Patented Welch Allyn Coaxial Vision optics, combined with 68 lenses in single-diopter steps, for the precision you need to conduct a quality eye exam.

Welch Allyn website for more information on the 3.5V AutoStep Coaxial Ophthalmoscope: https://www.welchallyn.com/en/products/categories/physical-exam/eye-exam/ophthalmoscopes--traditional-direct/35v_autostep_coaxial_ophthalmoscope.html