"A method and kit for providing glasses to a patient having refractive error" Introduction This invention relates to a method and kit for providing glasses to a patient having refractive error. More specifically, this invention relates to a method and kit for providing glasses to a patient having refractive error by a non-specialist healthcare worker. It is envisaged that the method and kit will be particularly applicable in the developing world. It has been reported that uncorrected refractive error is the leading cause of visual impairment and the second most common cause of blindness in the world. Globally, 153 million people are visually impaired due to uncorrected refractive error; 8.5 million of these are blind. These estimates are based on the definition of visual impairment as being a presenting vision less than 6/18 in the better eye and blindness as being less than 3/60. To have a vision of 6/18 means that the patient can only see the details on a chart placed 6 meters away that a normally sighted person could see at 18 meters. To be visually impaired due to refractive error means that the patient needs glasses in order to see properly but does not suffer from an eye disease which reduces vision. The difficulties in the developing world in particular are the lack of suitably qualified doctors and opticians, as well as the lack of resources available to provide glasses to the population.

Relatively recently, hand-held machines that quickly and accurately measure the refraction of an eye, known as autorefractometers, have become readily available. Using one of these machines, it is now possible for an unqualified person to determine the glasses prescription for a patient thereby reducing the need for a highly skilled professional. For the purposes of this specification, this unqualified person will be known as a "Glasses Provider".

People can have a combination of two types of refractive error in each eye which would be measured by the autorefractometer: The eye can be too big which is known as myopia, or too small, which is known as hyperopia; in both cases the eye has a normal spherical shape. When the light enters these eyes it focuses either in front of or behind the retina causing the vision to be blurred. The glasses required to correct vision in these eyes utilise spherically-shaped lenses which enable the light to correctly focus on the retina. These spherically-shaped lenses differ from each other only in terms of their refractive power which is measured in units called dioptres, indicated by the symbol D. Values can range from approximately -35D to +20D with the vast majority in the -10D to +10D range with lenses usually varying in steps of 0.25 dioptres.

Alternatively, or in combination with myopia or hyperopia, the eye (or its refracting components) can be naturally warped into an oblong shape similar to a rugby ball. When light enters these eyes it focuses unevenly across the retina. This is known as astigmatism. Astigmatism is corrected using cylindrically-shaped lenses which permit light to focus evenly on the retina. Again, the cylindrical power of a lens is measured using dioptres. In addition to the power variations, the axis at which the cylindrical lens is set in the frame relative to the axis at which the eye is distorted is important. The lens is usually set to the nearest degree in developed countries.

However, providing a prescription is only the first part of the process of producing a pair of spectacles. The glasses are normally custom-made in accordance with the prescription. There is a vast array of permutations of different lenses which might be prescribed meaning that there is a need for special machines to grind and cut lenses specific to the individual prescription. To purchase and run these machines in remote underprivileged communities would be an unrealistic proposition.

One proposed solution to the above problem is described in WO2004/053565 in the name of Tajiri. WO2004/053565 describes a frame and lens system that comprises a plurality of lenses with different spherical correction powers and a plurality of lenses with different spherical correction powers and different cylindrical correction powers. The cylindrical axis is marked on the lenses with cylindrical correction powers so that once the patients eyes have been tested with an autorefractor, the precise prescription lens may be obtained from a store of lenses and then cut appropriately so that the lens may be mounted on a glasses frame with the cylindrical axis correctly aligned to suit the patient. Although very effective, there are problems with this method. First of all, a very large stock of lenses must be supplied to cover all the combinations and permutations of spherical and cylindrical corrections required. This can be impractical if the stock of lenses must be transported to remote areas and is also expensive to provide. Secondly, the method described in WO2004/053565 requires cutting of those lenses with a cylindrical correction power so that they can be mounted on the frames in the correct orientation for the patient. This is time consuming and inconvenient.

It is an object of the present invention to provide a method and kit that overcome at least some of the problems with the known methods. It is a further object of the present invention to provide a method and kit that will allow a non-specialist healthcare worker with minimum training to prescribe and supply affordable glasses to patients that are visually impaired due to refractive error that adequately improve the patient's vision.

Statements of Invention

According to the invention there is provided a low-inventory method of providing glasses to a patient having refractive error comprising the steps of: selecting a glasses frame with suitable dimensions for the patient, the frame having a pair of standard-sized apertures each for reception of a lens having standard-sized peripheral dimensions; selecting a suitable lens with standard sized peripheral dimensions for each of the apertures from a limited stock of pre-manufactured lenses; and inserting each lens in the appropriate aperture; characterized in that the limited stock of pre-manufactured lenses comprises: a first set of lenses comprising a plurality of lenses of incremental spherical correction powers and no cylindrical correction power; and a second set of toric lenses comprising a plurality of lenses of incremental spherical correction powers and a common cylindrical correction power; and in which the step of selecting a suitable lens for each of the apertures comprises: for those patients requiring a lens with no cylindrical correction requirement, providing a lens from the first set of lenses; for those patients requiring a lens with a cylindrical correction requirement less than a magnitude of 2.00 dioptres, providing a spherical equivalent lens from the first set of lenses; and for those patients requiring a lens with a cylindrical correction requirement greater than or equal to a magnitude of 2.00 dioptres, providing a lens from the second set of lenses.

By having such a method, a very limited stock of lenses can be provided. These lenses will be pre-manufactured so that the external perimeter does not have to be cut and shaped by the Glasses Provider. This will significantly facilitate transportation and stocking of the kit and will reduce the cost and complexity of providing glasses to the patients. Rather than providing an exact match to the patient's prescription in all cases, in some cases the best available match of lenses to the patient's prescription is used to construct the glasses. By providing a limited stock of pre-manufactured lenses in a first set of lenses comprising a plurality of lenses of incremental spherical correction powers and no cylindrical correction power, and a second set of lenses comprising a plurality of toric lenses of incremental spherical correction powers and a common cylindrical correction power, it is possible to correct moderate to severe astigmatic refractive error, to an extent better than the WHO's definition of what constitutes visual impairment (vision of 6/18), in patients more comprehensively and with greater success than by using spherical equivalent methods alone and this is achieved without having to provide a very extensive inventory of lenses. It is also possible to achieve results comparable with the best possible improved visual acuity at a fraction of the cost and with a fraction of the resources.

In one embodiment of the invention there is provided a method in which for those patients provided with a lens from the second set of lenses, the method comprises the additional step of calculating an adjusted spherical element and providing a lens from the second set of toric lenses with a spherical correction power having the adjusted spherical element.

In one embodiment of the invention there is provided a method in which the adjusted spherical element is calculated according to the formula:

Adjusted spherical element = patients measured spherical requirement +

[0.5 ^* (patients cylindrical correction requirement - (common cylindrical correction power))].

The above equation assumes that the lenses and patient's refractive requirement are described using the same cylinder notation. The cylinder axes throughout this text refer to negative cylinder notation. In one embodiment of the invention there is provided a method in which the lenses of the second set of lenses are further provided in two subsets having different cylindrical axis meridians, a first subset with a cylindrical axis meridian at substantially 0 ° and a second subset with a cylindrical axis meridian at substantially 90° and in which the step of providing a lens from the second set of lenses comprises providing a lens from one of the subsets of lenses that has the axis meridian closest to the patients astigmatic axis meridian. It has been found that by providing a lens with a given cylindrical power at a limited number of cylindrical axis meridians, the vast majority of patients with astigmatic refractive error will experience a considerable improvement in their visual acuity to the extent that they will no longer be classified as visually impaired. Again, importantly this is achieved with a limited supply of pre-manufactured lenses.

In one embodiment of the invention there is provided a method in which the lenses of the second set of lenses are further provided in four subsets having different cylindrical axis meridians, a first subset with a cylindrical axis meridian at substantially 0 °, a second subset with a cylindrical axis meridian at substantially 90°, a third subset with a cylindrical axis meridian at substantially 160 ° and a fourth subset with a cylindrical axis meridian at substantially 20°, and in which the step of providing a lens from the second set of lenses comprises providing a lens from one of the subsets of lenses that has the axis meridian closest to the patients astigmatic axis meridian. In one embodiment of the invention there is provided a method comprising the initial step of measuring the patient's level of refractive error using an autorefractometer. This is seen as a particularly useful aspect of the present invention due to the fact that it is no longer necessary to have an optometrist or an ophthalmologist carry out the test and provide the prescription. Instead, the non-specialist healthcare worker with adequate training on the autorefractometer will be able to generate the prescription with the autorefractometer and provide a pair of glasses that will adequately improve the vision of the patient. In one embodiment of the invention there is provided a method in which the step of measuring the patient's level of refractive error using an autorefractometer comprises determining the level of spherical correction required and the level of cylindrical correction required including both the magnitude and the angle of cylindrical correction required.

In one embodiment of the invention there is provided a method as claimed in any preceding claim in which the standard-sized apertures are symmetrical about a horizontal axis of the apertures. By having the apertures symmetrical about a horizontal axis, the individual lenses can be interchanged between the left and right apertures of an individual frame. Again, this reduces the inventory required.

In one embodiment of the invention there is provided a method in which the first and second sets of lenses are provided with incremental spherical correction powers in increments of 0.50 dioptres.

In one embodiment of the invention there is provided a method in which the second set of lenses is provided with a common cylindrical correction power of between -1 .00 and - 4.00 dioptres. In one embodiment of the invention there is provided a method in which the second set of lenses is provided with a common cylindrical correction power of -2.50 dioptres.

In one embodiment of the invention there is provided a kit of parts comprising: a plurality of glasses frames, each frame having a pair of standard-sized apertures each for reception of a lens having standard-sized peripheral dimensions; a limited stock of pre-manufactured lenses with standard sized peripheral dimensions, the limited stock of pre-manufactured lenses comprising: a first set of lenses comprising a plurality of lenses of incremental spherical correction powers and no cylindrical correction power; and a second set of toric lenses comprising a plurality of lenses of incremental spherical correction powers and a single common cylindrical correction power of between -1 .00 and -4.00 dioptres. By having such a kit, a non-specialist healthcare worker can provide glasses to an individual that will improve the individual's corrected visual acuity. In many cases, the corrected visual acuity will be improved to such a degree that the individual will no longer be classified as visually impaired. Furthermore, the kit will be relatively lightweight with the minimum amount of equipment and will be portable to remote areas where it is often necessary to travel to reach the patient.

In one embodiment of the invention there is provided a kit of parts in which the second set of lenses have a single common cylindrical correction power of -2.50 dioptres. In one embodiment of the invention there is provided a kit of parts in which the second set of lenses are further provided in two subsets having different cylindrical axis meridians, a first subset with a cylindrical axis meridian at substantially 0 ° and a second subset with a cylindrical axis meridian at substantially 90 °. In one embodiment of the invention there is provided a kit of parts in which the second set of lenses are further provided in four subsets having different cylindrical axis meridians, a first subset with a cylindrical axis meridian at substantially 0 °, a second subset with a cylindrical axis meridian at substantially 90°, a third subset with a cylindrical axis meridian at substantially 160 ° and a fourth subset with a cylindrical axis meridian at substantially 20 °.

In one embodiment of the invention there is provided a kit of parts in which the frame apertures are symmetrical about a horizontal axis and the lenses are symmetrical about a horizontal axis.

In one embodiment of the invention there is provided a kit of parts in which the first and second set of lenses are provided with spherical correction powers in the range -20.00 dioptres to +20.00 dioptres in increments of 0.50 dioptres.

In one embodiment of the invention there is provided a kit of parts in which the plurality of glasses frames are provided in a plurality of different sizes to suit a plurality of different patients, and in which all of the different sizes of glasses frames are provided with standard sized apertures.

In one embodiment of the invention there is provided a kit of parts in which there is provided no more than four different sizes of frames. In one embodiment of the invention there is provided a kit of parts in which there is provided an autorefractometer.

Detailed Description of the Invention The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which :-

Figure 1 is a front view of a standard-sized lens according to the invention;

Figure 2 is a front view of a standard-sized lens according to the invention with a 0 ^Q cylindrical axis meridian; Figure 3 is a front view of a standard-sized lens according to the invention with a 90 ^Q cylindrical axis meridian;

Figure 4 is a front view of a standard-sized lens according to the invention with a 20 ^Q cylindrical axis meridian;

Figure 5 is a front view of a standard-sized lens according to the invention with a 160 ^Q cylindrical axis meridian; Figures 6(a) and 6 (b) are diagrammatic representations of two pairs of glasses that may be used in the method according to the present invention; and

Figures 7(a) to 7(d) are diagrammatic representations of toric lenses illustrating the inter-changeability of the toric lenses between left and right apertures of a pair of glasses.

Referring to Figure 1 , there is shown a lens, indicated generally by the reference numeral 1 , comprising a peripheral wall 3 that is of a standard size so that the lens 1 will fit into a complementary standard-sized aperture in a pair of glasses (not shown). The lens 1 comprises an optical centre indicated by dot 5 and the lens 1 is symmetrical about a horizontal axis indicated by dashed line 7. The lens 1 is suitable for insertion into either a right hand side aperture or a left hand side aperture of a pair of glasses. The lens 1 as shown is ready for insertion into a right hand side aperture of the glasses however in order to insert the lens into a left hand side aperture of a pair of glasses, the lens is simply rotated through 180 ^Q in the direction of the arrow 9.

Referring to Figures 2 to 5, there is shown a plurality of views of lenses 21 , 31 , 41 , 51 respectively with the various cylindrical axes meridians indicated by oblong 1 1 . The cylindrical axes meridians or Figures 2, 3, 4 and 5 are located on the 0 ^Q (also referred to as 180 ^Q ), 90 ^Q , 20 ^Q and 160 ^Q meridians respectively. Referring to Figures 7(a) to 7(d) inclusive, there is shown a plurality of views of the lenses 21 , 31 , 41 and 51 showing how when rotated through 180 ^Q , the lenses may be used interchangeably as right hand side or left hand side lenses in a pair of glasses due to the fact that the lenses are symmetrical about their horizontal axis. This reduces the required stock of toric lenses by half to four lenses for each spherical power.

Referring to Figures 6(a) and 6(b), there are shown diagrammatic representations of two pair of glasses 61 for use with the method and the kit according to the present invention. The glasses 61 have apertures 62 that are identical in dimensions with respect to each other however the glasses differ from each other in that a bridge section 63 of one of the pair of glasses [Figure 6(a)] is larger than the bridge portion 63 of the other pair of glasses [Figure 6(b)] to allow for different sized users with different sized interpupillary distances. If desired, frames can be provided in a variety of different styles, colours and materials provided that the apertures are standard sized across the range.

In use, a non-specialist healthcare worker will test the patient's eyes with an autorefractometer (not shown). The autorefractometer will provide a prescription of the patient's eyes including the spherical correction required in each eye and the cylindrical correction required in each eye. The healthcare worker will then select a pair of frames that fit the patient so that the optical centre of the lenses will be substantially over the visual axis of the patient when they are wearing the glasses. The spectacle frames 61 are provided in a number of different sizes with different sized bridges 63 to ensure that a pair of glasses that fit the patient is available. It has been found that approximately four different sizes of frames are adequate to ensure there is a reasonable fit of frame for most adults. Each of the frames will have apertures that are of a standard size to the other frames so that the lenses will fit into each different type of frame. Once the frames have been selected, the Glasses Provider will then select the appropriate lenses for each eye of the patient. For those patients with only a spherical error, the appropriate lens with spherical correction matching the patient's spherical error will be provided in the frame aperture. If the patient has a spherical error but also has a cylindrical error of less than 2 dioptres (2.00D), a spherical equivalent lens (that is, a spherical correction lens with a correction dioptre equal to the sum of the spherical correction required added to one half the cylindrical correction required) will be provided and inserted into the glasses aperture 62. If the patient has a spherical error and a cylindrical error of greater than 2.00D, a toric lens will be provided with a cylindrical corrective element and that lens' spherical corrective element will be appropriately adjusted to take account of the cylindrical element supplied.

According to a preferred embodiment of the present invention, the magnitude of the cylindrical correction will be fixed at 2.50D as this is seen as the value that adequately treats most patients with mild to moderate astigmatism conditions and the lenses will be provided in a plurality of different cylindrical axes meridians. According to a preferred embodiment of the present invention, four different lenses with a selection of axes meridians are provided. A first axis on 0 ^Q , a second axis on 20 ^Q , a third axis on 90 ^Q and a fourth axis on 160 ^Q .

For reasons of completeness, various problems addressed by the present invention and various solutions proposed by the present invention will now be discussed in more detail. When one considers the various combinations and permutations of the spherical and cylindrical corrections possible, it is clear to see that it would be impossible for a Glasses Provider to keep a stock of all the different pre-cut lenses. If it were just a matter of providing spherical lenses, the Glasses Provider could theoretically keep the required stock if they so wished. Correcting for astigmatism is far more complex.

The simplest solution would be to approximate prescriptions using the "spherical equivalent" formula. This is where the spherical and cylindrical components of a prescription are combined into a spherical lens using the formula: (spherical power) + ½(cylindrical power) = (spherical equivalent). This would be useful in some circumstances but has obvious drawbacks in terms of correcting the vision of people who have moderate to high astigmatism.

By providing spectacle frames with the frame aperture symmetrical across the horizontal axis designed to receive interchangeable lenses and with four pre-shaped lenses for each cylindrical power, it would be possible to provide cylindrical correction in either eye at the four meridians. The axis of the lens chosen for insertion would reflect the closest approximation to the patient's own optical axis. This would provide a good solution for the patient however, it is envisaged that there would still be too many lenses for a Glasses Provider to stock if every cylindrical power was to be provided for. Therefore, it is envisaged that a further compromise should be made. This compromise entails a reduced number of cylindrical powers being prescribed to patients with astigmatism, preferably a single cylindrical power being prescribed to patients with astigmatism. The single cylindrical power chosen would be influenced by 2 factors: (1 ) the maximisation of vision of people with mild to moderate astigmatism (indicating the use of a low powered cylinder) and (2) the correction of as much vision as possible for those with moderate to high astigmatism (indicating a higher power). According to a preferred embodiment of the present invention, the required stock of lenses is kept small by using spherical lenses to correct all patients with astigmatism less than 2.00 dioptres and toric lenses, incorporating a -2.50 dioptre cylinder set at one of 4 predetermined axis meridians, for all patients with astigmatism having a magnitude greater than or equal to 2.00 dioptres.

Of additional benefit is the provision of frame apertures and pre-manufactured lenses of standard peripheral dimensions. By providing frame apertures and lenses of standard sizes, all of the lenses will fit into any of the frames provided. In order to provide a pair of glasses with the distance between the optical centres of the lenses substantially matching the patient's interpupillary distance (and with the optical centres of the lenses substantially over the patient's visual axes), a range of frames with different sized bridges may be provided to ensure that the distance between the optical centres of the lenses is substantially correct. The lenses themselves do not have to be adjusted. This is far less time consuming and requires less skill than would otherwise be the case and cruicially allows for pre-manufactured lenses which do not have to be individually shaped for each individual patient. 1 ) First Trial

A confidential trial of the effectiveness of the compromise solution has been carried out with patients suffering from refractive error that are classified as visually impaired. The trials determined to what extent the patient's vision could be improved through implementation of the method and use of the kit of parts according to the invention. The trials were performed under conditions where the skills of a trained optometrist and or ophthalmologist were available to provide the best possible corrective action and the results of the compromise solution were compared with the best possible corrective action to determine the level of efficacy of the method according to the invention. The patients were not told what lenses they were looking through and the results of the patient's vision tests using a Snellen acuity chart were monitored. A thorough description of this trial will hereinafter be discussed.

Trial Conditions

The trial was a prospective, single-cohort exploratory study, with paired pre and post- correction comparison of outcome measures, therefore each case acted as its own control. Due to its pilot nature, no minimum sample size was defined a priori; however, post -hoc power calculations were made. A total of 41 patients were invited to participate. Patients with uncorrected vision worse than 6/18 (20/60) were enrolled in the study and those with a best corrected vision worse than 6/12 (20/40) were excluded. Each eye was individually considered as a case and 72 cases met the inclusion criteria (n=72). An auto-refractor was used to produce a basis for the correction to be tested. Eyes with astigmatism less than 2.00 dioptres were tested with a spherical equivalent lens. Eyes with astigmatism of 2.00 dioptres and greater were tested using a toric lens comprising of a 2.50 dioptre cylinder with the spherical element appropriately adjusted. The cylindrical axis was set at either 0 ^° , 20 ^° , 90 ^° or 160 ^° depending on which was closest to the patient's measured axis.

The spherical element was appropriately adjusted according to the following equation:

New Sphere = (spherical equivalent) - (0.5 x Cylindrical adjustment)

For example, if the patient's eye was 7.00D sphere and 2.00D cylinder and they were given a standard 2.5D cylinder, then they were provided with a lens having an appropriately adjusted spherical element with 6.75D of sphere. The "spherical equivalent" was worked out as per normal from the patient's autorefractor reading and the 1 .25D is half of the 2.50D cylinder that the patient was required to wear. Similarly, if the patient was required to wear a lens having a 3.0D cylinder, the new sphere would be calculated by subtracting 1 .5D (0.5 x Cylindrical adjustment (3.0D)) from the spherical equivalent.

The primary outcome was to assess and compare the vision achievable with glasses constructed in accordance with the method according to the present invention against the World Health Organisation (WHO) definition of visual impairment, i.e., vision worse than 6/18 (20/60). The secondary outcomes were to evaluate, by stratified analysis, the extent to which vision was corrected by glasses constructed in accordance with the method according to the present invention and to compare this vision with, 1 : best corrected visual acuity, 2: visual acuity achievable using the auto-refractor refraction and, 3: visual acuity achievable with just a spherical equivalent correction in the cases where astigmatism was greater than 2.00 dioptres. All acuities were measured using a projected Snellen acuity chart to the nearest letter and converted to LogMAR units for analysis. For ease of reading, results are reported in this specification using the Snellen notation to the nearest letter. For example 6/12 ⁺² (20/40 ⁺² ) implies that the patient could read all of the 6/12 (20/40) line and 2 out of five letters on the 6/9 (20/30) line. 6/9 ^~2 (20/30 ^~2 ) implies that 2 out of 5 letters were misread on the 6/9 (20/30) line.

The data was analysed by intention-to-treat approach. Descriptive statistics, frequency distribution methods, parametric and non-parametric tests for paired, within-group comparisons and general linear modelling (GLM) with repeated-measure analysis of variance (ANOVA) were applied.

Trial Results

The patients (n=41 ), who had a mean age of 57.1 (SD 18.3) years, had spherical refractive errors ranging from -9.50 to +7.00 dioptres (n=72) and cylindrical error ranging from 0.00 to -6.50 dioptres (n=72). Their mean uncorrected vision was 6/60 ⁺ (20/200 ⁺ ) (SD 4.8 lines).

All eyes with a cylindrical error less than 2.00 dioptres attained a better corrected visual acuity than the WHO'S 6/18 (20/60) definition of visual impairment. These cases achieved a mean vision of 6/9 ⁺ (20/30 ⁺ ) ± 1 .3 lines (n=33, p<0.05) which was, on average, within 1 .4 lines of the best corrected visual acuity.

All eyes with cylindrical error between 2.00 and 2.99 dioptres also attained a better corrected acuity than 6/18 and achieved a mean acuity of 6/12 ⁺² ± 1 .1 lines (n=15, p<0.05) which was on average within 1 .3 lines of their best corrected visual acuity. Of note, when a simple spherical equivalent correction was tested in this group only 33.3% attained a better corrected visual acuity than 6/18 (20/60) and the mean visual acuity was 6/24 ⁺² (20/80 ⁺² ) ±1 .1 lines. This is most significant as in other words, all patients with cylindrical error between 2.00 and 2.99 dioptres provided with glasses in accordance with the method of the present invention, achieved corrected sight that was no longer considered to be visually impaired according to the WHO criteria. On the other hand, two out of every three patients in this category taking part in the trial were still considered to be visually impaired according to the WHO criteria after being provided with glasses in accordance with other known methods, specifically providing a spherical equivalent lens, which might be used by unskilled health workers to correct the vision of a patient with astigmatism in the developing world.

66.7% of eyes with cylindrical error 3.00 dioptres and greater attained a better corrected visual acuity than 6/18 (20/60). The average corrected acuity of this entire group was 6/18 ⁺ (20/60 ⁺ ) ± 2.2 lines (n= 24, p<0.05). The average vision of the 66.7% who achieved an acuity better than 6/18 was 6/12 ^~2 (20/40 ^~2 ) ± 0.8 lines. Of note, when a simple spherical equivalent correction was tested in this high astigmatism group only 4.5% attained a better corrected visual acuity than 6/18 (20/60) and the mean vision was 6/30 (20/100) ±3 lines (n=24, P<0.05). Again, this is most significant as it shows that two out of every three people in this category in the trial that were provided with glasses according to the method described achieved corrected vision better than the WHO standard of visually impaired. This compares very favourably with the known methods that were successful in less than 1 in 22 cases.

Across all cases (n=72), the vision achievable using the autorefractor prescription correlated well with the best corrected vision. The average autorefractor vision was 6/9 ⁺² (20/60 ⁺² ) ± 1 .3 lines (n=72, p<0.05) and was within one line of the average best corrected vision. By this, it will be understood that "within one line" means within one line of the Snellen chart. Trial Conclusions

The method for prescribing glasses described in this specification and performed in the trial could be of great benefit to patients presenting with visual impairment due to uncorrected refractive error in regions of the world where there is no access to trained refraction ists or spectacle glazing laboratories. All people with mild to moderate astigmatism (<2.99 dioptres), which epidemiological^ represents the vast majority of individuals, can be corrected. Furthermore, most of those with severe astigmatism (>2.99 dioptres) can also be corrected. The novel approach, using a compromised cylindrical corrective element set at a compromised axis, results in a much improved visual acuity for patients with astigmatism than the practice of providing those people with a spherical equivalent alone.

2) Second Trial

A second confidential trial, that encompassed the results and subjects of the first confidential trial was also carried out with further analysis of the findings. This prospective, single-cohort exploratory study enrolled 53 patients with 94 eligible eyes having uncorrected vision of 6/18 or worse. Eyes with best corrected vision worse than 6/12 were excluded. An autorefractor was used to obtain refractions which were adjusted so that eyes with astigmatism less than 2.00 dioptres (D) received spherical equivalent lenses and eyes with more astigmatism received toric lenses with a -2.50D cylindrical element set at one of four meridians. The sight achieved through use of the glasses prescribed in accordance with the method according to the invention was compared to the WHO definition of visual impairment (6/18). Where astigmatism was 2.00D or greater, comparison to spherical equivalent was made. Mixed-model analysis with repeated effect was utilised to account for possible correlation between the vision of fellow eyes of the same individual. The glasses prescribed in accordance with the present invention again were found to correct 100% of eyes with astigmatism less than 3.00D and 69% of eyes with astigmatism of 3.00D or greater. Whereas, spherical equivalent lenses corrected 25% of eyes with astigmatism of 2.00 to 2.99D and 1 1 % with astigmatism of at least 3.00D.

Trial Conditions

This was a prospective, single-cohort exploratory study, with paired pre- and post- correction comparisons of outcome measures and, therefore, each case acted as its own control. Due to its pilot nature, no sample size calculations were necessary a priori; however, a post-hoc assessment of the statistical power of the significant comparisons was performed, as appropriate. A total of 53 patients were enrolled. The inclusion criteria were adult patients (aged >18 years) with uncorrected vision worse than 6/18 in both eyes who were capable of giving informed consent. The exclusion criterion was a best corrected visual acuity worse than 6/12 and this was applied to individual eyes. Therefore some patients were included in the analysis with one eye only. A total of 53 patients met the inclusion criteria and 12 individual eyes were excluded. There were 94 eyes tested with glasses prescribed in accordance with the present invention in total.

A Topcon KR8000P (Tokyo, Japan) autorefractor was used to measure the objective refraction for each patient. Refractions were recorded in minus cylinder notation and the S-Glasses algorithm was applied to these readings. Corrective lenses were presented to the patient using a Topcon phoropter and the vision using the glasses prescribed according to the present invention correction was recorded for each eye. The algorithm for prescribing the glasses according to the present invention is described as follows:

1 . Eyes with astigmatism less than -2.00 dioptres are corrected using a spherical equivalent lens.

2. Eyes with astigmatism of -2.00 dioptres or more are corrected using a toric lens comprising of a -2.50 dioptre cylinder with the spherical element appropriately adjusted and the axis set at either 0 ^° , 20 ^° , 90 ^° or 160 ^° depending on which is closest to the measured axis. The spherical element is adjusted by adding half the difference between the patient's cylindrical power and -2.50 dioptres to the spherical component of the objective refraction.

3. The spherical powers prescribed differ in steps of 0.50 dioptres. The vision in all eyes with astigmatism of 2.00 dioptres or greater was also recorded using a spherical equivalent of the objective refraction. Then the vision achieved using the precise objective refraction measured by the autorefractor was recorded. Finally, a subjective refraction was conducted by an optometrist and the best corrected visual acuity was recorded.

In relation to step 2 above, by way of a number of examples, if the measured eye objective refraction were -3.00D spherical and -4.50D cylindrical, the spherical element would be adjusted by adding -1 .00 (half the difference between the patients cylindrical power (-4.50D) and -2.50, the difference = -2.0, half of which is -1 .00) to the spherical component (-3.00D) of the objective refraction thereby resulting in an adjusted spherical element of -4.00D. Similarly, if the measured eye objective refraction were 4.00D spherical and -5.00D cylindrical, the spherical element would be adjusted by adding - 1 .25 (half the difference between the patients cylindrical power (-5.00D) and -2.50, the difference = -2.50, half of which is -1 .25) to the spherical component (4.00D) of the objective refraction thereby resulting in 2.75D. As the lenses are provided in 0.50D increments, it is not possible to provide 2.75D and therefore 3.00D spherical element corrective lens is provided. The correction is rounded up when the correction value is a positive correction and rounded down when the correction value is a negative correction value, e.g. 1 .75 becomes 2.00D adjusted spherical element correction whereas -1 .75 becomes -1 .50 adjusted spherical element correction.

The primary outcome was to assess and compare the vision achievable using glasses prescribed in accordance with the present invention against the World Health Organisation (WHO) definition of visual impairment, i.e. vision of 6/18 or worse. The secondary outcomes were to evaluate, by stratified analysis, the extent to which vision was corrected by the glasses prescribed in accordance with the present invention and to compare this vision with: (1 ) uncorrected vision, (2) visual acuity achievable with just a spherical equivalent correction in the cases where astigmatism was greater in magnitude than 2.00 dioptres, (3) visual acuity achievable using the auto-refractor refraction and (4) best corrected visual acuity. All acuities were measured using a projected Snellen acuity chart to the nearest letter and converted to LogMAR units for analysis. For ease of reading, results are reported below using the Snellen notation to the nearest letter. Where two methods of correction are compared, the difference in vision is expressed in lines and a line is defined by 0.1 LogMAR units.

Ninety-four eyes of 53 patients were included and eyes were analysed in 3 groups according to the level of astigmatism; low astigmatism was defined as smaller than 2.00 dioptres, while moderate astigmatism was between 2.00 and 2.99 dioptres and high astigmatism was 3.00 dioptres or more. Since some of the patients participated with only one eligible eye while others entered the analysis with both eyes, the mean values for comparative purposes were obtained by mixed models (see below) which allowed for possible interaction amongst fellow eyes of the same individual. Furthermore, nine patients were members of both the high astigmatism and moderate astigmatism groups by virtue of anisometropia and this is why the sum of the numbers of patients in each group exceeds the total number of patients in the entire study.

Descriptive statistics, with computation of the standard deviation (SD) and 95% confidence intervals (Cls) as well as tests for normality of distributions (e.g. Shapiro- Wilk) were applied. Frequency distribution methods, parametric and non-parametric tests for one-sample comparisons as well as paired, within-group comparisons were used. Paired parametric and non-parametric (e.g. Spearman) correlations were also computed, as appropriate. For the secondary outcomes, mixed models, with a repeated effect for the comparison between the methods, were used to obtain restricted maximum likelihood solutions with a compound symmetry of the covariance structures for all eyes as well as in the three sub-groups. Least square means with 95% Cls were obtained and a post-hoc Tukey-Kramer adjustment for multiple comparisons of the p-values was done. The statistical significance of the results was assumed at p<0.05, unless stated otherwise. All analyses were performed with the statistical software PASW Statistics Ver.18 (IBM Corporation, Armonk, NY, USA) and SAS Ver.9.3 (SAS Institute Inc., Cary, NC, USA).

Trial Results

The patients (n=53), of whom 32 were female and 21 were male, had a mean age of 60 (SD 19) years. Their spherical refractive errors ranged from -9.25 to +7.50 dioptres and cylindrical errors ranged from 0.00 to -6.50 dioptres (n=94 eyes). Every eye in the low astigmatism group (<2.00 dioptres) (n=34) achieved a vision better than 6/18 (Table 1 below). The mean vision in this group was less than one line worse than the mean best- corrected visual acuity and this difference was not statistically significant (p>0.05). The glasses prescribed in accordance with the present invention are referred to in the table as S-glasses for convenience.

Table 1 Results

Low astigmatism (<2.00 Dioptres) group 34 eyes from 19 people

Percentage of eyes seeing better than 6/18 with spherical equivalent 100% Percentage of eyes seeing better than 6/18 with S-Glasses method ^a 100%

Vision Snellen notation (95%

Mean confidence interval) uncorrected vision 6/45 (6/30 ² - 6/60) vision with spherical equivalent correction 6/9 (6/7.5 ⁺² - 6/12 ) vision with S-Glasses method ^a 6/9 (6/7.5 ⁺² - 6/12 ) vision with autofrefractor correction 6/9 ¹ (6/6 ² - 6/15 ) best corrected vision 6/7.5 (6/4 ^~2 - 6/9 )

Moderate astigmatism (2.00-3.00 dioptres) group 24 eyes from 19 people

Percentage of eyes seeing better than 6/18 with spherical equivalent 25% Percentage of people with at least one eye seeing better than 6/18

with spherical equivalent 21%

Percentage of eyes seeing better than 6/18 with S-Glasses method 100%

Mean Vision Snellen notation (95% confidence interval) uncorrected vision 6/60 ¹ (6/60 ⁺¹ - 6/120 ⁺¹ ) vision with spherical equivalent correction 6/21 (6/15 - 6/30 ⁺² ) vision with S-Glasses method 6/9 ^~2 (6/7.5 ² - 6/15 ⁺² ) vision with autofrefractor correction 6/9 ¹ (6/7.5 - 6/ir ² ) best corrected vision 6/9 ⁺² (6/6 6/12 ⁺² )

High astigmatism (>3.00 dioptres) group 36 eyes from 15 people

Percentage seeing better than 6/18 with spherical equivalent 11% Percentage of people with at least one eye seeing better than 6/18

with spherical equivalent 13%

Percentage seeing better than 6/18 with S-Glasses method 69% Percentage of people with at least one eye seeing better than 6/18

with S-Glasses method 80%

Mean Vision Snellen notation (95% confidence interval) uncorrected vision 6/45 ⁺¹ (6/30 - 6/60) vision with spherical equivalent correction 6/30 ⁺¹ (6/21 ⁺¹ - 6/45 ⁺¹ ) vision with S-Glasses method 6/15 (12 ⁺¹ - 6/2Γ ¹ ) vision with autofrefractor correction 6/9 ¹ (6/7.5 ⁺¹ - 6/12- ² ) best corrected vision 6/9 ⁺² (6/6 - 6/9 )

The S-Glasses method uses a simple spherical equivalent corrections for patients with astigmatism less than 2.00 dioptres In the moderate astigmatism group (2.00-3.00) the glasses prescribed in accordance with the present invention and the mean vision was 1 line worse than the best corrected acuity which was not statistically significant (p>0.05). However, when these eyes were corrected with a spherical equivalent lens only 25% corrected better than 6/18 and the mean vision was significantly worse, by 4 lines, than the best corrected visual acuity (p<0.0001 ). In the high astigmatism (>3.00 dioptres) (n=36) group, the mean vision using the glasses prescribed in accordance with the present invention was 2.6 lines worse than best corrected visual acuity which was of marginal statistical significance (p=0.0633) and 69% of eyes had vision better than 6/18, with 80% of individuals having at least one eye which could see better than 6/18. However, using the spherical equivalent correction, the mean vision was 5.5 lines worse than best corrected vision (P<0.0001 ) and only 1 1 % of the eyes corrected better than 6/18, with 13% of individuals having at least one eye which had vision better than 6/18. The vision achievable using the autorefractor-measured correction was similar to best corrected vision. The mean vision was less than one line worse than the best corrected acuity and this difference was not statistically significant. Across all eyes, the vision achievable using the autorefractor correction strongly correlated with the best corrected vision (n=94 eyes, Rho=0.842, p two-tailed <0.01 ). The advantage of the present methodology is that only a relatively small, finite number of individual lenses can be prescribed. Further, since the spectacle frames all have a standard-shaped aperture that is symmetrical about the horizontal axis, there would only be a relatively small stock of pre-formed and shaped lenses which could be used to assemble "off the shelf" glasses. Taken together, this means that a non-specialist health care worker could carry a small stock of glasses' lenses and frames and could dispense the glasses without the need for a spectacle glazing laboratory. Throughout this specification, whenever reference is made to a cylinder having a given dioptre correction being on a given axis, this will in all cases be understood to mean a minus cylinder having that given dioptre correction on that given axis. In this specification the terms "comprise, comprises, comprised and comprising" and the terms "include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation. The invention is in no way limited to the embodiments hereinbefore described but may be varied in both construction and detail within the scope of the claims.