Relationship between slow visual processing and reading speed in people with macular degeneration.
OBJECTIVE
People with macular degeneration (MD) often read slowly even with adequate magnification to compensate for acuity loss. Oculomotor deficits may affect reading in MD, but cannot fully explain the substantial reduction in reading speed. Central-field loss (CFL) is often a consequence of macular degeneration, necessitating the use of peripheral vision for reading. We hypothesized that slower temporal processing of visual patterns in peripheral vision is a factor contributing to slow reading performance in MD patients.


METHODS
Fifteen subjects with MD, including 12 with CFL, and five age-matched control subjects were recruited. Maximum reading speed and critical print size were measured with rapid serial visual presentation (RSVP). Temporal processing speed was studied by measuring letter-recognition accuracy for strings of three randomly selected letters centered at fixation for a range of exposure times. Temporal threshold was defined as the exposure time yielding 80% recognition accuracy for the central letter.


RESULTS
Temporal thresholds for the MD subjects ranged from 159 to 5881 ms, much longer than values for age-matched controls in central vision (13 ms, p<0.01). The mean temporal threshold for the 11 MD subjects who used eccentric fixation (1555.8 +/- 1708.4 ms) was much longer than the mean temporal threshold (97.0 +/- 34.2 ms, p<0.01) for the age-matched controls at 10 degrees in the lower visual field. Individual temporal thresholds accounted for 30% of the variance in reading speed (p<0.05).


CONCLUSIONS
The significant association between increased temporal threshold for letter recognition and reduced reading speed is consistent with the hypothesis that slower visual processing of letter recognition is one of the factors limiting reading speed in MD subjects.
Cheong
Allen M Y
AM
Minnesota Laboratory for Low Vision Research, University of Minnesota, Minneapolis, MN 55455, USA. cheon015@umn.edu
Legge
Gordon E
GE
Lawrence
Mary G
MG
Cheung
Sing-Hang
SH
Ruff
Mary A
MA
D000368:Aged; D000369:Aged, 80 and over; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008268:Macular Degeneration / Q000503:physiopathology* / Q000523:psychology; D010364:Pattern Recognition, Visual / Q000502:physiology; D011594:Psychometrics / Q000379:methods; D011601:Psychophysics; D011930:Reaction Time; D011932:Reading; D012684:Sensory Thresholds / Q000502:physiology; D014787:Vision Tests / Q000379:methods; D015348:Vision, Binocular / Q000502:physiology; D015354:Vision, Low / Q000503:physiopathology; D058609:Visual Field Tests / Q000379:methods; D014794:Visual Fields / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*