Contact lens

Abstract

A contact lens (10) comprising an anterior surface (14), a posterior surface (16), a central zone (12) with a first radius of curvature, a first peripheral zone (10) extending radially from the central optical zone, the first peripheral zone (1) having an inner margin (1a) having a radius of curvature that is substantially identical to the first radius of curvature of the central zone (12) and an outer margin (1b), wherein the first peripheral zone (1) is spherical at the inner margin (1a) and is aspheric at the outer margin (1b) and there is a change in a sphericity across the first peripheral zone (1) from the inner margin (1a) to the outer margin (1b) and the contact lens (10) comprises at least one further peripheral zone (2,3,4,5) having a radius of curvature that is less the first radius of curvature.

Claims

1. A contact lens comprising: an anterior surface; a posterior surface; a central axis; a central optic zone with a first radius of curvature; a first peripheral zone extending radially from the central optical zone, the first peripheral zone having an inner margin having a radius of curvature that is substantially identical to the first radius of curvature of the central optic zone and an outer margin, wherein the first peripheral zone is spherical at the inner margin and is aspheric at the outer margin and there is a change in asphericity across the first peripheral zone from the inner margin to the outer margin; a second peripheral zone that is spherical and has a steeper radius of curvature than the first radius of curvature; a third peripheral zone that has a steeper radius of curvature than the first radius of curvature; and a fourth peripheral zone has a flat surface that forms a tangent to the central axis of the contact lens.

2. The contact lens of claim 1, wherein the radius of curvature is between about 4 mm to about 12 mm, suitably between about 7 mm and about 9 mm.

3. The contact lens of claim 1, wherein the central optic zone is spherical.

4. The contact lens of claim 1, wherein the central optic zone is toric.

5. The contact lens of claim 1, wherein the first radius of curvature is described as an ellipse comprising apical curvature and eccentricity.

6. The contact lens of claim 1, wherein the asphericity at the outer margin is between about −3 to about +3, suitably between about −2 to about +2, suitably between about −1 to about +1.

7. The contact lens of claim 1, wherein the asphericity across the first peripheral zone is calculated to provide the change in sagittal height across the first peripheral zone.

8. The contact lens of claim 1, wherein the second peripheral zone has a width of between about 0.1 mm and about 2.0 mm.

9. The contact lens of claim 1 comprising a fifth peripheral zone that is spherical and has a reverse profile to the third and fourth peripheral zones.

10. The contact lens of claim 1, wherein the contact lens is an orthokeratology contact lens and the anterior surface is configured for use in a refractive manner such that the contact lens can provide active refractive correction when worn with an open eye.

11. The contact lens of claim 10, wherein the at least one further peripheral zone is non rotationally symmetric.

12. The contact lens of claim 11, wherein the central optic zone and the first peripheral zone have a vertical axis and a horizontal axis, each of the at least one further peripheral zone is divided into equal quadrants, and the vertical and horizontal axes are aligned differently to the quadrants in the at least one further peripheral zone.

13. The contact lens of claim 12, wherein the posterior surface has a peripheral or mid peripheral posterior surface that has a profile that facilitates tear exchange beneath the contact lens.

14. The contact lens of claim 13, wherein the central optic zone and the first peripheral zone have a profile that when worn by a patient moulds a cornea to provide an annulus of steepening in the cornea that surrounds a central region of the cornea such that peripheral refractive error is provided with hyperopic correction without changing refraction in the central region of the cornea.

15. A system for matching a patient with a refractive error with a stock contact lens for the patient comprising; a processor; an electronic display; a database containing information of parameters of a plurality of sets of stock contact lenses, wherein each contact lens in the plurality of sets of stock contact lenses is a contact lens of claim 1; a memory that contains instructions that are readable by the processor to control the processor to: (a) receive refractive error correction information for a patient; (b) receive corneal topography information for the patient; (c) calculate a cornea model of the patient from the received corneal topography information; (d) calculate parameters for an empirical contact lens for the patient from the received refractive error correction and calculated cornea model; (e) match at least one contact lens within the plurality of sets of stock lenses to the patient based upon the received refractive error correction and calculated cornea model; and (f) display the match on the electronic display.

16. The system of claim 15, further comprising an interface through which a user can interact with the processor to make a selection of a stock lens or an empirical lens such that if an empirical lens is selected, parameters for the empirical lens are calculated instead of matching with a stock lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic plan view of one aspect of a contact lens as disclosed herein;

(2) FIG. 2 is a schematic cross section of the contact lens of FIG. 1;

(3) FIG. 3 is a schematic cross section of the contact lens of FIG. 1 view showing the angle of the fourth peripheral zone;

(4) FIG. 4 is a schematic cross section of the contact lens of FIG. 1 in comparison with a cornea model and comparing sagittal heights of the central and first peripheral zones;

(5) FIG. 5 is a schematic cross sectional view of the contact lens of FIG. 1 in comparison with a cornea model and comparing sagittal heights of the second peripheral zone;

(6) FIG. 6 is a cross section of the cornea model showing the slope at a defined chord;

(7) FIG. 7 is a schematic cross section of the contact lens of FIG. 1 imposed upon the cross section of the cornea model;

(8) FIG. 8 is a contact lens of FIG. 1 in comparison with a cornea model and comparing sagittal heights of the third peripheral zone;

(9) FIG. 9 is a cross section of the contact lens of FIG. 1 overlying the cornea model;

(10) FIG. 10 is a schematic view of a contact lens;

(11) FIG. 11 is a flow chart showing a lens fitting procedure according to one aspect of the disclosure;

(12) FIG. 12 is a flow chart showing a computer implemented procedure for assessing the progress of an orthokeratological treatment of a patient;

(13) FIG. 13 is a flow chart showing a learning algorithm process;

(14) FIG. 14 is a perspective view of a mount for a corneal topography device according to a further aspect of the disclosure;

(15) FIG. 15 is a perspective view of a second component of the corneal topography device; and

(16) FIG. 16 is perspective view of a third component of the corneal topography device.

DETAILED DESCRIPTION

(17) FIGS. 1 and 2 respectively show a schematic plan view and cross section of one aspect of a contact lens 10 as disclosed herein.

(18) The contact lens 10 includes a spherical central optic zone 12, surrounded by five peripheral zones 1, 2, 3, 4, 5. The central optic zone 12 has a diameter of between 2 mm and 5 mm and is constructed from a spherical curve.

(19) The contact lens 10 has an anterior surface 14 facing outwardly away from the cornea and a posterior surface 16.

(20) The first peripheral zone 1 has a width of between 0.5 and 2 mm and is constructed from a graduating aspheric curve with a value of zero at the junction 1a with the central zone and a defined amount of asphericity at the outer edge 1b of the zone 1.

(21) The second peripheral zone 2 and third peripheral zone 3 have individual widths of between 0.1 and 2 mm and are each constructed from a spherical curve.

(22) The fourth peripheral zone 4 has a width of between 0.1 and 2 mm and is constructed from a straight line segment.

(23) The final peripheral zone 5 has a width of between 0.1 and 2 mm and is constructed from a spherical curve that has the opposite profile to the second 2 and third peripheral 3 zones.

(24) The outside diameter D of the lens 10 is defined as the outer edge of the final peripheral zone 5, and has a diameter of between 9 to 12 mm.

(25) The central zone 12 is formed from a spherical section with the principal axis aligned with the center, also known as the apex, of the central zone, and a radius of curvature between 4 and 12 mm.

(26) When designing the lens for a given eye the radius of curvature is calculated to differ from the corneal radius of curvature by the amount of refractive change required. Radius of curvature can be converted from mm to equivalent refractive power using a refractive index of 1.3375, which is the widely agreed average value of refractive index for the human cornea. Adopting the same refractive index for the lens surface allows easy calculation of the radius of curvature for the central zone 12, with the required radius of curvature for the central zone 12 in diopters being equal to the radius of curvature of the cornea in diopters+the refractive change required.

(27) For example for a cornea of radius 7.6 mm and targeted refractive change of −3D the radius of the cornea in diopters is (1-1.3375)/7.6=45 D. The required radius of curvature of the central zone 12 in diopters is 45 D+−3D=42 D. The required radius of curvature of the central zone in mm is (1.1.3375)/42 D=8.04 mm.

(28) From the previous example it can be seen that to correct myopia the radius of curvature for the central zone 12 has a larger radius of curvature than the radius of curvature of the cornea, indicating that the curvature for the central zone 12 is flatter than that of the cornea.

(29) The radius of curvature for the first peripheral zone 1 is identical to the radius of curvature for the central zone 12. The curve forming the first peripheral zone 1 is spherical at the inner edge 1a of the zone adjacent to the central zone 12 and aspheric at the outer edge 1b of the zone adjacent to the second peripheral zone 2.

(30) Across the width w from the inner 1a to outer 1b margins of the first peripheral zone 1, the asphericity of curvature increases from zero, being spherical, to a calculated value of asphericity at the outer margin.

(31) Asphericity is a term given to define the rate of flattening of an elliptical surface. An asphericity value of 0 is equivalent to a spherical surface; a negative value of asphericity indicates a flattening, also known as prolate, elliptical surface and a positive value of asphericity indicates a steepening, also known as oblate, elliptical surface.

(32) In the present disclosure the asphericity of the curve at the outer margin 1b of the zone 1, in a preferred aspect asphericity can be defined as negative through positive by a value of asphericity between −3 and +3. If the asphericity is zero at the outer margin 1b the curvature across the whole zone is spherical. The change from zero asphericity at the inner margin 1a of the zone 1 to the required amount of asphericity at the outer margin is calculated using a cubic function where the asphericity value at any point is defined as:
Required outer edge asphericity*root of(difference between the inner margin position and measurement point)

(33) For example, if the central zone 12 has a radius of curvature of 8 mm, the radius of curvature of the first peripheral zone 1 will also be 8 mm. The asphericity at the inner margin 1a of the first peripheral zone will be zero and in this example the asphericity at the outer margin 1b of the first peripheral zone is required to be −0.6, indicating a prolate flattening elliptical surface.

(34) In this example the width of the first peripheral zone 1 is 1 mm. Table 1 indicates the change in asphericity across the first peripheral zone as a function of distance from the inner margin 1a for this example.

(35) TABLE-US-00001 TABLE 1 Distance from Radius of inner margin (mm) curvature (mm) Asphericity 0 8 0 0.1 8 −0.006 0.2 8 −0.024 0.3 8 −0.054 0.4 8 −0.096 0.5 8 −0.15 0.6 8 −0.216 0.7 8 −0.294 0.8 8 −0.384 0.9 8 −0.486 1 8 −0.6

(36) In this manner the first peripheral zone 1 by virtue of being spherical at the inner margin 1a and of the same radius of curvature as the inner zone 12 maintains tangent continuity to create a smooth transition from the inner zone 12 into the first peripheral zone 1.

(37) This satisfies an important requirement of providing a smooth surface for the area of the lens 10 that is in compressive contact with the cornea.

(38) Previous proposals in the art have described the use of multiple defined zones to form the central and first peripheral zones. Multiple zones can be formed in such a way in a stepwise manner as to allow tangential continuity between zones, but by virtue of being discrete bands they will always have the same radius and asphericity at the start and end of each band.

(39) The presently disclosed lenses instead offer a gradual change in asphericity across the entire width of the zone in a non-stepwise manner and provides for a much greater degree of fine control than is offered by the conventional step-wise lenses.

(40) The second peripheral zone 2 and third peripheral zone 3 are both formed from spherical sections with their center of curvature positioned along the central axis of the lens and each having radii of curvature of between 3 and 15 mm. The purpose of these zones is to realign the lens with the corneal surface. To achieve this the second peripheral zone 2 and third peripheral zone 3 will each have a steeper radius of curvature than the central zone 12 and first peripheral zone 1.

(41) The fourth peripheral zone 4 is constructed to form a flat surface which in section will be shown as a straight line. This is shown in FIG. 3. in which the line extends so as to form an angle 9 is with a tangent 8 to the central axis of the lens 7. Angle 9 is given the term ‘Landing Angle’ and is calculated to bring the contact lens surface into tangent continuity of the underlying cornea at a defined location along the fourth peripheral zone 4.

(42) The fifth peripheral zone 5 is formed from a spherical section that has the reverse profile to the other spherical zones 2 and 3 of the lens design in that the center of curvature for the surface is anterior to the surface. This causes the most peripheral aspect of the surface to move away from the corneal surface to create what is known in the art as edge lift. The edge lift is analogous to the front of a ski which in the case of a contact lens prevents the edge of the lens digging into the eye and promotes flow of tears below the lens. The fifth peripheral zone 5 has a radius of curvature of between 4 and 15 mm with the radius center positioned to create tangent continuity at the junction with the fourth peripheral zone 4.

(43) The contact lenses 10 as disclosed herein can be calculated on an empirical basis to fit a given cornea or manufactured into range of stock lenses designed to fit the majority of normal eyes.

(44) In its empirical format the lens specifications are calculated in response to measurements of corneal shape taken by the lens fitter. Computer processed mathematical algorithms are used to build a mathematical model of the cornea depending on the information that is supplied by the lens fitter.

(45) The simplest corneal measurement that can be supplied by the lens manufacturer is the equivalent spherical shape defined by a radius of curvature, which is measured using an instrument called a Keratometer. For this reason, this value is called a keratometry measurement. Modern day computerized corneal topography instruments provide more detailed information on corneal shape which can be used to create an elliptical model of the cornea. Whether a spherical model of the cornea is created from keratometry measurements, or an elliptical model is created from computerized corneal topography measurements the lens design process is the same.

(46) The corneal measurements that form the basis of the calculations below are (1) the radius of curvature, (2) the sagittal height and (3) the mathematical slope of the cornea at a chord which coincides with the location of fourth peripheral zone 4. 1. The radius of curvature of the central zone 12 is calculated according to the principles described earlier, where the radius of curvature is flatter than the central corneal radius by the amount of refractive change being targeted. 2. The diameter 12d of the central zone 12 is set according to the lens fitters requirements. For correcting refractive error, the diameter is suitably set with a default value of 4 mm. For myopia control, the central zone may be set at a diameter less than 4 mm, suitably about 3 mm. 3. The radius curvature of the first peripheral zone 1 is given the same value as the central zone 12. 4. The width w1 of the first peripheral zone 1 is set according to the lens fitters requirements. Typically, the width of the first peripheral zone 1 is calculated to be the difference between half of the central zone diameter 12d and 3 mm. In this manner for a 4 mm central zone diameter the default width of the first peripheral zone is 3 mm−(4 mm/2)=3 mm−2 mm=1 mm. 5. FIG. 4 shows the model 20 of the cornea to be fitted. The sagittal height 23 of the cornea model 20 being fitted is calculated across the chord 24 defined by the outer margins 1b of the first peripheral zone 1. 6. The required change in height 1h across the first peripheral zone 1 is calculated by subtracting the sagittal height 12h of the central zone 12 from the sagittal height 23 of the cornea 20 being fit and then adding the lens clearance at the outer edge 1b of the first peripheral zone that is required—the default value being 55 um. 7. The asphericity value for the first peripheral zone 1 is calculated to provide the exact change in height across the first peripheral zone 1 established in Step 6 of the process. 8. As shown in FIG. 5 the sagittal height 26 across the band of the cornea model 20 being fitted that is coincident with the second peripheral zone 2 is calculated from the corneal model 20. The sagittal height 2h of the second peripheral zone 2 needs to be the same as the corneal sagittal height 26. This is achieved by calculating the radius of curvature that provides the measured sagittal height 26. 9. As shown in FIG. 6 the mathematical slope 27 of the cornea model 20 at a defined chord 28 is calculated. The slope of the fourth peripheral zone 4 is given the same value as the cornea slope 27. 10. FIG. 7 shows how the slope 27 measured in Step 9 of this method is mathematically calculated back to the start of the fourth peripheral zone 4 to calculate the difference in height 29 compared to the cornea model 20. 11. FIG. 8 shows how the radius of curvature of the third peripheral zone 3 is calculated by first determining the sagittal height 34 of the lens 10 at the start 3a of the third peripheral zone 3, which is easily calculated as the combined sagittal height of the already calculated central zone 12, first 1 and second 2 peripheral zones. The sagittal height change 3h required across the third peripheral zone 3 is the sagittal height of the cornea model 20 at the chord 32 coincident with the outer end 3b of the third peripheral zone 3, less sagittal height 34 of the lens at the start 3a of the third peripheral zone 3, plus the difference in height 29 to the corneal model 20 calculated in Step 10 of this method. Once the sagittal height change 3h required across the third peripheral zone 3 is known, the radius required to provide this measurement is a simple mathematical process. 12. At this stage the parameters of the central zone 12, first peripheral zone 1, second peripheral zone 2, third peripheral zone 3 and fourth peripheral zone 4 have all been calculated. Joined together these form the bulk of the lens 10 which, as shown in FIG. 9, will now rest exactly on the cornea model 20 to align with the cornea model at the apex 36 and align with the cornea model 20 within the fourth peripheral zone 4. 13. The radius of the fifth and final peripheral zone 5 is defined according to the clearance between the edge 38 of the lens 10 and the corneal model 20 that is required. A smaller radius creates greater edge lift and increasing the radius reduces edge lift.

(47) The construction of the stock lens parameters is handled in a similar way. Corneal topography data was sampled from 900 subjects to establish an average corneal topography profile distribution to extrapolate to the population at large. These data were segregated into 30 subgroups by their sagittal heights with a sagittal difference of 9 μm between subgroups.

(48) Individual corneal data within each subgroup were analyzed to measure the apical curvature and mathematical slope at a chord of 9.35 mm. These apical curvature and slope data were then averaged within each subgroup.

(49) The lens calculation process previously described was applied to each subgroup using the highest sagittal height value, subgroup average apical curvature, subgroup average corneal slope at 9.35 mm chord value and a targeted refractive error correction of −3.00 diopters. The central zone was formed over a diameter of 4 mm, the first peripheral zone width was 1 mm, the second peripheral zone width was 0.5 mm, the third peripheral zone was 0.9 mm.

(50) To allow easy lens fitting without need for look up tables or further computer calculations each stock lens parameter is given an identification value equal to the central zone radius in diopters less the refractive power being targeted. For example the lens with central zone radius in diopters of 36.50 less −3.00 targeted change has a lens identifier value of 39.50. This makes the lens identifier close in value to the keratometry value of the cornea model that it was used to create the lens, making it possible to fit the lens by keratometry value alone.

(51) The full range of these lenses is shown in Table 2.

(52) TABLE-US-00002 TABLE 2 Central zone Central zone Sagittal Lens radius in dioptres radius in mm height identifier 36.50 9.247 1.38301 39.5 36.75 9.184 1.39042 39.75 37.00 9.122 1.39668 40 37.25 9.06 1.40559 40.25 37.50 9 1.41499 40.5 37.75 8.94 1.42444 40.75 38.00 8.882 1.43337 41 38.25 8.824 1.44408 41.25 38.50 8.766 1.45437 41.5 38.75 8.71 1.46440 41.75 39.00 8.654 1.47361 42 39.25 8.599 1.48214 42.25 39.50 8.544 1.49048 42.5 39.75 8.491 1.49920 42.75 40.00 8.438 1.50857 43 40.25 8.385 1.51875 43.25 40.50 8.333 1.52820 43.5 40.75 8.282 1.53954 43.75 41.00 8.232 1.54999 44 41.25 8.182 1.56030 44.25 41.50 8.133 1.57244 44.5 41.75 8.084 1.58335 44.75 42.00 8.036 1.59260 45 42.25 7.988 1.60257 45.25 42.50 7.941 1.61493 45.5 42.75 7.895 1.62667 45.75 43.00 7.849 1.63805 46 43.25 7.803 1.64869 46.25 43.50 7.759 1.65708 46.5 43.75 7.714 1.66636 46.75

(53) To allow correction of different refractive errors for a range of −1.00 D to −4.50 D each lens in the range shown in Table 2 was expanded as follows. All peripheral zones except the first peripheral zone were not changed. The sagittal height at the outer end point of first peripheral zone was calculated and recorded to aid later calculations. The radius of the front central zone when measured in diopters was altered by the difference between the required targeted refractive and −3.00 D. For example, to create the −3.50 D target lens for the lens identified by lens identifier 45.00 D which has a central zone radius of 42.00 D, the new central zone radius will be −3.50 D less −3.00 D equals −0.50 D, which is then added to 42.00 D to give a new central zone radius of 41.50 D.

(54) The sagittal height of the new central zone is then calculated and subtracted from the previously recorded sagittal height at the outer end point of first peripheral zone to establish the sagittal height change required across the first peripheral zone. Finally, the curvature of the asphericity is changed to match the new central zone radius and the asphericity of the first peripheral zone is calculated to provide the required change in sagittal height across the first peripheral zone. This process is repeated to cover steps of refractive target in −0.50 D from −1.00 D to −4.50 D. In this manner the stock range includes 240 lenses encompassing lens identifiers 39.50 to 46.75 in 0.25 steps and powers −1.00 to −4.50 D in 0.50 D steps.

(55) Fitting a stock lens is performed by simply measuring the keratometry value of the cornea to be fitted and establishing the refractive error to target. For example, a cornea with 42.50 D keratometry value and targeted −2.50 D correction would be fitted with a lens identified at 42.50 with −2.50 D correction.

(56) The contact lens in accordance with this aspect of the disclosure by using the novel approach of maintaining consistent sagittal height measured at the outer limit of the first peripheral zone independent to the degree of refractive power being targeted allows greater prediction of change required at lens fit follow up visits. Assessment of a good fitting orthokeratology lens is currently established using existing lens designs by assessing the change that the lens has made to corneal shape during overnight wear, and altering lens parameters to compensate any shortfall identified from the corneal topography analysis. The contact lenses disclosed in some aspects improves the ability to make these changes by completely separating lens fit parameters from parameters affecting refractive change. In the case of required refractive change only the parameters defining the central zone and first peripheral zone are altered. In the case of change to lens fit, either to increase or decrease the sagittal height of the lens, or increase or decrease the lens edge lift, only the second, third, fourth and fifth peripheral zone parameters are altered.

(57) FIG. 10 is a schematic view of the contact lens 10 that has a non rotationally symmetric design to fit irregular shaped corneas. The progressive and continuous change in asphericity across the first peripheral zone enables the lens to have different sagittal heights in different meridians while maintaining tangent continuity at the junction between the central zone and the first peripheral zone.

(58) In this manner it is a straightforward process to create a lens that has greater sagittal depth in the vertical meridian 40 when compared to the horizontal meridian 42 while still using the same radius of curvature in both principal meridians. Any meridian can be altered in this way to make the lens highly adaptable.

(59) In its non rotationally symmetric form, the peripheral zones 3-5 outside of the central zone can be divided into equal sized quadrants 44, 46, 48, 49 each having different values so as to improve fit on asymmetric corneas. These quadrants can be set to align with the principle horizontal and vertical axes.

(60) Alternatively the progressive and continuous change in asphericity across the first peripheral zone enables the principle axes of the central zone comprising the central optic zone and first peripheral zone to be aligned differently to the peripheral zones.

(61) To utilize the new benefits provided by the present contact lens a new computer software process has been created to assist orthokeratology lens fitting practitioners with lens fitting. The computer software is provided with the full refractive error of the eye being corrected and measurements of corneal topography, either as user typed input with minimum requirement of measured corneal keratometry value or by directly importing the captured corneal topography map. The software uses these values to establish the best fit stock lens for the practitioner to select or calculate the empirical lens specification for bespoke individual manufacture.

(62) FIG. 11 shows a flow chart illustrating an example of an initial lens fitting process.

(63) In a first step 111, patient identification data is entered into a cloud based database. The patient's corneal topography is captured 114 and a cornea model is created 116 according to known methods. The patient's refraction is then measured. The lens fitter chooses to fit 118 either an empirical lens of or a trial lens from a stock sets of lenses as described above.

(64) All information regarding lens profile and patient's refraction measurements are stored in the cloud database 120.

(65) At the follow up visit the practitioner assess corneal topography by measuring the corneal surface using a computerised corneal topography measurement instrument and importing the captured data into the software.

(66) FIG. 12 is a flow chart showing the process of assessing whether a change of contact lens is required.

(67) The software retrieves the previous patient's data 122 and previous cornea model and lens data 124 from the database.

(68) The current corneal topography is captured 126 and imported to the database 128. The software subtracts the post lens wear corneal topography data from the corneal topography data measured before lens wear started to calculate the corneal topography shape change that the lens has induced 130.

(69) The contact lens practitioner has the choice of reviewing this data themselves to establish if any change is required to lens fit. In this scenario the lens fitting practitioner makes a visual assessment of lens induced change to corneal shape and classifies this against patterns of corneal topography change that are known to occur from orthokeratology lens wear. The computer algorithm then uses this classification alongside measured change to refraction to calculate whether the lens needs to be altered.

(70) Alternatively, the computer software itself will assess the data to establish the pattern of change that has been made and then establish if the lens needs to be altered based on established and known patterns of change that have been seeded into the software's learning algorithms 134.

(71) A flow chart of an exemplary learning algorithm is shown in FIG. 13.

(72) The software utilizes a computerized learning algorithm and cloud storage 120 to centralize data from a large number of contact lens fitters.

(73) A patient's corneal topography is measured 140 and the corneal topography plots is assed 142. The patient's previous baseline topography is retrieved from the cloud database 120 and the differences calculated 146. The fitting outcome is assessed from the difference map 148 and is suitably displayed 150 to the lens fitter in a simple manner, such as smiley face, bullseye, frowned face and the like.

(74) The residual refraction change is then assessed 152. The computer then compares this residual change against previously stored cases that have gone on to successful outcomes to establish the best change to make 154. The lens changes that were made are transferred to the new current case. A decision is then returned to process into a new lens selection 156.

(75) By constantly updating the learning algorithm with corneal topography change patterns that have led to successful outcomes, the software is able to improve its ability to suggest the required change to the lens when presented with a new case.

(76) FIGS. 14-16 show components of a corneal topographer device that may be mounted to a portable electronic device having an inbuilt camera.

(77) FIG. 14 shows a mount 50 that is U shaped in cross section having opposing side walls, 52, 54 a web 56 and a longitudinal slot 58. The slot 58 is dimensioned to snugly receive the edge of a portable electronic device such as a mobile phone. One side wall 52 has an aperture 60 for locating over the lens of the inbuilt camera of the portable electronic device and a mounting projection 62 for receiving and locating the other components as will be explained below.

(78) FIG. 15 shows the second component 64 of the corneal topographer device that is frustoconical in shape having a base 66 end and an opposed upper end 68. The inner surface of the second component has spaced transparent and opaque rings 70. The base end 66 is dimensioned to snugly receive projection 62 so as to engage the second component 64 with the mount 50.

(79) FIG. 16 shows the third component 72 of the corneal topographer device that is a housing for the second component 64 and is substantially conical in shape having an open base 73 and an opposite open upper end 74 that is dimensioned to correspond to a human eye. The housing 72 has an inner wall 76 that has a recess 78 having a curvature complimentary to the outer wall of the second component 64 so as to allow the second component 64 to be snugly received and held within the housing. The housing 72 is formed from an opaque material. When mounted, the base 73 extends over the lens aperture 60 in the mount 50.

(80) The device is used in association with a light source for illuminating the second component so as to create a concentric illuminated ring pattern that can be projected onto an eye to be measured. The housing 72 shields the light source. The light source may be an inbuilt flash on the electronic device. In this arrangement the mount 50 includes a lens for focusing the flash.

(81) Alternatively the mount 50 may include an inbuilt LED light(s), a small rechargeable battery, on/off switch and associated circuitry to control the LED illumination and battery charging through a USB interface. The base also contains a focussing lens calculated to ensure correct focus of the eye being image.

(82) To use the device, specific application software for the electronic device will be installed, which once installed and running will guide the image capture process. Once the device is correctly aligned, the software will automatically capture an image of the eye that contains the focussed ring images projected by the second component 64. The software then uses image recognition techniques to assess the location of each ring and through a mathematical process reconstruct the three dimensional shape of the cornea measured using the known position of the inner cone at the time of image capture and the measured ring spacing on the captured image.

(83) Once processed, the corneal topography data can be exported to the software described above that controls the contact lens fitting process, or utilised using contact lens fitting software installed on the phone. In this manner the corneal topography device offers a low cost solution to measuring corneal shape that extends the use of corneal topography measurement. For example it will allow any contact lens fitter that doesn't have access to a corneal topographer to be able to fit orthokeratology contact lenses. The device also allows the contact lens wearer to take corneal topography measurements that can be stored on the smart phone and transmitted to the lens fitter to assist in fitting evaluation over time.

(84) It will of course be realized that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of the invention as is herein set forth.