Patent Application
20130197636
The invention relates to an intraocular lens implant, a method for manufacturing an intraocular lens implant, and a kit for manufacturing an intraocular lens implant.
Replacing the lens of a human eye by means of an intraocular lens implant may be indicated when due to aging processes the natural lens hardens and accommodation may no longer be achievable. For quite a while lens implants allowing accommodation include a replacement of the natural lens mass of the human eye by means of a synthetic lens mass. Besides the requirement for adapting such lens implant according to the individual needs e.g. to a specific refraction index, the materials to manufacture such lens implant from are difficult to elect in view of the diverging needs of the lens implant being accommodatable on the one hand and persistent and long-living on the other hand.
Recently, it was proposed to replace a single body lens implant by a lens implant with two viewing elements, i.e. two lenses being coupled to each other by means of a spring element. Such a lens implant is, for example, referred to in US 2005/0228401 A1. The lens implant comprises an anterior portion including an anterior viewing element and an anterior biasing element. The lens further comprises a posterior portion including a posterior viewing element and a posterior biasing element. The anterior portion and the posterior portion meet at first and second apices of the intraocular lens. The anterior portion and the posterior portion and/or the apices are responsive to force the separation between the viewing elements to change. The lens implant is designed for being implanted into a lens capsule of the eye.
In the absence of any external forces, this lens implant takes a shape in which the viewing elements are at their maximum separation along the optical axis. The viewing elements may be moved towards each other in response to a ciliary muscle relaxation in order to reach a shape corresponding to a state of the lens implant suitable for distant vision, which is also denoted in this document as unaccommodated state. A relaxation of the ciliary muscle makes the zonule fibres become tense and pull the lens capsule radially outwards which invokes a force against the spring element of the lens implant in the lens capsule and compresses the viewing elements. As a result the lens capsule including the lens implant takes a flatter shape. At the other extreme, the ciliary muscle contracts such that the zonule fibres relax. The lens implant and in particular its spring element extends from its tense state into its relaxed state such that the viewing elements are moved away from each other. The lens implant takes a spherical shape corresponding to a state for near vision which is also denoted as accommodated state.
In another embodiment illustrated in the
Both variants above are not believed to be ideal in terms of adaptability of a lens implant to its natural environment. In the first variant, the relaxed state of the lens implant provides spaced apart viewing elements resulting in a shape representing the accommodated state of the lens implant suited for near vision. This does not reflect the shape of the natural lens mass without its capsule when not being exposed to any external forces: The natural lens mass rather takes a flattened shape representing the unaccommodated state suited for distant vision.
According to the second version, the relaxed state of the lens implant seems to be reversed with respect to the first variant and the shape of the lens implant represents an unaccommodated state of the lens suitable for distant vision. However, the actuation of such lens implant as well as the shape of such lens implant is not considered to be a best fit in terms of adaptability of such lens implant to its environment. One of the reasons is that in the human eye the ciliary muscle typically does not directly drive and engage with the lens.
Hence, the problem to be solved by the invention is to provide an intraocular lens implant which is adapted to the physiology of the eye, and which is suited for a long term deployment in the lens capsule.
According to a first aspect of the present invention there is provided an intraocular lens implant, comprising a first viewing element and a second viewing element, and a spring element for varying a distance between the first and the second viewing element along an optical axis of the lens implant for varying the focal length of the lens implant. The lens implant is designed to take a shape suitable for distant vision when the spring element is in its relaxed state. A spring constant of the spring element is dimensioned such that a force produced by a lens capsule of the eye for holding the lens implant transforms the spring element from its relaxed state into a stretched state.
According to another aspect of the present invention an intraocular lens implant is provided comprising a first viewing element, a second viewing element, and a spring element for varying a distance between the first and the second viewing element along an optical axis of the lens implant for varying the focal length of the lens implant. The lens implant is designed to take a shape suitable for distant vision when the spring element is in its relaxed state. A spring constant of the spring element has a value of less than 550 mN/mm. Specifically, the lens implant is designed to take a shape suitable for near vision when the spring element is in a stretched state such that the distance between the first and the second viewing element in the stretched state of the spring element exceeds the distance between the first and the second viewing element in the relaxed state of the spring element. Hence, the lens implant is designed to require an external stretch force preferably originating from the lens capsule acting on the spring element for stretching the spring element from its relaxed state into its stretched state.
Such lens implant is designed to reflect properties of the natural lens and its actuation mechanism as much as possible and respects the physiology of the eye. First, the lens implant although being designed by several components comprising two or more viewing elements and a spring element between the viewing elements is designed to—absent any external forces—take a flattened shape, which shape represents the shape of a natural lens enabling distant vision, i.e. what also sometimes is referred to as the lens being in an unaccommodated state. This shape reflects the shape of the natural lens and as such serves best for any accommodation processes as well as for any other physiological processes.
When the lens implant in its relaxed state takes a shape suitable for distant vision it needs to be convertible from there into a shape suitable for near vision. While in the state of the art this is achieved by members protruding from the viewing elements of the lens implant trying to directly engage with the ciliary muscle such actuation does not reflect the actuation used by the human eye.
For the current lens implant it is envisaged that the ciliary muscle is not itself pushing the lens implant or the lens capsule for the reason that such actuation is not conform with the natural accommodation and may only be achieved by training of the ciliary muscle and the human brain in order to switch to such actuation mechanism different to the one used for the natural eye. Instead, as is with the human eye, upon contraction of the ciliary muscle the zonule fibres relax and no longer stretch the lens capsula which stretching held the lens capsule in a flattened elongated state before.
It was observed that without or with little interaction of the zonule fibres only, it is the lens capsule itself which causes the lens mass transitioning from the flat shape representing distant vision into the more spherical shape representing near vision. The lens capsule is formed by a basement membrane which was built during the growth of the lens mass at its periphery by building subcapsular epithelium cells. The lens capsule encompassing the lens is elastic, and without any other external forces its surface tends to take a shape of lowest surface per volume which is a sphere. This is why absent any external forces the combination of lens mass and lens capsule takes a sphere-like shape which is the desired one for near vision. However, the tension built by the lens capsule needs to overcome the spring force generated by the spring element of the lens implant in a direction for stretching the spring element. Such tension may be between 2 to 50 g/mm in direction of the optical axis subject to the individual. Hence, the spring constant of the spring element may preferably have a value of less than 20 mN/mm. In any case, the spring constant of the spring element may preferably have a value of less than 550 mN/mm, and more preferably of equal to or less than 500 mN/mm, and more preferably of less than 300 mN/mm.
In a design step, the spring constant of the spring element of the lens implant is dimensioned such that a force produced by the lens capsule transforms the spring element from its relaxed state into a stretched state, i.e. pulls the spring element. The direction of transition is determined by means of the action direction of the spring element which typically is the optical axis of the lens implant. In a very advantageous embodiment, the spring constant is not only dimensioned such that it enables the lens capsule to stretch the spring element and by this enlarges the distance between the viewing elements along the optical axis, but is dimensioned such that the lens capsule is enabled to separate the viewing elements up to a distance which represents a state for near vision. The transition shall preferably be effected solely by means of tensions in the lens capsule.
It is believed that the present lens although comprising two spaced apart viewing elements may be closely aligned to the shape and the dimension of the natural lens mass and the lens implant as well as its actuation may be conform to the natural lens and its actuation. With the actuation being the same as with the natural lens, i.e. in particular without the ciliary muscle directly acting on the lens implant, a lens implanted person is not needed to experience, learn and adapt a different way of actuation/accommodation whereas a direct engagement of the ciliary muscle with a clamp of the lens implant may be irritating. In addition, it is believed that whenever the lens mass can be replicated into the synthetic lens implant at its best in shape and dimension, the basement membrane forming the lens capsule will likely better engage with the lens implant for the reason of a better fit and which may better prevent from corrosion and clouding. It is believed that the subcapsular epithelium from which the basement membrane is built will show a better sustainability when engaged with an aligned lens implant which follows the natural lens in the shape and actuation.
For other embodiments of the present aspect of the invention it is referred to the dependent claims.
According to another aspect of the present invention, there is provided a method for manufacturing a lens implant according to any one of the previous embodiments. The natural lens is measured. In particular its shape and dimensions are measured, e.g. by any imaging technique. The data derived from such measurement may be used for forming the lens implant. A spring element may be formed with a spring constant such that the spring element is expected to be stretchable by tension forces induced by the lens capsule surrounding the natural lens. Such tension forces may be measured or be estimated. At least one of the two viewing elements may be formed with a desired optical power which desired optical power may be derived from the measurement.
According to another aspect of the present invention, there is provided a kit for manufacturing a lens implant according to any one of the previous embodiments. Such kit may comprise multiple viewing elements with different focal lengths and/or different shapes, and a spring element for holding the viewing elements.
Any embodiments described with respect to the device shall similarly pertain to the method and the kit. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail.
Further on it shall be noted that all embodiments of the present invention concerning a method might be carried out with the order of the steps as described, nevertheless this has not to be the only essential order of the steps of the method all different orders of orders and combinations of the method steps are herewith described.
The aspects defined above and further aspects, features and advantages of the present invention can also be derived from the examples of embodiments to be described hereinafter and are explained with reference to examples of embodiments. The invention will be described in more detail hereinafter with reference of examples of embodiments but to which the invention is not limited.
Similar or relating components in the several figures may be provided with the same reference numerals.
In
In a state in which the lens 1 is adapted for distant vision, the ciliary muscle 6 is relaxed as shown in
When transitioning from distant vision to near vision, the ciliary muscle 6 contracts such that a diameter of the ciliary muscle 6 around the lens 1 decreases. As a result, the tension in the zonule fibres 7 drops and the zonule fibres 7 may only hold the lens 1 but not add any additional radial forces to the lens 1. In such state, i.e. for a lens without the application of any external forces, the lens 1 relaxes from its flat shape and returns to the near spherical shape for near vision in which the focal length of the lens 1 is much smaller than for distant vision.
It was observed that absent any external forces acting on the lens 1 the lens mass 3 takes a rather flat shape suited for distant vision. However, when the lens mass 3 will be encapsulated in the lens capsule 2 it will be deformed and transform from the flat shape into a more spherical shape suited for near vision, again, absent any external forces. The lens capsule contains fibres built during the building of the lens mass Absent any external forces these fibres make the lens capsule to take a shape of lowest energy which results in a form with the smallest surface per volume which presently is a sphere—or better a sphere-like—structure.
Summarizing, absent any external forces applied to the lens capsule the lens mass/lens capsule combination will take a rather spherical form representing a lens suited for near vision. The forces generated by the lens capsule are sufficient for effecting such deformation of the lens mass 3 as the zonule fibres 7 are effete with the cilicary muscle 6 being contracted. And returning to the distant vision, the surface tension paradigm prevailing for the near view will be overridden by zonula fibres 7 pulling the edge of the lens capsule 2 outwards in response to the ciliary muscle 6 relax which makes the zonula fibres 7 become tense. As a result, the lens capsule 2 is radially stretched and takes a rather flat form suitable for distant vision.
A lens implant in the present context is understood as an implant for replacing the lens mass but not the lens capsule. Accordingly, the lens implant is meant to be inserted into the lens capsule.
In an embodiment of the present invention
Axis A-A′ denotes the optical axis of the lens implant 1. Axis B-B′, denotes the longitudinal axis of the lens implant 1. The spring element 14 is connected to both viewing elements 13 and 14 and is arranged such that a distance between the viewing elements 12, 13 along the optical axis can be varied subject to the force applied to the viewing elements 12, 13. A sample focal point on the optical axis is denoted as FP.
In
In such relaxed state a width w of the lens implant 11 along the optical axis A-A′ between outer surfaces of the first and the second viewing element 12, 13 may preferably be between 2.5 mm and 5.5 mm in the relaxed state of the spring element 14, and in a very preferred embodiment be between 3.8 mm and 4.0 mm in the relaxed state of the spring element 14.
In contrast, in Fig. lb the spring element 14 is in a stretched, extended state, i.e. external forces are applied to the spring element 14 or the viewing elements 12, 13 and make the distance between the viewing elements 12, 13 increase, and in particular exceed the distance between the viewing elements 12, 13 compared to situation when the spring element 14 is unloaded according to
In such stretched state the width w of the lens implant 11 along the optical axis A-A′ between outer surfaces of the first and the second viewing element 12, 13 may preferably be between 2.7 mm and 5.7 mm in the stretched state of the spring element 14, and in a very preferred embodiment be between 4.0 mm and 4.2 mm in the stretched state of the spring element 14.
In
However, if the spring element 14 of the lens implant 1 would have been designed with a very high spring constant such that only for a large force applied the spring element 14 may stretch, the counteracting forces evoked by the lens capsule 2 would not suffice to exceed the spring force and the distance between the viewing elements 12, 13 would not change significantly.
In a preferred embodiment, the spring constant of the spring element 14 has a value of less than 550 mN/mm.
In a preferred embodiment, the spring constant of the spring element 14 has a value of less than 20 mN/mm.
In another preferred embodiment, the spring constant of the spring element 14 has a value of more than 2.5 mN/mm.
In another preferred embodiment, the spring constant of the spring element 14 has a value of more than 10 mN/mm.
Any combinations of the above ranges of the spring constant are considered as preferred embodiments: The spring constant may be designed in one of a range between 2.5 mN/mm and 20 mN/mm, a range between 10 mN/mm and 20 mN/mm, a range between 2.5 mN/mm and 550 mN/mm, and a range between 10 mN/mm and 550 mN/mm.
Taking the gravitational field strength into account, the above ranges may be described as one of less than 55 g/mm, more than 0.25 g/mm, more than 1 g/mm, a range between 0.25 g/mm and 55 g/mm, a range between 1 g/mm and 55 g/mm, a range between 0.25 g/mm and 2 g/mm, or a range between 1 g/mm and 2 g/mm.
For this reason the spring constant of the spring element 14 is dimensioned such that a force produced by the lens capsule 2 transforms the spring element 14 from its relaxed state into a stretched state. In other words, in a direction of the optical axis A-A′ of the lens implant 11, the forces generated by the lens capsule 2 need to exceed the counteracting force of the spring element 14. In a very preferred embodiment, the force generated by the lens capsule 2 in such direction needs to overcome the spring force by an amount that allows the two viewing elements 12, 13 travelling away from each other until the lens implant 11 is in a condition that allows viewing to the near which is illustrated in
In
A lens implant 11 implanted in the eye is schematically illustrated in the longitudinal cut of
Generally, for the present intraocular lens implant it is beneficial that a longitudinal extension of the lens implant along the optical axis in the relaxed state of the spring element is less than a longitudinal extension of the lens implant along the optical axis in the stretched state. This makes the lens implant be suitable for near vision in its excited state rather than to distant vision. In near vision, the focal length as distance between the focal point on the optical axis and the lens implant is less than the focal length in distant vision.
In particular, the lens implant lacks of elements to engage with the ciliary muscle of the eye upon contraction of the ciliary muscle. I.e., the lens implant is not directly or indirectly controllable in its shape by a contraction of the ciliary muscle. In other words, the shape of the lens implant will not be affected by a contracting ciliary muscle. Preferably, the shape of the lens implant is solely affected by forces induced via the two viewing elements. This may include, that protrusions designed to shorten the distance between the viewing elements and the ciliary muscle or zonule fibres for an engagement between the cilicary muscle or the zonule fibres and the protrusions are avoided. Advantageously, the lens implant lacks of elements exceeding a height of the lens capsule in its relaxed state wherein the height is defined along the axis B-B′ of
The viewing elements and the spring element may advantageously be formed integrally, as a single piece, or alternatively, may be formed from at least the individual viewing elements and the spring element. The viewing elements may comprise a lens with plus power, and a lens with negative power.
Kits for manufacturing a lens implant according to one of the preceding embodiments may be provided such kit comprising multiple viewing elements with different focal lengths and/or different shapes, and at least one spring element for holding the viewing elements. From such kit an individual lens implant may be assembled in an ophthalmic clinic where a patients lens is replaced by the lens implant. From the kit lenses are chosen that match the refractive index, dimension and shape of the patients needs.
The lens implant preferably is adapted to the natural lens of the patients eye it shall replace. For this reason, the lens implant preferably comprise outside surfaces for being in contact with the lens capsule in an implanted state which outside surfaces take the dimension and form of the specific natural lens mass. In order to get there the natural lens is measured e.g. by computerized imaging which may result in a computerized model of the lens. The lens implant may be formed according the model and as such according to the dimension and shape of the natural lens as far as the individual viewing elements and spring elements allow.
In the previous embodiments, the lens capsule 2 is closed after inserting the lens implant 11. However, precise cuts, for example, a circular cut may be generated at the front portion of the lens capsule 2 by means of laser technology which cut is aligned with the optical axis A-A′ such that such cut may not even be closed after inserting the lens implant 11 and may remain open.
While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CH2010/000246 | Oct 2010 | CH | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CH11/00234 | 10/3/2011 | WO | 00 | 4/5/2013 |
