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F. Tassi, P. Limoli, E. Vingolo, L. D'Amato, R. Solari, R. Di Corato, P. Costanzo; Comparison Between Virtual PRL and PRF (Preferential Reading Field): Rehabilitative Prognosis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3065.
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The PRF is a retinic area on which the patient can project the image of a reading string.The PRL is instead a preferred area of almost 2° in which fixation is possible. In a normal patient the PRL and the PRF always coincide, while in the low vision patient these areas not always are coincident.Knowing the correct position of the reading field is useful to understand the rehabilitative prognosis.Reading performances could vary, due to the mutual position of PRL and PRF. The aim of this study is to understand the role of the position of the PRL compared with the position of PRF on rehabilitative prognosis.
We have studied 41 eyes of 31 low vision patients. Each patient underwent a visual field examination which was analyzed by VirtualIPO©.We determinated BCVA, near visus in pts with and without a proper low vision aid, the position of PRL and PRF, the increase of reading speed during rehabilitation.
We have divided the low vision patients in three groups:A) Centred PRL-PRF (coincides on the fovea).B) Homogeneous PRL-PRF (decentrated but in the same direction).C) Not homogeneuous PRL-PRF (decentrated in different direction).Median BCVA (BCVA: A: 0,21; B: 0,15; C: 0,21) and visus in pts with the magnifying aids (pts: A: 7,35; B: 7,53; C: 8,1) is similar in the three groups.Reading speed depends on various items such as age, reading field amplitude, magnification, education, social class but we cannot find variation due to mutual position of the PRL and the prf (Par./min. A: 61,50; B: 39,64; C: 56,47).The delta, instead, could vary (A: 0,01; B: 2,49; C: 3,45) and also the increase of reading speed before and after rehabilitation (Par./min. A: 33,56 - 54,6%; B: 18,07 - 45,6%; C: 15,87 - 28,1%).For a low vision patient who uses a PRL to see the world is easier to improve his reading performances if his PRF coincides with his PRL particulary if it is centred of the fovea, and it is more difficult if PRL and PRF are on different areas and even worse if they are also disomogeneous.
We think that it is important to state in advance the virtual analysis of the visual field before rehabilitation, not only to understand the virtual magnification and the best visual aid, but also to know all the essential knowledges about reading phisiopathology , which could influence rehabilitation prognosis. Knowing the real position of PRL and PRF, if they are omogeneous or not allow us to plan the visual rehabilitation and the number of sessions of visual training which are necessaries to stabilize fixation on these determined areas.
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