CA2096706A1

CA2096706A1 - Soft toric lens for correction of astigmatism

Info

Publication number: CA2096706A1
Application number: CA 2096706
Authority: CA
Inventors: Robert Mercure
Original assignee: Laboratoires Opti Centre Inc
Current assignee: Laboratoires Opti Centre Inc
Priority date: 1993-05-20
Filing date: 1993-05-20
Publication date: 1994-11-21

Abstract

ABSTRACT OF THE DISCLOSURE

A toric contact lens for correction of astigmatism comprises a concave posterior surface to be applied to a wearer's eye, and a convex anterior surface symmetrical about an horizontal plane of symmetry. The anterior surface comprises a central optical zone, and a pair of upper and lower peripheral prismatic zones situated outside the central optical zone and symmetrical about the horizontal plane of symmetry. Each prismatic zone defines an apex along the peripheral edge of the lens, and the lens has, in the region of each prismatic zone, a thickness that gradually increases from this apex toward the central optical zone whereby sliding movement of the eyelids on the prismatic zones pushes these zones to produce a stabilizing effect that maintains the contact lens in a desired, predetermined orientation. The anterior surface further comprises an intermediate aspheric zone surrounding the central optical zone and forming a smooth transition surface between this optical zone and the two peripheral prismatic zones.

Description

SOFT TORIC LENS FOR CORRECTION OF ASTIGMATISM

BACKGROUND OF THE INVENTION

1. Field of the invention:

The present invention relates to a toric contact lens for astigmatic correction.

2. Brief description of the prior art:

As well known to those of ordinary skill in the art, the angular orientation of toric contact lenses must be maintained constant to prevent deviation of the astigmatic correction from the desired axis.
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To prevent rotation thereof, prior art i toric contact lenses comprise an anterior surface formed with a prismatic central optical ~one adapted - to increase the thickness of the lower portion of the lens. The additional weight in the lower portion of the lens then produces an effect of ballast that 3 , maintains the lens in the required angular orientation. A prismatic central optical zone presents the drawback of producing prismatic aberrations that r~duce the optical quality of the lens and therefore the visual acuity of the patient.
Moreover, the prismatic central optical zone increases the thickness of the lens to thereby recluce both the , , ~, ' . : ~ ' :: : .' . . : . : ' :: 2 ~ 9 ~
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- comfort of the patient's eye and the transmission of oxygen to the eye's cornea. As well known to those skilled in the art, tolerance of the eyes to contact lenses reduces with the thickness of the lenses.

Another prior art method to prevent rotation of a toric contact lens is described in United States patent N 5,020,898 ~Townsley). This method consists of forming the anterior surface of the lens with peripheral upper and lower non s~mmetrical prismatic zones creating an effect of ballast. More specifically, this prismatic geometry increases the thickness of the lower portion of the lens and the additional weight of this lower portion maintains the lens in the desired angular position. The drawbacks of this method are the production of prismatic aberrations in the lens's optical system and the `' increase of thickness in the central region of the lens.
A further prior art method to prevent -' rotation of the toric contact lens consists of forming 1 the lens with two diametrically opposed thinned zones.
Upon movement of the eyelids on these thinned zones, the eyelids tend to push th thicker central portion of the lens to ensure stability thereof. A major disadvantage of this method is that the lens should be made thicker in the central region to enable formation of efficient thinned zones.

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OBJECT OF THE INVENTION

An object of the present invention is therefore to provide a toric contact lens for astigmatic patients that eliminate the above mentioned . drawbacks of the prior art.

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SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there is provided a toric contact `. 15 lens for astigmatic correction, comprising a : peripheral edge, a concave posterior surface to be . applied to a patient's eye and formed with a , substantially central toric zone to optically correct asti~matism of the patient's eye, and a convex ~i 20 anterior surface symmetrical about an horizontal plane j of symmetry.
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The convex anterior surface of the toric -, contact lens of the invention comprises:
.' 25 a substantially central optical zone; and . a pair of upper and lower perip~neral ~ . prismatic zones situated outside the central optical zone and symmetrical about the horizontal plane of symmetry, wherein each prismatic zone dafines an apex : 30 along the peripheral edge of the lens, and wherein the :~ lens has, in the region of each prismatic zone, a thickness that gradually increases from this apex toward the central optical zone;

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c whereby sliding movement of the eyelids of the patient on the upper and lower pxismatic zones pushes these prismatic zones to procluce a stabilizing effect that maintains the contact lens on the 5 patient's eye in a desired, predetermined angular orientation.

In accordance with preferred embodiments of the present invention, the central optical zone is 10 spherical, the upper and lower prismatic zones have the general configuration of a crescent moon, and the anterior surface further comprises an intermediate aspheric zone surrounding the central optical zone and forming a smooth transition surface between this 15 optical zone and the upper and lower peripheral ; prismatic zones.
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Advantageously, the anterior surface is symm,etrical about a vertical plane of symmetry, the upper and lower prismatic zones are ~ymmetrical about this vertical plane of symmetry, and the anterior surface further comprises peripheral spherical zones symmetrical about the vertical plane of symmetry, the lens being thinned in the region of these peripheral j 25 spherical zones.

The combination of a spherical central optical zone, an intermediate aspheric zone, upper and lower peripheral prismatic zones and peripheral thinned zones enables production of a toric contact lens that is thin and free from prismatic aberrations.

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' In accordance with a further preferred embodiment of the invention, the posterior surface comprises the above mentioned central toric zone, an intermediate spherical zone, and a peripheral zone defining a surface tangential to the surface of the intermediate spherical zone, the intermediate spherical zone being located between the toric zone , and the peripheral zone of the posterior surface.
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.. 10 The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive .; description of a preferred embodiment thereof, given ,~j by way of example only with reference to the 7 15 accompanying drawings.

:, :7 BRIEF DESCRIPTION OF THE DRAWINGS

', 20 ~ In the appended drawings:

! Figure 1 is a front elevational view of il a soft toric contact lens in accordance with the . 25 present invention for astigmatic correction, showing an anterior surface of this lens;

., -~/ Figure 2 is a side elevational, cross ~ sectional view of the contact lens according to the -~ 30 invention, taken along line A-A of Figure 1 and ¦ showing details of a central optical zone of the I anterior surface of this lens;

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Figure 3 is a cross sectional, bottom plan view of the contact lens according to the invention, taken along line B-B o~ Figure 1 and showing details of the central optical zone of the anterior surface of this lens;

: Figure 4 is a side elevational, cross . sectional view of the contact lens according to the - invention, taken along line A-A of Figure 1 and - 10 showing details of upper and lower peripheral prismatic zones of the anterior surface of this lens;

Figure 5 is a cross sectional, bottom plan 'l view of the contact lens according to the invention, ` 15 taken along line B-B of Figure 1 and showing details - of an intermediate aspheric zone of the anterior surface of this lens;

Figure 6 i5 a cross sectional, bottom plan view of the contact lens according to the invention, taken along line B-B of Figure 1 and showing details of peripheral thinned zones of the anterior surface of i this lens;

Figure 7 is a rear elevational view of the soft toric contact lens in accordance with the present - . invention for the correction of astigmatism, showing a posterior surface of this lens;
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Figure 8 is a side elevational, cross sestional view of the contact lens according to the invention, taken along line C-C of Figure 7 and showing details of a central toric zone and an ~' 2 ~ 9 6 7 ~ ~
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intermediate spherical zone of the posterior surface of this lens;

Figure 9 is a cross sectional, bottom plan view of the contact lens according to the invention, taken along line D-D o~ Figure 7 and showing details of the central toric zone and intermediate spherical zone of the posterior surface of this lens;
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.~`; 10 Figure 10 is a cross sectional, bottom -. plan view of the contact lens according to the invention, taken along line D-D of Figure 7 and . showing details of the intermediate spherical zone of '! the posterior surface of this lens; and ' 15 Figure 11 is an enlarged view of the lower portion of the contact lens of Figure 8, showing -' details of a peripheral tangential zone of the I posterior surface and of a peripheral edge of the .~20 lens.
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:.1, ~DETAILED DESCRIPTIGN OF THE PREFERRED EMBODIMENT

; 25 ,In the specification and the appended .claims, the term "vertical" and "horizontal" are used 1with reference to the lens as it would be if ideally seated on the cornea of the eye without any shift in orientation resulting by movemenk caused by the eyelid. Regarding the term "rotation", it refers to rotation of the lens when seated on the cornea of the eye.

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., ~ As illustrated in Figure 1, the preferred : embodiment of the soft toric contact lens 1 in -:- accordance with the present invention comprises an , .
- anterior surface 2 formed with a central optical zone 3, an intermediate aspheric zone 4, two upper and lower peripheral prismatic zones 5 and 6, two - peripheral thinned zones 7 and 8, and two reference points 9 and 10. The anterior surface 2 of the lens , 1 is symmetrical about an horizontal plane of symmetry containing horizontal axis 11, and about a vertical : plane of symmetry containing vertical axis 12.

In Figures 1 and 7 of the appended drawings, while curves appear to delineate distinct zones of the lens they are shown Eor clarity of description of the invention only. It will be ; appreciated by those of ordinary skill in the art that : there are no sharp distinction between these different zones of the lens, but they are smoothly blended into 20 one another.
, ; Central optical zone 3:
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. The central optical zone 3 i5 the only zone of the anterior surface that optically corrects defects of the patient's eye.
: ' The central optical zone 3 is spherical and, therefore, has a constant radius R (Figure 2).
: 30 The axis of rotation of the central optical æone 3 corresponds to the axis of rotation 21 of the entire lens 1, whereby this central optical zone 3 is not a ~ : -: : ~ - - , : '`

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prismatic surface and accordingly does not present the drawback of producing prismatic aberrations.

;lReferring to Figures 2 and 3, the chord ~l5 C of the central optical zone 3 varies between 7,63 -and 8,80 mm, according to the relation C = 8,8/F, in which F = D~/15, DT being the diameter of the lens 1.
The central thickness E (Figure 2) may have values situated between 0,09 and 0,49 mm, depending on the dioptric power of the lens 1.
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,, ~Peripheral prismatic zones 5 and 6:
., As indicated in the foregoing description, rotation of a toric lens l must be prevented to avoid deviation of the astigmatic correction from the desired axis. In the lens l according to the invention, upper and lower peripheral prismatic zones 5 and 6 fulfill this function.

As illustrated in Figure 1, the prismatic zones 5 and 6 have the general configuration of a crescent moon and are situated outside the central optical zone 3. They are also symmetrical about the horizontal plane of symmetry containing horizontal axis ll.

The upper prismatic zone 5 is generated, -~30 as illustrated in Figure 4, by shifting its axis of rotation 13 vertically and downwardly from the axis of rotation 21 of the toric lens l by a distance D10.
The radius of curvature R10 of the zone 5 is constant.

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In the same manner, the axis of rotation 14 of the lower prismatic zone 6 :is vertically and upwardly shifted ~rom the lens' axis of rotation 21 by a distance D20. The radius o-f curvature ~20 of the zone 6 is again constant.

, The distances D10 and D20 are identical but opposite, and can vary between 0,10 and 0,60 mm.
The radius of curvature ~10 and R20 are also identical ; 10 and vary in function of the other parameters of the lens 1.

As illustrated in Figure 4, the prismatic zones 5 and 6 define an apex situated along the peripheral edge 20 (Figure 11) of the lens in the region of the vertical plane of symmetry containing axis 12. Also, the lens has, in the region of each prismatic zone 5, 6, a thickness that gradually increases from this apex toward the central optical zone 3.

From the foregoing description, one of ordinary skill in the art will appreciate that the ; zones 5 and 6 are prismatic and are opposed by their bases to simulate the conventional thinned zones discussed in the above brief description of the prior art. Indeed, due to their prismatic and cre~cent moon configuration, sliding movement of the wearer's upper and lower eyelids on the upper and lower prismatic zones 5 and 6, respectively, will tend to push these prismatic zones to thereby produce a stabilizing effect that maintains the contact lens 1 on the patient's eye in the desired, predetermined angular -:: : : . : ~,~ -! ! 2 0 9 6 l O G
i ~orientation corresponding to the orientation of Figure , .
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The advantage of that solution is that the two prismatic zones 5 and 6 are situated in the :i., periphery of the lens 1 and do not affect the central optical zone 3 of the lens 1. This enables production of a lens having a thinner central optical zone 3 free from prismatic aberrationsO

~'It should also be pointed out here that ,the transmission of oxygen through a contact lens reduces with the thickness of that lens. Accordingly, a thinner lens 1 transmits more oxygen to the cornea and therefore affects its metabolism to a lesser - extent.
. ., ,Those of ordinary skill in the art know ;ijthat the prismatic aberrations reduce the optical ':,J20 quality and therefore the visual acuity of the ~patient. Accordin~ly, a lens formed with no prism in 1the central optical zone provides the user with a higher visual acuity.
'.' Intermediate aspheric zone 4 .
The anterior surface 2 of the lens 1 is `therefore formed of three main zones: the central ,optical æone 1 and the upper and lower peripheral ;30 prismatic zones 5 and 60 A fourth zone, namely the intermediate aspheric zone 4 interconnects the central optical zone 3 and the two peripheral prismatic zones 5 and 6.

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The use of an aspheric intermediate zone 4 flattens the anterior surface 2 of the lens 1; the aspheric zone 4 enables elimination of the prior art abrupt junctions between the central optical zone 3 and the intermediate zone 4 which reduces the comfort of the patient's eye and the stability of the lens upon blinking movem0nt o~ the upper eyelid. In the same manner, the aspheric zone 4 eliminates any abrupt - junction between the intermediate zone 4 and the peripheral prismatic zones 5 and 6. Therefore, the aspheric zone 4 forms a smooth transition between the optical zone 4 and the upper and lower peripheral prismatic zones 5 and 6.

15More specifically, the surface of the intermediate aspheric zone 4 is defined by a progressive elongation of the radius of curvature (Rl < R2 < ~3 < ~n~ as shown in Figure 5. The transition j is progressive and invisible whereby the anterior - 20 surface 2 is smoother and interference of the lens l with movement of the upper and lower eyelids is, if not eliminated, substantially reduced.
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Peripheral thinned zones 7 and ~:
The two peripheral and spherical thinned zones 7 and 8 (Figures 1 and 6), which are symmetrical about the vertical plane of symmetry containing vertical axis 12, improve the comfort of the patient's eye. Indeed, by making the lens 1 thinner in the region of the zones 7 and 8, that is at the junction of the prism, lifting of the upper eyelid upon blinking movement thereof is reduced whereby ., ,. . ~ i .
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perturbation of the upper eyelid is also substantially reduced. Too important a mass at the periphery of the lens 1 would lift the upper eyelid upon movement i thereof and, therefore, would affect natural lubrication of the eye's sclera adjacent a peripheral thick portion of the contact lens.

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Reference points 9 and lO:
' 10 - Referring back to Figure 1, the anterior , surface 2 of the lens 1 is provided with a pair of diametrically opposed reference points 9 and 10 i situated along the horizontal axis ll. These reference points enable the practitioner to evaluate the direction and the amplitude of the rotation (shift of the axes 11 and 12) of the lens 1 on the eye of the patient. This will enable fabrication of a contact j lens whose parameters are chosen to eliminate this rotation.
-The lens 1 in accordance with the present invention further comprises a posterior surface 15 (Figure 7) formed with a central toric zone 16, an intermediate spherical zone 17, a peripheral tangential zone 18, and a lens edge 20.

Central toric zone 16:
;; 30 ! The c~ntral zone 16 o~ the posterior surface 15 is toric. More specifically, the central toric zone 16 comprises a first radius oE curvature ..... .

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-~ ~30 (Figure 8) corresponding to the minor meridian of the toric zone 16. It also comprises a second radius of curvature R40 (Figure 9) corresponding to the ma~or meridian of the toric zone 16, this major meridian being orthogonal to the minor meridian and intersecting the minor meridian at the geometrical center of the lens. As can be seen, R30 < R40. These two radii of curvature are determined by the optical prescription.
,', 10 Chord C30 (Figure 8) of the central toric zone 16 corresponds to the radius of curvature R30, -~ while chord C40 (Figure 9) corresponds to the radius of curvature R40. As can be seen in Figures 8 and 9, 15 C30 < C40. The longer chord C40 has a length varying between 10,40 and 12,00 mm proportionally to the total diameter DT of the lens 1, in relation to the above ~, mentioned factor F. The shorter chord C30 varies in ;~ relation to the radius of curvature R30.
In the embodiment illustrated in Figure ~ 7, the major meridian of the toric zone 16 lies on the - horizontal axis 11 while the minor meridian of the toric zone 16 lies on the vertical axis 12. However, it should be kept in mind that, alternatively, the major and minor meridians may be at an oblique angle to the axes 11 and 12 depending on the prescription of the patient.

The central zone 16 is therefore a toric -~ surface that is responsible for the astigmatic correction. It also enables a perfect alignment of :
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the lens 1 with the surface of the cornea which is ~ also toric.

-1 Intermediate spherical zone 17:
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: As illustrated in Figure 7, the intermediate spherical zone 17 surrounds the central toric zone 16 and interconnects this central toric . zone 16 and the peripheral tangential zone 1~. This lO zone 17 is spherical, generated by a single radius of curvature R50 (Figures 8, 9 and 10). The chord C50 of the spherical zone 17 which varies between 11,27 and 13,00, proportionally to the total diameter DT of the lens 1, is given by the relation C50 = 13 x F

where F = DT/15, as indicated in the foregoing description.
The radius of curvature R30 and R40 of the central toric zone 16 are shorter than the radius of .. curvature R50 of the intermediate spherical zcne 17 and define a toric vault having a deepness PVT varying between 0,13 and 0,15 mm proportionally to the total diameter DT of the lens 1, in accordance with the following relationship:

P~T = 0,15 ~ F
in which ~ = DT/lS.

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Peripheral tanqential zone 18:

. Referring to Figure 1:l, the peripheral -` tangential zone 18 is a conical surface defining an open angle ~ with the prolongation 19 of the : intermediate spherical zone 17. As the peripheral zone 18 is tangential to the intermediate spherical zone 17, no junction exists between these two zones of the posterior surface 15. The width L (Figure 7) of the tangential zone 18 varies between 0,87 and 1,00 mm proportionally to the total diameter D~ of the lens 1, in relation to the factor F.

The function of the peripheral tangential zone 18, defining an open angle ~, is to distribute the pressure of the lens 1 on the sclero-corneal l limbus, and to prevent (a) pressure indentation oP the :~, edge 20 (Figure 11) of the lens 1 into the sclera and (b) perturbation of the circulation in the small blood vessels of the sclera.

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; Lens edge 20:
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, 25 As illustrated in Figure 11, the peripheral edge 20 of the lens 1 is Pormed with a rounded profile to reduce to the minimum the :' interaction between the edges of the upper and lower .. eyelids with the edge 20 of the lens 1. This improves both comPort of the patient's eye and stability oP the contact lens.

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- Although other materials can be contemplated, the toric contact lens 1 in accordance with the present invention is advantageously made of ~ an hydrophillic material with a high content of water - 5 (at least 55%) in order to ensure comfort of the patient's eye and a permeability to oxygen sufficient to respect the corneal metabolism.

., The available parameter ranges for the , 10 lens 1 in accordance with the present invention are the following~
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` - Base curves 7,50 to 9,50 mm - diameters 13,00 to 15,00 mm - power sphere -20,00 to+20,00 diopters cylinders-0,75 to-10,00 diopters axes 0 to 180 -~The above wide ranges of available ~'20 parameters make the lens 1 according to the invention -a high performance contact toric lens.
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In the foregoing description, any numerical value or range is given for the purpose of exemplification only and should not be interpreted to limit the scope of the invention.
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`~Although the present invention has bean described hereinabove by way of a preferred embodiment thereof, this embodiment can be modified at will, within the scope of the appended claims, without departing from the spirit and nature of the subject .
lnventlon .

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Claims

1. A toric contact lens for astigmatic correction, comprising a peripheral edge, a concave posterior surface to be applied to a patient's eye and formed with a substantially central toric zone to optically correct astigmatism of the patient's eye, and a convex anterior surface symmetrical about an horizontal plane of symmetry and comprising:
a substantially central optical zone; and a pair of upper and lower peripheral prismatic zones situated outside the central optical zone and symmetrical about said horizontal plane of symmetry, wherein each prismatic zone defines an apex along the peripheral edge of the lens, and wherein said lens has, in the region of each prismatic zone, a thickness that gradually increases from said apex toward the central optical zone;
whereby sliding movement of the eyelids of the patient on the upper and lower prismatic zones pushes said prismatic zones to produce a stabilizing effect that maintains the contact lens on the patient's eye in a desired, predetermined angular orientation.

2. A contact lens as recited in claim 1, wherein said substantially central optical zone is spherical.

3. A contact lens as recited in claim 1, wherein said upper and lower prismatic zones have the general configuration of a crescent moon.

4. A contact lens as recited in claim 1, wherein said anterior surface is symmetrical about a vertical plane of symmetry, and wherein said upper and lower prismatic zones are symmetrical about said vertical plane of symmetry.

5. A contact lens as recited in claim 1, wherein said anterior surface further comprises an intermediate aspheric zone surrounding said optical zone and forming a smooth transition surface between said optical zone and said upper and lower peripheral prismatic zones.

6. A contact lens as recited in claim 1, wherein said anterior surface is symmetrical about a vertical plane of symmetry, and wherein said anterior surface further comprises peripheral spherical zones symmetrical about said vertical plane of symmetry, said lens being thinned in the region of said peripheral spherical zones.

7. A contact lens as recited in claim 1, in which said posterior surface comprises said substantially central toric zone, an intermediate spherical zone, and a peripheral zone defining a surface tangential to the surface of the intermediate spherical zone, said intermediate spherical zone being located between said toric zone and said peripheral zone of the posterior surface.

8. A toric contact lens for astigmatic correction, formed with a peripheral edge, a concave posterior surface to be applied to a patient's eye and formed with a substantially central toric zone to optically correct astigmatism of the patient's eye, and a convex anterior surface symmetrical about an horizontal plane of symmetry and comprising:

a substantially central optical spherical zone;
a pair of upper and lower peripheral prismatic zones situated outside the central optical zone and symmetrical about said horizontal plane of symmetry, wherein each prismatic zone defines an apex along the peripheral edge of the lens, and wherein said lens has, in the region of each prismatic zone, a thickness that gradually increases from said apex toward the central optical zone, whereby sliding movement of the eyelids of the patient on the upper and lower prismatic zones pushes said prismatic zones to produce a stabilizing effect that maintains the contact lens on the patient's eye in a desired, predetermined angular orientation; and an intermediate aspheric zone surrounding said optical zone and forming a smooth transition surface between said optical zone and said upper and lower peripheral prismatic zones.

9. A contact lens as recited in claim 8, wherein said upper and lower prismatic zones have the general configuration of a crescent moon.

10. A contact lens as recited in claim 8, wherein said anterior surface is symmetrical about a vertical plane of symmetry, and wherein said upper and lower prismatic zones are symmetrical about said vertical plane of symmetry.

11. A contact lens as recited in claim 8, wherein said anterior surface is symmetrical about a vertical plane of symmetry, and wherein said anterior surface further comprises peripheral spherical zones symmetrical about said vertical plane of symmetry, said lens being thinned in the region of said peripheral spherical zones.

12. A contact lens as recited in claim 8, in which said posterior surface comprises said substantially central toric zone, an intermediate spherical zone, and a peripheral zone defining a surface tangential to the surface of the intermediate spherical zone, said intermediate spherical zone being located between said toric zone and said peripheral zone of the posterior surface.