GB2503910A

GB2503910A - Multifocal contact lens with two sets of focal length zones and movement-sensitive biasing

Info

Publication number: GB2503910A
Application number: GB201212348A
Authority: GB
Inventors: John Clamp
Original assignee: Contact Lens Precision Laboratories Ltd
Current assignee: Contact Lens Precision Laboratories Ltd
Priority date: 2012-07-11
Filing date: 2012-07-11
Publication date: 2014-01-15
Anticipated expiration: 2032-07-11
Also published as: GB201212348D0; GB2503910B

Abstract

A multifocal contact lens has zones 2 having a first focal length and zones 3 having a second focal length. These zones may be radial and relate to near and distance vision. The lens also has an eye movement-sensitive biasing means such as peripheral prismatic area 6 so as to cause the lens to move on the subject's eye in response to movements thereof. Movement of the lens causes a preferred one of the optical zones to be located such that the subject is provided with a desired optical correction to allow viewing at a desired focal length. Zones for distance vision may be at an angle of 45 degrees and zones for near vision at 135 degrees to a horizontal axis.

Description

Multifocal Contact Lens

Field of the Invention

This invention relates to a multifocal contact lens and to a method of making a multifocal contact lens.

Background of the Invention

Presbyopia is a condition which affects the human eye, wherein the eye exhibits a progressive'y diminished ability to focus on near objects. The exact mechanisms which contribute to presbyopia are unknown at present, but research has suggested that the condition is caused by the hardening of the crystalline tens within the eyeball and the loss of power of the ciliary musc'es, causing a loss in the ability to shape the aforesaid lens.

Presbyopia is a symptom caused by the natural course of ageing. The first symptoms are usually noticed in peop'e over the age of 40 years, and progressively become more pronounced during the lifetime of the individual.

At present, there is no routine cure for the condition of presbyopia. However, the loss of focussing ability can be compensated by the use of using corrective lenses.

Until recently, reading glasses were the only option available to presbyopes who wanted to perform everyday tasks requiring good near vision. Typically, a pair of reading glasses provide the optical system with an additional prescription of between approximately + 1.00 and + 3.00 dioptres, allowing objects that are nearby to be seen with clarity.

Other so'utions have included bifocal glasses and the combination of contact lenses, which provide distance correction only, with reading glasses.

Recently, contact lenses have been used to treat the condition of presbyopia and, in some circumstances, may be the preferred choice. To date, however, the success of using contact lenses has been limited, when compared with that of using spectacles.

This can be mainly attributed to two technical problems associated with the use of contact lenses relative to spectacles.

Firstly, contact lenses utilise a small optical area when compared with the optical area used by spectacle lenses. Typically, contact lenses are the same size as the pupil of the eye, having a diameter of between 2.5 and 7mm, whereas the diameter of a typical spectacle lens may be 70mm when the lens is sitting in a position approximate'y 12mm from the front of the cornea. These dimensions limit the useful area that the contact lens designer can emp'oy to create complex surfaces which provide the desired optical outcomes. In addition, there is a tendency for the pupil to decrease in size with age.

Secondly, the contact lens tends to be re'atively stationary with respect to the eye.

Typically, movements of between only 0.25mm and 1.0mm are to'erated between the anterior surface of the cornea and the posterior surface of the contact lens. In contrast, the eye may be moved to look through any part of a spectacle lens. In general, the upper to middle area of the spectacle lens is used for distance vision and the lower area of the lens is used for near vision.

In an attempt to overcome these problems, contact lens designers have used three main techniques.

Simultaneous vision multifocal lenses present the wearer with a variety of focal lengths within a confined optical area, thus effectively providing the wearer with the choice of focal length for a particular task. Both distance and near vision portions of the lens are in front of the pupil at the same time, such that the brain must determine which area of the lens to emphasize and which area to ignore to provide the best image resolution. However, patients who use simultaneous vision multifocal lenses often complain that they see haloes and ghosting and have difficulty with night vision.

Alternating vision multifocal senses have distinct zones in the lens for distance and near vision. Different focal lengths are presented to the wearer, depending on the position of the lens within the eye. As in bifocal spectacles, the lower portion of the lens is typically configured for near vision, such that when the wearer looks down, the lower portion is positioned in front of the pupil of the eye. The top part of the lens is for distance vision such that when the wearer ooks straight ahead, the contact lens presents a portion of the tens that is configured for distance vision.

Patients who wear alternating vision multifocal lenses often complain that the lenses

are uncomfortable.

In cases where multifocal contact lenses are uncomfortable or provide inadequate vision, a monovision contact lens may provide a good alternative. With monovision, a subject wears one lens in one eye to correct for distance vision and another contact tens in the other eye to correct for near vision. Monovision uses the subject's dominant eye for distance vision and their non-dominant eye for near vision. The optical system then chooses the appropriate image from the appropriate eye when faced with a particular task. With monovision, depth perception will normally be compromised. However, patients usually adapt quickly and learn to use alternate visual cues when judging distances.

The above methods of using contact lenses to view multiple focal lengths are well known to those skilled in the art of contact lens design and may be used either separately or in combination with different levels of success. However, various limitations have resulted in unsatisfactory visual acuity under certain circumstances.

In view of the above limitations, there is a need for a contact lens design which provides a more acceptable performance for the combination of distance vision and near vision.

Sunmrnry of the Invention In a first aspect, the invention provides a multifocal contact lens comprising a first plurality of zones having a first focal length aixl a second plurality of zones having a second focal length; the lens further comprising an eye movement-sensitive biasing means so as to cause the lens to move on the subject's eye in response to movements thereof; and wherein movement of the lens causes a preferred one of the plurality of optical zones to be located such that the subject is provided with a desired optical correction to allow viewing at a desired focal length.

Preferably, the first focal length provides a subject with an optical correction for distance vision and a second focal length provides a subject with an optical correction for near vision. In the context of the present invention, the term distance vision means that a subject can view objects which are at a distance of 20 feet or more from the subject, and near vision means that a subject can view objects which are at a distance of 2 feet or less from the subject.

The contact lens of the present invention comprises a peripheral area, an inner generally concave surface and an outer generally convex surface.

Preferably, the zones are provided in the form of segments which extend radially from a central portion of the lens. Typically, eight zones are provided which extend radially from a central portion or point of the lens. Preferably, the zones for distance vision are provided at an angle of approximately 45° from the horizontal axis and the zones for near vision are provided at an angle of approximately 135° from the horizontal axis.

Each zone is preferably separated by a transition zone of minimal area.

Additionally, a small central optical zone may be present on the lens. In one embodiment, the central zone is substantially circular. Typically the diameter of the central zone is between 0.5mm and 5mm, more typically between 1mm and 4mm, and most typically approximately 2.5mm.

Preferably, the peripheral area of the lens is provided with a prismatic component.

This has the advantage of improving the stability of the lens whilst the lens is in situ on the eye. In one embodiment, the prismatic component extends across the entire lower end of the lens, when the lens is in the lIrst position on the eye. In another embodiment, the prismatic component extends across a portion of the lower end of the lens, when the lens is in the first position on the eye. Conveniently, the prismatic component of the thns engages with the lower eyelid of a subject. The central optical zone of the tens is typically the on'y point in the tens where no prismatic effect is provided.

Typically, when the lens is in a first position on the subject's eye a first plurality of optical zones are selected such that the subject is provided with an optical correction for distance vision. When the subject looks downwards, the tens moves on the subject's eye from a first position to a second position such that a second plurality of optical zones is selected that provide the subject with an optical correction for near vision. Thus, the subject can selectively look through an appropriate zone of the lens to select a desired focal length.

Preferably, the distance between the inner and outer surface of the lens increases differentially across the surface of the lens to improve the stability of the lens during movement on the eye.

Advantageously, the optical design of the lens is optimised for the neural interpretation of an image projected onto the retina of the optical system.

In a preferred embodiment, the contact lens of the present invention acts as a multifocal lens for correcting the vision of a presbyope.

Preferably, the contact lens of the present invention comprises a flexible transparent material, such as a soft hydrogel or silicon material.

The contact lens preferably has an overall size of between 10mm and 16mm, and more preferably between 12.5mm and 14.5mm.

According to a second aspect, there is provided a method of making a multifocal contact lens, the method comprising the steps of: forming a lens comprising a first plurality of zones having a first focal length and a second plurality of zones having a second focal length, wherein the lens is further provided with an eye movement-sensitive biasing means so as to cause the lens to move on the subject's eye in response to movements thereof.

In a preferred embodiment, the zones designed for distance vision are located on the horizontal and vertical axes of the lens, and the zones designed for near vision are located on the oblique axis of the lens.

The multifocal contact lens of the present invention may be manufactured by conventional techniques, such as machining on a lathe or molding if desired, from conventional, resinous, plastics materials, which are well known to those skilled in the art. The lens may also be sized and fitted in a conventional manner.

Description of Drawings

The invention is further described by illustrative example and with reference to the accompanying drawings, in which: Figure 1 shows a front perspective view of a contact lens in accordance with the first aspect of the invention; Figure 2 shows a front perspective view of a contact lens in accordance with the first aspect, wherein the lens is in situ on an eye in a first position such that a subject is provided with an optical correction for distance vision; and Figure 3 shows a front perspective view of a contact lens in accordance with the first aspect, wherein the lens is in situ on an eye in a second position such that a subject is provided with an optical correction for near vision.

Examples

With reference to Figure 1, a contact lens (2) is provided having eight radial zones (4, 6), each radial zone (4, 6) being separated by a transition zone (8) of minimal area. The lens (2) also comprises a small central optical zone (10). The radial zones (4, 6) are configured such that the zones designed for distance vision are located on the horizontal and vertical axes of the lens, whilst the zones designed for near vision are located on the oblique axis of the lens. The radial zones designed for distance vision are located at an angle of 45° from the horizontal axis, and the zones designed for near vision are located at an angle of 135° from the horizontal axis.

The lens (2) comprises a peripheral area which is provided with a prismatic component to improve the rotational stability of the lens whilst in situ on the eye.

Additionally, the peripheral area comprises an area of increased thickness (12) located at an oblique angle from the horizontal axis that will induce the contact lens to rotate when a person is looking downwards. Thus, the lens of the present invention allows for both distance and near vision.

With reference to Figure 2, an eye is shown having a bottom eye lid (14) and an upper eye lid (16). The position of the iris and pupil are shown by reference numerals 18 and 20, respectively. The contact lens is in situ on an eye in a first position, such that a subject is provided with an optical correction for distance vision. Whilst in this position, the prismatic component of the contact lens will rotationally position the contact lens on the eye such that the radial optical zones designed for distance vision are located along the horizontal and vertical axes. This configuration presents an image to the retina at the back of the eye which is focussed clearly along the horizontal and vertical axes for distant objects, whilst an image of near objects is presented on the retina that is out of focus along the oblique axes.

During the neural processing of the image, the privileged access to horizontal and vertical images will favour the distance image and disregard the near image.

In Figure 3, a contact tens is shown in situ on an eye in a second position such that the subject is provided with an optical correction for near vision. Whilst in this position, the area of thickening, depicted as 6 in Figure 1, interacts with the lower eye lid to cause anticlockwise movement of the lens with respect to the eye, countering the effect of the prismatic component of the contact lens. The result of this interaction is a set of reso'ved forces that modify the rotational position of the lens such that the radial optical zones designed for near vision are located along the horizontal and vertical axes. This configuration presents an image to the retina at the back of the eye that is focused clearly along the horizontal and vertical axes for near objects, whilst an image of distant objects will be presented on the retina, which image is out of focus along the oblique axes. During the neural processing of this image, the privileged access to horizontal and vertical images will favour the near image and disregard the distance inrnge.

On returning to the first position wherein the eye is looking straight ahead, the moment created by the interaction between lower eye lid and the area of thickness is removed and the forces due to the prismatic component will stabilise the lens such that the lens rotates to a position where the radial zones designed for distance vision are located along the horizontal and vertical axes.

Claims

Claims 1. A multifocal contact lens comprising a first plurality of zones having a first focal length and a second plurality of zones having a second focal length; the lens further comprising an eye movement-sensitive biasing means so as to cause the lens to move on the subject's eye in response to movements thereof; and wherein movement of the lens causes a preferred one of the plurality of optical zones to be located such that the subject is provided with a desired optical correction to allow viewing at a desired focal length.
2. A contact lens according to claim 1, wherein the first focal length provides a subject with an optical correction for distance vision and a second focal length provides a subject with an optical correction for near vision.
3. A contact lens according to claim 1 or 2, wherein the zones are provided in the form of segments which extend radially from a central portion of the lens.
4. A contact lens according to claim 3, wherein zones for distance vision are provided at an angle or about 45° to the horizontal axis, and zones for near vision are provided at an angle of about 135" to the horizontal axis.
5. A contact lens according to any one of the preceding claims, comprising a central optical zone that is substantially circular and with a diameter in the range 1-4mm.
6. A contact lens according to any one of the preceding claims, comprising a peripheral area provided with a prismatic component.
7. A contact lens according to any one of the preceding claims, formed from a flexible transparent material, such as a soft hydrogel or silicon material.
8. A contact lens substantially as hereinbefore defined and with reference to the accompanying drawings.
9. A method of making a multifocal contact lens, the method comprising the steps of: forming a lens comprising a first plurality of zones having a first local length and a second plurality of zones having a second focal length, wherein the lens is further provided with an eye movement-sensitive biasing means to as to cause the lens to move on the subject's eye in response to movements thereof
10. A method according to claim 9, wherein the zones designed for distance vision are located on the horizontal and vertical axes of the lens, and the zones designed for near vision are located on the oblique axis of the lens.
11. A method according to claim 9 or 10, performance of which results in manufacture of a contact lens in accordance with any one of claims 2-8.