I came across this British low vision study (Moorfields Eye Hospital, NHS) and thought others may find its outcomes helpful in recommending low vision aids. A paper describing the study’s results is in preparation.
I corresponded with lead author Michael Crossland to learn if two concerns I have regarding intense use of digital devices are addressed in these trials:
“…two concerns have arisen and continue to increase in importance to me. These are retinal issues: for all consumers at all ages, retinal desensitization over time to the high luminosity of screens that create the sharply defined visual contrast that’s so appealing; and developmentally, a desensitization of the perifoveal area of the retina that is a likely outcome of the reduced user head, eye, and arm movements by touch screen commands which accommodate a static, prolonged view of the screen’s imagery at a relatively fixed viewing distance.”
Michael replied that trial participants have considered the myopic effects associated with digital magnifiers and have determined that the devices benefits outweigh this potential risk. He acknowledged that participants do practice a strategy similar to the 20/20/20 Rule to systematically reduce eye strain.
To my second concern Michael asked, “Do you have any scientific references for the ‘desensitization of the perifoveal area of the retina’ which you describe? I am not aware of any scientific literature which describes any long-term difficulties associated with screen use.”
My phrase “desensitization of the perifoveal area of the retina” is based on considering the consistently sustained fixation of head and eyes by the virutal imagery of digital devices to be, albeit voluntary, a field restrictive factor.
This phrasing is based on readings, such as the following: Identification of Peripheral Visual Images in a Laterally Restricted Gaze (Chapter 68 in The Head-Neck Sensory Motor System, Edited by Alain Berthoz, Pierre Paul Vidal, and Werner Graf, 1992) which states, “The purpose of the study reported in this chapter was to evaluate the effects of degraded peripheral vision on visual performance… When the peripheral field is restricted, the range of eye positions for successful stimulus acquisition is limited (McCormack et al,. 1987; Obrecht et al., 1987) hence, a gaze position must be established by a change in head position rather than eye position. Typically, an initial eye movement does occur but the eye returns to the central position in coordinated compensation to the head movement. When peripheral vision is restricted, the identification time (i.e., the time for correct identification) increases, as shown in the identification function of Figure 68-1 (solid circles). In addition, the slope of the identification function decreases, showing increased variability in the identification task.”
I read this as eye movements are “nested”, meaning that the nine positions of gaze are available from all head positions, but the eyes are inclined to quickly return to a central gaze position, the “coordinated compensation to head movement”. While my eyes make lateral and vertical saccades, without head movement, they do not need to identify anything new in the environment to update my postural and spatial orientations. As I write this note, I can cast my gaze to the far right or far left without moving my head — but it takes energy; I must work to keep my gaze in any non-central position . If I am motivated (so the effort is not work per se) to look in a specific direction, or just relaxing by starring off into space with eyes centered, I am practicing the restful gaze we discussed as the 20/20/20 rule. Without stimulus (external events/head movement) or motivation my eyes remain in a central position. If the natural environment is not providing stimulation for head movement, the variety of positions from which the nine points of gaze are elicited and stimulated is limited. In certain situations – unregulated use during child development years, recovery from trauma, learning disabilities – the power of digital devices likely favors and facilitates a dominant head position; it is a practitioner’s hunch that the perceptual skills that underpin good functional vision may be diminished as an unanticipated side effect of this bias.
The study’s protocols will make systematic measures of visual acuity and formal interviews will be held with participants at predetermined intervals in the trials. Acuity measures will not recognize diminished peripheral sensitivities. While the interviews will provide participants with an opportunity to discuss any changes in their peripheral alertness, such changes would be subtle and may go unnoticed for long periods of time until an event that requires quick identification and responsiveness to the full visual scene occurs, an event such as recognizing the extruding metal edge of a street at an intersection’s curbing, the swinging action of a baseball bat or golf club, detecting other vehicles when shifting lanes while driving.