The effect of a nitrous oxid-oxygen mixture on the lateral heterophoria

The distance and near lateral heterophorias were investigated in 10 subjects to determine the effect of a nitrous oxide (N2O)-oxygen (O2) mixture. The heterophorias were measured by the Maddox method before and after a 3-minute induction period of nitrous oxide. It was found that the distance lateral heterophoria for all 10 subjects changed toward more esophoria, whereas the changes in the near lateral heterophoria were inconsistent in their direction.