A R Whatham, A Deruaz, C Mermoud, A B Safran
Geneva University Hospitals, Ophthalmology, Geneva, Switzerland
Background
It has previously been reported that individuals with central scotomas and multiple PRL, determined from viewing a series of isolated letters and words, can use these PRL in combination during paragraphed text reading. However the presence of multiple PRL leads to the possibility that reading strategy could change as a function of text character size. This issue is very important for the understanding of reading strategy in patients with central scotomas and for determining whether their reading behaviour is stable over a range of character sizes.
Methods
The reading behaviour of three patients with central scotomas (2 Stargadt's, 1 AMD) and multiple PRL was analysed in detail according to text character size. Number and location of PRL were first determined using a series of 32 words varying in length and character size. Passages of paragraphed text were presented to each subject through a scanning laser ophthalmoscope (Rodenstock, Germany). Each subject was presented with text progressively decreasing in size from 2.25° to 0.50° or until the text could no longer be read. Fundus images were recorded directly onto videotape and analysed frame by frame.
Results
All PRL determined from the word series were used during text reading at all character sizes. That is, the number and location of PRL were consistently observed not to change as a function of text size. However the frequency of each PRL used by patients with multiple PRL changed as a function of character size. This change in frequency of usage of each PRL varied according to the function attributable to each PRL - determined by each PRL's selective usage during reading of the word series.
Conclusion
PRL usage during paragraphed text reading can change as a function of text size, while number and location of PRL appears to remain constant in patients with central scotomas and multiple PRL..
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