IMPROVING VISION - NEURAL COMPENSATION FOR OPTICAL DEFOCUS

Anecdotal reports abound of vision improving in myopia after a period of time without refractive correction. We explored whether this effect is due to an increased tolerance of blur or whether it reflects a gen uine improvement in vision. Our results clearly demonstrated a marked improvement in the ability to detect and recognize letters following p rolonged exposure to optical defocus. We ensured that ophthalmic chang e did not occur, and thus the phenomenon must be due to a neural compe nsation for the defocus condition. A second set of experiments measure d contrast sensitivity and found a decrease in sensitivity to mid-rang e (5-25 cycles deg(-1)) spatial frequencies following exposure to opti cal defocus. The results of the two experiments may be explained by th e unmasking of low contrast, high spatial frequency information via a two-stage process: (1) the pattern of relative channel outputs is main tained during optical defocus by the depression of mid-range spatial f requency channels; (2) channel outputs are pooled prior to the product ion of the final percept. The second set of experiments also provided some evidence of inter-ocular transfer, indicating that the adaptation process is occurring at binocular sites in the cortex.