Plus acceptance in hard contact lens wearers.

Hyperopes fitted with contact lenses often exhibit more plus acceptance compared to full spectacle correction beyond that accounted for by vertex distance considerations. The objective of this investigation was to attempt to identify the possible factors involved with this phenomenon. Eight hyperopes, one myope, and one control hyperope between 20 and 30 years of age were fitted with polymethyl methacrylate lenses, and over-refractions performed on different days with and without corneal anesthesia. The result was that every test hyperope accepted more plus without anesthetic than with anesthetic, by an average of 0.725 D, which was significant (p = 0.0000). One possible mechanism appears to be neurosensory feedback between corneal sensation and the level of accommodative tonus of the ciliary body.