The purpose of this report is to further analyse the findings of the RNIB Smart Glasses project in order to comment on the characteristics of people who are more likely to gain benefit from the device. Particular emphasis is given to analysis of the visual field data provided by a subset of participants.
The Smart Glasses (Glasses) have a restricted field of view compared to the normal extent of visual field. It might therefore be considered that people with a visual field that extends beyond that of the Glasses will be losing visual extent by using the Glasses, so the appearance of the image within the screen would have to be significantly better to outweigh the restricted field of view. For those with visual field restricted to within the limits of the Glasses, vision is not being ‘lost’ by wearing them, and so the Glasses may need to provide less improvement in vision to be of benefit overall. To understand this further, visual field whilst wearing the Glasses was assessed.
Binocular visual field was assessed kinetically on the Octopus 900 with the Glasses in mode 5 (with filter in place, maximum contrast, and minimum zoom). As shown in Figure 1, the vertical extent of the field was approx. 35 deg, and horizontal extent approx. 55 deg. In addition, a 50 cm horizontal object fills the Glass screen from a distance of 40cm, indicating a field of 51 deg, consistent with the perimetric findings. Thus the Smart Glasses in mode 5 will be potentially of most use to patients who have vision retained within the central 35 deg vertically (approx. 15 deg above and below fixation) and 55 deg horizontally (approx. 25 deg either side of fixation).
Figure 1. Binocular visual field of the Glasses in mode 5.
In use, modes 1-3 have the same apparent magnification and field of view. Assessing the field of view perimetrically was more problematic as it was difficult to distinguish between the single target being seen through the Glasses and through the periphery of the filter. However, a 50cm horizontal object fills the Glasses screen from a distance of 50cm, which implies a horizontal field of 45 deg, slightly smaller than in mode 5.