| 摘要 |
An ophthalmic prescription lens series in which each lens has a concave rear base curve selected from a family of curves, differing in nominal power by steps of 0.50 D, in such a manner as to minimize the maximum in absolute value of the astigmatic error for distant points, the positive power error for distant points, half the negative power error for distant points, and the astigmatic error for a near point of approximately 40 centimeters. The errors are computed for an approximate angle of 28 DEG between the line of sight of the wearer and the optical axis of the lens for both major meridians of the lens, for a first eye-to-lens distance measured from the nasal bevel of the lens to the center of rotation of the eye of approximately 24 millimeters, and for a second eye-to-lens distance similarly defined of approximately 34 millimeters for prescriptions between approximately +2.00 and -2.00 D and 32 millimeters for other prescriptions. Refractive errors are further minimized by the use of true-power concave surfaces, the curvatures of which take into account the index of refraction of the material of which the lens is formed, and by the selection of concave base curves with the assumption of a central power bias or offset of about +0.04 to +0.10 D for plus lenses and about -0.04 to -0.10 D for minus lenses to compensate for off-axis power errors.
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