A Deruaz, A R Whatham, C Mermoud, A B Safran
Geneva University Hospitals, Ophthalmology, Geneva, Switzerland
Background: The reading strategies of five patients with a central scotoma (Stargardt's disease or AMD) and who had naturally developed, without specific training, multiple PRL were investigated in detail in order to determine whether their complex reading behaviour could be used both to further understand the reading process and also in the development of a precise rehabilitation program using the scanning laser ophthalmoscope (SLO).
Method: Subjects read successively isolated letters, words of 2, 5 and 10 letters presented in a random order and paragraphed text, which varied in size from 0.5° to 2.25°. All stimuli were projected directly onto the retina using an SLO (Rodenstock, Germany). Fundus images were recorded and analysed frame by frame.
Results: The same number and location of PRL were used for reading the word series and text passages. The choice of PRL for word-reading changed according to character size and word length. This indicated that more than one stimulus is necessary to determine the existence of multiple PRL. During text reading, all PRL were used and alternation between PRL appeared mainly when word decoding was very difficult. Analysis of word and text reading enabled the role of each PRL to be determined. We observed in all patients the combined use of two or more PRL fulfilling the functions of global viewing and detailed discrimination.
Conclusion: This indicated that for an efficient reading strategy at least these two requirements must be met, accomplished by one PRL in some patients (or fovea in normal subjects) or, as observed here, by two or more PRL, each having a specific functions. These findings have implications for the development of structured rehabilitation programs using the SLO to improve reading performance in patients with central scotomas.
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