Handwriting with a preferred retinal locus for AMD with scotomas

Individuals with macular scotomas from age-related macular degeneration frequently have difficulty writing legibly. The purpose of this study was to investigate the causes of this difficulty by documenting the location of the retinal image of the pen used for writing in relation to the scotoma and fixational preferred retinal locus (fPRL).

Subjects with macular scotomas from age-related macular degeneration and visually normal age-matched controls wrote words while observing their hand, pen, and text in a scanning laser ophthalmoscope. Scanning laser ophthalmoscope video images were analyzed to find the retinal positions of the subject's scotoma, fixation area, and pen tip.

Control subjects placed their fovea and scotoma subjects placed their fPRL on or very close to the pen tip for both cursive writing and printing. Scotoma subjects' written text sloped downward at a greater angle than controls'. Text angle was negatively correlated with fPRL eccentricity, visual acuity, and the amount the scotoma obscured the writing guides. When printing, control subjects placed their fovea precisely in the center of printing box guides, whereas scotoma subjects exhibited highly dispersed placement of the fPRL.

The principal finding is that, because the retinal locations of the pen tip and the fPRL or fovea are coincident or very close, the fPRL and fovea are "monitoring" the pen tip and its location on the page. It is the PRL determined by asking subjects to fixate (i.e., the fPRL) that is used when handwriting, not a separate "handwriting" PRL. The poor handwriting performance of those with macular scotomas seems to be primarily caused by difficulty in placing letters in the appropriate location probably because of reduced visual acuity of the fPRL and scotoma obscuration of the area on which to write.