Measurement and Analysis of Whole-surface Power Distribution in Single Tilted Spectacle Lenses.

SIGNIFICANCE: Face-form tilt spectacles are sometimes tilted such that the optical properties of the embedded prescription lenses and the lens power change. If the lens power is not plano, the vision quality of the wearer may be affected.

PURPOSE: This study aimed to measure the whole-surface power distributions of tilted spectacle lenses for different lens powers and tilt angles.

METHODS

Spherical spectacle lenses with a refractive index of 1.56 and powers of -4.00 D, -2.00 D, plano, +2.00 D, and +4.00 D were measured. Their whole-surface power distributions were measured at different tilt angles, up to 20°, using a commercially available Hartmann wavefront aberrometer. The measured data were limited within a 40-mm diameter and analyzed to obtain contour plots of the spherical equivalent (M) and astigmatism (J).

RESULTS

The measured whole-surface power profiles of the nontilted lenses showed both M and J as being symmetrical and increasing outward up to -0.52 and +0.24 D, respectively, for the -4.00 D lens and +0.22 and +0.05 D, respectively, for the +4.00 D lens, corresponding to the spherical design. The profiles of the tilted lenses showed both M and J as unevenly increasing from the center to the peripheral area along the downward tilt direction; however, the plano lens exhibited no effect of tilt on both M and J. The powers at the optical center of the lens increased with tilt angle and lens power. The maximum differences for M and J at a 15° tilt angle in the -4.00 D lens were -2.46 and +1.43 D, respectively. Conversely, at a 17° tilt angle, the maximum differences in the +4.00 D lens were +0.96 D in M and +0.46 D in J.

CONCLUSIONS

Tilt angle and lens power strongly affect the power profiles of tilted spectacle lenses.