The "thin man" phenomenon: a sign of cortical plasticity following inferior homonymous paracentral scotomas

Aim-To investigate an image distortion, experienced by patients with homony mous paracentral scotomas. Methods-Two consecutive patients with right inferior homonymous paracentral scotomas resulting from ischaemic brain insults were examined. Neuroophtha hmological examination included tangent screen and Amsler grid evaluation. In addition, the patients were asked to describe a figure showing two verti cal lines, identical in length and symmetrically located on either side of a fixation point. This figure was presented in such a way that when the sub ject looked at the fixation point the right line crossed the scotoma. Final ly, the patients were asked whether, when looking at the face of an interlo cutor, both sides of the body looked the same. Results-In both patients field defects were markedly smaller when delineate d with Amsler grids than using a tangent screen. With the parallel line tes t, the right line appeared uninterrupted in patient 1, whereas in patient 2 it looked slightly blurred in a two degree long segment corresponding to t he middle of the scotoma. To both subjects the right line appeared shorter than the left line. Finally, both subjects indicated that, after steadily f ixating their interlocutor's face or neck for 5-10 seconds, the left should er appeared narrower than the right one, which made him look surprisingly t hin. This perceptual alteration was called the "thin man" phenomenon. Conclusions-Paracentral homonymous scotomas can be associated with perceptu al completion and shape distortion, owing to apparent displacement of image s adjacent to the scotoma towards the field defect. Occurrence of such a pe rceptual change should alert one to the possibility of paracentral homonymo us scotomas, which often go undetected when using routine visual field test ing procedures.