Section 120. Lenses and frames standards

A. Power Tolerance (diopters).

Sphere: Plano to ±.6.50	±.13 diopter
Above ±.6.50	±2%
Cylinder: Plano - 2.00	±.13 diopter
-2.12 to -4.50	±.15 diopter
above -4.50	±4%

B. Cylinder Axis.

Cyl. Power Diopters	Degrees ±
0.12 - 0.37	7°
0.50 - 0.75	5°
0.87 - 1.50	3°
1.62 and above	2°

C. Distance Optical Center. Contribution to net horizontal prism from processing should not exceed 2/3 prism diopter. A maximum of ±2.5mm variation from the specified distance optical center is permissible in higher power lens combinations.

D. Prism Tolerances (Vertical). Contribution to imbalance from processing should not exceed 1/3 prism diopters. A maximum of 1.0mm difference in vertical level is permissible in higher power lens combinations.

E. Segment Location.

Vertical	±.1.0 mm
Horizontal	±.2.5 mm

Tilt or twist in the case of a flat-top segment, the tilt of its horizontal axis should be less than 1/2 mm in differential elevation between the segment edges.

F. Multifocal Additions.

Plano + 8.00	±.13 diopter
Above + 8.00	±.18 diopter

G. Base Curve. When specified, the base curve should be supplied within ±0.75 diopter.

H. Warpage. The cylindrical surface power induced in the base curve of a lens should not exceed 1 diopter. This recommendation need not apply within 6mm of the mounting eyewire.

I. Localized errors (aberration). Areas outside a 20mm radius from the specified major reference point or optical center need not be tested for aberration. Progressive lenses are exempt from this requirement.

Historical Notes

Former 18VAC100-20-85 derived from Volume 17, Issue 09, eff. March 1, 2001; amended and renumbered as 18VAC80-30-120, Virginia Register Volume 28, Issue 23, eff. August 15, 2012.

Statutory Authority

§ 54.1-201 of the Code of Virginia.