Brain correlates of adaptation to multifocal contact lenses.

One billion and 300 million people worldwide are currently affected by presbyopia. One common option to correct presbyopia is providing simultaneous images with multifocal contact lenses (MCLs). However, patient satisfaction with MCLs is not uniform and not fully predictable. Understanding the neuroadaptation mechanisms behind MCLs use would have important clinical implications. In this study the cortical activity in visual and non-visual areas just after neophyte presbyopes were corrected with MCLs, was studied measuring visual evoked potentials with a high-density electrode array. Multifocal presbyopia corrections produced a loss of feedforward activity in the primary visual cortex (C1 and N1 amplitude reduction) that was compensated by extra feedback activity from other areas (enhanced amplitude of the P1 and the P2 components). This compensation seems to be engaged only in extrastriate areas, but in both early and late visual processing.