Illusory stimuli can be used to identify retinal blind spots


Crossland MD, Dakin SC, Bex PJ. Illusory stimuli can be used to identify retinal blind spots. {PLoS} {ONE} [Internet]. 2007;2 :e1060.


{BACKGROUND:} Identification of visual field loss in people with retinal disease is not straightforward as people with eye disease are frequently unaware of substantial deficits in their visual field, as a consequence of perceptual completion ("filling-in") of affected areas. {METHODOLOGY:} We attempted to induce a compelling visual illusion known as the induced twinkle after-effect ({TwAE)} in eight patients with retinal scotomas. Half of these patients experience filling-in of their scotomas such that they are unaware of the presence of their scotoma, and conventional campimetric techniques can not be used to identify their vision loss. The region of the {TwAE} was compared to microperimetry maps of the retinal lesion. {PRINCIPAL} {FINDINGS:} Six of our eight participants experienced the {TwAE.} This effect occurred in three of the four people who filled-in their scotoma. The boundary of the {TwAE} showed good agreement with the boundary of lesion, as determined by microperimetry. {CONCLUSION:} For the first time, we have determined vision loss by asking patients to report the presence of an illusory percept in blind areas, rather than the absence of a real stimulus. This illusory technique is quick, accurate and not subject to the effects of filling-in.