Patent Description:
Myopia (short-sightedness) is a disorder of the eye in which distant objects cannot be clearly focused, but near objects can be. Images of distant objects are brought to focus in front of the retina, that is, the focusing power of the eye is too strong 'at distance'. The condition may be corrected by the use of a negatively powered lens, which causes the distant images to focus on or nearer the fovea. Myopia can be a serious and progressive condition that leads to increasing visual impairment despite the use of corrective lenses. It is becoming increasingly common, with some countries in South-East Asia reporting that <NUM>% of children aged <NUM> years suffer from the condition.

Hyperopia (long-sightedness) is a disorder where distant objects can be focused, but near objects cannot be focused. Hyperopia may be corrected by the use of positive power lenses.

It is generally agreed that the process of normal eye development - emmetropization - is regulated by a feedback mechanism, which regulates the length of the eye to maintain good focus both at distance and at near - or emmetropia. While it is also generally agreed that this feedback mechanism is somehow disturbed in eyes with refractive error, so that the eye grows too long in myopia and not long enough in hyperopia, there has not been consensus about the nature of the feedback mechanism or how the progression of myopia and hyperopia can be controlled. Both biochemical and optical (focal defect) mechanisms have been suggested.

While it is generally assumed that the feedback stimulus is somehow related to focal defects of the eye, the matter cannot be simple because, in progressive myopia, the condition may become worse - i.e., the eye continues to lengthen excessively - even though lenses that correct for distance vision are worn.

It has been proposed that an optical feedback mechanism is somehow upset by deficiencies in the accommodative effort of the eye due to excessive near work. The deficiency is considered to manifest as lag of accommodation (imprecise and insufficient accommodation) in some myopic eyes at near, resulting in defocus, which stimulates further undesirable axial elongation of the eye.

Bifocal lenses and PALs (progressive addition lenses) in spectacles have been proposed as a possible way to relieve the accommodative stress and defocus in the hope that the stimulus for elongation would be removed. <CIT>) describes prescribing commercially available bifocal contact lenses for myopic eyes that also exhibit near point esophoria to control the progression of myopia. Both concentric distance center and near center contact lenses were employed in myopic eyes with near point esofixation disparity. The zones of the concentric distance and near zones lie within the pupil.

In <CIT>) it is proposed that emmetropization is regulated by the degree and direction of a spherical aberration present at the fovea. It is proposed that young myopes have higher levels of negative spherical aberration that promotes inappropriate eye growth and that the use of ophthalmic lenses to impart positive spherical aberration will counteract axial growth and thus the progression of myopia.

In international patent publication number <CIT>) it is proposed that defocus at the fovea for both distance and near vision inhibits the feedback stimulus for excessive eye growth. This publication proposes the use of a bifocal contact lens that simultaneously provides the central retina with (a) clear vision for both distance and near and (b) myopic defocus for both distance and near. Again, the visual image will be degraded if this proposal is used.

<CIT>) describes the results of animal trials demonstrating that it is the optical state of the peripheral retina, not the fovea, that dominates the feedback stimulus for emmetropization. Thus, Smith et al proposes that controlling off-axis focal points of the eye relative to the central on-axis focal points through manipulation of the curvature of field of the visual image provides a method of abating, retarding or controlling the progression of myopia and hypermetropia (impaired near vision caused by insufficient eye length).

<FIG> show how Smith et al describe an eye <NUM> that has a positive curvature of field. Since the central on-axis image point <NUM> is located in front of (i.e. opposite to the direction of light) the retina <NUM>, this eye is considered myopic when measured using standard techniques such as auto-refractors, refractor-heads or trial frames, in the manner that eye-care practitioners are familiar. In this representative eye, the off-axis peripheral image points <NUM> for large field angles are located behind (i.e. in the direction of light) the retina <NUM>. Thus the eye <NUM> of this example is relatively hypermetropic for the peripheral visual field. <FIG> shows a relative field curvature graph for the eye <NUM>, which shows that the central to mid-peripheral field <NUM> is myopic (focus in front of retina <NUM>) but the mid-peripheral to far-peripheral field <NUM> is hypermetropic (focus behind retina <NUM>).

<FIG> show how the eye <NUM> of <FIG> is prescribed an optical device <NUM> for the control of the progression of myopia, as described by Smith et al. This optical device <NUM> is designed so that it would generate a negative relative curvature of field <NUM> on the eye <NUM>. The central, on-axis image <NUM> is focused sharply to the fovea <NUM> enabling good visual acuity. The optical device <NUM> introduces sufficient negative relative curvature of field <NUM> to focus the peripheral image points <NUM> more anteriorly, or in front (i.e. in the direction against the direction of light in the eye) of the retina <NUM>.

<CIT>) describes providing one or more vision priority zones in which peripheral defocus or another aberration is corrected, with the lens also controlling the relative curvature of field for the peripheral retina in another region outside of the vision priority zone(s).

There remains a need for methods and optical devices that address the suggested optical (focal defect) mechanisms of progression of refractive error, particularly in relation to the progression of myopia.

<NPL>) discloses an investigation of peripheral optical quality and how it is affected by accommodation. The refraction and aberrations of the right eyes of five emmetropes and five myopes were measured. It is reported that the emmetropes had a higher relative peripheral myopia than the myopes, and that the difference was asymmetric over the visual field and that increased with accommodation.

<NPL>) discloses an investigation of the influence of accommodation on peripheral refraction and curvature of field of the eye.

<CIT> discloses methods and apparatuses for improving peripheral vision by positioning the peripheral image points at a pre-determined position relative to the retina.

<CIT> discloses kits of anti-myopia contact or spectacle lenses, along with methods for their use.

The present invention relates to the utilization of the finding that refraction in central and peripheral areas of the retina of human eyes, or at least the eyes of a substantial or significant number of people, is such that the natural curvature of field of the visual image is asymmetric around the visual axis of the eye. In more detail, the invention relates to the control of off-axis focal points of the eye relative to the on-axis focal points in an asymmetric manner through the use of an optical device that controls refraction of light for the eye.

The present invention provides a method of designing and manufacturing a contact lens or spectacle lens, according to claim <NUM>. Certain more specific aspects of the invention are set out in the dependent claims.

<FIG> shows a plot of the refractive state for <NUM> eyes of children with myopia at the peripheral retina in the horizontal meridian, with measurements for the both the nasal and temporal quadrants taken. The horizontal (independent) axis indicates the peripheral angles at which measurements were taken. Measurements at the nasal retina represent the temporal visual field and measurements at the temporal retina represent the nasal visual field. The vertical (dependent) axis is the amount of defocus of the light rays at the retina, in diopters (D), relative to the amount of defocus along the visual axis of the eye. Accordingly, positive values indicate relative hyperopic defocus and negative values relative myopic defocus. Measurements of defocus were taken on axis and at <NUM>, <NUM> and <NUM> degrees from the optical axis, both temporally and nasally. The eyes had a spherical equivalent refractive error of -<NUM> ± <NUM> D on axis. All measurements were taken using an open field Shin Nippon autorefractor utilizing head-turn for off-axis measurements so the eyes were in the primary position for all measurement angles. The plot was completed by simple straight line interpolation between the measured points.

<FIG> shows that at <NUM> degrees, the nasal retina is experiencing <NUM> D of hyperopic defocus relative to central retina. In contrast, the temporal retina is experiencing only <NUM>. 14D of hyperopic defocus relative to the central retina. At <NUM> degrees, the amount of hyperopic defocus experienced by the nasal retina increases to <NUM>. 92D relative to central retina and the temporal retina experiences <NUM>. At <NUM> degrees, the hyperopic defocus experienced by the nasal retina increases to <NUM>. 64D compared to central retina. At the temporal retina, there is a significant increase in the hyperopic defocus and increases to <NUM>. 47D relative to central retina.

<FIG> shows that whilst there may be relative hyperopic defocus experienced at both the nasal and temporal retina relative to the central retina, the amount of defocus experienced at each point measured varies and is asymmetric around the central on axis image point. <FIG> also shows the standard deviation of the measured relative defocus at each measurement angle for the same set. For some eyes in the sample set, the asymmetry was such that there was relative myopic defocus on one side of the peripheral retina and relative hyperopic defocus on the other side.

The measurement of the eye, as represented by the plot in <FIG> differs substantially from the representation described in <CIT>), which assumes the curvature of field of this eye is rotationally symmetric relative to the central on-axis image point. Thus, the manipulation of the curvature of the field in a symmetric fashion, as taught in <CIT>), is unlikely to eliminate the defocus in all quadrants of an eye having characteristics shown in <FIG> and may be under-correcting or over-correcting for either the hyperopic or myopic defocus present in at least some locations of the peripheral retina.

Accordingly, the present disclosure involves modifying the wavefront of light received by an eye by creating an ocular system including the eye that takes into account asymmetry in the curvature of field of the eye to be treated. In other words, if the relative curvature of field was controlled in a symmetrical manner, then the peripheral image would remain asymmetrical, however if the asymmetry of the eye is taken into account, this asymmetry can be reduced or eliminated. This allows placement of the image substantially on the retina on both the nasal and temporal sides of the fovea. Alternatively, this allows the substantially symmetrical profile shown in <FIG> to be achieved for a myopic eye, despite asymmetry in the refractive characteristics of the eye for peripheral images.

<FIG> show examples of the general structure of four different contact lenses <NUM>, <NUM>, <NUM>, <NUM>, for controlling the relative position of peripheral images of an eye with asymmetric relative curvature of field in the horizontal direction. The contact lenses are obtainable by the method of the invention. Each lens is for a left eye and generally has a different refractive power in a region on the nasal side to that on the temporal side. A design for the right eye may be mirror image in structure, but the power profile in each optic zone will be selected dependent on the characteristics of the right eye. Each lens has an optic zone <NUM>, <NUM>, <NUM>, <NUM>, which may be between approximately <NUM> to <NUM> mms in diameter, depending on the particular implementation. Outside the optic zone <NUM>, <NUM>, <NUM>, <NUM> is a carrier portion <NUM>, <NUM>, <NUM>, <NUM>, which provides stability for the lens when applied to the eye. The carrier portion may for example extend for another <NUM> to <NUM>, so that the total lens diameter up to the lens edge <NUM>, <NUM>, <NUM>, <NUM> may be about <NUM>. Other lenses may have differing dimensions, and particular dimension lenses may in some cases be selected according to the eye to which the lens is to be applied, for example to reflect differences in size of the pupil <NUM>. In <FIG> the outer periphery of the carrier zone is represented in dashed lines.

The lenses are each oriented on the eye with the utilization of a suitable lens stabilization technique. The requirement to stabilize the orientation of the lens arises since the power of the contact lens varies across the surface and is effected to ensure application of power to selected regions of the central and the peripheral regions of the retina. The lenses may be stabilized on eye with a lens stabilizing mechanism selected from a prism ballast, double slab-off and truncation.

For the representative eye plotted in <FIG>, between the field angles of <NUM> to <NUM> degrees, the temporal peripheral retina is experiencing <NUM> to <NUM>. 4D of relative hyperopic defocus and the nasal peripheral retina is experiencing <NUM> to <NUM>. 64D of relative hyperopic defocus. The following description of the lens structures shown in <FIG> assumes that the power profile of the optic zones in the contact lens is designed with this defocus in mind.

In the example shown in <FIG>, the lens <NUM> has a disc-shaped central optic zone <NUM>. The central optic zone <NUM> has a diameter selected from the range of from about <NUM> up to about <NUM> mms. The central optic zone <NUM> is located and provided with a power to correct for the central refractive error of the eye (measured at the fovea). With this selection of power, the central optic zone <NUM> allows for clear vision at all distances (assuming that the eye can accommodate to provide in focus near vision). The power profile of the lens varies between the nasal optic zone <NUM> and temporal optic zone <NUM> on either side of the central optic zone <NUM>. The power in these zones is selected to correct for the defocus measured in the temporal and nasal quadrants of the peripheral respectively.

The nasal and temporal optic zones <NUM>, <NUM> carry a plurality of powers, selected with regard to the defocus measured at two or more locations of the peripheral retina. For example, the power of the nasal optic zone may be set taking account of the relative defocus experienced by the temporal peripheral retina at <NUM>, <NUM> and <NUM> degrees and include a smooth transition between the powers required at these angles. If measurements are taken for an eye at more angles or at only two angles, then the power may be set in the nasal and temporal optic zones <NUM>, <NUM> having regard to those measurements. The variation may reflect the measured curvature of field of the eye to which the lens is to be applied. For example, a lens may be selected with a power profile across the nasal optic zone <NUM> that has the objective of a substantially constant distance (which may be zero) between the focal point and the retina. Similarly variations in power occur across the temporal optic zone.

In the example shown in <FIG>, the lens <NUM> has a central optic zone <NUM> extending along the vertical meridian of the lens <NUM>. The central optic zone <NUM> has a constant power from the centre to the periphery of the optic zone in both directions. The width of the meridian is in the range from about <NUM> to about <NUM> mms. The power profile of the lens <NUM> varies between the nasal optic zone <NUM> and temporal optic zone <NUM> on either side of the central zone <NUM> and will correct for the defocus measured for the peripheral retina on the temporal and nasal sides respectively, as described for the example shown in <FIG>.

In the example shown in <FIG>, the lens <NUM> has a central optic zone <NUM> between approximately <NUM> to <NUM> in diameter with a refractive power selected to correct for the central refractive error of the eye. In the horizontal meridian, the power profile of the lens <NUM> varies between the nasal and temporal optic zones <NUM>, <NUM> on either side of the central optic zone <NUM>, as described for the example shown in <FIG>. The nasal and temporal optic zones <NUM>, <NUM> have a height of approximately <NUM> to <NUM>, which may be selected to match the diameter of the central optic zone <NUM>, although in other embodiments the height of these zones may be more or less than the diameter of the central optic zone <NUM>. The nasal and temporal optic zones <NUM>, <NUM> both extend from the central optic zone <NUM> to the edge of the optic zone <NUM> of the lens <NUM>. The central optic zone <NUM> is extended into the regions <NUM>, <NUM> outside of the peripheral optic zone. In other words, in this example, in the optic zone <NUM>, the lens <NUM> has a power selected to correct for the central refractive error of the eye in all regions outside of the nasal and temporal optic zones <NUM>, <NUM>.

In the example shown in <FIG>, the lens <NUM> has a central optic zone <NUM> between approximately <NUM> to <NUM> in diameter that corrects for the central refractive error. In the horizontal meridian, the power profile of the lens varies between the nasal and temporal optic zones <NUM>, <NUM> on either side of the central optic zone <NUM>. The nasal temporal zone <NUM> and temporal optic zone <NUM> correct for the defocus measured in the temporal and nasal quadrants of the peripheral retina respectively, as described above with reference to the example shown in <FIG>. Both the nasal and temporal optic zones <NUM>, <NUM> have an oblong shape of width of about <NUM> to <NUM>. These zones need not be oblong and could be other shapes, like circular or substantially rectilinear. The remainder of the lens carries the same power profile as the central optic zone.

For each of the examples shown in <FIG>, there may be a transition zone connecting the central optical zone (and any other region with the same power profile as the central optic zone) to the peripheral optic zones (consisting of the nasal and temporal optic zones). The transition zone is at the boundary of the central and nasal or temporal optic zones and can vary in width from about <NUM> to about <NUM>. The transition zone bridges the difference in power profile and in some embodiments is shaped to provide a smooth curve transition between the zones. In other embodiments, there may be a point on the lens where the central optical zone finishes and the peripheral optic zone commences.

As will be appreciated from the description herein, including but not limited to the examples shown in <FIG>, the shape and layout of the optic zones in a contact lens may be varied substantially, creating a large range of different embodiments. By way of example, the central optic zone <NUM>, <NUM>, <NUM>, <NUM> may be asymmetrical about a vertical meridian of the lens through the centre of the lens. This asymmetry may reflect a low rate of change in the curvature of field for one side of the peripheral retina. Referring to <FIG>, the rate of change between zero to twenty degrees for the temporal retina is low, and so lenses obtained by the method of the invention have a power selected to correct on-axis vision for these field angles. Each lens is characterized by different power profiles in a nasal optic zone and a temporal optic zone, selected to control the off-axis focal points of the eye relative to the central on-axis focal points in an asymmetric manner.

The lens power profile may not consider the refractive error state of the eye in the vertical direction, as differences along vertical meridians are not considered as important. However, in other embodiments, the refractive error state of the eye in the vertical direction may also be corrected, in the same way as described herein for the horizontal direction. In other words, the relative curvature of field naturally occurring in the eye in the vertical direction may also be measured and the lens may include upper and lower optic zones to control the curvature of field for the lower and upper potions of the peripheral retina respectively. Where there is asymmetry in the vertical direction, this may be accounted for in the same manner as asymmetry in the horizontal direction. Where both the horizontal and vertical directions are controlled, the peripheral image will be controlled in all quadrants of the eye.

The examples shown in <FIG> show a central optic zone <NUM>, <NUM>, <NUM>, <NUM>. In the examples, a central optic zone of diameter or width of about <NUM> to <NUM> is provided. The size of the central optic zone may be selected regarding to the pupil diameter of the recipient of the lens or having regard to the average pupil diameter of a population sample most representative of the recipient or a sample representing the general population. Generally, a larger central optic zone allows for clearer vision, particularly if the central optic zone has a constant or substantially constant power profile across the area of the pupil. However, a lens with a smaller central optic zone may be required for some recipients where control of peripheral defocus close to the fovea is needed. Some sacrifice of on axis image quality may then result.

Also, the central optic zone <NUM>, <NUM>, <NUM>, <NUM> may have a power profile selected to correct on-axis vision, with a substantially uniform power across its diameter in all directions. Having a central optic zone may be advantageous in minimizing defocus of the image received by the fovea. In other embodiments, the power profile of the central optic zone may be allowed to vary to some extent. For example, the lens may be designed to have a power profile that progressively changes from the centre point of the lens out to the nasal and temporal optic zones. The power at the centre point of the lens may be selected to correct on-axis vision, or selected to provide substantially clear vision on axis.

The contact lenses shown in <FIG> may be silicone hydrogel lenses, rigid lenses, scleral lenses or hybrid lenses. Similar lens designs may be made for spectacle lenses and corneal implants. For both these types of lenses the carrier portion is not required. A suitable structure for spectacle lenses may be that shown in <FIG>, except with a central optic zone of a width of about <NUM> to <NUM>. Some embodiments of spectacle lens may have a large transition zone between the central optic zone and the peripheral optic zone, so as to avoid visible lines on the lenses and to reduce interference with the clarity of vision of the wearer when their eyes are not directed straight ahead. Corneal implants will be shaped to create a conreal surface profile that results in the refractive characteristics described. An orthokeratology lens may similarly reshape the cornea to achieve the relative curvature of field required for the peripheral retina.

A collection of lenses may be provided from which a selection is made for individual recipients. For example, for each power in the central optic zone, there may be a selection of asymmetric peripheral optic zones. The selection may be made with reference to a population norm and the deviation for the population, for example as represented in <FIG>. Where there a significant variations in classes of recipients, different population norms may be constructed for each class. The number of selections for each power in the central optic zone may vary. One example may be a selection of: one for the average for the population four for the standard deviation either side (which takes into account that a eye with relatively more myopic defocus in comparison to the norm on one side of the peripheral retina may my more myopic or more hyperopic in comparison to the norm on the other side of the peripheral retina) and another four at <NUM> standard deviation. Additional lenses may be available for one or more of: <NUM> of the standard deviation, <NUM> of the standard deviation, <NUM> of the standard deviation and <NUM> standard deviations. It will be appreciated that some of the lenses in the collection may be symmetrical or substantially symmetrical, which may be selected for appropriate recipients. There may be selections for the power profile of the central optic zone and/or the structure (for example two of more of the structures shown in <FIG>) as well.

<FIG> shows a flow diagram of a series of steps for prescribing a lens for the correction of refractive error of an eye with the purpose of also attempting to control the change in refractive error over time. In step <NUM> a patient is identified with refractive error. This identification step may be achieved by a simple examination of the history of on-axis refractive error of a patent, for example over the past <NUM> months or <NUM> to <NUM> years, or longer. Alternatively, the identification step <NUM> may be replaced with identification of a patient that has refractive error without reference to any history of error or its progression.

In step <NUM> the on-axis refractive error is measured. This measurement is used to identify the required correction on-axis. For example, the patient may be measured as having refractive error of -<NUM> D, in which case the central optic zone of the lens, for example the central optic zone <NUM>, <NUM>, <NUM>, <NUM> shown in <FIG> is selected to have a power to correct this error.

In step <NUM> the off-axis refractive error is measured. Measurements are taken for off-axis field angles nasally and temporally. As previously described, variation in field of curvature for vertical angles may be ignored, but may be measured and included in the lens design if required. Step <NUM> comprises taking measurements at more than one angle in the nasal and temporal directions. For example two measurements may be taken at <NUM> and <NUM> degrees, three measurements taken at <NUM>, <NUM> and <NUM> degrees or six measurements taken at <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> degrees. The angle need not be a multiple of five, these angles being described for illustrative purposes only. More than one measurement may be taken at a single angle and these may be combined, for example through averaging or otherwise or may be subject to evaluation, for example with reference to the position of the eye when the measurement was taken, with the measurement expected to be the most accurate selected.

Depending on the instrument used, step <NUM> may include separate steps for measuring the refractive characteristics of an eye at each required angle relative to the optical axis of the eye. For example, this may be required if the patient has to be physically moved or asked to move their line of sight, or if the instrument needs to be physically moved relative to the patient's eye to obtain the measurements.

In step <NUM> a new lens design is formed for manufacture with the required power profile for the eye. The power profile corrects for the on-axis refractive error measured in step <NUM> in the central optic zone and has a power selected with regard to the refractive characteristics of the eye in the nasal and temporal peripheral regions.

For example, the power profile may be selected to place the image of peripherally viewed objects on the retina in both the nasal and temporal directions, or on the retina for at least those angles which have been measured in step <NUM>. Alternatively, where there are constraints on the power profile across the lens, the power profile may be selected to place the image of peripherally viewed objects as close as possible to the retina within those constraints. The constraints may include a constraint on the maximum rate of change or constraints due to requirements to correct other conditions, such as astigmatism.

Alternatively, the power profile may be selected to place the image of peripherally viewed objects at another position relative to the retina, where that is viewed as potentially providing benefit. For example, for a myopic eye, the power profile may be selected to place the image of peripheral objects in front of the retina. The objective for placement of the image of peripheral objects need not be symmetrical - for example the lens for a myopic eye may place the peripheral image on the temporal side on the retina and the peripheral image on the nasal side in front of the retina.

The refractive state of the eye, both on-axis and for peripheral objects, is measured using retinoscopy. Either manual or autorefractors may be used to take the measurements. An example of an instrument specifically designed for measuring both on axis and peripheral refraction will now be described.

<FIG> and <FIG> show an instrument <NUM> suitable for measuring peripheral refraction, determining the amount of decentration and applying a correction factor to obtain a corrected measurement of peripheral refraction. The instrument is not independently claimed. The present concepts may be implemented in software in the controller <NUM> (see <FIG>). The apparatus, together with possible variations of the instrument <NUM> and alternative apparatus that may be adapted to implement the current concepts is described in international patent publication <CIT>, published as <CIT>. The instrument <NUM> uses the general methodology of 'instrument rotation' described in relation to <FIG>. Other instruments with which the present concepts may be implemented may use the 'eye turn' or 'head turn' methodologies.

<FIG> shows the basic layout of the instrument <NUM>. An array <NUM> of deflector elements <NUM> is in this example instrument a linear row that extends symmetrically and laterally on either side of the optical axis <NUM> of the eye-related optical system <NUM> under investigation. It will be assumed that system <NUM> is the eye of a patient with or without the addition of prosthetic lenses or other modifications. An illuminating light source, controlling processor and return-beam detector are indicated by a single undifferentiated unit <NUM> arranged on axis <NUM>, which is described in more detail with reference to <FIG>. Unit <NUM> directs illuminating beams, indicated by arrow heads <NUM>, to array elements <NUM> to generate a corresponding set of interrogating beams, indicated by arrow heads <NUM>, that are directed into eye-system <NUM> at different peripheral angles relative to axis <NUM>. A return beam, indicated by arrow heads <NUM>, is generated by each interrogating beam <NUM> and is directed back to unit <NUM> via the respective element <NUM> for detection. It is convenient for illuminating beams <NUM> to be directed in sequence from one element <NUM> to the next to thereby sequentially generate the interrogating beams <NUM> and return beams <NUM>.

In this example, a central illuminating beam, a corresponding central interrogation beam and a corresponding central return beam are indicated by arrow heads <NUM>, <NUM> and <NUM>. Also in this example, each deflector element is a prism (except central element 14c) that has an apex angle such that each interrogation beam <NUM> is directed into eye <NUM> and each return beam <NUM> is directed to unit <NUM>. Central element 14c is effectively a null element that does not deflect the illuminating beam; it may be a parallel-sided plain glass as shown, but that is not even necessary. Also in this example, array <NUM> is substantially linear so that interrogating beams <NUM> and <NUM> are substantially co-planar allowing one meridian - the horizontal in this example - of system <NUM> to be investigated. Non-horizontal meridians of the system can be investigated by simply rotating the instrument <NUM> about optic axis <NUM> relative to eye <NUM>.

The transmission of interrogating beams <NUM> and <NUM> one at a time into eye <NUM>, and the generation of a corresponding sequence of return beams <NUM> and <NUM>, can be effected in a variety of ways. First (as will be described below), unit <NUM> may include a beam scanner that directs a single narrow illuminating beam from one element <NUM> to another. Second, multiple elements <NUM> can be illuminated at one time and interrogating beams <NUM> and <NUM> can be gated to effect scanning of eye <NUM> and the generation of a sequence of return beams <NUM> and <NUM>. This can be done by, for example, inserting an electronically controllable LCD shutter <NUM> between array <NUM> and eye <NUM> and using it as scanning means by which interrogating beams <NUM> from prisms <NUM> are admitted into eye <NUM> one at a time. Third, a similar shutter <NUM> may be inserted between array <NUM> and unit <NUM> to gate illuminating beams <NUM> and <NUM> to illuminate one or more elements <NUM> at a time. Thus, it is not essential for unit <NUM> to include scanning means and it is possible to distribute the scanning function between scanner means in unit <NUM> and shutters such as indicated at <NUM> and/or <NUM>.

In this way, successive interrogation/return beam pairs diverge/converge at successively larger/smaller angles with respect to axis <NUM> as they pass into and out of eye <NUM>. Sequential scanning from one angle to the next adjacent will probably be most convenient but many other scan sequences may be used to minimise biases that might arise due to fixed sequential scanning. While illumination of more than one beam deflector element <NUM> at a time can easily be achieved by use of a scanner in unit <NUM>, it is then necessary to distinguish the multiple simultaneous return beams that will result. This can be done by using shutter <NUM> or <NUM> as a beam-chopper or selective polariser to differentially encode each return beam that needs to be distinguished from another at the detector.

<FIG> is a more detailed side elevation of instrument <NUM> of <FIG> in which the principal components of unit <NUM> are shown separately. A light source <NUM> directs a collimated source beam <NUM> via a beam-splitter <NUM> to an oscillating mirror scanner <NUM> that is moved by actuator <NUM> to generate illuminating beams <NUM>. The illuminating beans <NUM> are scanned from deflector to deflector in array <NUM> to generate the sequence of interrogating beams <NUM> that are directed into the eye-system <NUM> and onto the retina <NUM> over the desired range of incident angles. Scanning mirror <NUM> thus forms a point source or common point for beams <NUM> and a common point (indicated at X) for all return beams. Thus, each return beam <NUM> returned from retina <NUM> passes back via deflector array <NUM> and scanner mirror <NUM> to beam-splitter <NUM> by which it is diverted via a focusing system <NUM> to a photo detector <NUM>. System <NUM> includes a moveable lens assembly <NUM> that can be moved axially back and forth through a focus range, as indicated by arrows <NUM>. While the source beam <NUM> (and, thus, the illuminating, interrogating and return beams <NUM>, <NUM> and <NUM>) can have any desired spot, disc or annular cross-section desired, an annular cross-section like that commonly used in known autorefractors (such the Shin-Nippon SRW-<NUM> mentioned above) is preferred as it can be analysed and processed in a substantially standard manner.

Each return beam <NUM> - or more correctly its image <NUM> at detector <NUM> - thus contains information of the (uncorrected for decentration) refractive status of the eye-system that is captured or quantified by the photo detector <NUM>, which is preferably a two-dimensional array of photo sensors. The photo detector <NUM> also captures ah image of the pupil corresponding to the image shown in <FIG> for the determination of the deceleration of the illuminating beams <NUM>. An image of the pupil is captured when each refraction measurement is made, so that there is one image for each illuminating beam <NUM>. This allows the refraction measurement to be individually corrected at each incident angle, dealing with relative movement of the eye-system <NUM> and the measurement axis between measurements.

The unit <NUM> includes a central processor and controller <NUM> that may conveniently comprise a dedicated PC and is connected to accept and analyse the output of detector <NUM> and to drive lens assembly <NUM> under servo-control. Processor <NUM> is also connected to control scanner driver <NUM> and to ensure correct timing of illumination and return signal detection. A connection between light source <NUM> and processor <NUM> is also shown as it will be convenient to ensure that source beam <NUM> is correctly configured and that a representation of the current source beam sectional pattern is stored for comparison with image <NUM>.

While each return beam <NUM> is being received, focusing lens assembly <NUM> is moved along the direction of the optical axis to vary the focus size and shape of the image <NUM>. Commonly, three positions of the focusing assembly <NUM> are recorded for each of three return beam image shapes: one position where the image (spot or ring) appears smallest and in sharpest focus, a second position where the image appears maximally elongated in one meridian and a third position where the image is maximally elongated in a different meridian, usually one that is orthogonal to the first meridian. The three positions of lens assembly <NUM> respectively indicate the spherical equivalent power of the eye, the sagittal astigmatic component and the tangential astigmatic component of the refraction. The significance of spot/ image size in relation to spherical equivalent power of eye <NUM> can be understood in the following elementary way. Since the interrogating beam <NUM> that enters eye <NUM> is collimated, a normal or emmetropic eye will return a parallel collimated beam, a myopic eye will return a convergent beam and a hyperopic eye will return a divergent beam, both of which will result in larger images sizes.

The central processor and controller <NUM> stores in memory the correction algorithm, either as a function or as a look-up table, it also includes instructions to receive and/or automatically determine the decentration and to apply the correction algorithm to the measured refraction values to calculate a corrected refraction value. The corrected refraction values may then be stored, displayed or communicated to another device.

Claim 1:
A method of designing and manufacturing a contact lens (<NUM>) or a spectacle lens for a myopic eye (<NUM>),
which method comprises designing the contact lens or spectacle lens (<NUM>) based on measurements of an on-axis refractive error, off-axis refractive errors on the nasal side, and off-axis refractive errors on the temporal side, the contact lens or spectacle lens comprising:
a central optic zone (<NUM>) with a first power profile for images received by the retina (<NUM>) on the fovea, the first power profile having a negative refractive power;
a nasal optic zone (<NUM>) with a second power profile different from the first power profile for images received by the peripheral retina on the temporal side;
a temporal optic zone (<NUM>) with a third power profile, different from the first power profile and the second power profile, for images received by the peripheral retina on the nasal side; and
wherein, in the case the method relates to a contact lens, the contact lens (<NUM>) comprises a lens stabilizing mechanism for orienting the contact lens (<NUM>) on the eye (<NUM>),
wherein the nasal optic zone (<NUM>) and the temporal optic zone (<NUM>) are arranged on either side of the central optic zone (<NUM>) to provide an asymmetric relative curvature of field in a horizontal direction;
wherein the nasal optic zone (<NUM>) and the temporal optic zone (<NUM>) each carry a plurality of powers and include a smooth transition between the powers;
wherein a boundary between the central optic zone (<NUM>) and at least one of the nasal optic zone (<NUM>) or the temporal optic zone (<NUM>) is at a horizontal peripheral angle of at least <NUM> degrees relative to the visual axis of the eye; and
wherein the method further comprises manufacturing the contact lens or spectacle lens (<NUM>).