded areas, and noticing objects off to the side when walking. The questionnaire was administered at baseline (without prisms) and after each period of the crossover. Interval scale measures of perceived difficulty with overall mobility for each participant were estimated using Rasch analysis of the responses to all seven items (Winsteps software, version 3.70.0.226). Rasch measures were expressed as logits (log odds ratios). Mobility change scores for real and sham prisms were defined as the difference in perceived difficulty relative to baseline (in logits).

Perceived difficulties with mobility were quantified using a 5-point rating scale (no difficulty to extreme difficulty) for 7 situations (items) relevant to people with hemianopia, including at home, in stores, outdoors, in unfamiliar areas, in familiar areas, in crowded areas, and noticing objects off to the side when walking. The questionnaire was administered at baseline (without prisms) and after each period of the crossover. Interval scale measures of perceived difficulty with overall mobility for each participant were estimated using Rasch analysis of the responses to all seven items (Winsteps software, version 3.70.0.226). Rasch measures were expressed as logits (log odds ratios). Mobility improvement scores for real and sham prisms were defined as the difference in perceived difficulty relative to baseline (in logits).

Inclusion Criteria: At least 18 years of age. Sighted in both eyes, with monocular visual acuity (best corrected vision), of at least 20/50 in each eye. Complete homonymous hemianopia of more than 3 months duration Refractive error within the -5 dioptre to +5 dioptre range No significant cognitive impairment No history of wearing the Peli system of peripheral prisms for hemianopic field expansion (patients who have worn another type of prismatic correction for hemianopia such as yoked prisms or the Gottlieb VAS system can participate in the study) No physical or mental disabilities, including cognitive dysfunction, balance problems or other deficits that could impair ability to walk or use the peripheral prism spectacles. Able to walk (using a cane or walker is OK) or control the movements of their own wheelchair. In sufficiently good health to attend four in-office visits. Exclusion Criteria: Diagnosis of dementia Diagnosis of visual neglect History of seizures in the last 6 months Incomplete hemianopia

Peli E. Field expansion for homonymous hemianopia by optically induced peripheral exotropia. Optom Vis Sci. 2000 Sep;77(9):453-64. doi: 10.1097/00006324-200009000-00006.

Bowers AR, Keeney K, Peli E. Community-based trial of a peripheral prism visual field expansion device for hemianopia. Arch Ophthalmol. 2008 May;126(5):657-64. doi: 10.1001/archopht.126.5.657.

Bowers AR, Keeney K, Peli E. Randomized crossover clinical trial of real and sham peripheral prism glasses for hemianopia. JAMA Ophthalmol. 2014 Feb;132(2):214-22. doi: 10.1001/jamaophthalmol.2013.5636.