Reading with optical magnifiers: page navigation strategies and difficulties.
OBJECTIVE
To read efficiently with a simple hand or stand magnifier, people with visual impairment have to move (navigate) the device along each line (forward phase) and back to the correct position at the start of the next line (retrace phase). Page navigation difficulties have been implicated as limiting factors when reading with hand and stand magnifiers, but have not been objectively measured.


METHODS
Magnifier movements were recorded using a 3SPACE Isotrak system for 43 participants with age-related macular degeneration (AMD) who read two short stories using their habitual hand or stand magnifier. Page navigation was quantified in terms of magnifier movements and navigation errors for the forward and retrace phases. Visual acuities and visual fields were measured, and magnifier usage and page navigation difficulties were surveyed.


RESULTS
During the forward phase, participants primarily used either a straight (47%) or diagonal downward (46%) movement, whereas during the retrace phase, the majority (56%) used a downward movement. On average, forward navigation time was four times longer than retrace navigation time (p<0.001). The most common navigation error was incorrect positioning of the magnifier at the end of the retrace movement. Near word acuity correlated strongly with forward time (r=0.78), and moderately with retrace time (r=0.53) and forward errors (r=0.50). Vertical field of view correlated with retrace errors (r=-0.53). Participants' estimates of page navigation difficulties were not predictive of objective measures of performance.


CONCLUSIONS
We quantified page navigation strategies and difficulties of people with AMD reading with magnifiers. Retrace, which presents the most common difficulty, is not well predicted by vision measures or magnifier characteristics; future studies should investigate the relationship between motor skills and navigation performance, and the impact of training or devices on reducing retrace navigation difficulties.
Bowers
Alex
A
The Schepens Eye Research Institute, Harvard Medical School, Boston, MA 02114, USA. alex.bowers@schepens.harvard.edu
Cheong
Allen M Y
AM
Lovie-Kitchin
Jan E
JE
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D011932:Reading; D012682:Sensory Aids / Q000592:standards*; D015354:Vision, Low / Q000534:rehabilitation*; D014792:Visual Acuity