Vision restoration therapy: confounded by eye movements

Recently Sabel, Kenkel, and Kasten co-authored a report showing that vision restoration therapy does not improve field defects in patients with cortical lesions.1 This finding was a disappointment because it dashed hopes that vision restoration therapy might benefit patients who suffer visual field loss from stroke, tumour, or trauma involving the occipital lobe. In a new twist, Sabel and colleagues have now written an editorial stating that “we have no objections to the data as presented” (an unusual remark from the co-authors of a study), followed in the next breath by a long argument repudiating the main thrust of their report.2 If readers are confused, they are not to blame.

Vision restoration therapy was described previously in a series of papers by Sabel and colleagues.3–8 In brief, it attempts to restore visual field defects by having patients practise perimetry every day at home using a software package loaded onto their personal computers. The idea is that repeated visual stimulation, especially just inside a scotoma boundary, can salvage neurons in damaged cortex at the fringe of a lesion. Sabel’s previous studies suffered from a major flaw: eye movements were not recorded or controlled. Patients with homonymous field loss often compensate by making surveillance saccades into their blind hemifield. Although Sabel and colleagues used the blind spot position to monitor fixation, they never reported fixation losses, false positives, or false negatives in their papers. Moreover, the blind spot position is an imperfect method for detecting small saccades, and useless for fixation assessment in an eye with a temporal hemianopia. For these reasons, most neuro-ophthalmologists were sceptical of Sabel’s claims for vision restoration therapy.

To his credit, Sabel responded by undertaking a collaborative study with scientists employing the scanning laser ophthalmoscope.1 This …