Abstract A zonal focus test used in the prior art to locate a principal meridian of an astigmatic optical system is adapted for use in determining the amount of astigmatic correction necessary for such an optical system. After the principal meridians of the astigmatic subject optical system are located, after the principal meridians of variable optical correcting means are aligned with the principal meridians of the subject optical system, and after the optical correcting means are varied to correct one specified meridian of the subject optical system according to prior art techniques, the zonal focus test of the present invention is applied to the combination of the subject optical system and the optical correcting means in a nonprincipal meridian, preferably one of the meridians 45* to the principal meridians of the optical correcting means, whereupon an error is indicated by the test. The dioptric power of the optical correcting means is then varied, holding the power in the previously corrected meridian constant, until the zonal focus test no longer indicates an error. At this point the principal meridians of the total optical combination have disappeared, the corrected subject optical system is anastigmatic, and the amount of astigmatic correction for the subject optical system that is necessary for this condition is represented by the astigmatic power of the optical correcting means.
A method for determining the amount of astigmatic correction necessary to be added by optical correcting means in conjunction with spherical correction to an optical system to cause the optical system to be optically corrected to be anastigmatic for a specified pair of points comprising the steps of: locating the principal meridians of said optical system; aligning the principal meridians of said optical correcting means with the principal meridians of said optical system; correcting the dioptric power of one meridian of said optical system by said correcting means; applying a principal-meridian-locating zonal focus test to the combination of said optical system and said correcting means, by applying said zonal focus test in a non-principal meridian thereby imaging the parts of a test image in a laterally displaced manner; examining said test image; maintaining the dioptric power correction of said one meridian constant and simultaneously varying in other meridians the power of said correcting means so as to remove the previously effected lateral displacement of parts of said test image; and noting the astigmatic component of said correcting means whereby said astigmatic component represents the amount of astigmatic correction necessary for said optical system to be anastigmatic.
Claim 2
Independent Claim
196 words
A method for determining the amount of astigmatic correction necessary to be added by optical correcting means in conjunction with spherical correction to an optical system to cause the optical system to be optically corrected to be anastigmatic for a specified pair of points comprising the steps of: locating the principal meridians of said optical system; aligning the principal meridians of said optical correcting means with the principal meridians of said optical system; correcting the dioptric power of one meridian of said optical system by said correcting means; applying a principal-meridian-locating zonal focus test to the combination of said optical system and said correcting means, by applying said zonal focus test in a non-principal meridian thereby imaging the parts of a test image in a laterally displaced manner; examining said test image; maintaining the dioptric power correction of said one meridian constant and simultaneously varying in other meridians the power of said correcting means so as to remove the previously effected lateral displacement of parts of said test image; and noting the astigmatic component of said correcting means whereby said astigmatic component represents the amount of astigmatic correction necessary for said optical system to be anastigmatic.
Claim 3
Dependent Claim
20 words
The method of claim 1 wherein said zonal focus test utilizes a plurality of small zones of said optical system.
Claim 4
Dependent Claim
35 words
The method of claim 1 wherein said zonal focus test utilizes substantially all zones of said optical system through the use of target means equivalent to an array of astigmatic images of points of light.
Claim 5
Dependent Claim
37 words
A method as in claim 1 where said zonal focus test is applied in one of the non-principal meridians within the range extending approximately 10* to 80* from one of the principal meridians of said correcting means.
Claim 6
Dependent Claim
16 words
A method as in claim 4 where said range extends from approximately 30* to 60* .
Claim 7
Dependent Claim
29 words
A method as In claim 5 where said zonal focus test is applied in one of the non-principal meridians 45* away from the principal meridians of said correcting means.
Claim 8
Dependent Claim
27 words
A method as in claim 1 wherein said optical system comprises the human eye and said test image is examined directly by the retina of said eye.