WO2025257548A1

WO2025257548A1 - Method of determining an angle of repose of a contact lens

Info

Publication number: WO2025257548A1
Application number: PCT/GB2025/051283
Authority: WO
Inventors: Arthur Bradley; Nancy J. KEIR; Percy Lazon De La Jara
Original assignee: CooperVision International Ltd
Current assignee: CooperVision International Ltd
Priority date: 2024-06-12
Filing date: 2025-06-11
Publication date: 2025-12-18
Anticipated expiration: 2026-12-12
Also published as: GB202509226D0; GB2700764A

Abstract

A method of determining an angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising, at a computing device: obtaining data indicative of a refractive error of the user's eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user's eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user's eye.

Description

METHOD OF DETERMINING AN ANGLE OF REPOSE OF A CONTACT LENS

Technical Field

The present invention concerns techniques for determining an angle of repose of a contact lens on a user’s eye. More particularly, but not exclusively, this invention concerns a computing device configured to determine an angle of repose of a contact lens on a user’s eye.

Background

Astigmatism is a form of refractive error that arises when an eye has a refractive power that is not rotationally symmetric (i.e. when the refractive power at a first angle differs from the refractive power at a second angle). In such cases, the eye provides a refractive power in a first meridian that differs from that provided in a second meridian, and thus can be said to be meridionally asymmetric. Correcting for astigmatism therefore requires a lens (for example, a contact lens) that is also rotationally asymmetric. Furthermore, such a lens must, in use (i.e. when on a user’s eye), be correctly aligned with respect to the asymmetry of the eye if it is to provide the appropriate refractive correction. Incorrect alignment of the lens with respect to the eye results in the lens providing an incorrect refractive correction, and thereby providing reduced quality of vision to the user of the lens. In the case of a toric contact lens, the lens can be defined by a spherical power, a cylindrical power, and an axis. The spherical power defines a refractive power provided by the lens in all meridians surrounding an optical axis of the lens (i.e. in all planes containing the optical axis). The cylindrical power defines a further refractive power (which may be positive or negative) provided by the lens in one direction (i.e. in one plane containing the optical axis, with zero additional refractive power provided in the orthogonal plane containing the optical axis). Thus, the cylindrical power defines either a most or a least (depending on the choice of convention for defining a contact lens) myopic meridian of the lens. The axis defines the angle of the cylindrical power with respect to the intended orientation of the lens on the user’s eye.

Contact lenses which are meridionally asymmetric (for example, toric contact lenses) are designed with features (for example, ballast) which act to impose a particular orientation of the contact lens on the eye when in use. Once such a contact lens has been placed on the user’s eye, those features act to attempt to rotate the contact lens to settle at an intended angle of repose on the user’s eye. However, in many cases, features of the user’s eye (for example, its shape) result in the contact lens settling at an angle of repose which differs from the intended angle. In such circumstances, an eye-care practitioner can measure the angle of repose at which the contact lens has settled and attempt to select an alternative lens to correct for any unexpected rotation of the lens. For example, in the case of a toric contact lens, if the lens has rotated by plus 20° away from the intended orientation of the lens, the eye-care practitioner may select a toric lens having an axis that differs by minus 20°, so as to deliver the cylindrical power at the desired orientation.

However, measuring the angle of rotation of a contact lens once placed on a user’s eye (as is necessary to determine the angle of repose) requires specialist equipment (for example, a slit lamp or biomicroscope) to observe to position of an index mark on the contact lens. Such specialist equipment is expensive and requires specialised training and therefore is often unavailable to eyecare practitioners.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of determining an angle of repose of a contact lens on a user’s eye.

Summary

According to a first aspect of the present invention there is provided a method of determining an angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising, at a computing device: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

According to a second aspect of the invention there is also provided a computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method of determining an angle of repose of a contact lens on the eye of a user of the contact lens, the method comprising: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

According to a third aspect of the invention there is also provided an apparatus for determining an angle of repose of a contact lens on an eye of a user of the contact lens, the apparatus comprising: a data retrieval module configured to: obtain data indicative of a refractive error of the user’s eye; and receive input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and a processing module configured to calculate, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a schematic view of a device according to a first embodiment of the invention; and

Figure 2 shows a flow chart illustrating the steps of a method according to a second embodiment of the invention.

Detailed Description

The first aspect of the present invention provides a method of determining an angle of repose of a contact lens on a user’s eye. The method is performed at a computing device. Data indicative of a refractive error of the user’s eye is obtained. Input indicative of a residual refractive error arising when the user is wearing the trial toric contact lens is received. The angle of repose of the trial toric contact lens on the user’s eye is calculated, on the basis of the indicated refractive error of the user’s eye and the residual refractive error.

As discussed above, an eye-care practitioner typically provides a contact lens user with a trial toric contact lens intended to at least partly correct for the refractive error in the user’s eye. Any refractive error still present when the user is wearing the trial toric contact lens (i.e. refractive error arising from the combination of the user’s eye and the trial toric contact lens) can be referred to as residual refractive error. Rotation of a toric contact lens on the user’s eye can be one source of residual refractive error. Based on the sphero-cylindrical refractive error of the user’s eye, which can be measured using conventional techniques (for example, by performing an over-refraction or using an autorefractor) and a measurement of the residual refractive error, it is possible, using the techniques of the present invention, to calculate the angular misalignment of the trial toric contact lens. It will be appreciated by the skilled person that the angle of repose of the contact lens results from the combination of the intended orientation of the trial toric contact lens and the angular misalignment. Thus, the method enables an eye-care practitioner to determine the angle of repose of a contact lens on a user’s eye without the need for specialised equipment, such as a slit lamp or biomicroscope.

It may be that the method is performed without the use of a slit-lamp.

It may be that the method is computer implemented (for example, performed on the computing device).

It will be appreciated that the method is performed in respect of a single one of the user’s eyes. A user’s eyes are very rarely identical, and therefore it is common for each eye to have a different refractive error and/or to give rise to different angles of repose. Thus, it may be that the method is performed twice for a given user (i.e. once in respect of each eye).

It may be that the trial contact lens comprises a multifocal toric contact lens.

The obtaining of the data indicative of the refractive error of the user’s eye may comprise receiving (for example, at the computing device) data indicating a spherical power, a cylindrical power, and an axis of the refractive error of the user’s eye. It may be that the obtaining comprises receiving input (for example, on an input device of the computing device) indicative of the refractive error of the user’s eye. It may be that the obtaining comprises retrieving the data from a remote computing resource.

It may be that the residual refractive error is at least in part due to rotation of the trial toric contact lens on the user’s eye. It may be that the trial toric contact lens has been selected to fully correct for the refractive error of the user’s eye. Thus, it may be that the residual refractive error is entirely due to rotation of the trial toric contact lens on the user’s eye. It may be that the trial toric contact lens has been selected purely to enable calculation of the angle of repose of the contact lens, and thus does not fully correct for the refractive error of the user’s eye. Thus, it may be that the residual refractive error is only partly due to rotation of the trial toric contact lens on the user’s eye.

Where a trial toric contact lens which does not fully correct for the refractive error of the user’s eye has been selected, it will be appreciated that the residual refractive error will include a component that is attributable to the mismatch between the selected trial toric contact lens and the refractive error of the user’s eye. It may be that the method comprises obtaining data indicative of the trial toric contact lens. It may be that the method comprises determining (for example, on the basis of the data indicative of the selected trial toric contact lens and the data indicative of the refractive error of the user’s eye) the mismatch between the selected trial toric contact lens and the refractive error of the user’s eye. It may be that the calculating of the angle of repose is performed further on the basis of the mismatch. That is to say, it may be that the calculating of the angle of repose is performed further on the basis of a known expected component of the residual refractive error (for example, that arises due to use of a trial toric contact lens that does not fully correct for the refractive error of the user’s eye).

It may be that the method further comprises determining the residual refractive error. It will be appreciated that such determining is performed by an eye-care practitioner, rather than by the computing device. The determining of the residual refractive error may comprise placing the trial toric contact lens on the user’s eye and allowing the trial toric contact lens to settle at an angle of repose on the eye. The determining may comprise performing (for example, by an eye-care practitioner), whilst the trial toric contact lens is on the user’s eye (for example, after allowing the trial toric contact lens to settle at the angle of repose), an over-refraction (for example, a spherocylindrical over-refraction). It will be appreciated that performing an over-refraction comprises providing one or more additional lenses to the user whilst they are wearing the trial toric contact lens to evaluate, and establishing (for example, based on feedback from the user) whether the one or more additional lenses provide any visual improvement compared to the trial toric contact lens alone. The determining may comprise using an auto-refractor (for example, after allowing the trial toric contact lens to settle at the angle of repose).

The calculating of the angle of repose may comprise performing a vector subtraction of the residual refractive error from the refractive error of the user’s eye. The calculating of the angle of repose may comprise converting one or both of the refractive error of the user’s eye and the residual refractive error (for example, from negative cylinder or positive-cylinder notation) to vector notation (alternatively known as Fourier notation). It may be that the subtracting is performed after the conversion to vector notation. It may be that the refractive error of the user’s eye is (for example, prior to the converting) defined in terms of a spherical power, a cylindrical power, and an axis. Similarly, it may be that the residual refractive error is (for example, prior to the converting) defined in terms of a spherical power, a cylindrical power, and an axis. It will be appreciated by the skilled person that the measured axis of the residual refractive error does not itself directly indicate the angle of repose of the contact lens. Rather, the residual refractive error, despite having been caused at least in part (and sometimes only) by an angular misalignment of the trial toric contact lens manifests itself as a combination of a spherical power and a cylindrical power having an axis. However, the measured axis of the residual refractive error does not denote the axis of the rotated contact lens.

Converting the refractive error of the user’s eye and the residual refractive error to vector notation can simplify the maths required to calculate the angle of repose. In particular, in vector notation, all components of the optical powers of the trial toric contact lens and the optical power of the residual refractive error are defined in dioptres. Thus, the optical power of the trial toric contact lens can be readily subtracted from the optical power of the residual refractive error to determine a difference value (for example, arising from the rotation of the trial toric contact lens on the user’s eye).

It may be that the method comprises causing the calculated angle of repose to be displayed on a display. It may be that the method comprises displaying the calculated angle of repose on a display of the computing device. It may be that the causing comprises transmitting the calculated angle of repose to a further computing device (for example, for display on a display of the further computing device).

It may be that the method comprises obtaining an initial measurement of the refractive error of the user’s eye. It may be that obtaining the initial measurement comprises measuring the refractive error of the user’s eye (for example, by performing an over-refraction or using an autorefractor). It may be that obtaining the initial measurement of the refractive error of the user’s eye comprises obtaining a spectacle prescription for the user. It may be that the method further comprises calculating (for example, at the computing device) a contact lens back vertex power to correct for the untreated refractive error. It will be appreciated by the skilled person that the back vertex power refers to the effective lens power as measured from the back surface of the lens (i.e. the surface of the lens that, in use, is closest to a user’s eye). It may be that the method comprises receiving, at the computing device (for example from a remote computing resource), data indicative of the refractive error of the user’s eye (for example, in the form of an existing spectacle prescription for the user).

It may be that the method further comprises retrieving (for example, at the computing device) a list of candidate trial toric contact lenses available, at the user’s location, for use in correcting the user’s vision. It may be that the retrieved list includes only candidate trial toric contact lenses that are in stock at the user’s location. It may be that the list of candidate trial toric contact lenses is retrieved from a remote computing resource (for example, via the internet). Alternatively, it may be that the list of candidate trial toric contact lenses is retrieved from a memory on the computing device. It may be that the method comprises filtering (for example, at the computing device) the retrieved list on the basis of the calculated back vertex power. The filtering may comprise identifying a subset of candidate trial toric contact lenses from the list. In such cases, it may be that each candidate trial contact lens in the identified subset has a back vertex power that differs from the calculated back vertex power by an amount less than a predetermined threshold. It may be that one or more (for example, all) of the candidate trial toric contact lenses comprise multifocal toric contact lenses.

It may be that the method further comprises displaying (for example, at the computing device) the retrieved list on a display (for example, a display of the computing device). In embodiments in which the method comprises filtering the retrieved list, it may be that the displaying is of the filtered list. It may be that the displaying comprises causing a further computing device to display the retrieved list (or the filtered list). Thus, the displaying may comprise transmitting the retrieved list (or the filtered list) to the further computing device.

It may be that the method further comprises obtaining data indicative of the trial toric contact lens. The obtaining of the data indicative of the trial toric contact lens may comprise receiving (for example, at the computing device) input indicating a specific trial toric contact lens. For example, the input may indicate a part or model number of the trial toric contact lens. The obtaining may comprise receiving (for example, at the computing device) input indicating one or more (for example, all) of a spherical power, a cylindrical power, and an axis of the trial toric contact lens. The obtaining of the data indicative of the trial toric contact lens may comprise receiving (for example, at the computing device) input indicating a selection of one of the listed candidate trial toric contact lenses.

It may be that the method further comprises determining (for example, at the computing device), on the basis of the trial toric contact lens and the calculated angle of repose, whether use of an alternative toric contact lens to the trial toric contact lens is recommended to correct the user’s vision. It may be that the determining is performed on the basis of a magnitude of the cylindrical power of the trial toric contact lens and a magnitude of a difference between the calculated angle of repose and an intended orientation on the user’s eye of the trial toric contact lens. It may be that the method further comprises receiving input indicative of a visual acuity of the user when wearing the trial toric contact lens. It may be that the determining is performed on the basis of the indicated visual acuity. It will be appreciated by the skilled person that, for any given misalignment, a greater magnitude of the cylindrical power will have a more detrimental effect on the user’s vision. Thus, a greater degree of angular misalignment of a toric contact lens is more likely to be acceptable to the user when the toric contact lens has a relatively weak cylindrical power than when it has a relatively strong cylindrical power. The recommendation may comprise an indication that a different contact lens would better correct the user’s vision. The recommendation may comprise an indication that no change in contact lens is needed. It may be that the method further comprises displaying (for example, at the computing device) the recommendation on a display (for example, a display of the computing device).

It may be that the method further comprises retrieving (for example, at the computing device) a list of alternative contact lenses. In such cases, it may be that retrieving the list of alternative contact lenses comprises retrieving the list from a remote computing resource. It may be that the method comprises identifying (for example, at the computing device) an alternative contact lens from the list for use in correcting the user’s vision. It may be that the identifying of the alternative contact lens is performed on the basis of the trial toric contact lens and the calculated angle of repose. It may be that the identifying of the alternative contact lens is performed on the basis of the trial toric contact lens and the calculated angle of repose. It may be that the alternative contact lens comprises a multifocal toric contact lens. It may be that the method further comprises receiving input indicating that the user requires a multifocal contact lens. In such cases, it may be that the method comprises, in response to receipt of the indication that a multifocal contact lens is required, filtering the list of alternative contact lenses to remove alternative contact lenses in the list which are not multifocal contact lenses.

It may be that the method further comprises offering (for example, at the computing device) the identified alternative contact lens for sale to the user. It may be that the method further comprises providing the identified alternative contact lens to the user for use in correcting the user’s vision. It may be that the providing is not performed by the computing device. For example, the providing may be performed by an eye-care practitioner or an operator of the computing device.

The second aspect of the invention provides a computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method of determining the angle of repose of a contact lens on a user’s eye. Data indicative of a refractive error of the user’s eye is obtained. Input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens is received. An angle of repose of the trial toric contact lens on the user’s eye is calculated, on the basis of the refractive error of the user’s eye and the residual refractive error.

The third aspect of the invention provides an apparatus for determining the angle of repose of a contact lens on a user’s eye. A data retrieval module is configured to obtain data indicative of a refractive error of the user’s eye. The data retrieval module is configured to receive input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens. A processing module is configured to calculate, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Figure 1 shows a schematic view of a computing device 100 according to a first embodiment of the invention. The computing device 100 is operable to determine the angle of repose of a toric contact lens on the eye of a contact lens user. The angle of repose of a toric contact lens will be understood by the skilled person to refer to the angle of rotation on the user’s eye at which a toric contact lens settles during prolonged use (for example, longer than five minutes) of the contact lens. The term “user” refers in this context to a user of contact lenses, not to an operator of the computing device 100.

The computing device 100 comprises a data retrieval module 101. The data retrieval module 101 is configured to operate with a user input device 103 to enable an operator of the computing device 100 to input data. The user input device 103 is configured to receive input from the operator and generate corresponding input data 105. In this example embodiment, the data retrieval module 101 is further configured to operate with a transceiver 107 to enable data to be received from and transmitted to one or more further computing devices. In this example embodiment, the transceiver 107 is configured to operate with an antenna 109 to enable a wireless communication link between the computing device 100 and the one or more further computing devices. It will be appreciated by the skilled person that, in other embodiments, it may be that the computing device 100 does not include an antenna and that the transceiver 107 instead operates over a wired communication link. The transceiver 107 is configured to receive and generate transceiver data 111 corresponding to data received or to be transmitted over the communication link. The data retrieval module 101 is further configured to communicate data (for example, received via the user input device 103 or the transceiver 107 and antenna 109) to a processing module 113.

The processing module 113 is configured to operate with a memory 115. The memory 115 is operable to store and facilitate retrieval of data. The memory 115 also stores a set of instructions to be executed by the processing module 113 (for example, to cause the processing module 113 to perform its described functions). The processing module 113 is further configured to operate a display 117 of the computing device 100. Thus, the processing module 113 is configured to generate display data 119 for the display 117.

In use, the data retrieval module 101 is configured to receive, via the user input device 103, input indicative of a refractive error of a contact lens user’s eye. In this example embodiment, the data retrieval module 101 is configured to obtain the data by receiving input via user input device 103 indicating a spherical power, a cylindrical power, and an axis of the refractive error of the user’s eye. In this example embodiment, the input comprises direct input of numerical indications of the spherical power, the cylindrical power, and the axis. The refractive error of the user’s eye may, for example, have been determined by an eye-care practitioner having performed an overrefraction on the user’s eye or by use of an autorefractor. Whilst in this example embodiment, the data retrieval module 101 is configured to receive the indication of the untreated refractive error by input to the user input device 103, it will be appreciated by the skilled person that, in other embodiments, the indication of the untreated refractive error may alternatively be received via the transceiver 107 (for example, from a remote computing device). The data retrieval module 101 is further configured to retrieve from a remote computing resource (for example, via transceiver 107 and antenna 109) a list of candidate trial toric contact lenses available and in stock at the user’s location. It will be appreciated by the skilled person that, in other embodiments, the indication of the untreated refractive error may alternatively be stored in and retrieved from a memory on the computing device (for example, the memory 115).

The processing module 113 is configured to receive the indication of the untreated refractive error and calculate a contact lens back vertex power to correct for the untreated refractive error. The processing module 113 is further configured to receive the list of available candidate trial toric contact lenses and filter the list on the basis of the calculated back vertex power. The filtering is performed by identifying a subset of candidate trial toric contact lenses from the list having a back vertex power that differs from the calculated back vertex power by less than a predetermined threshold. Thus, the filtering produces a reduced selection of candidate trial toric contact lenses suitable for use in correcting the user’s vision. The processing module 113 is further configured to operate the display 117 to display the filtered list of candidate contact lenses.

The data retrieval module 101 is further configured to receive, via the user input device 103, input indicative of a residual refractive error arising when the user is wearing the trial toric contact lens. The residual refractive error is at least in part due to rotation of the trial toric contact lens on the user’s eye. It may be that the residual refractive error has been determined by: placing the trial toric contact lens on the user’s eye; allowing the trial toric contact lens to settle at an angle of repose on the eye; and performing, whilst the trial toric contact lens is on the user’s eye, an over-refraction. In other cases, the residual refractive error may be determined by use of an autorefractor instead of by performing an over-refraction.

The processing module 113 is further configured to calculate, on the basis of the refractive error of the user’s eye and the residual refractive error, the angle of repose of the trial toric contact lens on the user’s eye. The residual refractive error arises at least in part due to rotation of the trial toric contact lens on the user’s eye. Based on the refractive error of the user’s eye and the residual refractive error, it is possible to calculate the angle of rotation of the trial toric contact lens that has given rise to the residual refractive error.

The optical power of the trial toric contact and the optical power of the residual refractive error are each normally expressed using either a negative-cylinder or a positive-cylinder notation. Thus (for both negative-cylinder and positive-cylinder notation), the optical power of the trial toric contact is expressed as a spherical power, a cylindrical power, and axis (i.e. of the cylindrical power). Similarly, the optical power of the residual refractive error is also expressed as a spherical power, a cylindrical power, and an axis (i.e. of the cylindrical power). These notations are used by eye-care practitioners to define contact lens optical powers because they are readily understandable and easy to work with. However, whilst the spherical power and cylindrical power are both defined in units of dioptres, the axis is defined in units of degrees. It is not therefore possible, using negative-cylinder or positive-cylinder notation, to readily add or subtract optical powers from one another.

Thus, the processing module 113 is further configured to convert the refractive error of the user’s eye and the residual refractive error (for example, from a negative-cylinder or a positivecylinder notation) to vector notation. The use of vector notation to define sphero-cylindrical refractive error is described in “Power Vectors: An Application of Fourier Analysis to the Description and Statistical Analysis of Refractive Error”; LARRY N. THIBOS, PhD, FAAO, WILLIAM WHEELER, PhD, and DOUGLAS HORNER, OD, PhD, FAAO; OPTOMETRY AND VISION SCIENCE; VOL. 74, NO. 6, PP. 367-375 (incorporated in its entirety by reference herein). The conversion from negative-cylinder notation is performed using the following formulae:

C

Jo = - y cos(2cr)

C

J 45 = - y sin(2a)

Where:

M = sphere Jo = horizontal / vertical astigmatism

/₄₅ = oblique astigmatism

S' = spherical power

C = cylindrical power a = axis.

It will be appreciated that conversion of sphero-cylindrical refractive powers between negative-cylinder and positive-cylinder notations (for example, to enable use of the formulae above) is known in the art.

The processing module 113 is further configured to subtract, in vector notation, the residual refractive error from the refractive error of the user’s eye to determine an effective optical power of the rotated lens on the user’s eye. The processing module 113 is further configured to convert the determined effective optical power from vector notation to negative cylinder notation. It is then possible to calculate a corrected contact lens optical power (i.e. one which accounts for the determined angle of repose). Whilst in this example embodiment the determined effective optical power is converted from vector notation to negative-cylinder notation, in alternative embodiments it may be that the determined effective optical power is converted to positive-cylinder notation. The conversion from vector notation to negative-cylinder notation is performed using the following formulae:

The following example illustrates the operation of the method of the present invention in determining the angle of repose of a contact lens on the eye of an example contact lens user.

The eye of the example user has a refractive error (in negative-cylinder notation) of SPH: -1.00, CYL: -1.00, AXIS: 180. In vector notation (converted using the formulae above), this is M: -1.50, Jo: 0.50, J45: 0.00. When the example user is wearing a trial toric contact lens, the lens rotates -10° to give a residual refractive error (in negative-cylinder notation) of SPH: 0.17, CYL: -0.35, AXIS: 40. In vector notation (again converted using the formulae above), this is M: 0.00, Jo: 0.03, J45: 0.17.

The residual refractive error is subtracted from the refractive error of the example user’s eye to give an effective optical power of the rotated lens on the example user’s eye (in vector notation) of M: -1.50, Jo: 0.47, J45: -0.17. In negative cylinder notation (converted using the formulae above), this is SPH: -1.00, CYL: -1.00, AXIS: 170.

The angle of repose of the contact lens on the example user’s eye is thereby calculated to be -10°. Thus, to correct for the rotation of the lens on the example user’s eye a corrected lens power of SPH: -1.00, CYL: -1.00, AXIS: +10 should be used.

The processing module 113 is further configured to generate display data 119 to cause the display 117 to display the corrected lens power. It will be appreciated that, determining a corrected lens power is, in effect, also determining the angle of repose of the contact lens. In particular, the angle of repose is apparent from the difference between axis of the corrected lens power and the axis of the refractive error of the user’s eye. In alternative embodiments, it may be that the processing module 113 is further configured to generate display data 119 to cause the display 117 to display the calculated angle of repose.

The processing module 113 is further configured to determine, on the basis of the trial toric contact lens and the calculated angle of repose, whether use of an alternative toric contact lens to the trial toric contact lens is recommended to correct the user’s vision. The determining is performed on the basis of a magnitude of the cylindrical power of the trial toric contact lens and a magnitude of a difference between the calculated angle of repose and an intended orientation on the user’s eye of the trial toric contact lens. It will be appreciated by the skilled person that the strength of the cylindrical power determines how detrimental to the user’s vision a given misalignment is. A greater degree of angular misalignment of a toric contact lens is more likely to be acceptable to the user when the toric contact lens has a relatively weak cylindrical power than when it has a relatively strong cylindrical power. The processing module 113 is configured to determine, on the basis of the cylindrical power of the trial toric contact lens, a threshold for the angle of repose, above which a change in contact lens is recommended. For example, it may be that for a cylindrical power of up to -0.75 dioptres an angular misalignment of up to 20 degrees is acceptable, for a cylindrical power of up to -1.24 dioptres an angular misalignment of up to 10 degrees is acceptable, and for a cylindrical power of up to -1.75 dioptres an angular misalignment of up to 5 degrees is acceptable. Thus, the recommendation may comprise an indication that no change in contact lens is needed.

The data retrieval module 101 is further configured to retrieve a list of alternative contact lenses. In this example embodiment, the list of alternative contact lenses is retrieved from a remote computing resource (for example, via transceiver 107 and antenna 109). However, it will be appreciated that, in other embodiments, the list of alternative contact lenses may be retrieved from memory 115. In some embodiments, it may be that the previously retrieved list of candidate trial toric contact lenses also acts as the list of alternative contact lenses. The processing module 113 is further configured to identify, on the basis of the trial toric contact lens and the calculated angle of repose, an alternative contact lens from the list for use in correcting the user’s vision.

The processing module 113 is further configured to generate display data 119 to cause the display 117 to display the recommendation. The displayed recommendation comprises an indication as to whether a change in contact lens is recommended. Where a change in contact lens is recommended, the displayed recommendation comprises an indication of the identified alternative contact lens.

The processing module 113 is further configured to generate display data 119 to cause the display 117 to offer the identified alternative contact lens for sale to the user. In this example embodiment, the processing module 113 is configured to generate display data 119 causing the display 117 to present the user with the identified alternative contact lens and an associated price. The user input device 103 is also operable to provide input of a decision by the user to purchase the identified contact lens.

Figure 2 shows a flow chart illustrating the steps of a method 200 of determining an angle of repose of a contact lens on a user’s eye according to a second embodiment of the invention. It may be that one or more of the following steps of the method 200 is performed at a computing device.

A first step, represented by item 201, of the method 200 comprises obtaining data (for example, at the computing device) indicative of a refractive error of the user’s eye. It may be that the obtained data indicates one or more parameters of the refractive error. The one or more parameters may comprise one or more (for example, all) of a spherical power, a cylindrical power, and an axis of the refractive error. It may be that the obtaining data indicative of the refractive error comprises receiving input (for example, at the computing device) of the refractive error. It may be that the method comprises obtaining an initial measurement of the refractive error of the user’s eye. It may be that obtaining the initial measurement comprises measuring the refractive error of the user’s eye (for example, by performing an over-refraction or using an autorefractor). It may be that obtaining the initial measurement of the refractive error of the user’s eye comprises obtaining a spectacle prescription for the user.

An optional second step, represented by item 203, of the method 200 comprises calculating (for example, at the computing device) a contact lens back vertex power to correct for the refractive error of the user’s eye.

An optional third step, represented by item 205, of the method 200 comprises retrieving (for example, at the computing device) a list of candidate trial toric contact lenses available, at the user’s location, for use in correcting the user’s vision. In such cases, it may be that the method 200 comprises displaying the retrieved list on a display of the computing device.

An optional fourth step, represented by item 207, of the method 200 comprises filtering (for example, at the computing device) the retrieved list on the basis of the calculated back vertex power. In embodiments where the method comprises displaying the retrieved list, it may be that the displaying is of the filtered list. It may be that the filtering comprises identifying a subset of candidate trial toric contact lenses from the list. In such cases, it may be that each candidate trial contact lens in the identified subset has a back vertex power that differs from the calculated back vertex power by less than a predetermined threshold.

An optional fifth step, represented by item 209, of the method 200 comprises obtaining (for example, at the computing device) data indicative of a trial toric contact lens provided to the user. It may be that the method 200 comprises selecting the trial contact lens. The selecting of the trial contact lens may be performed on the basis of the displayed list. In embodiments, in which a list (or filtered list) of available candidate trial toric contact lenses is obtained and displayed, it may be that the obtaining of data indicative of the trial toric contact lens comprises receiving input indicating a selection of one of the listed candidate trial toric contact lenses. It may be that obtaining the data indicative of the trial toric contact lens comprises receiving input indicating a specific trial toric contact lens. It may be that obtaining the data indicative of the trial toric contact lens comprises receiving input indicating one or more parameters of the trial toric contact lens. In such cases, the one or more parameters may comprise one or more (for example, all) of a spherical power, a cylindrical power, and an axis of the trial toric contact lens.

A sixth step, represented by item 211, of the method 200 comprises receiving (for example, at the computing device) input indicative of a residual refractive error arising when the user is wearing the trial contact lens. It may be that the residual refractive error is at least in part due to rotation of the trial toric contact lens on the user’s eye. It may be that the method 200 comprises determining the residual refractive error. It may be the determining the residual refractive error comprises placing the trial toric contact lens on the user’s eye and allowing the trial toric contact lens to settle at an angle of repose on the user’s eye. It may be that determining the residual refractive error comprises performing, whilst the trial toric contact lens is on the user’s eye (for example, after the contact lens has been allowed to settle at the angle of repose), an over-refraction.

A seventh step, represented by item 213, of the method 200 comprises calculating (for example, at the computing device), on the basis of the refractive error of the user’s eye and the residual refractive error, the angle of repose of the trial toric contact lens on the user’s eye. It may be that the method 200 comprises displaying the calculated angle of repose on a display of the computing device. It may be that calculating the angle of repose comprises converting one or both of the refractive error of the user’s eye and the residual refractive error (for example, from negative cylinder or positive-cylinder notation) to vector notation. It may be that calculating the angle of repose comprises subtracting the residual refractive error from the refractive error of the user’s eye.

An optional eighth step, represented by item 215, of the method 200 comprises determining (for example, at the computing device), on the basis of the trial toric contact lens and the calculated angle of repose, whether use of an alternative toric contact lens to the trial toric contact lens is recommended to correct the user’s vision. In such cases, it may be that the method 200 comprises displaying the recommendation on a display of the computing device. It may be that the determining is performed on the basis of a magnitude of the cylindrical power of the trial toric contact lens and a magnitude of a difference between the calculated angle of repose and an intended orientation on the user’s eye of the trial toric contact lens.

An optional ninth step, represented by item 217, of the method 200 comprises retrieving (for example, at the computing device) a list of alternative contact lenses and identifying, on the basis of the trial toric contact lens and the calculated angle of repose, an alternative contact lens from the list for use in correcting the user’s vision.

An optional tenth step, represented by item 219, of the method 200 comprises providing the identified alternative contact lens to the user for use in correcting the user’s vision. It may be that the providing comprises offering (for example, at the computing device) the identified alternative contact lens for sale to the user.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In some cases, the trial toric contact lens may be selected to fully correct for the refractive error of the user’s eye. In such cases, the residual refractive error is attributable to rotation of the trial toric contact lens on the user’s eye. However, in other cases, the trial toric contact lens is selected purely to enable calculation of the angle of repose of the contact lens and does not fully correct for the refractive error of the user’s eye. Thus, in such cases, the residual refractive error is only partly due to rotation of the trial toric contact lens on the user’s eye.

Whilst, in the embodiments described above, the computing device operates to calculate a contact lens back vertex power to correct for the refractive error of the user’s eye, it will be appreciated by the skilled person that, in other embodiments, the computing device does not perform such functions. In such cases, it may be that the necessary contact lens back vertex power is calculated by the eye-care practitioner using conventional methods. Similarly, in other embodiments, the computing device does not retrieve, filter, and display a list of suitable candidate trial toric contact lenses. In such cases, the computing device may obtain data indicative of the trial toric contact lens provided to the user by input (for example, on the user input device) of a contact lens model or part number or by input of parameters (for example, a spherical power, cylindrical power, and axis) of the trial toric contact lens.

Whilst, in the embodiments described above, the computing device operates to determine whether use of an alternative toric contact lens to the trial toric contact lens is recommended and identify a suitable alternative contact lens, it will be appreciated by the skilled person that such features are optional and that, in other embodiments, the computing device does not perform such functions. Whilst the computing device has been illustrated and described as being a single device, it will be appreciated by the skilled person that its described functions may, in other embodiments, be performed collectively by a plurality of computing devices (for example, with the described functionality divided between devices in the plurality).

Whilst the embodiments describe above operate to explicitly determine an angle of repose of a contact lens on a user’s eye, it will be appreciated by the skilled person that other embodiments may determine a corrected contact lens optical power. However, the skilled person will further appreciate that such a corrected contact lens optical power necessarily involves a determination of the angle of repose of the contact lens on the user’s eye.

It will be appreciated that, in the embodiments above, input to the computing device is provided by an operator of the computing device. It will further be appreciated that the operator of the computing will generally not be the user of the contact lens.

It will be appreciated that the data retrieval module 101, the user input device 103, the transceiver 107, the processing module 113, and the display 117 may each comprise one or more processors and/or memory. Thus, in embodiments, the computing device 100 comprises a processor and an associated memory. The processor and associated memory may be configured to perform one or more of the above-described functions of the computing device 100. Each device, module, component, machine or function as described in relation to any of the examples described herein (for example, data retrieval module 101, the user input device 103, the transceiver 107, the processing module 113, and the display 117) may similarly comprise a processor or may be comprised in apparatus comprising a processor. One or more aspects of the embodiments described herein comprise processes performed by apparatus. In some examples, the apparatus comprises one or more processors configured to carry out these processes. In this regard, embodiments may be implemented at least in part by computer software stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Embodiments also include computer programs, particularly computer programs on or in a carrier, adapted for putting the above-described embodiments into practice. The program may be in the form of non-transitory source code, object code, or in any other non-transitory form suitable for use in the implementation of processes according to embodiments. The carrier may be any entity or device capable of carrying the program, such as a RAM, a ROM, or an optical memory device, etc. The one or more processors of the computing device 100 may comprise a central processing unit (CPU). The one or more processors may comprise a graphics processing unit (GPU). The one or more processors may comprise one or more of a field programmable gate array (FPGA), a programmable logic device (PLD), or a complex programmable logic device (CPLD). The one or more processors may comprise an application specific integrated circuit (ASIC). It will be appreciated by the skilled person that many other types of device, in addition to the examples provided, may be used to provide the one or more processors. The one or more processors may comprise multiple co-located processors or multiple disparately located processors. Operations performed by the one or more processors may be carried out by one or more of hardware, firmware, and software.

The one or more processors may comprise data storage. The data storage may comprise one or both of volatile and non-volatile memory. The data storage may comprise one or more of random access memory (RAM), read-only memory (ROM), a magnetic or optical disk and disk drive, or a solid-state drive (SSD). It will be appreciated by the skilled person that many other types of memory, in addition to the examples provided, may also be used. It will be appreciated by a person skilled in the art that the one or more processors may each comprise more, fewer and/or different components from those described.

The techniques described herein may be implemented in software or hardware, or may be implemented using a combination of software and hardware. They may include configuring an apparatus to carry out and/or support any or all of techniques described herein. Although at least some aspects of the examples described herein with reference to the drawings comprise computer processes performed in processing systems or processors, examples described herein also extend to computer programs, for example computer programs on or in a carrier, adapted for putting the examples into practice. The carrier may be any entity or device capable of carrying the program. The carrier may comprise a computer readable storage media. Examples of tangible computer- readable storage media include, but are not limited to, an optical medium (e.g., CD-ROM, DVD- ROM or Blu-ray), flash memory card, floppy or hard disk or any other medium capable of storing computer-readable instructions such as firmware or microcode in at least one ROM or RAM or Programmable ROM (PROM) chips.

Thus, embodiments of the present disclosure also provide a computer program comprising a set of instructions, which, when executed by one or more computing devices (for example, data retrieval module 101 and processing module 113), cause the computing devices to perform out a method of determining the angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

Embodiments of the present disclosure also provide a method of determining an angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

It may be that the method comprises determining the residual refractive error. Determining the residual refractive error may comprise: placing the trial toric contact lens on the user’s eye; allowing the trial toric contact lens to settle at an angle of repose on the eye; and performing, whilst the trial toric contact lens is on the user’s eye, an over-refraction.

The method may further comprise providing the identified alternative contact lens to the user (for example, for use in correcting the user’s vision).

It may be that the method is performed without the use of a slit-lamp.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A method of determining an angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising, at a computing device: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

2. The method of claim 1, wherein the method further comprises calculating, on the basis of the obtained data indicative of the refractive error of the user’s eye, a contact lens back vertex power to correct for the refractive error.

3. The method of claim 1, wherein the method further comprises: retrieving a list of candidate trial toric contact lenses available, at the user’s location, for use in correcting the user’s vision; and displaying the retrieved list on a display of the computing device.

4. The method of claim 3, wherein: the method further comprises: calculating, on the basis of the obtained data indicative of the refractive error of the user’s eye, a contact lens back vertex power to correct for the refractive error, and filtering the retrieved list on the basis of the calculated back vertex power; and the displaying is of the filtered list.

5. The method of claim 4, wherein the filtering comprises identifying a subset of candidate trial toric contact lenses from the list, each candidate trial contact lens in the identified subset having a back vertex power that differs from the calculated back vertex power by less than a predetermined threshold.

6. The method of claim 3, wherein the obtaining of data indicative of the trial toric contact lens comprises receiving input indicating a selection of one of the listed candidate trial toric contact lenses.

7. The method of claim 1 , wherein: the trial toric contact lens has been selected to correct the refractive error of the user’s eye; and obtaining the data indicative of the refractive error of the user’s eye comprises receiving input indicating the trial toric contact lens.

8. The method of claim 1, wherein obtaining the data indicative of the refractive error of the user’s eye comprises receiving input indicating one or more of a spherical power, a cylindrical power, and an axis.

9. The method of claim 1, wherein the residual refractive error is at least in part due to rotation of the trial toric contact lens on the user’s eye.

10. The method of claim 1, wherein the calculating comprises subtracting the residual refractive error from the indicated refractive error of the user’s eye.

11. The method of claim 1 , wherein calculating the angle of repose comprises converting one or both of the refractive error of the user’s eye and the residual refractive error to vector notation.

12. The method of claim 11, wherein the calculating comprises subtracting the vector notation residual refractive error from the vector notation refractive error of the user’s eye.

13. The method of claim 1, wherein the method further comprises: determining, on the basis of the trial toric contact lens and the calculated angle of repose, whether use of an alternative toric contact lens to the trial toric contact lens is recommended to correct the user’s vision; and displaying the recommendation on a display of the computing device.

14. The method of claim 13, wherein the determining is performed on the basis of a magnitude of a cylindrical power of the trial toric contact lens and a magnitude of a difference between the calculated angle of repose and an intended orientation on the user’s eye of the trial toric contact lens.

15. The method of claim 13, wherein the method further comprises: retrieving a list of alternative contact lenses; and identifying, on the basis of the refractive error of the user’s eye and the calculated angle of repose, an alternative contact lens from the list for use in correcting the user’s vision.

16. The method of claim 15, wherein the method further comprises offering the identified alternative contact lens for sale to the user.

17. The method of claim 15, further comprising providing the identified alternative contact lens to the user for use in correcting the user’s vision.

18. The method of claim 1, wherein the residual refractive error has been determined by: placing the trial toric contact lens on the user’s eye; allowing the trial toric contact lens to settle at an angle of repose on the eye; and performing, whilst the trial toric contact lens is on the user’s eye, an over-refraction.

19. A non-transitory computer readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out a method of determining the angle of repose of a contact lens on an eye of a user of the contact lens, the method comprising: obtaining data indicative of a refractive error of the user’s eye; receiving input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and calculating, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

20. A computing device for determining the angle of repose of a contact lens on an eye of a user of the contact lens, the apparatus comprising: a data retrieval module configured to: obtain data indicative of a refractive error of the user’s eye; and receive input indicative of a residual refractive error arising when the user is wearing a trial toric contact lens; and a processing module configured to calculate, on the basis of the refractive error of the user’s eye and the residual refractive error, an angle of repose of the trial toric contact lens on the user’s eye.

21. The method of claim 1, wherein said obtaining data indicative of the refractive error of the user’s eye comprises measuring the refractive error of the user’s eye to obtain a measured refractive error, and inputting said measured refractive error to the computing device.

22. The method of claim 1 or claim 21, wherein said receiving input indicative of the residual refractive error of the user comprises measuring the residual refractive error of the user’s eye to obtain a measured residual refractive error, and inputting said measured residual refractive error to the computing device.

23. The method of claim 21 or claim 22, wherein the measuring of the refractive error and/or the residual refractive error is with the use of a phoropter, auto-refractor, or optometer.

24. The method of claim 21 or claim 22, wherein the measuring of the refractive error and/or the residual refractive error is by an eye-care practitioner.

25. The method of any one of claim 21-24, wherein a device that measures said measured refractive error and/or measured residual refractive error is in electronic communication with the computing device so that the measured refractive error and/or measured residual refractive error is automatically communicated to the computing device so that said calculating occurs.

26. The method of claim 22, wherein said measuring the residual refractive error of the user’s eye comprises placing a trial toric contact lens on the user’s eye and allowing the trial toric contact lens to settle at an angle of repose on the eye.

27. The method of claim 26, wherein the method of said measuring further comprises performing an over-refraction.

28. The method of claim 26, wherein the angle of repose is determined using an autorefractor.