Use of the humphrey lens analyzer for off-axis measurements of spectacle lenses

• Published in: Optometry and vision science Vol. 68; no. 4; pp. 299 - 308
• Main Authors: ATCHISON, D. A, KRIS, M, SHEEDY, J. E, BAILEY, I. L
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 01.04.1991
• Subjects: Biological and medical sciences; Eyeglasses; Investigative techniques of ocular function and vision; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Optics and Photonics; Vision Tests - instrumentation; Optical aberration; Exploration; Automatic analysis; Ophthalmic glass
• ISSN: 1040-5488; 1538-9235
• DOI: 10.1097/00006324-199104000-00007

Automated focimeters can be used to make quick, precise measurements of off-axis power and prismatic effects corresponding to an eye rotating behind a spectacle lens. An automated focimeter, the Humphrey Lens Analyzer, was assessed in this regard. The Humphrey Lens Analyzer can be used to give a valid measure of off-axis power of lenses with low power, but not of lenses with moderate to higher power (greater than 3 D). For 3 D spherical lenses discrepancies of the order of 0.1 D occur at 30 degrees rotation, and 6 D spheres give discrepancies of 0.5 D at the same rotation. Small discrepancies were found for measurements of prism. The Humphrey Lens Analyzer was also used in a mode where the lens being tested is rotated about the center of curvature of its back surface. This is the mode often used to assess aberrations and prism of progressive-addition lenses. In this mode, the instrument provides reasonable accuracy in estimating off-axis power corresponding to eye rotation for lenses with low power, but not for lenses with moderate to higher power (greater than 3 D). However, it provides accurate values of the variation in off-axis surface power for low powered lenses with aspheric front surfaces. There were considerable systematic errors associated with the measurement of prism. A simple raytracing method was developed to predict the results of measurements with the Humphrey Lens Analyzer. Predictions of off-axis power were good when lenses were rotated about a position corresponding to the center-of-rotation of an eye, but were poorer when lenses were rotated about the center of curvature of their back surfaces. Predictions of primatic efforts were good in both situations. A method by which the Humphrey Lens Analyzer should provide an accurate measurement of off-axis powers corresponding to eye rotation behind a spectacle lens is described, but has not been tested.