Tolerance and Nature of Residual Refraction in Symmetric Power Space as Principal Lens Powers and Meridians Change

Figure 1

A manual lensometer measures meridians and corresponding powers on crosses. The lens centre is at the origin. Distinct lens principal powers and in (a) define eigenvalues of matrix in (6) in columns of . These powers are along meridians at and in (b) that define eigenvectors of matrix in (6) in the corresponding columns of [6].

(a)

(b)