Method Of Making Contact Lenses

Abstract

The invention relates to a method of making a contact lens, the method comprising identifying the eccentricity of a lens produced in a mould half, lathing the lens and adjusting the path of the lathe to take account of the eccentricity, and a computer programme for controlling the lathe.

Claims

1. A method of making a contact lens, the method comprising: (i) providing a first master mould for producing a first mould half and a second master mould for producing a second mould half (ii) producing at least one precursor mould comprising the first mould half and the second mould half, wherein the first mould half is for providing a first lens surface having at least one optical feature and the second mould half is for providing a second lens surface which requires lathing to provide at least one added optical feature; (iii) producing a moulded precursor contact lens in each of the at least one moulds, wherein the step of producing the lens results in at least one identifiable undesirable attribute; (iv) identifying the at least one undesirable attribute on the precursor contact lens; (v) determining the extent of the at least one undesirable attribute; (vi) providing at least one lens producing mould formed from the master moulds, each lens producing mould having a first mould half and a second mould half, wherein the first mould half is for providing a first lens surface having at least one optical feature and the second mould half is for providing a second lens surface which requires lathing to provide at least one added optical feature; (vii) producing the contact lens in at least one lens producing mould; (viii) removing the second mould half, whereby the contact lens remains positioned on the first mould half; and (ix) lathing the second lens surface using a lathe tool, wherein the path of the lathe tool is controlled by a computer programme, and wherein the computer programme adjusts the path to compensate for the undesirable attribute of the test contact lens identified in step (iv).

2. The method of claim 1, wherein at least one of the undesirable attributes is a property of the lens.

3. The method of claim 1 or claim 2, wherein at least one of the undesirable attributes is caused by the positioning of the lens on the mould half.

4. The method of any one of claims 1 to 3, wherein after step (iii), the second mould half is removed, whereby the at least one precursor contact lens remains positioned on the first mould half for identification of the undesirable attribute.

5. The method of any one of claims 1 to 3, wherein after step (iii), the precursor contact lens is removed from the mould halves and the undesirable attribute is identified on the lens.

6. The method of any one of claims 1 to 5, wherein the at least one undesirable attribute is selected from: the eccentricity of the lens from the centre of the mould half; the residual toricity on the front or rear surface of the lens; prism correction; spherical aberration; comatic aberration; or trefoil aberration.

7. The method of claim 6, wherein the at least one undesirable attribute is the eccentricity of the lens from the centre of the mould half.

8. A method of making a contact lens, the method comprising: (i) providing a first master mould for producing a first mould half and a second master mould for producing a second mould half (ii) producing at least one precursor mould comprising the first mould half and the second mould half, wherein the first mould half is for providing a first lens surface having at least one optical feature and the second mould half is for providing a second lens surface which requires lathing to provide at least one added optical feature; (iii) producing a moulded precursor contact lens in each of the at least one moulds; (iv) removing the second mould half, whereby the at least one precursor contact lens remains positioned on the first mould half; (v) identifying the eccentricity of the at least one precursor contact lens from the centre of the first mould half; (vi) providing at least one lens producing mould formed from the master moulds, each lens producing mould having a first mould half and a second mould half, wherein the first mould half is for providing a first lens surface having at least one optical feature and the second mould half is for providing a second lens surface which requires lathing to provide at least one added optical feature; (vii) producing the contact lens in at least one lens producing mould; (viii) removing the second mould half, whereby the contact lens remains positioned on the first mould half; and (ix) lathing the second lens surface using a lathe tool, wherein the path of the lathe tool is controlled by a computer programme, and wherein the computer programme adjusts the path to compensate for the eccentricity of the test contact lens identified in step (iv).

9. The method of any one of the preceding claims, wherein the first lens surface is the front surface and the second lens surface is the rear surface.

10. The method of any one of the preceding claims, wherein the at least one optical feature is selected from a spherical optical zone, an aspherical optical zone, a toric optical zone, a prism ballast or combinations thereof

11. The method of any one of the preceding claims, wherein the at least one undesirable attribute comprises the eccentricity of the test contact lens, and the eccentricity is characterized by defining an angle and magnitude of offset.

12. The method of any one of the preceding claims, wherein the steps of producing the moulded test lens and producing the contact lens comprise the steps of adding a contact lens monomer mixture to one of the first or second mould halves, closing the mould using the other of the first or second mould halves and curing the mixture in the mould.

13. A computer programme for controlling a lathe for lathing an optical feature onto a surface of a contact lens, wherein the contact lens is positioned on a mould half, wherein the computer programme comprises: a) an input for inputting the extent of at least one undesirable attribute of a lens; and b) an output for controlling the lathe to produce the optical feature on the surface of the lens, wherein the output is modified by the input, such that the optical feature is correctly produced on the contact lens.

14. The computer programme of claim 13, wherein the undesirable attribute comprises an offset of the lens relative to the centre of the mould half, and wherein the output is modified such that the optical feature is correctly positioned relative to the centre of the contact lens.

15. The computer programme of claim 13, wherein the undesirable attribute comprises the formation of a toric region on the front of the lens, and wherein the output is modified

16. A method of making a contact lens substantially as hereinbefore described with reference to and as illustrated by the drawings.

17. A computer programme for controlling a lathe substantially as hereinbefore described with reference to and as illustrated by the drawings.

Description

[0071] The invention will now be further described with reference to the following drawings in which:

[0072] FIG. 1 shows two mould halves containing lenses.

[0073] FIG. 2 shows the effect of different angles of offset for a given magnitude of offset

[0074] FIG. 3 shows the effect of using different angles of offset for a given magnitude of offset over a narrower angle range

[0075] FIG. 4 shows the effect of using different magnitudes of offset for a constant angle.

[0076] FIG. 5 shows the variance in sphere power caused by residual toricity

[0077] FIG. 6 shows the variance in cylinder power caused by residual toricity

[0078] FIG. 7 shows the variance in axis caused by residual toricity

[0079] FIG. 8 shows how lathe cutting can accommodate residual toricity to produce the desired lens.

[0080] In FIG. 1, there is shown a first female mould 1 and a second female mould half 10. In each mould half 1, 10 is a contact lens 15, 20 respectively. As can be seen, the lens is offset from the centre of the female mould half. The offset is significantly exaggerated to demonstrate the problem identified and solved by the present invention.

[0081] For the first mould half, a toric feature 25 has been lathed into the lens 15, using the centre of the mould half 1 as the centre point of the lens. The toric feature 25 can be seen to be offset from the centre of the lens. In practice, the offset here would be sufficient to make the lens unwearable.

[0082] The second female mould half 10 shows a lens where the lathing has been adjusted to take account of the eccentricity produced by the moulding process. Here is can be seen that the toric feature 30 is centred on the lens 20 rather than the mould half 10. As a result, the lens is wearable.

[0083] FIG. 2 shows the effect of varying the offset angle from 300 to 60 in 60 increments for an offset magnitude of 0.065 microns for a lathed toric section.

[0084] FIG. 3 shows the effect of varying the offset angle from 345 to 15 in 5 increments for an offset magnitude of 0.065 microns for a lathed toric section.

[0085] FIG. 4 shows the effect of varying the offset magnitude from 0.03 to 0.08 microns in 0.01 micron increments for a lathed toric section.

[0086] In each of these figures, it can be seen that a change of angle or magnitude has an impact on the positioning of the lathed toric section. The need to identify the correct eccentricity is therefore clear. One identified, it is possible to produce a series of contact lenses in which the toric section is correctly positioned.

[0087] In FIGS. 5 to 7, an example is given of how residual toricity produced in a series of lenses, can affect the sphere power, cylinder power and toric axis lathed into a contact lens. In this case the residual toricity introduced into a series of lenses as approximately 0.40 cylinder power at an axis of 140. The charges show actual values as small dots and average values as large diamonds.

[0088] In each case, the chart shows the difference between the target value and the actual value measured for a series of different lenses after a toric cylinder was lathed into the rear of the lens surface at a series of different axes.

[0089] For contact lenses to meet ISO standards, the sphere power and cylinder power should be accurate to within +/0.25D of the target value for many of the lower powers, which make up the majority of the astigmatic populationspecifically sphere powers of less than or equal to a magnitude of 10DS, and cylinder powers of less than or equal to 2DC. The toric axis should be accurate to within +/5.

[0090] It can be seen from FIGS. 5 and 6 that the spherical and cylinder powers fall outside the required tolerance range. Similarly, albeit to a lesser extent, there is a variation of for the toric axis which falls outside the permitted tolerance range. It is to be further noted that the errors are at their maximum at different target axes. Therefore, it is likely that at least one parameter will fall outside the tolerance range.

[0091] FIG. 8 shows how it is possible to combine the residual toricity and a selected lathed value to arrive at the required prescription range. Using the residual toricity described above, the skilled person can select a specific angle, sphere power and cylinder power to arrive at the desired prescription powers and angle. In each case, the resultant lens has the required properties, having taken account of the residual toricity.

[0092] Whilst the invention has been described with reference to a preferred embodiment, it will be appreciated that various modifications are possible within the scope of the invention.

[0093] In this specification, unless expressly otherwise indicated, the word or is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator exclusive or which requires that only one of the conditions is met. The word comprising is used in the sense of including rather than in to mean consisting of. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date hereof.