Full text reading with a central scotoma: pseudo regressions and pseudo line losses

Aims-To investigate the reading strategy of a patient with central scotoma, using several preferred retinal loci (PRL). Methods-A 47 year old man with Stardardt's disease was asked to decipher te xts projected onto his retina using a scanning laser ophthalmoscope. A reco rding of the fundus image, on which the projected texts were superimposed, was analysed frame by frame. Results-The subject used a combination of three PRL, located above the scot oma and laterally to the left and right of it. He first used his left PRL t o search for the beginning of a line, then switched to his right PRL, thus performing an apparent regression which was called "pseudo regression", to read the line with successive rightward saccades. To decipher a particularl y difficult word, he switched to his upper PRL, showing an apparent line lo ss which was called ("pseudo line loss"), and then used his three PRL in co mbination. Conclusion-The patient used a complex, well structured reading strategy. Th ese data showed that backward saccades and unexpected line losses, hitherto thought to be inappropriate and uneconomical, may in fact represent purpos eful changes of PRL. It is thought that this is the first structured readin g behaviour ever identified in such a condition. Such adaptive oculomotor b ehaviour should be taken into account when considering rehabilitation proce dures.