The relationship between word length and threshold character size in patients with central scotoma and eccentric fixation.
BACKGROUND
Understanding limitations on text reading with eccentric fixation is of major concern in low vision research. Our objective was to determine, in patients with a central scotoma, whether threshold character size is similar for different word lengths and paragraphed texts.


METHODS
In 19 patients, we retrospectively analyzed the relationship between minimum readable character size for isolated words and text. Isolated letters, two, five, and ten-letter words and a paragraphed text were presented randomly through a scanning laser ophthalmoscope in eight different character sizes.


RESULTS
Threshold character size varied according to the text stimulus (p<0.05). Threshold character sizes for single letters and two-letter words were matched (p>0.99), as were those for five-letter words, ten-letter words, and paragraphed text (p>0.99). Threshold character size for single letters and two-letter words was significantly lower than that measured with other text stimuli.


CONCLUSIONS
Reading performance is influenced by a variety of factors such as crowding, contextual effects, visual span, degree of oculomotor adaptation needed, and frequency of a defined word. Globally, when reading with a central scotoma, it appears that within word characteristics have more impact than inter-word parameters on threshold character size.
Déruaz
Anouk
A
Clinique d'Ophtalmologie, Hôpitaux Universitaires de Genève, 22, Alcide-Jentzer, 1211, Genève 14, Switzerland. anouk.deruaz@hcuge.ch
Goldschmidt
Mira
M
Mermoud
Christophe
C
Whatham
Andrew R
AR
Safran
Avinoam B
AB
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008268:Macular Degeneration / Q000503:physiopathology*; D008875:Middle Aged; D011932:Reading; D012189:Retrospective Studies; D012607:Scotoma / Q000503:physiopathology*; D012684:Sensory Thresholds / Q000502:physiology*; D014787:Vision Tests / Q000379:methods; D015354:Vision, Low / Q000503:physiopathology*; D014792:Visual Acuity