A set of contact lens with power dependent spherical aberration

Abstract

This article describes a soft contact lens kit and a method for designing the soft contact lens kit by incorporating varying degrees of spherical aberration into the lens design and depending on the target spherical refractive power. These varying degrees of spherical aberration are equal to or less than zero D / mm², and take into account clinically measured population-average ocular spherical aberration, manufacturing variability, and generalized accommodative ability.

Description

[Technical Field]

[0001] This invention relates to soft contact lens sets, and a method for designing soft contact lens sets that improve vision by incorporating spherical aberration in a manner that takes into account variations in wearers, lens manufacturing, and accommodative capabilities. [Previous Technology]

[0002] Myopia, or nearsightedness, is a refractive defect of the eye in which light from an object focuses in front of the retina. Myopia occurs because the eyeball elongates along the optical axis or the cornea's contour is too steep. Minus-powered spherical lenses can be used to correct myopia. Hyperopia, or farsightedness, is a refractive defect of the eye in which light from an object focuses behind the retina. Hyperopia occurs because the eyeball shortens along the optical axis or the cornea's contour is too flat. Plus-powered spherical lenses can be used to correct hyperopia. Both negative and positive spherical lenses have spherical surfaces that are not perfect at refocusing light from an object into an image. One known aberration is spherical aberration (SPHA). Spherical aberration degrades image quality because light from an object refracted at different radial positions by the lens is refocused at different positions or focal points along the optical axis, resulting in blurred images. Astigmatism occurs when the cornea is not rotationally symmetrical or when the lens is misaligned, resulting in two orthogonal image focal points. Astigmatism is usually caused by a non-rotationally symmetrical corneal surface and requires negative or positive diopter lenses directed onto the eye to correct myopia or hyperopia. Orientation requires the lens to maintain rotational stability around a fixed axis on the eye, generally achieved by positioning a thickness profile on the surface anterior to the lens periphery. Lenses for correcting astigmatism often refer to toric lenses. On the other hand, multifocal lenses are used to treat presbyopia and can also be toric lenses.

[0003] Like other curved refractive surfaces, the ocular system (including the cornea, lens, etc.) exhibits some SPHA (Spectral Spatial Harm). As a result, when myopia, hyperopia, astigmatism, or presbyopia is corrected with soft contact lenses, the SPHA of the soft contact lens and the cornea may combine uncontrollably, potentially reducing the visual acuity of the contact lens wearer. Accordingly, it is advantageous to design soft contact lenses symmetrically, taking into account the many factors that cause or affect SPHA, to produce a series of contact lenses that improve visual acuity across a spherical refractive power range. [Summary of the Invention]

[0004] This document describes soft contact lenses and soft contact lens sets, and a method for designing soft contact lenses and soft contact lens sets based on incorporating different degrees of spherical aberration into the lens design and depending on the target spherical refractive power. Different degrees of spherical aberration are selected by compensating for a group-average ocular spherical aberration curve and a spherical comparator lens spherical aberration curve. The method of this invention provides an effective means of addressing spherical aberration errors by limiting the number of incorporated spherical aberrations across a range of spherical refractive power. The soft contact lenses and soft contact lens sets of this invention provide improved visual acuity relative to spherical comparator lenses with the same base curve radius.

[0005] According to one embodiment, a contact lens assembly is provided, wherein each contact lens in the assembly has a first surface and a second opposing surface adapted to be placed against a user's eye, wherein the first surface and the second surface meet at a lens boundary that defines a periphery of the lens. Each lens has an optical diopter curve and a SPHA curve, such that for the diopter of a positive optical lens, the SPHA curve is less than or equal to zero (0) D / mm² and greater than or equal to -0.055 D / mm²; for the diopter of a negative optical lens between approximately -3D and 0D, the SPHA curve is less than or equal to 0.0167*SP D / mm² and greater than or equal to -0.055 D / mm²; for the diopter of a negative optical lens between -3.5D and approximately -3D, the SPHA curve is less than or equal to 0.0167*SP D / mm² and greater than or equal to 0.0356*SP+0.0467 D / mm²; and for the diopter of a negative optical lens between -8D and -3.5D, the SPHA curve is less than or equal to 0.0082*SP-0.0301 D / mm² and greater than or equal to 0.0356*SP+0.0467 D / mm2. "SP" represents the spherical diopter in these mathematical formulas, and SP is expressed in diopter.

[0006] In another embodiment, for negative optical refractive power between -8D and -3.5D, the SPHA curve is less than or equal to 0.0082*SP-0.0301 D / mm2 and greater than 0.0167*SP D / mm2. In yet another embodiment, for negative optical refractive power between -8D and approximately -3D, the SPHA curve is less than 0.0167*SP D / mm2 and greater than or equal to 0.0356*SP+0.0467 D / mm2.

[0007] The first surface and the second surface may be selected from the group consisting of: aspherical, spherical, and mixtures thereof, and may be toric lenses and / or multifocal lenses.

[0008] This contact lens set can provide improved visual acuity compared to a contact lens set with a spherical comparator.

[0009] Also provided is a contact lens assembly, wherein each contact lens in the assembly has a first surface and a second opposing surface suitable for placement against a user's eye, wherein the first surface and the second surface intersect at a lens boundary defining a periphery of the lens. The lens has an optical power and an SPHA curve, such that for a positive optical lens power, the SPHA curve is equal to 0 D / mm²; for a negative optical lens power between approximately -3.5D and 0D, the SPHA curve is equal to 0.0167*SP D / mm²; and for a negative optical lens power between -8D and -3.5D, the SPHA curve is 0.0082*SP - 0.0301 D / mm².

[0010] The first surface and the second surface may be selected from the group consisting of: aspherical, spherical, and mixtures thereof, which may include toric lenses and / or multifocal lenses. Furthermore, this group may provide improved visual acuity compared to a spherical comparator contact lens group.

[0011] In another embodiment, a contact lens assembly is provided, wherein each contact lens in the assembly has a first surface and a second opposing surface adapted to rest against a user's eye, wherein the first surface and the second surface intersect at a lens boundary defining a periphery of the lens. Each lens has an optical diopter profile and a SPHA profile, such that for negative optical diopter between approximately -3D and 0D and all positive optical diopter, the SPHA profile is equal to -0.055 D / mm²; and for negative optical diopter between approximately -8D and approximately -3D, the SPHA profile is equal to 0.0356*SP + 0.0467 D / mm².

[0012] The first surface and the second surface may be selected from the group consisting of: aspherical, spherical, and a combination thereof, and the lenses may be toric lenses and / or the lenses may be multifocal lenses.

[0013] This contact lens set can provide improved visual acuity compared to a contact lens set with a spherical comparator.

[0014] Also provided is a contact lens assembly, wherein each contact lens in the assembly has a first surface and a second opposing surface suitable for placement against a user's eye, wherein the first surface and the second surface intersect at a lens boundary defining a periphery of the lens. Each lens has an optical power and a SPHA curve such that for negative optical powers between -2.9D and 0D and all positive optical powers, the SPHA curve is equal to -0.055 D / mm²; and for negative optical powers between approximately -8D and -2.9D, the SPHA curve is equal to 0.0356*SP + 0.0467 D / mm².

[0015] The first surface and the second surface may be selected from the group consisting of: aspherical, spherical, and a combination thereof, and the lenses may be toric lenses and / or the lenses may be multifocal lenses.

[0016] This contact lens set can provide improved visual acuity compared to a contact lens set with a spherical comparator.

[0017] A method for manufacturing a contact lens assembly is also provided, comprising the following steps: measuring a group average ocular spherical aberration curve; comparing the group average ocular spherical aberration curve with a spherical aberration curve of a spherical comparator lens; generating a spherical aberration curve that compensates for the group average ocular spherical aberration curve, which is related to the spherical aberration curve of a spherical comparator lens, the degree of user accommodation as a function of spherical diopter, and manufacturing precision; and forming a soft contact lens assembly that exhibits the spherical aberration curve across a range of spherical diopter.

[0018] The spherical aberration curve spanning the spherical refractive power range may be equal to or less than zero (0) D / mm2. The spherical aberration curve may be described by two or more linear equations spanning the spherical refractive power range. The contact lens assembly may consist of aspherical lenses, toric lenses, multifocal lenses, and combinations thereof.

Implementation Method

[0020] As described above, the present invention provides an improved soft contact lens design, a method for designing such a lens, and a lens assembly that improves vision by minimizing image blurring caused by SPHA. As described below, the design takes into account ocular SPHA across patient groups, the effects of manufacturing variations on SPHA, and the patient's accommodative ability to accommodate varying refractive errors.

[0021] The group-averaged ocular SPHA curve is generated by plotting the average calculated ocular SPHA as a function of spherical diopter (P0). The calculated ocular SPHA is determined from wavefronts measured clinically from approximately 3,500 subjects. This wavefront is obtained using a wavefront sensor or aberrometer, such as instruments available from Visionix, Luneau Technology Inc. The ocular diopter curve P(r) is defined as P(r) = (1 / r)∂w / ∂r, where w is the measured wavefront and r is the lens radius. The ocular diopter curve P(r) is fitted to an even-degree polynomial: the second-order coefficient (SA4) is the ocular SPHA, and the unit is D / mm2, where D = diopter and mm = millimeter. Following the above method, the ocular SPHA is calculated for each subject and then averaged to produce the average calculated ocular SPHA, as shown by line 100 in Figure 1. Line 101 in Figure 1 also shows the spherical aberration curve of the comparator lens calculated for a lens with a base curve radius of 8.5 mm. Other comparator lenses with different base curve radii can be used. Not all comparator lenses exhibit linear or near-linear SPHA curves. In any case, for a given base curve radius, a comparator lens with negative spherical power exhibits negative SPHA, and a comparator lens with positive spherical power exhibits positive SPHA. Regardless of spherical power, only planar lenses exhibit zero SPHA. Lens Design Principles

[0022] The lens assembly of this invention incorporates several specific design principles and clinical observations. First, referring to Figure 2, the lens design of this invention incorporates a limited degree of zero or negative SPHA into the specific target spherical refractive power range by taking into account the eye, SPHA, manufacturing variation, and accommodative ability, rather than simply setting the target to cancel out the eye's SPHA and produce a net zero SPHA for all spherical refractive powers. Designing a net zero SPHA in this way ignores two other interactively related factors affecting SPHA and overall visual acuity: variation in SPHA due to lens manufacturing and variation in the amount of accommodation available to the contact lens wearer. Generally, manufacturing SPHA variation depends on spherical refractive power and can be corrected within the range of -0.02 D / mm² to +0.02 D / mm². The effect of manufacturing-related negative SPHA variation on visual acuity is less significant than that of positive SPHA variation because negative SPHA can be at least partially compensated for by the contact lens wearer's accommodation. Therefore, SPHA has a larger tolerance for negative SPHA shift than positive shift. Generally, a manufacturing tolerance of -0.1 to approximately +0.03 D / mm² [where pupil sizes are 3, 4, and 5 mm] will be sufficient to meet the precision requirements of SPHA. Since myopia and hyperopia generally have different accommodative abilities, another operational design feature is to divide the SPHA curve into two to five segments within that spherical refractive power range. In this way, the amount of SPHA incorporated into the lens design can be customized to the degree of accommodation of the contact lens wearer within the range of refractive error. Two or three segments are preferred.

[0023] The lens design of the present invention is best suited for optimizing distance vision without significant accommodative delay. However, with age (but before the onset of presbyopia), small to moderate accommodative delay may occur, significantly affecting near vision. In this case, the lens design of the present invention incorporates more negative SPHA to a higher negative refractive power than the spherical comparator lens, and incorporates less negative SPHA to a lower negative and positive refractive power. This exact value is determined in part by confirming that negative 3D lenses generally provide the best subjective vision. The negative 3D comparator spherical lens shown in Figure 1 displays an SPHA of approximately -0.05 D / mm².

[0024] In summary, the lens design of the present invention specifies an SPHA value calculated from an SPHA curve. This SPHA curve is defined as a continuously segmented function dependent on its spherical diopter (D), with each segment relating an SPHA value (D / mm²) to the lens design of the present invention. This SPHA value is equal to or less than zero (0) D / mm², compensating for clinically measured ocular SPHA, manufacturing errors, and accommodative ability.

[0025] Referring to the previous diagram, for a lens with a base curvature of approximately 8.5 mm and a refractive index of approximately 1.42, Figure 1 shows how a group of SPHA curves (line 100) varies as a function of diopter, compared to the SPHA curve (101) of a spherical comparator lens. The SPHA curve of this spherical comparator lens is calculated and is substantially linear by the equation Y = 0.0167 * SP, which is negative for negative diopter and positive for positive optical diopter. "SP" refers to spherical diopter and is expressed in diopter (D). This group of SPHA curves (derived from the group data described above) is slightly positive for all spherical diopters.

[0026] Figure 2 illustrates the SPHA curve of Figure 1, and the SPHA curves of two exemplary lens group embodiments of the present invention. For the first embodiment referred to as example lens 1, as shown by line 102, the SPHA curve is approximately zero for positive spherical diopter. For negative spherical diopter between approximately -3.5D and -3.0D, the SPHA curve is defined by 0.0356*SP + 0.0467 D / mm², and for negative spherical diopter greater than -3.5D, the SPHA curve is defined by 0.0082*SP – 0.0301 D / mm². For example lens 2 illustrated by line 103, the SPHA curve is defined by -0.055 D / mm² for negative optical diopters greater than approximately -3.0D up to and including all positive optical diopters, while for all optical diopters less than approximately -3D, the SPHA curve is defined by y = 0.0356*SP + 0.0467D / mm².

[0027] Although the specific SPHA curves of Example Lens 1 and Example Lens 2 are described in detail above, a lens group that provides improved visual performance across the entire spherical refractive power range compared to the spherical control lens will be achieved by a SPHA curve for the two example lenses, where the SPHA curve for positive optical refractive power falls between or between the lines depicted in Figure 2. In other words, it is less than or equal to Y=0 and greater than or equal to Y=-0.055 D / mm2. Similarly, for optical refractive errors between 0 and -3D, the SPHA curve is less than or equal to Y = 0.0167 * SP D / mm², and greater than or equal to Y = -0.055 D / mm²; for optical refractive errors between -3.5D and approximately -3.0D, the SPHA curve is less than or equal to 0.0167 * SP D / mm², and greater than or equal to 0.0356 * SP + 0.0467 D / mm²; and for negative optical refractive errors between -8.0D and -3.5D, the SPHA curve is less than or equal to 0.0167 * SP D / mm², and greater than or equal to 0.0356 * SP + 0.0467 D / mm².

[0028] As previously stated, for positive refractive power, the lens system of the present invention is designed to incorporate less SPHA than the spherical control lens, thereby providing improved vision. For higher negative refractive power, SPHA is less critical, because normal accommodation can offset some of the SPHA in the lens.

[0029] The lens group described herein is a cross-spherical refractive power test. Visual acuity testing was performed on 39 subjects (78 eyes), of whom 36 eyes had spherical refractive power between -4D and -7.25D, 20 eyes had spherical refractive power between -0.075D and -3.0D, and 22 eyes had spherical refractive power between 0.5D and 3.0D. These subjects were between 18 and 65 years of age and were all habitual users of disposable silicone hydrogel or silicone hydrogel soft lenses (daily, bi-weekly, or monthly). All subjects had a cylindrical error of less than or equal to -0.75D in each eye and a corrected visual acuity of 20 / 25 (Snellen or equivalent) or better in each eye.

[0030] Visual acuity is measured in both monocular and binocular cases by requiring the subject to read the smallest letter on a Snellen visual acuity chart at a distance of four meters. According to Table 1, visual acuity is expressed in logMAR units. [Table 1.] Snellen to LogMAR Conversion Table Snailon LogMAR 20 / 200 1 20 / 160 0.9 20 / 125 0.8 20 / 100 0.7 20 / 80 0.6 20 / 63 0.5 20 / 50 0.4 20 / 40 0.3 20 / 32 0.2 20 / 25 0.1 20 / 20 0 20 / 16 -0.1 20 / 12.5 -0.2 20 / 10 -0.3

[0031] The results of the visual acuity tests were averaged together, and both monocular and binocular visual acuity are reflected in Figure 4. As illustrated, for both monocular and binocular visual acuity, the visual acuity of Example Lens 1 and Example Lens 2 is greater than 20 / 20 (represented by zero on the LogMAR scale), indicating that the lens group of the present invention provides improved vision across the spherical refractive range. [Simplified Explanation of the Diagram]

[0019] The following figures are shown by way of example, not limitation, of the various examples discussed in this disclosure. In the figures: [Figure 1] shows how a group average ocular SPHA curve (line 100) varies as a function of refractive power, compared to the SPHA curve of a spherical comparator lens (line 101). [Figure 2] shows the SPHA curves of example lens 1 (line 102) and example lens 2 (line 103) of the lens design of the present invention, compared to the group average ocular SPHA curve (line 100) and the SPHA curve of the spherical comparator lens (line 101). [Figure 3] shows only the SPHA curves of example lens 1 (line 102) and example lens 2 (line 103) of the lens design of the present invention. [Figure 4] shows the monocular and binocular visual acuity measured for example lenses 1 and 2.

Claims

1. A contact lens assembly with refractive power dependent spherical aberration, comprising: each contact lens in the assembly having a first surface and a second surface suitable for placement against a user's eye, wherein the first surface and the second surface intersect at a lens boundary, the lens boundary defining a periphery of the lens, an optical refractive power curve, and a spherical aberration (SPHA) curve; wherein the optical refractive power is positive, and wherein the SPHA curve is less than zero (0) D / mm² and greater than or equal to -0.055 D / mm².

2. The contact lens assembly as claimed in claim 1, wherein the first surface and the second surface are selected from the group consisting of: aspherical, spherical, and mixtures thereof.

3. The contact lens set as described in claim 1, wherein the set includes tortuous lenses.

4. The contact lens set as described in claim 1, wherein the set includes multifocal lenses.

5. The contact lens assembly as described in claim 1, wherein the assembly includes improved visual acuity compared to a contact lens assembly with a spherical comparator.

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