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The relationship between word length and threshold character size in patients with central scotoma and eccentric
Anouk Déruaz1, Mira Goldschmidt, Christophe Mermoud
1Clinique d'Ophtalmologie, Hôpitaux Universitaires de Genève, 22, Alcide-Jentzer, 1211, Genève 14, Switzerland. anouk.deruaz@hcuge.ch
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.
Discussion:
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.
