If both sets of lines making up the lensometer target come into focus at the same time, the neutralized lens is a:

• A. Sphere
• B. Cylinder
• C. Spherocylinder
• D. Plano

Answer: (A)

In a lensometer, the two sets of lines test the power in two principal meridians. When both sets come into focus at the same distance, the lens has identical refractive power in all meridians, so there is no cylindrical (astigmatic) component. That means the neutralized lens is spherical—its power is the same in every meridian (it could be positive, negative, or zero). Plano is simply a special case of spherical power equal to zero, but the general classification for simultaneous focus of both line sets is spherical. If the lines focused at different distances, that would indicate cylinder and astigmatism.