CN112370212B

CN112370212B - Focal length adjusting method for combining intraocular lens with extraocular zooming

Info

Publication number: CN112370212B
Application number: CN202011243972.5A
Authority: CN
Inventors: 房丰洲; 梁庆
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-11-10
Filing date: 2020-11-10
Publication date: 2024-07-23
Anticipated expiration: 2040-11-10
Also published as: CN112370212A

Abstract

The invention provides a focal length adjusting method for combining intraocular lens with extraocular zooming, which has the original part that the whole adjustable design is divided into an intraocular part and an extraocular part, a larger adjusting range is realized by smaller adjusting amplitude, the adjusting effect is good, and the limitation that the traditional intraocular lens is only adjustable in the eye is broken through. Wherein the intraocular portion is a spherical, aspherical or other optically designed intraocular lens for partially correcting aberrations of the human eye and having fine tuning capabilities. The interocular and extraocular functions similar to the natural lens, i.e. a stepless zoom from near to far, providing continuous clear vision for the patient.

Description

Focal length adjusting method for combining intraocular lens with extraocular zooming

Technical Field

The invention belongs to the technical field of medical instruments, and relates to an intraocular lens and a variable-focus lens, in particular to a focal length adjusting method for combining the intraocular lens with external zooming.

Background

Cataracts are the first global, generally blind ophthalmic disease that can cause clouding of the lens and even loss of vision, requiring surgical removal of the clouded lens, followed by placement of an artificial lens (IOLs) that both restores vision and ensures the integrity of the eye's physiology. However, most intraocular lenses have a single focal length, so that the patient cannot see things at different distances after surgery, and even if multiple focal IOLs allow the patient to achieve good distance and intermediate vision, the detail of the things cannot be seen at near, and halos and glare are caused by the superposition of different distance vision.

The natural lens has a refractive power of +19.11d, allowing for a change in surface curvature and thickness under contraction and relaxation of the ciliary muscle, thereby allowing for a continuous change in near to distance vision. Modern studies have shown that the ciliary muscle of the elderly has a substantial portion of its ability to contract after surgical removal of the lens. Based on this principle, many accommodating intraocular lenses (AIOLs) have emerged, the basic principles of which are two: one is to move the intraocular lens back and forth along the optic axis under the action of the ciliary muscle as in WO2008/014496; the other is that the compression of the ciliary muscle is transferred to the lens through the haptics so that its flexible surface bulges to enhance diopter, as in patent WO2007/067867. However, the former has weak accommodation, usually only 1-2D, much less than the natural lens; although the latter has a strong accommodative ability, the facial form is not controllable, the specific accommodative process is difficult to predict, and the AIOLs have complex structures and are difficult to implant into the eye through small incisions (below 3 mm). In addition, it is a great difficulty how to balance these aberrations and to eliminate the aberrations that are introduced during the accommodation process, when the cornea of the human eye has positive spherical as well as coma.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a focal length adjusting method for combining an intraocular lens with external zooming, which has good adjusting effect and clear near, middle and far vision; the optical part surface shape is fixed, and the adjusting process is controllable; the flexible material is adopted, the structure is simple, and the implantation can be realized through a small incision.

The technical scheme adopted for solving the technical problems is as follows:

An intraocular lens and extraocular zooming focal length adjusting method is composed of an intraocular lens adjusting and an extraocular adjusting, wherein the intraocular lens adjusting is realized by adjusting the intraocular lens, and the extraocular adjusting is realized by adjusting a lens with zooming capability.

The specific adjusting method comprises the following steps: the object under different distances can be seen clearly by fine adjustment of the artificial lens and then adjustment of the lens with zooming capability.

Furthermore, the manner in which the lens with zoom capability is adjusted is manual or motorized or user controlled by body, and the manner in which the intraocular lens is fine-tuned is by motorized or user controlled by body.

The intraocular lens has a characteristic surface shape, and the surface shape is a spherical surface or an aspheric surface or a free-form surface or a diffraction optical surface.

Moreover, the intraocular lens is a monofocal intraocular lens or a multifocal intraocular lens or an extended depth of focus intraocular lens.

Moreover, the lens with zooming capability is realized by any one mode or combination of any two modes of axial movement, axial movement along a direction perpendicular to the axis, surface shape change, material refractive index distribution change; or a plurality of lenses by any one or a combination of two or more of moving in an axial direction, moving in a direction perpendicular to the axis, changing the shape of the surface, changing the refractive index profile of the material.

An intraocular lens-associated extraocular variable focus accommodation design method comprising the steps of:

Establishing a human eye model with corneal spherical aberration;

Setting object distance, setting the curvature radius of the front and back surfaces of the artificial lens and the refractive index of the material as variables, and calculating the root mean square of the distance between each ray on the image plane and a reference point to minimize the root mean square;

changing the front surface and the rear surface of the artificial lens into a surface type with characteristics, and setting the surface type coefficient as a variable so as to minimize root mean square;

setting the refractive index, thickness and zoom displacement of a material of a lens with zoom capability as variables, and calculating an MTF curve to enable imaging to be clear;

Fixing other parameters, respectively setting different object distances, then setting zoom displacement as a variable, and calculating MTF curves of the different object distances to enable imaging to be clear;

clear vision can be obtained through combined intraocular and extraocular adjustment.

The eye model is a Lion model eye, a Brennan model eye, a Gullstrand I model eye, a Gullstrand-LeGrand model eye, a Navarro model eye or an Isabel model eye.

And the lens with zooming capability is an Alvarez zoom lens,

The Alvarez zoom lens has at least one surface defined by the formula: the lens surface type coordinate transformation matrix is determined after the lens surface type coordinate transformation matrix rotates by an angle theta DEG around a y axis in an XOZ plane and is as follows:

Setting the material refractive index, thickness, surface type coefficient A, zoom displacement d and inclination angle theta of the Alvarez zoom lens as variables, and calculating an MTF curve of the system to be more than 0.2 at a position of 50-100lp/mm under a 0-degree visual field to obtain MTF curves at different object distances of 250-5000 mm;

Fixing other parameters, setting different object distances respectively, setting a zooming moving distance d as a variable, and calculating an MTF curve of the system to be larger than 0.43 at a position of 50-100lp/mm under a 0-degree visual field to obtain MTF curves of different object distances of 250-5000 mm;

The zoom is controlled by adjusting the displacement d of the Alvarez lens.

Moreover, the intraocular lens is a monofocal intraocular lens, and the characterization equation of the even aspherical surface of the monofocal intraocular lens is as follows:

c is the curvature radius of the curved surface vertex, k is the conical constant, a _n is the coefficient of the even higher-order term, the 4-order term a ₁ = -2.68E-4 for the IOL anterior surface aspheric surface, and the 4-order term b ₁ = -2.68E-4 for the IOL posterior surface aspheric surface.

The invention has the advantages and positive effects that:

(1) The larger adjusting range is realized by smaller adjusting amplitude, and the adjusting effect is good;

Since the accommodation structure is on the outermost side of the eye, accommodation power is stronger than in the manner in which AIOLs are placed in the eye, in the example, it is found that the accommodation amplitude is only 3.7D from 5000mm to 250mm of the outer portion of the eye, the maximum diopter is 8.6D (at 250 mm), and the required maximum diopter is 12D or more in the manner in which only the Alvarez lens is placed in the eye.

(2) The surface shape of the intraocular and extraocular optical part is fixed, and the adjusting process is controllable;

(3) The intraocular part is simple in structure and can be implanted through a small incision.

Because the zooming and aberration correction are separated, the part implanted in the eye can be realized by the existing minimally invasive surgery, and the part cannot be implanted through a small incision due to the excessively complex design.

Drawings

FIG. 1 is a schematic view of an extraocular portion, an intraocular portion, and a model eye;

fig. 2 is an MTF (meridian direction) curve.

In fig. 1: 1 is Alvarez lens group, 2 is cornea, 3 is iris, 4 is aqueous humor, 5 is aspheric IOLs, 6 is vitreous, 7 is retina, θ is tilt angle.

Detailed Description

The invention is further illustrated by the following examples, which are intended to be illustrative only and not limiting in any way.

The invention provides an intraocular lens combined extraocular zooming adjustable design method, which is originally characterized in that the whole adjustable design is divided into an intraocular part and an extraocular part, and a larger adjusting range is realized with smaller adjusting amplitude, so that the adjusting effect is good. The intraocular part is an aspheric monofocal intraocular lens for correcting human eye aberration, the external part is an Alvarez zoom lens with zooming capability, the Alvarez lens (US-A-330594) can realize zooming through two lenses which move transversely, and the cooperation of the intraocular lens and the external part can realize the function similar to se:Sup>A natural crystalline lens, namely stepless zooming from near to far, so as to provide continuous and clear vision for patients.

Aspherical IOLs have a good balancing ability for corneal aberrations. The even aspheric surface takes a quadric surface as a basal plane, and an even higher-order term is overlapped, so that the even aspheric surface can be used for correcting spherical aberration of a larger-caliber element, such as a Schmidt correcting plate. The characterization equation of the even aspherical surface is:

Note that: c is the curvature radius of the curved surface vertex; k is a conic constant (Conic Constant); a _n is a coefficient of even higher-order term.

Most of spherical aberration of human eyes can be balanced through adjustment of the a _n, and the spherical aberration can be eliminated due to the fact that the spherical aberration and the cornea are symmetrically placed about a pupil.

The zoom function is achieved by an extraocular part belonging to the Alvarez zoom lens comprising two lenses placed in central symmetry, at least one of which is movable perpendicular to the optical axis, in the following basic form in cartesian coordinates:

Note that: a represents the surface form factor in mm ^-2.

To obtain a thinner lens, a wedge DX needs to be subtracted while a constant E is added to ensure sufficient strength, resulting in the following equation:

When the two lenses are relatively displaced d, the thickness formulas are respectively as follows:

The formula of the combined lens is as follows:

the combined lens is a perfect spherical lens, and the focal length formula is not difficult to calculate:

Note that: where n is the refractive index of the lens material.

It can be seen that the focal length is affected by the three components a, d and n, and once the surface shape and material are determined, the focal length is only related to x.

However, due to the asymmetry of the Alvarez lens, the on-axis light and the one-side field of view cannot converge to a point, but form an aberration similar to coma, and the other-side field of view can converge to a point, so that the lens group needs to be rotationally tilted by a certain angle θ° for optimization.

The rectangular coordinate system where the lens group is positioned before rotation is xyz, and the Alvarez lens group rotates by an angle theta DEG (anticlockwise positive) around the y axis in the XOZ plane, then the coordinate transformation matrix of the lens surface after rotation is:

the specific implementation mode of the invention is as follows:

(1) The model eye in this example is an established 60 year old national model of human eyes, (Chen Xin. Lens paradox analysis research based on human eye optical model [ D ]. Nanjing university of post, 2019.) which is more in line with national demands. Parameters are shown in table 2, other eye models, such as the Lion and Brennan model eyes, may also be used.

(2) Setting an object distance of 250mm (simulating near vision, but other object distances are also possible, wherein 250mm is only used as an initial structure); the natural lens is replaced by a spherical IOL, the radius of curvature of the anterior and posterior surfaces (the absolute value of the radius of curvature of the anterior and posterior surfaces is the same) and the refractive index of the material are set as variables, and the Root Mean Square (RMS) of the distance between each ray on the image plane and a reference point (the geometric center of the chief ray or the diffuse spot) is calculated to minimize.

(3) The front and back surfaces of the IOL are changed to even aspherical surfaces, the aspherical coefficients are set as variables so as to minimize RMS, the 4 th order aspherical coefficients are set as variables in the embodiment, and the related parameters are shown in Table 1.

(4) The MTF curve (modulation transfer function) of the system was calculated to be greater than 0.2 at a field of view of 0 degrees and 100lp/mm by adding the extraocular portion, setting the refractive index, thickness, surface type coefficient a, zoom displacement d, and tilt angle θ (the rotation surface is x0z surface, and counterclockwise positive) as variables, and the results obtained by optimization in this example are shown in table 1.

(5) Fixing other parameters, setting different object distances respectively, setting a zooming moving distance d as a variable, and calculating an MTF curve of the system to be larger than 0.43 at a 0-degree view field and a 100lp/mm position to obtain MTF curves at different object distances; in this example 250mm, 750mm (simulated working distance) and 5000mm (simulated distance vision), the relevant data are shown in table 3 (the following data are for the central 0 degree field of view).

TABLE 1 250mm object distance Alvarez lens parameters

TABLE 2 parameters relating to 60 year old national eye model loaded with aspherical IOLs

Note that: the incident light wavelength is λ=546 nm, and the pupil diameter d=3 mm.

TABLE 3 MTF values at 100lp/mm for eye models of different object distances

When the lens is actually used by a patient, the displacement d of the Alvarez lens is adjusted, so that objects at different distances can be seen clearly.

The intraocular portion of the present invention refers not only to aspherical monofocal IOLs, but any IOLs that can achieve correction of aberrations of the human eye may be suitable. The principle of zooming of the extraocular part may also be other principles such as axial movement zooming of the lens and liquid crystal zooming. The intraocular and extraocular portions are integral and cooperate to reduce aberrations and provide diopters to the human eye. The intraocular and extraocular parts should not be designed separately, and form a system with the human eye at the time of design. Similar structural implications for the method of the present invention, using other eye models (e.g., lion and Brennan model eyes), materials that achieve the optical effects of the present example, should be considered as part of the present invention.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that variations and modifications can be made without departing from the scope of the invention.

Claims

1. A method of focal length adjustment for intraocular lens combination extraocular zooming, characterized by: consists of two parts, an intraocular accommodation, which is achieved by accommodation of an intraocular lens, and an extraocular accommodation, which is achieved by accommodation of a lens with zoom capability; objects at different distances can be seen through fine adjustment of the intraocular lens and then adjustment of the lens with zooming capability, wherein the mode of adjustment of the lens with zooming capability is manual control or electric control or body control of a user, and the fine adjustment mode of the intraocular lens is electric control or body control of the user.

2. The method according to claim 1, characterized in that: the intraocular lens has a characteristic surface shape, and the surface shape is a spherical surface or an aspheric surface or a free-form surface or a diffraction optical surface.

3. The method according to claim 1, characterized in that: the intraocular lens is a single focal intraocular lens or a multifocal intraocular lens or an extended focal depth intraocular lens.

4. The method according to claim 1, characterized in that: the lens with zooming capability is realized by any one mode or combination of any two modes of axial movement, axial movement along a direction perpendicular to the axis, surface shape change, material refractive index distribution change; or a plurality of lenses by any one or a combination of two or more of moving in an axial direction, moving in a direction perpendicular to the axis, changing the shape of the surface, changing the refractive index profile of the material.

5. An intraocular lens-associated extraocular variable focus adjustable design method, characterized by: the method comprises the following steps:

Establishing a human eye model with corneal spherical aberration;

clear vision can be obtained through the combined regulation of the inside and the outside of eyes;

the lens with zooming capability is an Alvarez zoom lens,

The zoom is controlled by adjusting the displacement d of the Alvarez lens.

6. The method according to claim 5, wherein: the eye model is a Lion model eye, a Brennan model eye, a Gullstrand I model eye, a Gullstrand-Le Grand model eye, a Navarro model eye or an Isabel model eye.

7. The method according to claim 5, wherein: the artificial lens is a single-focus artificial lens, and the characterization equation of the even aspherical surface of the single-focus artificial lens is as follows: