REFRACTIVE VARIATION UNDER ACCOMMODATIVE DEMAND - CURVITAL AND SCALEDTORSIONAL VARIANCES AND COVARIANCE ACROSS THE MERIDIANS OF THE EYE

Autorefractor measurements were taken on the right eye of 10 students with an external target at vergences -1.00 and -3.00 D. The refractive errors in the form of sphere, cylinder, and axis were converted to ve ctors h and variance-covariance matrices calculated for different refe rence meridians. Scatter plots are drawn in symmetric dioptric power s pace. The profiles of curvital and scaled torsional variances, the sca led torsional fraction, and the scaled torsional-curvital correlation are shown using a polar representation. This form of representation pr ovides a meridional pattern of variation under accommodative demand. T he profile for scaled torsional variance is characteristically in the form of a pair of rabbit ears. At both target vergences curvital varia nce is larger than scaled torsional variance in all the meridians of t he eye: the relative magnitudes are quantified by the scaled torsional fraction. An increase in accommodative demand generally results in an increase in variance. The rabbit ears usually become larger but less well divided. The correlation between curvital and torsional powers is usually positive in the first quadrant and negative in the second qua drant. Typical, atypical, and mean typical responses are discussed.