HK1138381B - Method for designing multifocal contact lenses - Google Patents

Description

Method of designing multifocal contact lenses

Technical Field

The present invention relates to multifocal ophthalmic lenses. In particular, the invention provides methods of designing contact lenses that provide correction for presbyopia, taking into account pupil size and vergence.

Background

As an individual ages, the eye's ability to accommodate or bend the natural lens to focus on objects that are relatively close to the viewer becomes worse. This condition is known as presbyopia. Also, people with natural lenses removed and intraocular lenses substituted lack accommodation ability.

Among the methods used to correct for eye accommodation failure are contact lenses having more than one optical refractive power. In particular, multifocal contact lenses and intraocular lenses have been developed in which both the distance and near zones, and in some cases the intermediate distance zone, have provided refractive power. However, none of the known designs have proven to be widely successful for spectacle wearers.

Detailed description of the invention and preferred embodiments

The present invention provides methods of designing contact lenses, lenses according to the design methods, and methods of producing the lenses, which lenses provide presbyopia correction by taking into account pupil size and vergence in the lens design. The lenses of the invention are advantageous in that their design increases the eye accommodative gain, meaning an increase in the diopter measured positive refractive power (power) as the eye responds to accommodative or convergence stimuli. In addition, the design utilizes the residual amplitude of accommodation of the eye, or the full accommodative capacity based on age and the physiology of the individual's eye.

The present invention provides a method of designing a multifocal lens, the method comprising, consisting of, and consisting essentially of: a) selecting a resting (restig) pupil diameter; b) calculating a pupil diameter when viewing a close object; c) selecting a ratio of near to far vision correction area for the lens; d) calculating a ratio value as a function of add power (add power) for viewing near and far objects using the resting and near viewing pupil diameters; and e) adding an amount of optical convergence to the lens.

In the first step of the lens design method of the present invention, the pupil size is considered in the following way. The resting pupil diameter, or the pupil diameter for viewing objects above about 500cm from the eye, is selected based on an average of the population data or a measurement of the individual's pupil. When viewing a near object or an object within about 100cm from the eye, the pupil diameter as a function of the add power is calculated based on the add power, the remaining accommodation, and the resting pupil diameter. In order to perform this calculation, the total add power required by the lens wearer must be determined. A portion of this add power will be provided by the add power of the lens and a portion by the residual accommodation of the lens wearer's eye.

The residual add power may be calculated by subtracting the add power from the total add power required. The total amount of add power required is made dependent on optics, clinical experience of add power for products determining the range of refractive power typically from 1.00 to 3.00D, and known knowledge of accommodation needs of the presbyopic population as a function of age. This remaining regulation can be a physiologically determined quantity, primarily dependent on age, typically ranging from 10+ D for less than about 15 years of age to less than 0.5D for those greater than 65 years of age. For purposes of illustration, it may be assumed that an individual may require a total of 2.85D of add power to read clearly from 35cm from the eye. The add power will be 1.00D and the remaining add power will be 1.65D.

There is a functional correlation between pupil size and accommodation at constant brightness measurement, which is well known. Based on this, the adjustment response is calculated by obtaining the inverse of the object distance, and the adjustment response is measured based on a wide range of intensities. For example, such data is described in the am.j.physio.regul.integra.comp.physiol., 258, Glen Myers, Shirin Berez, William Krenz, and lawrence stark: 813-819 (1990). These data are the basis of a pupil constriction model that assumes that the independent linear effect between accommodation stimulus and brightness increase is shown by the following equation:

A＝A₀-B-C (I)

wherein:

a is the pupil size;

A₀is the resting pupil size;

b is 1/unit object distance in meters; and

c is logFL.

Clinically measured, B is 0.27 and C is 0.19. Assuming a luminance of 1.0FL, equation I can be rewritten as:

A＝A₀-0.27D (II)

where D is the residual accommodation of the lens wearer's eye. Applying equation II to 2.85D is the above example of the total increase in refractive power required and assuming a resting pupil diameter of 7.5mm, Table 1 below represents the calculated value of the difference between the resting pupil diameter and the pupil diameter resulting from applying equation II.

TABLE 1

Specified increase in refractive power	Residual adjustment	Reduction of pupil size	Pupil size when looking at a close object
				1.0D	1.85D	0.50mm	7.0mm
1.5D	1.35D	0.36mm	7.14mm
				2.0D	0.85D	0.23mm	7.27mm
2.5D	0.35D	0.09mm	7.41mm

The lens area provided by the lens design for correcting the wearer's distance viewing or the ratio of the lens' distance area to the viewing area for correcting the near or near viewing (A) can then be selected_F/A_N) And the ratio is used to calculate the lens area set for near and distance vision optics. The selection may be based on the measured visual acuity and the contrast sensitivities of the individual or persons on average in the far and near luminance ranges. The preferred ratio of refractive optics is 70/30 in favor of the distance viewing area when viewing a near object. The preferred ratio of refracted light is 50/50.

A_F/A_NThe values can be calculated as a function of the increasing refractive power for viewing near and far objects, the results for the ratio of 70/30 are shown in table 2. The calculated area ratio is given by the square of the diameter ratio.

Specified increase in refractive power	AF/AN(near object)	AF/AN(distant object)
			1.0D	1.89(65∶35)	2.33(70/30)
1.5D	2.02(67∶33)	2.33(70/30)
			2.0D	2.13(68∶32)	2.33(70/30)
2.5D	2.25(69/31)	2.33(70/30)

For example, based on pupil sizes of 7.5mm when viewing distant objects and 7.0mm when viewing near objects, the visual area for distance vision is π (7.5/2)²0.70 square millimeter, and pi (7.5/2) for near vision²0.30 square mm. When viewing a close object, the area is reduced to pi (7.0/2)². The ratio of the myopia area to the total optical area is pi (7.5/2)²×0.30/π(7.0/2)²Or (7.5/7.0)²X 0.30-1.072 × 0.30-1.145 × 0.3-0.343 or 34.3%. Thus, 65.7% is reserved for the far visible area.

Thus, the method of the present invention allows the lens designer to provide a larger portion of the pupil aperture to the retinal image of the distant object image, without including the brightness of the near object image. This is due to the fact that the near vision zone is placed within the pupillary region of the constricted pupil, the far vision zone is located within the pupillary aperture of the pupil at rest, or the non-accommodated pupil and the accommodated pupil constriction excluding some far vision zones.

In another step of the method of the present invention, vergence or optical convergence, effectively bringing both eyes of the individual into common focus with the object being viewed, is incorporated into the lens. The increased optical convergence will depend on the increased refractive power designed into the lens, which increases as the increased refractive power increases. Typically, it may be increased to about 2.0D.

The optical convergence is preferably incorporated into the lens by adding base prisms, i.e. horizontal prisms with the base oriented in the direction of the lens nose. Optical convergence can also be incorporated into the lens in a single vision design by adding sufficient positive refractive power to reduce the overall accommodation requirements. In addition, convergence may also be added by removing the center of the near vision zone from the geometric center of the lens.

The preferred lens resulting from the present invention is bifocal, wherein the optical zone comprises two radially symmetric zones: a first, central region, and a second, annular region surrounding the central region. The distance and near vision zones are located in the pupillary aperture of the resting eye. The near vision zone is located in the pupil aperture when the eye is fully accommodated and has a zone of about 30% to 50% of the optical zone within the pupil aperture for near vision, while the radius of the optical zone matches or exceeds the pupil aperture for far vision. The ratio between the near and far vision regions is calculated as described above, and when the eye is unadjusted the ratio contributes to far vision and when the eye is adjusted the ratio contributes to near vision. In addition, the near vision zone is provided with a horizontal prismatic correction, the prism having a base oriented in the nasal direction. In a preferred embodiment, the location of the near vision zone is specified in the pupil aperture of the accommodative eye, but is not limited to its placement relative to the pupil center.

In the lenses of the invention, the optical zone, and the near and far vision zones therein, may be at the anterior surface, or object side, posterior, or eye side of the lens, or the cleft between the anterior and posterior surfaces. The cylinder refractive power may be provided on the back or concave surface of the lens to correct for the wearer's astigmatism. Alternatively, the cylinder refractive power may be coupled with either or both of the distance and near vision refractive powers on the anterior or posterior surfaces. In all lenses of the invention, the distance, intermediate or and near optical refractive power may be spherical or aspherical.

The contact lenses used in the present invention are preferably soft contact lenses. Preferably, soft contact lenses made of any material suitable for making such lenses are used. Illustrative materials for forming soft contact lenses include, but are not limited to, silicone rubber, silicon-containing macro-split spheres including, but not limited to, those disclosed in U.S. patent nos. 5371147, 5314960 and 5057578, which are incorporated herein by reference in their entirety, as well as hydrogels, silicon-containing hydrogels, and the like and combinations thereof. More preferably, the surface is silicone or contains silicon functionality including, without limitation, polydimethylsiloxane spheres, propoxylated silicones and mixtures thereof, silicone hydrogels or hydrogels, such as etafilcon a.

Preferably, the lens-forming material is a poly 2 hydroxyethyl methacrylate polymer, i.e., having a peak molecular weight between about 25000 and about 80000 and a polydispersity of less than about 1.5 to less than about 3.5, respectively, and covalently attached thereto, at least one cross-linked functional group. This material is described in U.S. patent No. 6846892, which is incorporated herein by reference in its entirety. Suitable materials for forming intraocular lenses include, but are not limited to, polydimethylacrylic acid, hydroxyethylacrylic acid, inert clear plastics, silicon-based polymers, and the like, as well as combinations thereof.

Curing of the lens-forming material may be performed by any known means, including, but not limited to, heating, irradiation, chemical, electromagnetic radiation curing, and the like, and combinations thereof. Preferably, the lens is injection molded using ultraviolet light or using the full spectrum of visible light. More preferably, the precise conditions suitable for curing the lens material will depend on the choice of material and the lens to be formed. The polymerization process for ophthalmic lenses includes, but is not limited to, known contact lenses. A suitable process is disclosed in U.S. patent No. 5540410, which is incorporated herein by reference in its entirety.

The contact lenses of the invention may be formed in any conventional manner. For example, the optical zone may be created by diamond turning or diamond turning to form the mold of the present invention. Subsequently, after compressing and curing the resin, a suitable liquid resin is placed between the molds to form the lenses of the invention. Alternatively, the region may be diamond turned into a lens button.

Claims (4)

1. A method of designing a multifocal lens, said method comprising the steps of: a.) selecting a resting pupil size; b.) calculating pupil size when viewing a close object; c.) selecting a ratio of a far vision correction area to a near vision correction area for the lens; d.) calculating a ratio as a function of increasing refractive power for viewing near and far objects using the resting and near viewing pupil diameters; and e.) adding an amount of optical convergence to the lens, wherein step b) further comprises (i) determining the total add power required by the lens wearer, and (ii) calculating the remaining add power.

2. The method of claim 1, wherein the ratio of the far vision correction area to the near vision correction area is 70: 30.

3. The lens of the method of claim 1, comprising an optic zone having a first zone and a second annular zone surrounding the first zone, and a horizontal prism having a base oriented in a nasal direction.

4. A lens according to the method of claim 2, said lens comprising an optic zone having a first zone and a second annular zone surrounding the first zone, and a horizontal prism having a base oriented in the nasal direction.