HK1161365B - Fitting method for multifocal lenses - Google Patents

Description

Fitting method of multifocal lens

Technical Field

The present invention relates to fitting ophthalmic lenses useful for correcting presbyopia. In particular, the present invention provides methods of fitting multifocal contact lenses to correct presbyopia.

Background

As individuals age, the eye becomes difficult to accommodate or bend the natural lens to focus on objects that are relatively close to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens implanted as a replacement, the accommodative ability has also been lost.

The loss of accommodative ability of the eye can be corrected using a variety of methods, one of which is known as "monocular vision", in which a single vision correcting single optic is used for the wearer's dominant eye and a single vision correcting single optic is used for the wearer's non-dominant eye. Another known method for correcting presbyopia is to use bifocal or multifocal contact lenses in both eyes of an individual. Another approach to treating presbyopia requires the use of bifocal or multifocal lenses for one eye and a single vision lens for the other eye.

Regardless of the correction method used, successful fitting of the lens using conventional methods is determined by trial and error. Typically, after an individual is optometrized to determine the required vision correction, an eye care practitioner will strive to maximize visual comfort while viewing standard visual targets by using a set of test strips. One of the advantages of using this method to fit a multifocal lens is that the simultaneous images presented on the lens wearer's retina require the effects of image blur to be minimized. To minimize blur, it is desirable to use the natural depth of focus, pupil size change relative to accommodation, and monocular dominance to obtain both near and far vision images with optimal sharpness, but there is no established diagnostic scheme to obtain such information from an individual. Thus, the success of fitting multifocal lenses varies greatly among different eye care practitioners, and by averaging 3.2 fitting cases, the average success rate is less than about 52%.

Detailed Description

The present invention provides methods for fitting multifocal contact lenses. The method of the present invention provides a multifocal lens fitting step that is less time consuming and results in more successful fits than conventional methods.

In one embodiment, the present invention provides a method for fitting a multifocal contact lens, said method comprising, consisting essentially of, and consisting of: a.) assessing the likelihood of an individual successfully fitting a multifocal lens; b.) determining dominant and non-dominant eyes of the individual; c.) measuring the dominant refraction (manifest refraction) of each eye of the individual; d.) determining the add power of the individual; e.) fitting a multifocal lens on each of an individual's dominant and non-dominant eyes; and, optionally, f.) assessing the visual needs of the individual's lifestyle and in step e.) improving the fit for dominant eye, non-dominant eye or for both based on the results of the assessment.

For the purposes of the present invention, by "dominant eye" is meant an eye determined by an eye care practitioner to be optimized for distance vision correction, and by non-dominant eye is meant an eye optimized for near vision correction.

In the first step of the method of the invention, the likelihood of successfully fitting the individual with a multifocal lens is assessed. The purpose of the evaluation step is to identify those individuals who are unable to accommodate multifocal lenses and those who may be dissatisfied with the visual performance of the lenses. One discovery of the present invention is that visual satisfaction with the new customized multifocal lens is closely related to his or her individual satisfaction with the habitual vision correction. In addition, in determining visual satisfaction with habitual correction, four parameters were identified as being most important, these factors being distance vision satisfaction, near vision satisfaction, overall visual satisfaction and glare perception. The indicators of satisfaction with habitual correction are:

S＝f(D，N，O，G)

wherein D is distance vision satisfaction;

n is near vision satisfaction;

o is overall vision satisfaction; and is

G is the glare perception.

Variables may be rated on a scale such as 1 to 5, with 1 being the lowest scale and 5 being the highest scale. At such a level, if D, N, O and G are summed, S is 16 or more and 19 is very high. Individuals with high or very high S-values are unlikely to be successfully fitted because they are sufficiently satisfied with their habitual correction that the benefits of fitting a multifocal lens from which they are screened will be unlikely to be perceived. Thus, only individuals with a satisfaction index of less than 19 and preferably less than 16 are fitted with multifocal lenses.

Optionally, one or more variables may be added. For example, if an individual is strongly motivated to wear multifocal lenses or they have dry eye symptoms, some variable may be added to determine a satisfaction index. As another alternative, other factors may be included, such as parallax or anisometropic blur between the eyes and comfort of wearing contact lenses. Additionally, the function may be improved based on the lifestyle assessment. For example, if the individual is a truck driver, the weights of D and G may be set to be greater than the weights of N and O. This can be reflected, for example, in the following equation:

S＝W_DD+W_NN+W_OO+W_GG

wherein W_DIs the weight of the distance vision score;

W_Nis the weight of the near vision score;

W_Ois the weight of overall visual satisfaction; and

W_Gis a weight for the glare perceptibility score.

As another alternative, a target visual property may be included. For example, an individual with visual acuity equal to or better than 20/25 for far vision and equal to or better than 20/30 for near vision would be significantly less likely to successfully fit a new multifocal lens.

Alternative or additional steps for evaluating the likelihood of success are: blur tolerance is assessed by having the individual view a distant object (preferably a chart at a distance of about 20 feet) while sequentially adding measured defocus or positive power to each eye. More preferably, the blur tolerance is measured at 20 feet and at a close distance of about 40 cm. The individuals being measured may be classified according to fuzzy response. For example, an individual may be classified as double sided blur tolerance, single sided blur tolerance, double sided blur sensitivity, or single sided blur sensitivity. Those individuals belonging to either unilateral category will be more likely to successfully fit multifocal lenses than those individuals belonging to either of the two bilateral categories.

After determining that the individual will fit a multifocal lens, determining the dominant eye, measuring the dominant refraction, determining the add power, and optionally, assessing lifestyle visual need. The dominant eye may be determined by any convenient method, but preferably is determined by evaluating binocular blur tolerance as described above.

Dominant refraction, which means far and near vision correction at infinity required for comfortable reading vision, is measured without cycloplegia on the eye. The measuring step is performed using any convenient method and apparatus, including (but not limited to) using a phoropter or aberrometer. Comfortable vision can be defined by: subjectively by individual response, or objectively by determining at what distance the individual undergoes binocular fusion and the image size is optimized with respect to convergence needs.

The add power, which means a spherical positive power in addition to the power required for distance vision correction, is determined by any convenient method. Preferably, the add power is determined using a binocular cross or fused cross cylinder.

After the dominant refraction was measured, increasing positive power was added to each eye while the visual performance was measured. Typically, an individual will prefer that the power be a positive power that is greater than the dominant refraction by an amount equal to half the depth of focus. The depth of focus will vary with the physiology of the eye, corneal and lens aberrations, and the length of the optical axis of the eye. The additional positive power will range from about 0.5 to about 1.5 diopters and typically will be about 0.5 diopters. It is important to achieve minimal image blur for both eyes at the same distance, unless the individual is fitting monocular vision or improved monocular vision, to minimize the anisometropic image blur and achieve the best stereoscopic imagery.

The individual's dominant and non-dominant eyes are then fitted with lenses. The dominant eye is fitted with a multifocal lens that provides visual acuity correction substantially equal to spherical equivalent or spherocylindrical dominant refraction. Fitting the non-dominant eye with the lens according to the add power. Typically, a non-dominant eye will have less than about 0.5 diopters of positive power, greater than the spherical equivalent of that eye.

After the initial fitting of the lens to the individual, the lens is preferably worn for a period of time while the individual is in the eye care practitioner's facility to assess the initial fit. The evaluation step may include one or more of an on-chip prescription (over-prescription), a tolerance test, an image blur suppression test, and a target image quality test to ensure that the lens provides the desired correction. Thereafter, the individual is re-evaluated, preferably within seven to ten days.

The fit to the dominant and non-dominant eyes can be (preferably) optimized to obtain the best target distance and near vision in view of lifestyle vision needs. Thus, in an optional step, individual lifestyle needs can be assessed and the fit of the lens optimized based on these needs. The step of evaluating may be performed by any convenient method, including (but not limited to) directly querying the individual or by querying the individual using a questionnaire.

These responses may be weighted and then added to arrive at a weighted score for determining the balance between far and near vision needs. Alternatively, the responses may be grouped into two groups: one set for accommodating lens selection for dominant eye and one set for accommodating lens selection for non-dominant eye. Weighted scores for each group can be obtained and used to determine the first fit.

The fitting method of the invention can be used to fit a variety of multifocal lenses, however it has been found to be most advantageous when fitting lenses in a three-lens set, each lens having a power profile that is different from the power profiles of the other lenses, and the lenses satisfy the following relationships:

whereinIs the average of the weighted hyperopia ratios for both eyes at pupil diameters of 2.5 to 6 mm;

rx add is the add power (in diopters) required to add to the distance prescription to provide the individual with near vision correction;

is the average value of the weighted myopia ratio of the two eyes when the diameter of the pupil is 2.5 to 6 mm;

is the average value of distance vision parallax between the first lens and the second lens at a pupil diameter of about 2.5 to 6 mm; and is

Is the average value of the near vision parallax between the first lens and the second lens at a pupil diameter of about 2.5 to about 6 mm.

Binocular weighted far vision ratio ("D") refers to the weighted far vision ratio of the dominant eye ("D₁") and a weighted far-vision ratio for non-dominant eye (" d)₂"), or D ═ max (D)₁，d₂). The weighted myopia ratio ("N") refers to the weighted myopia ratio ("N") of the dominant eye₁") and a weighted myopia ratio for non-dominant eyes (" n₂") or N ═ max (N)₁，n₂)。

A monocular weighted far vision ratio and a monocular weighted near vision ratio for each eye (with different pupil sizes) are calculated and these ratios are used to measure the degree to which the power of any given lens radius meets the lens wearer's far vision and near vision requirements, respectively. These ratios are also used to measure the degree to which a single lens would be expected to conform to a given wearer's spherical lens and add power formulation relative to ideal conditions. The weighted far vision ratio and the weighted near vision ratio will range from 0 to 1.0, where 0 means that the lens has no beneficial effect on the desired far vision of the lens wearer and 1.0 means that the lens is fully corrected for the desired far vision of the wearer. For a rotationally symmetric power profile, the lens radii can be integrated to calculate the monocular weighted distance vision ratio, as follows:

wherein R is the pupil radius;

rx sphere is the spherical prescription power (in diopters) of the eye for which the monocular weighting ratio is calculated;

tan h is the hyperbolic tangent value; and is

P (r) is the lens plus eye power, which is calculated as follows:

P(r)＝P_CL(r)+SA_eye*r²+F

(II)

wherein SA_eyeIs the spherical aberration of the eye, and its value is preferably 0.1 diopter/mm²；

F is the lens fit (in diopters), meaning the change from the nominal value;

r is the radial distance from the center of the contact lens; and is

P_CL(r) is the radial power profile or power profile of the contact lens. For a particular design, the power profile provided is a series of P in 0.25 diopter increments_CL(r)。

Radial power profile or power profile (P) of a lens_CL(r)) is the axial power of the lens in air and can be calculated from the surface shape, thickness and refractive index of the lens.

The radius of the lens can be integrated, and the monocular weighted myopia ratio can be calculated according to the following formula:

wherein R is the pupil radius;

rx sphere is the spherical prescription power (in diopters) of the eye for which the monocular weighting ratio is calculated;

tan h is the hyperbolic tangent value;

p (r) is the focal power of the contact lens plus eye, and can be calculated by formula II; and is

Rx _ add is the add power (in diopters) required to add to the distance prescription to provide the individual with near vision correction.

For non-rotationally symmetric power profiles, the monocular weighted distance vision ratio may be calculated by integrating the lens radii as follows:

wherein R, Rx _ sphere, tanh, and P (r) are as described above, and

phi is the polar angle.

For non-rotationally symmetric power profiles, the monocular weighted near vision ratio may be calculated by integrating the lens radii as follows:

for a symmetric diffractive lens, the lens radius can be integrated to calculate the monocular weighted distance vision ratio, as follows:

wherein m is the diffraction order;

P_m(r) is the power profile in the m order;

ε_mdiffraction efficiency in m order;

is 1.

Similar modifications can be made to equations II, IV and V.

For the purposes of the present invention, reference to a "three-lens set" does not literally refer to only three lenses, but rather three lens subsets, each subset consisting of a plurality of lenses that provide a spherical power and add power within a desired range. Preferably, the plurality of lenses making up each lens subset provides a spherical power in the range of-12.00 to +8.00 diopters (in 0.25 diopter increments); while the add power provided is in the range of 0.75 to 2.50 diopters (in 0.25 diopter increments). More preferably, one lens subset provides spherical power in the range of-12.00 to +8.00 diopters (in 0.25 diopter increments) and add power in the range of 0.75 to 1.75 diopters (in 0.25 diopter increments); the second lens subset provides spherical power in the range of-12.00 to +8.00 diopters (in 0.25 diopter increments) and add power in the range of 0.75 to 2.50 diopters (in 0.25 diopter increments); and the third lens subset provides spherical power in the range of-12.00 to +8.00 diopters (in 0.25 diopter increments) and provides add power in the range of 1.25 to 2.50 diopters (in 0.25 diopter increments).

More preferably, the method of the invention is used for fitting lenses in a set of three lenses, each lens having a power profile different from the power profile of each of the other lenses and the lenses satisfying the following relationship:

wherein the front or object side surface of the lens is a regional multifocal surface or a continuous aspheric multifocal surface, and the back or eye side surface of the lens is an aspheric surface. By "zone multifocal surface" is meant a surface that is discontinuous when moving from one power zone to another. The radius of the aspheric back surface (i.e., the distance from the geometric center to the lens edge) is preferably about 7.20 to 8.10mm, more preferably 7.85mm, with a conic constant of-0.26.

In a still more preferred embodiment, the fitting method of the invention is used for fitting a lens having: an anterior multifocal surface comprising five radially symmetric zones, these zones being alternately myopic and hyperopic corrective zones or myopic, hyperopic and mesopic corrective zones; and an aspheric back surface having a radius of about 7.20 to 8.10mm, more preferably 7.85mm, and a conic constant of-0.26. More preferred values for the three lenses A, B and C in this set of lenses in this embodiment are listed in Table 2 below.

TABLE 2

	A	B	C
				Nominal zone height (diopter)	0.6	0.9	1.9
Extent of zone height	0.3 to 0.8	0.7 to 1.2	1.7 to 2.1

Spherical aberration (diopter/mm)2)	-0.1	-0.17	-0.1
				Range of spherical aberration	-0.08 to-0.12	-0.14 to-0.20	-0.8 to-0.12
First transition region	0.75	0.7	1
				First transition region range	0.65 to 0.85	0.6 to 0.8	0.9 to 1.1
Second transition region	1.25	1.3	1.95
				Second transition region range	1.15 to 1.35	1.2 to 1.4	1.85 to 2.05
Third transition region	2	1.95	2.5
				Third transition region range	1.9 to 2.1	1.85 to 2.05	2.4 to 2.6
Fourth transition region	2.5	2.55	3.45
				Fourth transition region range	2.4 to 2.6	2.45 to 2.65	3.35 to 2.55

In a still more preferred embodiment, the fitting method of the invention is used for fitting a set of three lenses, each lens having a power profile that is different from the power profiles of the other lenses, and the lenses satisfying the following relationship:

wherein the anterior surface is a zone multifocal surface, wherein each zone incorporates spherical aberration that may be increased plus or minus 0.05 to 0.2 diopters/mm based on spherical aberration in the distance vision zone²。

Alternatively, whether the multifocal surface is a continuous surface or a discontinuous surface, the spherical aberration for the far vision zone and the near vision zone can be adjusted according to the following formula:

SA_RX＝SA₀+c*Rx_sphere

0.0044＜c＜0.0052

wherein SA₀Spherical aberration designed for Rx _ sphere, which is equal to 0.0 diopter;

c is a constant with a value between 0.0044 and 0.0052, preferably 0.0048.

In these embodiments, the back surface of the lens is preferably aspheric having a radius of about 7.20 to 8.10mm, more preferably 7.85mm, and a conic constant of-0.26.

In another embodiment of the invention, the fitting method is used to fit a set of three lenses, each lens having a power profile that is different from the power profiles of the other lenses, and the lenses satisfy the following relationship:

STD(P_E(r)) < 0.15 is 1.25 < r < 3.

Wherein STD is the standard deviation; and is

P_E(r) is the effective power of the lens plus eye, and can be calculated by the following formula:

wherein P (r) is the power of the on-eye contact lens calculated by the formula:

P(r)＝P_CL(r)+SA_eye*r²+F

(VIII)

wherein SA_eyeIs the spherical aberration of the eye, and its value is preferably 0.1 diopter/mm²；

F is the lens fit (in diopters), meaning the change from the nominal value;

r is the radial distance from the center of the contact lens; and is

P_CL(r) is the radial power profile or power profile of the contact lens. For a particular design, the power profile provided is a series of P in 0.25 diopter increments_CL(r)。

In the zone design used in the fitting method of the invention, the first zone or zone located at the central position of the geometric center of the lens may be, and preferably is, a zone providing distance vision correction, or the zone may provide near or intermediate vision correction. The first zones may be the same or different in the lens pair. Similarly, in a continuous aspheric multifocal design, the correction in the center of each lens may be the same or different and may be selected from the group consisting of distance vision correction, intermediate vision correction, and near vision correction.

The contact lenses useful in the fitting method of the present invention are preferably soft contact lenses. Soft contact lenses made of any material suitable for making such lenses are preferably used. Exemplary materials for forming soft contact lenses include, but are not limited to, silicone elastomers, silicone-containing macromers (including, but not limited to, U.S. Pat. Nos. 5,371,147, 5,314,960, and 5,057,578 incorporated in their entireties herein by reference), hydrogels, silicone-containing hydrogels, and the like and combinations thereof. More preferably, the surface is a siloxane, or contains siloxane functionality, including but not limited to polydimethylsiloxane macromers, methacryloxypropyl polyalkyl siloxanes, and mixtures thereof, silicone hydrogels, or hydrogels such as etafilcon a.

The preferred lens-forming material is a poly 2-hydroxyethyl methacrylate polymer, i.e., having a maximum molecular weight between about 25,000 and about 80,000, a polydispersity of less than about 1.5 to less than about 3.5, and covalently bonded thereto at least one crosslinkable functional group. Such materials are described in U.S. patent No.6,846,892, which is incorporated herein by reference in its entirety. Suitable materials for forming intraocular lenses include, but are not limited to, polymethyl methacrylate, hydroxyethyl methacrylate, inert light-transmitting plastics, silicone-based polymers, and the like, and combinations thereof.

The lens-forming material may be cured by any known method, including but not limited to thermal, irradiation, chemical, electromagnetic radiation curing, and the like, and combinations thereof. Preferably, the lens is molded using ultraviolet light or the full spectrum of visible light. More specifically, the precise conditions suitable for curing the lens material will depend on the material selected and the lens to be formed. Polymerization processes for ophthalmic lenses, including but not limited to contact lenses, are well known. Suitable processes are disclosed in U.S. Pat. No.5,540,410, which is incorporated herein by reference in its entirety.

Claims (8)

1. A method for fitting a multifocal contact lens, said method comprising the steps of: a.) assessing the likelihood of an individual successfully fitting a multifocal lens; b.) determining dominant and non-dominant eye of the individual; c.) measuring dominant refraction of each eye of the individual; d.) determining the add power of the individual; e.) fitting a multifocal lens on each of the dominant and non-dominant eyes of the individual, wherein step a.) comprises determining an index of satisfaction with the habitual correction, S ═ f (D, N, O, G), where D is far vision satisfaction; n is near vision satisfaction; o is overall vision satisfaction; g is glare perception; each variable is rated on a scale of 1 to 5, with 1 being the lowest scale and 5 being the highest scale, and multifocal lenses are fitted to individuals with a satisfaction index of less than 19.

2. The method of claim 1, further comprising: f.) assessing the individual's lifestyle visual need and improving the fit made in step e) for the dominant eye, the non-dominant eye or for both based on the results of the assessment.

3. The method according to claim 1, wherein step a) comprises calculating an indicator of satisfaction of the individual with the habitual correction.

4. The method of claim 1, wherein step a.) includes evaluating each eye for blur tolerance.

5. The method of claim 3, wherein step a.) further comprises evaluating each eye for blur tolerance.

6. The method of claim 3 or 4, further comprising classifying the individual as bilateral fuzzy tolerance, unilateral fuzzy tolerance, bilateral fuzzy sensitivity, or unilateral fuzzy sensitivity.

7. The method of claim 2, wherein step f) further comprises providing a weighted score for determining a balance between the desired far and near vision of the individual.

8. The method of claim 2, wherein step f.) further comprises grouping evaluation responses into a first group for the dominant accommodative lens selection and a second group for the non-dominant accommodative lens selection and deriving a weighted evaluation score for each group.