| 摘要 |
An improved method is disclosed for determining the refractive correction for an eye. The method is an improvement over the method described by W. E. Humphrey in his U.S. Pat. No. 3,947,097. The improved method uses apparatus having only one variable astigmatic sub-system to achieve the same optical effects for which Humphrey specifically requires apparatus having two separate variable astigmatic sub-systems. The apparatus used is well-known in the art and includes variable spherical optics in combination with variable astigmatic optics, said variable astigmatic optics being equivalent to a rotatable, variable-power cross cylinder. Two stationary straight line targets, oriented in meridians substantially 45 DEG from one another are alternately focused by the patient. To focus each straight line target the patient adjusts separately both sphere power and cross cylinder. Whenever the cross cylinder is adjusted, both the orientation and the power of the cross cylinder change as necessary to maintain constant the dioptric power of the cross cylinder acting in the meridian of the straight line target being focused. In the preferred embodiment of the method, the patient adjusts the orientation of the cross cylinder, and a servo mechanism adjusts the power of the cross cylinder as necessary. In an alternate embodiment, the patient adjusts the power of the cross cylinder, and a servo mechanism adjusts the orientation of the cross cylinder as necessary.
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