Continuously variable contact lens

BACKGROUND OF THE INVENTION

This invention relates to contact lenses, and more particularly to continuously variable multi-focal soft contact lenses suitable for creating sharp images of far objects, intermediate objects and near objects simultaneously on the retina of a wearer,

<img file="AU2711684A_D0001.tif" />

<img file="AU2711684A_D0002.tif" />

'including lenses which may be used to correct for astigmatism.

' There is great demand, and interest in providing a contact lens that can be successfully used for both distance vision as v»cll ’ as for close-up reading. Currently, there are three approaches ' ^:' _e attempting to solve this problem. These approaches include the

Φ 9 ·* alternating vision bi-focal contact lens and the simultaneous vision bi-focal contact lens which encompasses both the right &lt;&gt;£,« eye/left-eye method and the blended bi-focal lens.

© &lt;r.

The alternating vision bi-focal contact lens generally has

..=, two optical zones. The first optical zone for viewing distant a ·' c ®· objects generally is in the middle of the lens. The optical zone for viewing near bbjects generally surrounds the first optical .« ·· “ * zone. Each optical zone is larger than the normal pupil opening

o

2(/ so that a wearer must adapt to position the lens properly for proper application. This is a difficult task to train the patient to move the two optical zones when desired. This is particularly true with large comfortable soft contact lenses which do not move freely to switch the position of the optical zones at will. Thus, 25 such lenses are not fully satisfactory and often the transition between the two optical zones is positioned in front of the pupil resulting in blurred vision. ’ ' ³ . I ' i

! . - Ο c ’ ..

t.

-2Simultaneous vision bi-focal contact lenses take advantage . '·' A of the ability of the human brain which has the capability of

Because c~ es .te selectively choosing a sharp blurry images projected on image when there are both sharp and the retinas simultaneously. This this method. In the right-eye/left-eye method one eye is fitted · distant an automob out of· study when is very di distant vision lens and the other eye is fitted with a near with a desirable vision

1.

time.

LCt looses the sense of depth perception.

:11

The second approach utilizing the simultaneous vision biles optical focal contact lens is the blended bi-focal lens with one she to the

3US improved optical ,ittical powe is made pupil open smaller than the normal pupil opening to insure that both optical has desired di ant and the p * © one diameter i

the abrupt discontinuity and glare caused by a sharp transition cal ing for of a weare.

ent rly symmetry.

cause confusion to the wearer.

iove negative p lUS , increases 1 attempting to provide multi-focal contact lenses currently under ;ion to the ed

Sxtidy have severe problems which are inherent in any bi-focal lens.

ipil diameter.

other surf

16 « ©

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to© c

Γ· £·.

« © ζ} © ©

Obviously, since only one eye is used at a time the wearer alternating vision lens described above which has two

Based on the above, it can be seen that all three approaches between zones. Notwithstanding that the transition is blended, it • O 0» •e w © ¢- 9 q zones aresimultaneously presented to the pupil. The transition zone smaller than the pupil opening. This is similar zones. The distant vision zone in the center of the lens lens. The brain then selects the vision in one eye at a does· not provide continuity between the two vision zones. Signi-

<img file="AU2711684A_D0003.tif" />

0.07mm₍ from

In order to make the junction thickness JTK =

Figure 4:

V

16— j

-3ltage

Sc-f :y of

Because the lenses have two optical zones, one for reading and for expansion :

□ and distant vision, most anything ill between, such as the dashboard of

This an automobile, is either blurred or forms double images, equally power. Opt ising out of focus. Another draw back of each of the approaches under wet (or so itted · study when applied to the more comfortable soft lenses is that it' the approp near is very difficult to correct for astigmatism. Accordingly, it is

P_w at a desirable to provide improved continuously variable multi-focal sarer contact lenses which overcome the drawbacks present in the prior wherein:

n biSUMMARY OF THE INVENTION tical the reo a r e·

Γ0

Generally speaking, in accordance with the invention, an a» o q the center tical improved contact lens with a continuously varying multi-focal opmade tical power gradient having a diameter smaller than the normal

The tical pupil opening in the middle of the contact lens is provided. The ition £} c ft dpsired distance vision power is at the center region of the lens squeezing while held educe and the power increases to the desired near vision power as the polishing.

ition diameter approaches the normal pupil opening, or about 5 to 7 mm ical and »d, it in the Mate to be worn for creating sharp images of far objects, iigni3 ft

- s deformat ii two.

: will &gt;aches uhder lens.

: rom intermediate objects and near objects simultaneously On the retina of a wearer.

which indj is set foj

Xn a non-toric lens, the lens has complete rotational symmetry. In a typical lens for a near-sighted eye the greatest negative po(yer of -3 to 5 diopters at the center continuously increases to zero at the 5 to 7 mm diameter and remains at 0 diopter to the edge of the optical zone at approximately 9.7 mm diameter. The concave surface of the lenses is aspheric and

Other surfaces can be spheric, aspheric or toric.

// from eq. (7) :

-1.762K - -______________

N6.3706 Cp² - 3.847KCp + 0.58K² - 40.38

Th( essential^ expansion in the

In (8) maintain for high!

\ '

175 expansion so that all calculations are performed using the dimen sions in the dry (or hard) state, except for calculation of optical curve r2.

* at the cei power. Optical powers for an expandable lens are calculated in the

1*2' and Γ2 curve and the appropriate expansion factor:

P_w ri x Exp

1___________ t x Exp n-1 _ r2' x Exp ball n-1 cut wherein:

Exp is the expansion factor;

lens t n is the index of refraction of the material when wet;

t is the thickness of the lens;

thickness r2* is the radius of curvature of the concave surface at parameter the center; and ry is the radius of curvature of the convex surface.

contour w

The lenses '^Ln accordance with the invention are prepared by squeezing a blank(button by a ball and cutting the blank button while held squeezed and then releasing the button after cutting and

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© &lt;5 a Ό 0 elliptica retina as zontal polishing. The cut and polished surface before releasing is spherpupil o ical and after release it becomes aspherical. The amount of deformation created by the squeeze is measured by a micrometer expand n which indicates the amount of displacement. A detailed procedure • O i Φ ’O’ © .ec

Ac&lt;

improved is set forth in Our U.S. Patent No. 4,C74j469.

Anc mhe concave aspherical surface generated by this method is continuous essentially spherical from approximately a $ mm diameter (before

It expansion) and out and it has a base curve radius of r2. The continuous cave surfs

A.

In .'A maintain the junction thickness to be 0.07mm for example. However, for highly minus power lenses, the computation may give too thin

Ha .= C

-184 ί

<img file="AU2711684A_D0004.tif" />

aspherical curve in the middle has a steeper radius than the base curve Γ2· The radius of curvature of this curve is the steepest at the center and is a designated as r2*. The difference between r2* and r2r as well as the displacement distance between the actual 5 curve and the spherical curve and the gradient, diameter size are controlled by the amount of squeeze , the size of the squeezing ball diameter, and the depth of cut (or remaining thickness of the cut blank). Cnee r2 and x*2' afe determined, the thickness of the lens t and the convex radius of curvature rj. are calculated using the desired optical power at the apex of the lens and the desired thickness at the junction of the optical zone. The remaining © ..

⁰⁰⁰ parameters of the lens are designed by conventional means.

Since the lens has rotational symmetry, the equi-power contour will be a circle. For an eye with astigmatism, an 5_0o elliptical contour will create a sharp image of an article on the

Ci retina as long.as the necessary vertical optical power and horizontal optical power are available on the lens within the normal

5' o ❖ ., pupil opening, namely within about a 5 mm diameter region before expans^'p. of the lens.

&gt;q* Accordingly, it is an object of the invention to provide an

s.

. 6 ®.

improved contact lens.

Another object of the invention is to provide an improved continuously variable multi-focal contact lens.

It is a further object of the invention to provide a 25 continuously variable multi-focal contact lens wherein the concave surface is aspheric.

<img file="AU2711684A_D0005.tif" />

»

6//

It is another object of the invention to provide a multi focaUcontact lens having a continuously variable optical zone at the middle of the lens with a diameter less than the normal pupil

V&lt;i'; .

opening.

Still another object cf the invention is to provide a method for forming a continuously variable multi-focal contact lens.

Still a further object of the invention is tc provide an improvedcontinuously variable multi-focal contact lens which will correct for astigmatism.

Still other objects and advantages of the invention will in tion.

The invention accordingly comprises the several steps and il J d the relation of one or more of such steps with respect to each of

Q £? O &amp;

w ·:· the and others _f and relation of the article possessing the features, properties elements, which are exemplified in the following © &lt;? «&gt;

i « o .

r· detailed disclosure, and the scope of the invention will, be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to the following description taken in connection with, the accompanying drawings, in which

FIG. 1° is a plan view illustrating the optical power gradient view of a soft contact lens constructed and arranged in accordance with the invention;

FIG. 2 is cross-sectional view of the soft contact lens of

Fig before expansion;

If calculated t

0. Olma for example:

. ds = 0.0857 + 0.04(-0.0Γ) = 0.1357· v

i to

-7process of preparing the lens of Figs. 1 and 2;

FIG'. 4 is a cross-sectional view of a portion of the lens

J' of Figs. 1 and 2 illustrating dimensional relationships for design of the lens;

FIG. 5 is a partial cross-sectional view of the peripheral

2;

FIG. 6 is plan view of the lens of Fig. 1 illustrating circular shaped bands of the optical zone used for distant viewing and near viewing in the lens of Figs. 1 and 2; and band

FIG. 7 is a plan view of the lens of Fig. 6 illustrating a used for distant viewing which corrects for astigmatism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS oft c e « a ft © o O

- « ft ft

Fig. 1 is a plan view illustrating a continuously varying

15_e«_en imilti-focal soft contact lens in the expanded wet state or in ♦ «/©ft ., ·/ . .

condition for wearing as prepared in accordance with the invention. The lens has complete rotational symmetry with the greatest ft ft «&gt; ft ;· ’ . _v. '

Φ ® ft ' . ·⁴⁶ “negative power of approximately -4 diopters at the centv-τ which c-c·©” ©ft ft ft X., increases to 0 diopter within a zone having a diameter of approxizoqe of approximately 9.7 mm in diameter. The overall diameter of the expanded lens is approximately 14.7 mm.

The lens of Fig. 1 may be formed of any commercially available soft contact lens material. For example, the specific lenses fabricated in accordance with the invention and described herein are formed of HEMA material, such as hydroxyethyl methaI

B 5 *_&gt;j

Bl · , if

-21crylate. The invention is applicable equally to all soft contact lens materials of HEMA analogs, ethylene glycol dimethacrylate (EGMA) or its analogs, polymethylacrylate (PMMA) or its analog, polyvinyl pyrrolidone (PVP) and the like. Generally, these soft.

. lens materials swell and absorb varying .amounts of water depending on the specific pblymer material... ΗΕΜΆ lens blanks are generally available*‘which· swell to a water content of 55%, 45% or 38%.

<img file="AU2711684A_D0006.tif" />

Referring now tp Fig. 2, a cross-sectional view of the lens illustrated in

Fig. 1 in its dry state before expansion is shown.

All.dimensions in Fig. 2 are reduced by 17% from that in Fig. 1.

This is due to the fact that the design and manufacture of soft lenses in accordance with the invention are performed in the hard state before expansion. Thus, the following descriptions performed using the dimensions in the dry state, except for calculation of optical power. The optical power is calculated the wet' state using the dry state dimensions multiplied by are the for the appropriate expansion factor. For the HEMA material utilized in the exemplary embodiments, the expansion factor is 1.21 and the

SO 9 0 a go ' St

2Q^o,‘^ei factor for a lens material including 35 percent water is 1.18 and expanded lens contains about 45 percent water. The expansion for 55 percent water is 1*31

In the lens illustrated in Ficr 2, all the curves are spherical except the inside concave cur*e Which is aspherical

This base curve is essentially spherical from approximately a 5 mm ‘25 diameter and out and which base curve has a radius of r2· If the inside concave curve was spherical with the same r2 radius, the

- ' ' ' . ' ’ * · ’

-.1 tional means used to correct astigmatism of any mono-vision contact lens. In a multi-focal toric lens, the equi-power contours will nnl· h&lt;=» nnnri&gt;n1-rin nirnles as shown in Fis. 1. but they will contact crylate analog, ise soft.

^pending tnerally

38%.

the lens shown.

Fig. 1.

of soft uhe hard ons are for the

a. ted for l· by the

Lized in and the spans ion

1.18 and ves ai'e lerical

Ly a 5 mm

If the

Lus, the o-vision contours

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Eg

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&lt;s © © a fc© o iSr^e.

rt ¢13

O 6b * , a . » ·© 6 P

Οί,Οβ

I inside concave middle of the lens'. As shown in Fig. 2, the curve is steeper in curve would follow the dotted line curve in the

1/

Z the middle than base curve r^. The radius of curvature of this aspheric curve is steepest at the center and is designated as r2*.

Control of the difference between r2* and r2, as well as the displacement distance between the actual curve (the solid line curve) and the spheri-.il -nrve (the dotted line curve) and how to fabricate the gradient within the desired diameter represent important aspects of the invention. The concave surface of the or toric. Outside the center optical region, the concave surface of the lens is essentially spherical.

Once the dimensions of r2 and r2‘ curve are determined, the thickness of the lens (t) and the convex curve having a radius Of curvature ri are apex of the lens &gt;k calculated using the desired optical power at and the desired thickness at the junction of zone (AOZ) which has nominally been set at 8 the the i ^»©0 4 « « © ά ft b gene grad

5.5 less imag lens the the anterior optical

The remainder of \\

The bevel width and bevel diameter are selected arbitrarily, based mm.

the on at is experience. In the exemplary embodiments the bevel width is set

0.85 mm and the bevel radius is set at 10.3 mm. Since curve r2 essentially spherical at the 8 mm junction .point, one can calculate the curvature Of the peripheral convex curve having a radius, r_CXp, based on the designed junction thickness and desired edge, thickness of. the lens. In order to obtain the desired ,&lt;pro^erties ofe the lens, namely a simultaneous multi-focal lens, the optical power gradient from the desired dista.nce vision ft®Sf eat®

'. d y»©® s B V «* o €&gt; &lt;k©

IS /2 cont an a:

the desc issu c

prov erit^y attained and, since certain changes may be made in carrying . out the above process and in the article set fortho without •1

-23I hev will departing from the spirit and scope of the invention, it is w

; I the center must increase about 3 to 5 diopters within a region having a diameter less than a normal pupil opening. A normal pupil opening is the maximum opening in the dark and is generally about 6 mm· in diameter. Accordingly, the optical power gradient is formed in a region of the l^ns between about 4.5 mm and 5.5 mm in diameter in the dry state. -\ . . . \ ·

The simultaneous multi-focal contact lens provides gradually varying focal power within a .central .Region of a dimension less than the normal opening of the pupil of ajearer. Due·to this, at least some part of the lens in the central region forms a sharp image of a distant object on the retina while another part of the the retina simultaneously, the human brain selectively picks up the sharper image of the desired object. It is this selective r&gt; ft ft ft ft .power of the human brain tu select the sharp image which enables the lenses prepared in accordance with the invention to provide a continuously variable multi-focal effect.’ ’ ·' v The soft contact lenses with the concave surface including an aspheric curve which provides the optical power gradient within the pupil opening may be prepared by the apparatus and method.

described

United States Patent No. 4,074,469 which issued on Ifebruury 21, 19/8. The apparatus disclosed therein &lt; Q/' U^; ' •provides for forming aspheric surfaces in.an optical lens by dis|\

D2 AND D3

39.

<img file="AU2711684A_D0009.tif" />

If torting the lens blank in a predetermined manner and forming spherical surface in the distorted lens button. The distorted lens button is released and the formed concave surface becomes aspheric. Accordingly, the entire specification of our earlier patent is incorporated by reference as if fully set forth herein.

In accordance with our method, an uncut blank lens button is squeezed by a ball having a radius R. The button is then cut

<img file="AU2711684A_D0010.tif" />

and pciished while held in the squeezed position and then released.

The amount of displacement created by the squeeze is measured by a micrometer so that one can tell exactly how much displacement is imparted. This amount of displacement is exactly the same as the ft « aft® · ft ft · ft ft.

. . ;

ft ft ¢1 . ft.· · ft ft ft ' · Si displacement distance between the aspherical solid line and the aspheric dotted line curve in Fig. 2.

The greater the deformation imparted to the lens blank' ft ft · ft.

prior to cutting results in a greater optical power gradient final lens. At times, a dry blank of soft lens material may in the be too ft»· * brittle to squeeze the desired amount before cracking. In this case, it is advisable to precut the blank to prevent cracking.

There is no need to polish this cut and the amount of displacement . **· a . A + 9.

... 4 ft ft » G • a· ' » caused by the squeeze is also measured by a micrometer.

Fig. 3 illustrates the relative position of a ball 11 having a radius R and an uncut blank lens button 12 to be deflected when ball 11 is displaced in the direction of positioned above uncut lens blank 12 the arrow. A micrometer is utilized to determine

3a illustrates the

Fig.

the distortion applied to lens blank 12.

lens button 14 and position of ball 11, a cut but not polished

<img file="AU2711684A_D0011.tif" />

THE

CLAIMS DEFINING THE INVENTION ARE AS

FOLLOWS:

<img file="AU2711684A_D0012.tif" />

g micrometer 13. The details of construction of an apparatus suitable for holding lens blanks 12. and 14 and micrometer 13 is described in detail in our prior patent. Accordingly, the details of constructipn need not be set forth herein.

It has been found for a given amount of center displacement (squeeze), the final thickness of the cut button and the size of the radius of the squeezing ball R changes the size of the lens

<img file="AU2711684A_D0013.tif" />

<img file="AU2711684A_D0014.tif" />

•q iai&amp;&amp;

&gt;© U © © O

Λ&gt;-3 region within which the optical power gradient occurs, A steeper radius R of ball 11 yields narrower regions for the aspheric zones and a flatter radius R of ball 11 yields wider regions for· the aspheric zones. The thinner the final thickness of the lens button, the narrower the region of the aspheric zone and the thicker the final thickness of the lens button, the wider the region of the aspheric zone. Similarly, for the same amount of squeeze, a smaller aspheric gradient or a steeper aspheric curve Γ2» for r2- The opposite is also true.

The following exemplary embodiment is tion of squeeze and cuts which results in

Typical Combination

Radius of ball used to squeeze

Amount of squeeze the*same base curve a typical combinaa lehs having the itim

Q == 25 micron

Final thickness of cut and polished button

Typical Results .

GOZ

7. The contact lens of claim 6, wherein the diameter of the region of the continuously varying optical power gradient is

V .-25-.

•1

<img file="AU2711684A_D0015.tif" />

^r2

Pw ’_e That is., an ® .

increase of

Once ft ' ¹ . ' _ -J**³' - ' · ' ” ., * : ’. .. · ... .-isO

..Blifctr^nce between r2 and r2’ Vr2“*^r2‘) Ar2 ·== 0,6mm

Optical power gradient (after, wet) ' A?w == 4 diopter

The above results are typical average figures in accordance with the invention and are presented by way of illustration only. They are not presented in a limiting sense. These results are governed by the following relationships:

GOZ - f (Q+Tb+R) ·

- g (Q-Tb-R) . ’

- h (Q-Tb-R) increase in Q increases GOZ, Δ r2 and 0P_W while an

Tb and R. increases GOZ, but decreases Ar2 and Δ P_w. a button is squeezed, cut and polished for the concave surfaces, (the center base curve and the bevel curve), the button

<td></td><td> is released and measurements are made.</td><td> The following information</td>

<td> oeo 93</td><td> is kept with the button.</td><td></td>

<td> 0 &gt; &amp; 0©</td><td> 1. The amount of . squeeze</td><td> Q</td>

<td> ’ Q.&amp;9 a</td><td> 2. The periphery, base curve</td><td>^r2</td>

<td> .</td><td> 3. The central curve ?</td><td>^r2'</td>

<td></td><td> 4. The thickness of the cut button</td><td> Tb</td>

<td> © tr , 1 tf &amp;</td><td> 5. The bevel radius</td><td> Γ3 (normally fixed)</td>

<td></td><td> 6. The peripheral OZ</td><td> POZ (normally fixed)</td>

<td></td><td> In order to complete the lens</td><td> design, the following re-</td>

quirements are established or known.

7o The power of the lens (when wet) at the center p_w . '. ·: . :· ' ·· ..

8. The Overall lens diameter DL

9. The anterior OZ AOZ

1.

&lt;

• A'

Λ

A%

<td></td><td></td><td></td><td> -14-</td><td></td>

<td></td><td> The</td><td> junction thickness</td><td> at AOZ</td><td> JTK</td>

<td> 11.</td><td> The</td><td> edge thickness</td><td></td><td> ETK</td>

<td> 12,</td><td> The</td><td> index of refraction</td><td> when wet</td><td> n</td>

<td> 13.</td><td> T-h^</td><td> expansion factor</td><td></td><td> Exp</td>

I»

The remaining unknown parameters to be calculated are:

a)

The thickness of the lens

b)

The radius of curvature of the anterior OZ ^rl

d) . The

The angle of r₃ for a given AOZ •&amp;1 ^rexp

In this numerical example, several parameters are assumed to be non-variablee and typical values are assigned for practical flF ft ft ft ft «· « ft # &lt;5 ¢¢¢)3

4k ft Λ ft e - o ® «3 ft ft i

<td> 1)</td><td> Q = 1</td>

<td> 2)</td><td>^r2 =</td>

<td> 3)</td><td> r₂« ^:</td>

<td> 4)</td><td> Tb =</td>

<td> 5)</td><td> r₃ =</td>

<td> 6)</td><td> POZ =</td>

<td> 7)</td><td> P_w =</td>

<td> 8)</td><td> DL =</td>

<td> 9)</td><td> AOZ -</td>

<td> 10)</td><td> JTK</td>

<td> 11)</td><td> ETK</td>

<td> 12)</td><td> n -</td>

<td> 13)</td><td>_)VEXp</td>

variable mm

0.07mm

1.21

0.025mm variable variable

1.8mm

10.3irun

10.45mm

12.15mm = 0.06mm

1.4325 v\V '

Using the numerical values (1) through (13) above, the .Mg

<img file="AU2711684A_D0016.tif" />

Ύ

<img file="AU2711684A_D0017.tif" />

<img file="AU2711684A_D0018.tif" />

Pw =

<img file="AU2711684A_D0019.tif" />

<img file="AU2711684A_D0020.tif" />

<img file="AU2711684A_D0021.tif" />

x Exp - t x Exp

<img file="AU2711684A_D0022.tif" />

n-1

0.4325 o ©o ft ft ft ft -fcft O a ©»«©&lt;&amp;© © © «

ft» 09 ft 0 ft fi·

9®

O O o &amp;aa

0© © o « « ύ o ©

Pw = ______________________ x 1,21 t x 1,21

0.4325 1.4325 for r and r^' in mm

Pw =. __________________ r_n t r₂' x 1.21

357 __(1)

<td> Λ 6C ft 9</td><td> 357</td><td> 1184</td>

<td> ft 99 9 &amp; ft© O ® ft</td><td> Rearranging the eq</td><td> (1)</td>

<td> ft ©9</td><td> Γ,</td><td> t</td>

<td> 99 Oft.</td><td> M</td><td></td>

<td> fl , »h €</td><td> 357</td><td> 1184</td>

ft© fiO

0. ft ft ft ft.

&amp; eif e·«9 o© v

Pw + 357 r, = 0.3019t +

Pw 1

Γ_χ - 0.3019Ί+ Cp r = 0.3019t + Cp

357 r ' (2)

Where Cp

357 r ’

Note: r^ , r^ in equation (1)&gt; .(2) and//3) are all in mm.

(3)

<img file="AU2711684A_D0023.tif" />

’X

<img file="AU2711684A_D0024.tif" />

i.Ο ftO e « ΰ ' Q • » ft ft 9' ft ©

ftcetr ft ©

Q ft © ft ft • © a©

GO ft ft ' ft ft &amp; ft©

Β4ί!ί&lt; 9 © ft tS o ΰ -ft© co v* a ο o • ft • &amp;

o r ft &gt;

90n &amp;

&amp; 0 ft Oft

-16 In order to make the junction thickness JTK = 0.07mm, from

Figure 4:

r₂ -jr2² -16 + 0.025 + t and -&amp;₂ - sin -1

Solving for t t = r - Jr1² -16 t - r^ -Nrl² -16 where K - r^ ^Γ2 ^(ri

-bl²

-16)=0.07 cos Og (4) r₂ -Jr2² -16 +

<img file="AU2711684A_D0025.tif" />

+ 0.025 (t and r₂ in ram)

0(-.025

0.07 cos (sin-1.)

A

0.07 ^Γ2 cos (sin-1 4) (5) :

t = 0.3019t + Cp - *J(0.3019t + Cp ) ² -16 by substituting r . from eq. (2) into (5) (6) ^Γ2

-K eq(7) (5) (JLXXeL surisces can

<img file="AU2711684A_D0026.tif" />

spheric, aspheric or toric ύβ +

<img file="AU2711684A_D0027.tif" />

“•S

-17s'

D &lt;3 0 » « © &amp; &lt;2/a a

O*«b6b &amp; n a ©«a©

O Q

4&gt;G © c* a ana

Ost? ii ft O © β ΰ ©

Solving for t from eq. (7):

<td> t = 2.524Cp -</td><td> -1.762K -</td><td> (8)</td>

<td> 1\ Λ</td><td> ^6.3706 Cp² - 3.847KCp + 0.58K² - 40.38</td><td></td>

<td> K - r₂ -Ί r2² ·</td><td> -16 + 0.025 - 0.07</td><td> (6)</td>

<td></td><td> cos(sin -1 4 )</td><td></td>

<td> Cp =</td><td> r2 1</td><td></td>

<td> Pxv +</td><td> 1</td><td> (3)</td>

<td> 357 ·</td><td> r ¹ 2</td><td></td>

o © Φ ?j ©«CO © i&gt;&lt;5 © b *

S? G tt

OS

O © c . 4S6

For a given set of r„, r ' and P Cp and K can be calculated and t can be calculated using Cp and k. Then r^ and 0^ are calculated.

Example: r₂ = 6.94, r₂' = 6.44, P_w = -3 .

Cp = __P_________________ = 6.808

- 3 1

<img file="AU2711684A_D0028.tif" />

«9 »#wi &amp;

3m· «J

357________ 6.44

K = 6.94 - -^6-94² -16 + 0.025 - 0.07 / cos(sin-1 4 )

1.2080

6.94

Oft

S3.

t = 2.524 x 6.808 - 1.762 x 1.2080 φ.3706 x 6.8082

3.847 x 1.2080 x 6.80« 0,58 x 1.20802

-r

<img file="AU2711684A_D0029.tif" />

<img file="AU2711684A_D0030.tif" />

40.38 = 0.085

<td> Γ_χ = 6.808+ 0 0, = sin -1 ,</td><td> .3019 X 0.085 - 6.83</td><td> (9)</td>

<td> rl</td><td> — /</td><td></td>

<td> =_ sin ¹</td><td> 4 35.8°</td><td></td>

<td></td><td> 6.83 </td><td></td>

i

<img file="AU2711684A_D0031.tif" />

J t

i.

In the computation of thickness /thickness is maintained, preferably for example about 0.04mm.

such cases, the junction thickness may have to be fixed at a value greater than 0.07mm.

decreases.

The following is an example calculation to \[r3- - 6.0752 = 0.5586

Ch for

0-07 / cos (sin d3

♦.

for d3 = 0.07 /‘cos (sin r, tjp 0.0,4mm (10) o C 4i ©ft , © « ft O .

e ΰ b *

-1 ⁴ ) * °·⁰⁴¹¹. Γ2 ' © ©*·

Fig. 5:

maintain the junction thickness to be 0.07mm for example. However, t &lt; 0.04mm (11) .

Knowing the ro And r3,. POZ, DL AOZ, and ETK and using the for r_CXp, referring anterior curve ry is less than 7.03mm. This gives r_CXp value of 8.13mm. For ry’greater than 7.03mm, the JTK increases and r_CXp y « dy + d£ + 03-0^ calculated junction thickness JTK (0.07mm or greater), the anter12,15rom, ETK = .0.06mm, the JTK tan be made 0.07mm as long as the ior peripheral curve r_CXp can be calculated, in a conventional way.

• For example, when r2 = 6.94mm, r3 = 10.3mm, POZ = 10.45mm, DL = is desirable to for highly minus power lenses, the computation may give too thin a lens, or a negative thickness. For proper design, a minimum )

·,^Γ2

V calculated lens thickness according to equation (8) ., 04 0106 / cos (sin -1 6.075 ) = 0.0743

For *2 ~ 6.94mm, r₂' above, the-t is 0.085mm which is greater

- 6.4 4mm and p_w =-3 used in the Example than the practical minimum y = 0.434 + ς|τ2² 42 ..- Γ2³ ~ 5.2252 ) ^{+ d}3 (13) =,0.484+ 1.1037 + 0.0857 = 1.6734 « 3 *? * &amp;. »9 &amp; ft « « ·«♦ . 71 ^x 2.075 _£ y - y = 3.2866 (14) _y2 = 6.075 x 2.075 σ

y = 7.5329 • (15) »iSs® » ff ft ♦ 9 ¢» ft C (15) φχρ = \Γ/1 ⁴ 72 £ * 6.0752 (17)‘

8.13ηΰ1

8.13mm

-fa

V t

-fc ('

-20If calculated t

0.01mm for example:

d3 = 0.0’857 + 0.04(-0.01) = 0.1357' ’ *

&amp;

« ©

which will be the actual JiK to make the center thickness 0.04mm &lt;

I

I

I

I

I

I j

I ⁿ i.

•In that case:

0.484 + 1.1037 + 0.1357 = 1.7234 · x 2.075 1.7234 - 1.7234 = 3.0927

Y2 = 7.3144 (/1 + yg) -i- 2 = 5.2035 tt

DcxpT 45.20352 + 6.0752 = 8-ΟΟπτη

Equations (3), (6), (8), (2), (9), (10), (11), (13), (14), (15), (16) and (17) can be solved by hand or programmed into a programmable calculator or computer to print out:

uring procedures for the simultaneous multi-focal soft contact «0*4 η V * ·$&lt;» ¹

Q C lenses using the squeeze, cut and polish methods. Once a lens is made in this manner, the lens can be duplicated readily by casting or molding. Another alternative method may be to duplicate the aspheric buttons by casting or molding means and cut the anterior

For the purpose of making a mold or die, a suitable metal instead of plastic lens ' - . O ? .

material may be used to make the positive slope in accordance-with the invention.

The same technique can be applied to a hard .contact lens.

However, the effqct of the variable focal length is greatly reduced ¢1

Λ «

-21irf a hard contact lens because the tear layer, formed by the aspheric, but tends to be spheric in the centerand greatly ./

<img file="AU2711684A_D0032.tif" />

flattening towards the edge. This is opposite to surface qif the lens created by the squeeze method.

Soft lenses.

however, conform to the surface of the cornea so that the tear layer is negligible. This means that when wearing soft lenses, the posterior surface of the lenses become spherical (if the cornea is spherical) with the anterior surface becoming aspherical and maintaining the same variable focal length effect for which the lens is designed.

Figure 6 illustrates a circular shaded band in the middle of the lens which may represent the band used for distance viewing.

This band has a power of about -3 diopter. The outside shaded band may be the one used for near vision and has a power of -0.5 diopter.

&amp;©

S s’©

S i G © « C ' t .©

Fig. 7 illustrates the same lens as in Fig. 6 showing an elliptic band in the optical zone of the lens which may be used for distance viewing to correct for astigmatism. The example shown in .Fig. 7 is for an eye with -2.5 diopter in the vertical meridian and

-3.5 diopter in the horizontal meridian. As long as the lens is analytic (continuously smoothly varying) and the power gradient region is within the 6mm diameter of the pupil opening, the lens has the property of simultaneous vision multi-focal effect with greater astigmatism (greater than the variation of the lens power can correct), the anterior surface may be made toric by convenI·.;· o

i

-_g

S' by the

4-ional means used to correct astigmatism of any mono-vision ϊ works contact lens. In a multi-focal toric lens, the equi-power contours out the nea is will not be concentric circles as shown in Fig. 1, but they will departin [reatly be concentric ellipses.

ipheric

Accordingly, by providing a soft contact lens wherein the

Shown in .enses,

<img file="AU2711684A_D0033.tif" />

» aspheric properties are concentrated in the center portion in the trative ie tear

2S, the lens in a region generally less than the normal pupil opening

.. Vi · - i provides a lens having simultaneously multi-focal properties. By :nea is al and and the power increases in an aspheric region having gradually

Ct ώ ft ch the varying optical power within the normal opening of the pupil, some part of the lens near the central portion will form a sharp image middle of a distant object on the retina and another part of the lens in .ewing.

the peripheral part will form a sharp image of near by object. Even t*

V id band aft ft® c .£^&gt;0 a opter.

^ring an though the center portion of the lens forms a blurred image of the near-by object, as long as there is a sharp image of the object on retina simultaneously, the human brain selectively picks up the sed for ft the sharp image of the desired object. Thus, a lens suitable for town in fa£ vision, intermediate vision and near vision is readily pro.an and ens is vided in accordance with the invention. Elliptical /- B\ the puslj/ opening permit forming a sharp image by bands within an eye with adient e lens astigmatism. The continuously variable multi-focal contact lens- V\ es may be prepared by distorting the lens blank in a predetermined t wi th manner and forming spherical surfaces in the distorted blank to ses of yield the aspheric region within the normal pupil opening.

; power

It will thus be seen that the objects set forth above, among onventhose made apparent from the preceding description, are efficir t7( ft

<img file="AU2711684A_D0034.tif" />

i

<img file="AU2711684A_D0035.tif" />

(A eritj^ attained and, since certain changes may be made in carrying . out the above process arid in the article set forth? without departing from ^ethe spirit and scope of the invention, it is intended that all matter contained in the above description and Shown in the accompanying drawing shall | trative and not in a limiting sense.

“ It is also to be understood that ‘ intended to cover all-of the generic, and _B invention herein described, arid all statements of the scope of the '

^δ invention which as a matter of language might be said to fall therebetween.

be interpreted as illusthe following claims are specific features of the

<img file="AU2711684A_D0036.tif" />

<img file="AU2711684A_D0037.tif" />

<img file="AU2711684A_D0038.tif" />

,t