visual acuity. The attention itself that is directed to this eye by virtue of the intervention may improve the patient’s ability to use peripheral retina and thereby improve the visual acuity. This phenomenon may be addressed in part by providing some low vision training prior to the clinical trial.

5.8  Photopsias

5.8.1  Photopsias in RP

The basis of photopsias, or light flashes, in RP and other conditions is not wellunderstood. They may be manifestations of spontaneous activity in compromised retinal cells, or in retinal microneuromas, triggered through inner plexiform layer connections, possibly due to remodeling and/or ganglion cell and axon loss in the degenerating retina. Photopsias may be linked in important ways to the processes occurring during retinal implant stimulation, and their characterization may be helpful for the future development of prosthetic vision. Photopsias may interfere with visual function testing during clinical trials, as well as RP patients’ vision while performing daily activities, underscoring the importance of their characterization among this patient population.

A survey of RP patients conducted in the clinic indicated that 35% reported flashes of light [24]. A more recent internet-based anonymous survey of photopsias in RP patients found that 93% of those who completed the survey had experienced photopsias. The photopsias in this survey were described as phosphenes (slow, localized dots or shapes) by 71%, flashes (all or most of the field at once) by 58%, static noise (like on a television without reception) by 31%, and fluorescence (a background glow) by 20% of those who noted photopsias [6]. Photopsias were most commonly reported to have a shape of a crescent, arc or semi-circle by over half of the respondents. The factors that were most commonly reported to be associated with an increase in photopsias were bright light, fatigue, stress, exercise and absence of light.

Photopsias are commonly noted by RP patients in both the earlier stages of the disease, as well as in those with end-stage retinal degeneration. Nearly half of those who have photopsias experienced them before they were diagnosed with RP, and 60% stated that they first noticed photopsias when they were less than 30 years of age [6].

RP patients who were able to read normal or small sized font without magnification, were driving currently, or who could easily navigate or had only some difficulty with mobility in unfamiliar areas, were two to three times more likely to note photopsias mostly or only peripherally versus in their central vision. Therefore, the extent and location of photopsias appear to be related to residual photoreceptor function assessed by self-reported vision and performance of daily living activities. Photopsias tend to start in the periphery early in RP and then later occur more centrally and in areas with vision as deficits in visual function occur. Therefore RP patients may become more aware of photopsias as vision loss becomes more advanced.