CA1077315A - Ophthalmic lenses and method of achieving off-axis correction thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Corrected ophthalmic lenses wherein off-axis correction is accomplished with a gradation of index of refraction between optical center and edges of the lenses together with proper control of surface curvature and center thickness.
Utilizing regular spherical and/or toric lens surfaces of preselected dioptric values, off-axis corrections of lens aberrations comparable to and improved over those which may be accomplished with aspheric surface design are possible.
The relatively complex and expensive processes of applying aspheric corrections to glass lenses can be avoided without sacrifice of oblique correction quality. In this connection, a lens base curve may be chosen so as to minimize astigmatism and a refractive index gradient used to control curvature of field. Still higher degrees of correction are contemplated by using an index gradient along with an aspheric surface and, with careful selection of base curve. Base curve selection may be made with reduction of distortion in mind, asphericity chosen to minimize astigmatism and a refractive index gradient utilized to reduce curvature of field (power error).

Description

s B~ckground of the Invention Field of the Invention:
This invention relates to improvements in ophthalmic lenses and more particularly to the correction of off-axis errors by means of a radial gradation of refractive index between the optical center and edges of the lenses together with proper control of surface curvatures and center thicknesses.
Discussion of the Prior Art:
In the designing of corrected spectacle lenses, it is common practice for the designer to make extensive off-axis computation and select the base curve which achieves the best performance, i.e. the "tool" used by the designer is the overall amount of bending employed in a given lens.
Off-axis errors of prime concern are astigmatism and curvature of field (power error) with a third aberration, distortion, being of lesser but important consideration.
Relatively recent approaches to improving off-axis correction in ophthalmic lenses have included the use of aspherics wherein non-spherical surface curvatures are used in conjunctin with proper base curve selection to further reduce off-axis astigmatism and curvature of field with improvement in distortion as well.
While aspheric surface curvatures in off-axis correction situations are most easily and economically applied to lenses which can be cast, e.g. resin lenses, this approach to oblique correction can also be used on glass.

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Thc art, beinL pres~!rlcly Llmil:ecl to ooe or combinations of the ~Eoresaid tecllni(lues for redllclng o~-axLs aberratlons in ophthalmic lens desigrl~ Ls need~ll of improved designs and methods o~ their applicatlon which can be i~nplemented wlth greater ease and economy, especlally on glass, and which can offer greater variety and versatiliî:y to designers in their selections oE aberrations to be corrected and the order of priority or emphasis applLed thereto ln particular oblique correction situations.
Accordingly, lt is an object of the present invention to make possible off-axis correction in ophthalmic lens design without aspheric surface tre~tmel-t, if desired, but which is comparable to and/or improved over prior art accomplishments with aspherics.
Another object is to apply a novel conjunct to aspheric correction in lens design wherewith a higher degree of oblique correction can be achieved and further wherewith more than the , usual prime aberrations of astigmatism and curvature of field may be successfully dealt with.
~20 ~ Still another object is to render possible a designer's selection of aberrations to be attended to with emphasis thereon in an order of his choice and with greater versatility than the hèretofore limited "tool" of controlled surface bending but not without surface bending; and A more general object is to provide for greater ease and versatility in the designing of corrected ophthalmic lenses, improvements of substantial significance and importance in `
resulting lenses, greater economy in the implementation of corrections of prime concern aberrations and others of importance and greater freedom of manner of applying variables of base curve selection and asRhericity in the correction of oblique aberrations.

jl/ -3-Other ob~ects and advantages of the inventlon will become apparent fron~ the ~ollowlng summary of the invention and descript:ion of preferred embodiments.
SU~MARY OF T~IE INVENTION
The present invention relates to the method of ~ correcting off-axis errors in the manufacture of an : ophthalmic lens comprising in addition to affording the lens with optically finished conve:~ and concave opposite sides of preselected curvatures, a particular center thickness and a pr~-established refractive index value adjacent its axis, further effecting a gradation of refractive index in the material of the lens radially from its axis toward its edge.
In its article aspect, the invention relates to a corrected ophthalmic spectacles lens of meniscus config-uration having optically finished convex and concave opposite - side surfaces of preselected curvatures and a particular : center thickness and refractive index value adjacent its axis, one of the curvatures being the base curve of the lens and there being a gradation of refractive index in the material of the lens extending in directions radially from ~ :
its axis toward its edge, the geometrical surface configura- :
tion of said base curve being selected and formed in conjunc~
tion with the axial refractive index value, center thickness and opposite surface curvature according to off-axis correction ;~
desired for at least one of ophthalmic lens aberrations including power error, astigmatism and distortion and the gradation of refractive index affording off-axis correction of at least one of the lens aberrations of power error and astigmatism.
In another aspect, the invention relates to an ophthalmic lens blank having at least one curved side surface, bc/~.

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the curved surface constitutil-g tl~e basc curve of a lens to be produced from the blank and t~lcre bcing a gradatLon of refractive index in the material of the lens blank extending in directions radially from its axis toward its eclge, the geometrical surface configuration of the base curve being selected and formed in conjunction with the axial refractive index value according to a center thickness and opposi te surface curvature required for off-axis correction of at least one of ophthalmic lens aberrations including power error, astigmatism and distortion and the gradation of refractive index affording off-axis correc-tion of at least one of the aberrations of power error and astigmatism in the finished lens to be formed from the blank.
Thus, according to the present invention, off-axis correction in ophthalmic lens design is accomplished, at least in part, by varying the index of refraction of a lens by controlled amounts from its optical center radially to its . j .
edge. Utilizing regular spherical and/or toric lens surfaces of preselected dioptric values, off-axis corrections of lens aberrations comparable to and improved over those which may be accomplished with aspheric surface design are possible. Thus, the relatively complex and expensive processes of applying aspheric corrections to glass lenses can be avoided without sacrifice of oblique correction quality. In this connection, a lens base curve may be chosen so as to minim;ze astigmatism `~ and a refractive index gradient used to control curvature of `~ field.
Still higher degrees of correction are contemplated by using an index gradient along with an aspheric surface, and, of course, with careful selection of base curve. Base curve selection may be made with reduction of distortion in mind, asphericity chosen to minimize astigmatism and a refractive - 4a -,,~ .
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index gracl:ient util:iæed to reducc curvatllre of field tpower error).
Details of the invent:Lon will become more readily apparent Erom the following description when taken in conjunction with the accompanying drawings.

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Fig. I is ~ scllemltlc illustration of traditionnl geometry and Issumptions basic to spectacle lens desig-l;
Fig. 2 is a chart indicating the optical perforlnance of a conventional +3.00 diopter spherical lens prescription in terms of its tangential and sagittal power errors;
Fig. 3 is a chart similar to Fi~. 2 but illustrating the optical performance of a +3.00 diopter lens having off-axis corrections applied according to the invention;
Fig. 4 is a cross-sectional view of an ophthalmic lens with strippling included for purposes of illustrating a refractive index gradient;
Figs. 5 and 6 illustrate a technique useful in preparing lens blanks having radially directed gradations of refractive index; and Figs 7 and 8 are illustrations of other techniques for accomplishing gradations of refractive~index in lens blanks.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For ease in understanding principles o~ the present invention, Fig. 1 illustrates the traditional geometric assumptions which are basic to spectacle lens design. In Fig. 1 point P is a point on the reference sphere C at which it would be desirable to present the same optical corrections as are present~at the vertex V of lens L. Problems associated with this endeavor are classical and reported in the literature, e.g.
Bechtold, Edwin W. "The Aberrations of Ophthalmic Lenses", Am. Jl. of Op. and Arch. Am. Acad. Optom., 35 (1) 10-24, 1958;
Davis, John K., Henry G. Fernald, and Arline W. Raynor, "An Analysis of Ophthalmic Lens Design", Am. Jl. of Op. and ~Arch. Am. Acad. Optom. 41 (7) 400~421, 1964; Davis, John K., Henry G. Fernald, and Arline W. Raynor, "The Design of a . .

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~en~raL Purpos~ ~LIl~Le VisiOll l.el1.Y Scri~s" ~m. _1 o~ æ~ and ~rch. Am. Acad. Optom., ~prll 19G5; an(l DavLs, .lohn K. "Stock Lenses and C~stom Design" m._Jl. of 0~ , December, 1967.
Fig. 2 disp]ays the result of the traditional calculations and indicates in terms of tlle tangclltial (t) and sagittal (s) meridional power errors the performance possible for a -~3.00 spherical prescription. Data is given for a commonly encountered 28.5 mm center-of-rotation (CR) distance and index of refraction of 1.56. Curvatures of front surface, rear sur~ace and center thickness are 6.72 diopters, -4 diopters and 3.76 mm respectively.
It is immediately obvious that for a concave base curve of approximately -4.00 diopters, the average field curvature (power error) is approximately "O", i.e. the sagittal error is about -0.9 diopters and the tangential error is about +0.9 diopters. In order to reduce this astigmatism to "O", however, ` a concave base curve slightly steeper than -6.00 diopters would be required and the field curvature (power error) would become increased to about -.17 diopter. Thus, it can be seen that ; power error and astigmatism cannot both be reduced to zero by - 20 conventional lens design techniques. Accordingly, the differences in lenses produced by various manufacturers stem from differences in the type of compromise favored by their designers.
Table I which follows sets forth sagittal and tangential powers, sagittal and tangential errors and astigmatisn occurring in the exemplary +3.00 diopter lens at various angles A (Fig. 1).

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11 20~ 2~97 3~06 ~0~03 0~06 0~09 12 j 25~ 2~95 3~08 -0.05 0~09 0~14 13 jj 30~ 2~92 3~11 ~0~09 0~09 0~19 14 j 35~ 2~88 3.12 -0~12 0~12 0~2~
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'''~'' r - 15 The optimum in o-axis ophthalmic len~ correction would, - 16 of course, be to accomplish simultaneouR correction of oblique .: 17 astigmatism and fiela curvature (power error). This can be 18 ¦accomplished according to the present invention through the use 19 If' a gradient index of refraction in the lens blank used to ~prepare the lens as showp in T~le I~ which follows:

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Table Il rel)r~e~ C119 II~IViIIg n Lront surf.lce curvature of ~8.64 diopters, n rcar surface curvatllre of -6.00 diopters, thicklless of 3.8~ mm alld index o~ re~raction o 1.56 at its axis affording an axlal power of 3.00 diopters. The lens is provided ~ith a re~ractive index gradient increasing from center to edge by increments of 0.0050 per each 5 increase in angle ~ (Fig. 1). The center of rotation (CR) distance is 28.5 mm which is most common in ophthalmic lens precriptions. At a point of 30 obliquity astigmatism is reduced to nearly "0" (i.e.
0.02) while field curvature ~power error) has been reduced to essentially "0" (i.e. sagittal error is -0.00 and tangential error is 0.02). At this 30 position, the refractive index has been increased to 1.5900.
Referring more particularly to Fig. 3, the sagittal (s) and tangential (t) errors have been plotted for the lens used in the example of Table II. This illustrates that by the selection of a concave base curve of -6.25 diopters or slightly less, essentially complete correction of oblique astigmatism and field curvature (power error) can be accomplished for a viewing angle A of 30. For obliquities less or greater than 30, it can be seen from Table II that only slightly less but sub-stantially complete correction of oblique astigmatism and field curvature has occurred.
It should be understood that all examples given hereinabove have employed a stepped gradient of refractive index, i.e.
0.0050 per each 5 changes in angle A. By employing a continuous and/or non-linear gradient of refractive index between the center and edges of a lens, a still further improvement in oblique astigmatism and field curvature correction can be accomplished.

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,1~ .7 r~ 5 Using the fore~oing exilm~le o~ a lens llavlng axlal power of 3.00 diopters and a center of rotutlon (CR) distance of 28.5 mm, Table III which follows illustrates a variation in index of refraction between the lens center and peripheral portions which may be incorporated to accomplish the effect of off-axis correction over the entire lateral fleld of view, e.g. from 0 to 35 in ophthalmic lens design.

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Rcferring in sLill Illore dctail ~o l'ables tl and ~[r~ it can be seen th~lt tllc graclation of re~rilctlve -Index has very little effect on of~-axls astlgmatism. Astlgmatism remains at zero or very close thereto throughout aLl lateral viewing angles A, i.e. from 0 to 35. The refractive index ~radation, however, has the effect of dran~atically reducing Eield curvature (power error~. It can be seen, for example, that at a 35 obliquity (Table II) the error in the sagittal meridian has been reduced to -0.04 diopters, and in the tangential meridian to -0.03 diopters. Thus, one may strategically select base curve to correct for off-axis astigmatism according to conventional practice, and then be able to employ a gradient of refractive index according to the present invention to eliminate or reduce field curvature (power error) to an insignificant value.
In the foregoing examples of the use of a refractive index gradation according to the present invention, the index of refraction has been lowest at the center or axis of the lens and increased in directions outwardly toward the edge of the lens.
This, however, is not necessarily the direction of refractive - index gradient which should be used for a]l lenses. The direction of index gradation, i.e. whether decreasing or increasing in ; directions away from the center of a lens will depend upon the power range in which one is working and just what is being attempted to achieve in terms of off-axis correction. For example, in working with lenses of high plus power such as cataract lenses, a refractive index of highest value at the lens center and dropping off from center to edge may produce the most ; desirable results.
The following tables IV, V and VI demonstrate that a ~-useful direction of index gradation for a high plus power lens e.g. a cataract lens, is one which decreases from center of the lens toward its periphery.

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1~'7'~ 5 Tabl~ IV ilLustr~ltes wh.lt Call llat)pell with respect to off-axis aberrations in a lens of constall~ index value from center to edge wllen, for e~clrnple, axial power is 1~.00 diopters with a concave curve of -3.50 tliopters ~nd center thickness of 11 mm. Sagittal power remains nearly constant Erom center to edge of the lens, i.e. ~rom 0 to 35 of angle A while the tangential power increases in value to a point where at 35, it is nearly 3.00 diopters strong. The resulting astigmatism at 35 rotation in the eye is 2.72 diopters.
Table V, with the same prescription of 14.00 diopters axial power illustrates the improvement that can be accomplished with an incremented index of refraction according to the invention. The index incrementation in this example is provided by dropping .005 for each 5 of eye rotation away from the center of the lens. By such means, it can be seen that while the less important sagittal power errors have increased somewhat, the more important tangential errors have dramatically decreased.
, At 35 the tangential error has been reduced to approximately 2.00 diopters with astigmatism accordingly being reduced to about 2.00 diopters.
By employing a non-linear refractive index gradient as shown in Table VI, a substantially constant tangential power (nearly 0 tangential error) can be accomplished. It should be understood that although tangential error is generally considered more serious than sagittal error, it is not necessary to reduce it to zero at the expense of substantial amounts of sagittal error. Accordingly, Table VI is intended mainly to show that additional control in off-axis correction according to the present invention can be achieved by ~arying the refractive -index gradient not only in predetermined increments but rather in a non-linear manner.

jl/ -15-~3'~ 5 ~ hile the exalllpLes o~ 'l`abLes I-VI h.lve Lllustruted the invention as applled to conclitions using the most common 28.5 mm center of rotation distance (CR) for genelal purpose ophthalmic lens prescriptions and 25 mm CR for high plus Si.e.
cataract lens) prescriptions, it should be understood that astigmatism and curvature of field tpower error) can be essentially eliminated, i.e. reduced to negligible amounts, for other center of rotation (CR) distances as follows:
Tables VII and VIII illustrate a control of astigmatism and power error available by gradation of refractive index in a lens having a front surface curvature of +8.64 diopters, a rear surface curvature of -6.00 diopters1, center thickness of 3 84 mm and index of refraction of 1.56 at its axis affording aXial power of 3.00 diopters. The refractive index is increased radially from center to edge of the lens.

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Refcrring now to 'I.lbl.~s L~C nnd X wh:i.cll follow, the same lens design datl but w:i.thout refractivc index gradation is presented to iL:Lustrate l:he respective correctlons in curvature of field (power crror) wh:ich were accomplished wlth tlle refractive index gradation of the Tables VII and VIII
situations.
Comparing Tables VII and IX it can be seen that curvature of field (sagittal and tangential errors) was considerably reduced by refractive index gradation (Table VII). For the :~ 10 25 mm center of rotation distance situation, l.e. with constant refractive index (Table IX) s error equals -0.20 and t error equals -0.14 at 35 while with refractive index gradation (Table VII) s error equals 0.02 and t error equals 0.10.
Similarly, a comparison of Tables VIII and X shows a highly significant correction of curvature of field for the 32 mm center of rotation situation. There, for the 45 angle of viewing, s error has been reduced from -0.25 to -0.03 and t erro~ from -0.30 to -0.06.
TABLE IX
Index is 1.56 ; ~ Center of Rotation Distance is 25.0 mm Axial Power is 3.00 diopters Angle Sagittal Tangential s t Astig- :
Power Power Error Error matism

5. 3.00 3.00 -0.00 -0.00 0.00 10. 2.99 3.00 -0.01 -0.00 0.01 : 15. 2.97 2.99 -0.03 -0.01 0.02 20. 2.94 2.98 -0.06 -0.02 0.04 25. 2.91 2~96 -0.09 -0.04 0.05 2.86 2.92 -0.14 -0.08 0.06 35. 2.80 2.85 -0.20 -0.14 0.05 jl/ - -15c-. ~ ... . ~

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2 ~ Index i9 l 56 3 Center o~ Rotation Di~tance is 32.0 mm 4 Axial Power is 3.00 diopter~ I
lj Angle Sagittal Tangential 3 t A3tig-

6 , Pow~r PowPr Error Error mati?m

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8 lO. 2.98 2.98 -0.02 -0.02 0 00

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~given hereinabove have been based upon the use of an ind~x of refraotion of 1.56 at the enter of a lena, hl3her or low~r ' ' ` ' , ' ' .. . .
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~efractive indiccs ~Ily bc u~d for purpose~ oF nvol~llng undue lowering or raising of re~ractlve iu(lex at e~ges of the lenses.
The fore~oLng illustrcltcs the advantages of deslgning ophthalmic lenses according to the :Lnventlon with refractive index gradients uniquely employed ac; "tools" in the correction of of f-axis aberrations. Data emboclied in the various examples of Tables I-VIII has been arrived at by conventional lens designer's ray tracing calculations and the assistance of ; programmable electronic computer technology, the latter being dispensable but extremely useful to the designer. While the data of Tables I-VIII has been selected to illustrate principles of the present invention, it is believed to have been made apparent that similar information can be arrived at or adjusted according to the requirements of any one of the virtually unlimited number of ophthalmic lens prescriptions encountered in the art whether these prescriptions are for spherical lenses of the single vision or multifocal types or whether, in either case, they contain a cylinder correction.
` Those interested in details of ray tracing as used in ophthalmic lens design work may refer to U.S. Patents Nos.
` 3,434,781 and 3,169,247 and/or one or more of the above-identified pieces of literature on the subject.
As mentioned earlier in this specification, the present inventive concept of correcting off-axis aberrations in ophthalmic lenses with a controlled gradation of refractive index can be utilized to obviate a need for aspheric surface ` design or may be incorporated in and/or with aspheric design for greater "fine tuning", i.e. correction, of oblique aberrations.
A~ in all cases of lens design including the present concept of using refractive index gradation) base curve is carefully chosen and in using a refractive index gradient to replace or obviate a need for off-axis correction by aspheric ... .
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'7;~5 urv.lture, base curve can he so choscn ~s to miniml~e a~stigmatism and the rcfractlv~ lndex gradient so applied as to minimi~e curvature of field (power) error.
In the case of 'If ine tuning" with aspheric surface design, particular attelltion may be paid to correction of a third off-axis aberration, distortion whether of the "barrel" or "pin cushion" type. In this case, base curve selection may be made more specifically with reduction of distortion in mind, surface asphericity chosen to minimize astigmatism and a refractive index gradient chosen and utilized ~o reduce curvature of field (power error), the latter having been demonstrated hereinabove. Those interested in details of manipulating base curves and applying surface asphericity for reduction of oEf-axis aberrations may refer ~o applicant's U.S. Patents Nos.
3,169,247 and 3,960,442, issued February 9, 1965 and June l, 1976, respectively.
While the present invention relates more particularly to matters of the use of a refractive index gradient in ophthalmic lenses as a "tool" for correcting off-axis aberrations and is applicab~e to lens blanks having a gradation of refractive index ` from center to edge regardless of how the lens blanks may be fabricated, treated or otherwise provided with the refractive index gradation, examples of techniques useful in producing such ; lens blanks have been illustrated in Figs. 5-8. These exemplary lens blank manufacturing techniques, however, are not intended to be restrictive to matters of the present invention but merely illustrative of some of the schemes available to the artisan for providing lens blanks which are useful in practice of the above-described invention.
Referring to Figs. 5 and 6, a billet 10 of lens material e.g. optical glass, having a diametral dimension equal to or greater than that of the maximum transverse dimension required jl/ -17-` : -. ~ . '. :

t 7 ~ - ~ 5 ~E an opllthalrllic ~ s lo be produced ~ccordlng to the inventlon, is providcd. ~illc~ 10 is -Immersed in a salt 12 contalning alkali metals to cause ion-excilang~ between ions in the glass and those ill the salt in amounts graclually penetrating radially into billet 10.
Details of techniques having utility in the manufacture of ion-exchanged billets may be had by reference to U.S. Patents Nos. 3,650,598 and 3,827,785.
With a controlled passage of time in salt 12, ion exchange can be caused to proceed a predetermined distance toward and/or to the axis of billet 10 with refractive index varylng according to the gradation of ion exchange having taken place.
- The resulting substitution of monovalent alkali metal ions of one size in salt 12 for ions of another si~e in billet 10 pro-gressively radially inwardly thereof produce a variable denseness of the material of billet 10 which results in corres-ponding refractive index changes. While not shown in Fig. 5, opposite ends of billet lO are preferably covered with a protective coating or the like which prevents ion exchange in direction axially of billet 10.
~ aving so treated billet lO in salt 12, removal from salt 12 and cleaning to terminate the ion exchange process renders ` billet 10 adaptable to transverse cutting into sections 14 (Fig. 6) of thickness and diameter necessary for the formation of lenses such as lens L in Fig. 3. The meniscus configuration of lens L is accomplished with conventional grinding and polishing operations.
; As illustrated with stippling and arrow 16 in Fig. 4, lens L is provided with a gradation of refractive index from its axis outwardly in the direction of arrow 16. The density or refractive index may be caused ~o decrease in the direction of arrow 16 or vice-versa.

jl/ -18-.~ ........... . ...................................... .
: ~

~8'7 7~15 In Fi~. 7 ~.n ~llL~rnaL~ t~chni(lue ~or ~abricatLng lens blanks h~vin~ a gr~dat~d refractlv~ index is illustrated. Thls comprises Ll~e fabrication of a bil]et lO' of a central rod 18 having a preselec~ed refractive lndex and successively surrounding closely inte~fitted sleeves 20 each of a preselected different refractive index. The assembly may comprise more or less than the five concentrically related components which have shown, i.e. the incremental gradation of refractive index from rod 18 radially outwardly may be of any desired step function either increasing or decreasing in value.
Components 18 and 20 of billet 10' would normally be heated and/or otherwise fused together as a unit and cut trans-versely to the thickness desired of a lens blank 22, for example. Fusion of components 18 and 20 together and transverse cutting of billet 10' to form blank 22 can be followed by irradiation and/or other treatment of blank 22 to produce a blending or gradation of index of refraction of one of components - 18 and 20 with an adjacent component. It is also contemplated - that components 18 and 20 may be surface treated before assembly by immersion in a diffusant such as heated silver chloride to provide a graduated transition of refractive index therebetween in the final assembly. Operations of producing refractive index gradation by irradiation and/or diffusion are well-known in the art. For those interested in details, however, reference may be made to U.S. Patents Nos. 3,610,924 and 3,563,057.
Still another technique for producing a gradient refractive index billet 10" from which lens blanks may be cut is illustrated in Fig. 8. This includes the provision of a multiple chamber g:Lass furnace 24 having a plurality of con- ~;
centric orifices through each of which a lens material of a preselected refractive index may be directed and caused to form the composite billet 10". Following the formation of billet 10"

j 1/ -19-', , ~L~l'î'7~
and coolinE~ ~hereo~ ~o a ~;ol:id state, transverse c~ltting a].ong lines 28 w:ill pro~uce lens blanks 30. tt should be understood that a multiple oriEicc plastic (i.e. ophthalmic resin) dispenser may be substit-lted ~or furnace 24.
The artisan will readily appreciate that there are various other modifications and adaptations of the precise forms of the invention herein shown which may be made to suit particular requirements. Accordingly, the precise forms of the invention presently shown and described have been presented for purposes of illustration only and are not to be interpreted as restrictive of the invention beyond that necessitated by the following claims.

jl/ -20-

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of correcting off-axis errors in the manufacture of an ophthalmic lens comprising in addition to affording the lens with optically finished convex and concave opposite sides of preselected curvatures, a particular center thickness and a pre-established refractive index value adjacent its axis, further effecting a gradation of refractive index in the material of said lens radially from its axis toward its edge.

2. The method according to Claim 1 wherein said radial gradation of refractive index increases in directions away from said lens axis.

3. The method according to Claim 1 wherein said radial gradation of refractive index decreases in directions away from said lens axis.

4. The method according to Claim 1 wherein said radial gradation of refractive index is effected in step fashion between said axis and edge of the lens.

5. The method according to Claim 1 wherein said radial gradation of refractive index is in the form of a continuous change of value between said axis and edge of the lens.

6. The method according to Claim 4 wherein said radial gradation of refractive index increases in directions away from said axis.

7. The method according to claim 4 wherein said radial gradation of refractive index decreases in directions away from said axis.

8. The method according to claim 5 wherein said radial gradation of refractive index increases in directions away from said axis.

9. The method according to claim 5 wherein said radial gradation of refractive index decreases in directions away from said axis.

10. The method according to claim 1 wherein an aspheric correction is applied to at least one of said opposite sides of said lens.

11. A corrected ophthalmic spectacles lens of meniscus configuration having optically finished convex and concave opposite side surfaces of preselected curvatures and a particular center thickness and refractive index value adjacent its axis, one of said curvatures being the base curve of said lens and there being a gradation of refractive index in the material of said lens extending in directions radially from its axis toward its edge, the geometrical surface configuration of said base curve being selected and formed in conjunction with said axial refractive index value, center thickness and opposite surface curvature according to off-axis correction desired for at least one of ophthalmic lens aberrations including power error, astigmatism and distortion and said gradation of refractive index affording off-axis correction of at least one of said lens aberrations of power error and astigmatism.

12. An ophthalmic lens blank having at least one curved side surface, said curved surface constituting the base curve of a lens to be produced from said blank and there being A gradation of refractive index in the material of said lens blank extending in directions radially from its axis toward its edge, the geometrical surface configuration of said base curve being selected and formed in conjunction with said axial refractive index value according to a center thickness and opposite surface curvature required for off-axis correction of at least one of ophthalmic lens aberrations including power error, astigmatism and distortion and said gradation of refractive index affording off-axis correction of at least one of said aberrations of power error and astigmatism in the finished lens to be formed from said blank.

13. A corrected ophthalmic lens according to claim 11 wherein said radially gradated refractive index increases in directions away from said axis.

14. A corrected ophthalmic lens according to Claim 11 wherein said radially gradated refractive index decreases in directions away from said axis.

15. An ophthalmic lens blank according to Claim 12 wherein said gradation of refractive index decreases in directions inwardly from said edge.

16. An ophthalmic lens blank according to Claim 12 wherein said gradation of refractive index increases in directions inwardly from said edge.

17. A corrected ophthalmic lens according to Claim 11 wherein said radial gradation of refractive index is effected in step fashion between said axis and edge of the lens.

18. A corrected ophthalmic lens according to Claim 11 wherein said radial gradation of refractive index is in the form of a continuous change of value between said axis and edge of said lens.

19. An ophthalmic lens blank according to Claim 12 wherein said gradation of refractive index is effected in step fashion inwardly from said edge of said blank.

20. An ophthalmic lens blank according to Claim 12 wherein said radial gradation of refractive index is applied in the form of a continuous change of value in directions inwardly from said edge of said blank.