3. Accommodative function in young emmetropes and transitional presbyopes: This is a volunteer study to develop a descriptive model of the human eye's focusing mechanism based on ultrasound morphometric measurements and spectral parameter assays. This study will measure dynamic changes in ciliary body spectral assays (size, CQ2) during calibrated accommodative tasks in volunteers with good amplitude of accommodation and those with accommodative loss do to aging and model 3-D conformal changes in anterior segment structures during accommodation. There is minimal risk that the ultrasound procedure may reveal an occult ocular disease process, but the probability is very small. Patients will be informed and assisted in obtaining appropriate care if any abnormality is seen.