Fig. 20.1  Horizontal diameters of visual fields are plotted across luminance. Each symbol identifies an individual subject

well above what is normally required, say at daylight levels (10,000+ cd/m2) in order to maximize the contribution from the remaining functional retina beyond the prosthesis­ . This may be done in log unit steps of 10 cd/m2 (white paper under living room level), 100 cd/m2 (white paper under office light levels), 1,000 cd/m2 (white paper outdoors in overcast) and 10,000 cd/m2 (white paper outdoors in sun).

20.3  Vision Assessment in Prosthesis Recipients: Overview

We consider vision assessment as two components. They are, in our terminology, visual function and visual performance. Visual performance is itself comprised of two components: objective (measured) and subjective (self-reported) ability to accomplish tasks. In this regard, the point of view of this chapter is similar to the three-pronged approach suggested by Wilke et al. [112].

20.3.1  Visual Function Assessment: Overview

Visual function forms the basis of evidence for evaluating benefit/risk to relevant parties (e.g., other researchers, funding agencies, the FDA). Acceptable outcome measures of clinical trials have classically been visual function, most notably visual acuity, as described above. Four aspects of vision accepted by the FDA are, with constraints, visual acuity, visual fields, contrast sensitivity, and color vision [24]. Visual function may be more reliable, objective, and sensitive than either aspect of visual performance; however, it may be the least relevant to real-life conditions to