Evaluating the latest additions in trial lenses

One of the core functions in an eye examination is to refract. Also, whether we like it or not, refraction is indirectly responsible for the success of our practices.
Therefore, there is a need to place emphasis on the importance of trial lens sets within the consulting room. Practitioners must have confidence in the accuracy of lenses within their trial lens sets, so how accurate are they? The question of accuracy is important Ð particularly when one invests a reasonably large amount of money (approximately £600-£1,000) that they are accurate, well constructed and manufactured according to International Standards.
Few independent studies have been published regarding the accuracy of trial lenses. The present study examines three new trial lens sets recently launched onto the market by OptiMed Ophthalmic Medical Instruments (available through Topcon UK). The trial lens sets comprise of 232 lenses in the trial lens types shown in Figure 1.
The lenses are contained in a sturdy, wooden case (Figure 2). For those practitioners who prefer to mount trial lenses into their own consulting room furniture, the trays can easily be removed. The lens mounts for the reduced aperture metal lenses are made of a light, strong alloy and the plastic mount of a rigid polymer. All lenses are colour coded (red for minus, black for plus and white for prisms and auxiliary lenses) and marked according to the BS ISO 9801:1997. A very useful aspect of all three trial lens types was that all the lenses had markings on both sides of the lens, although this is a minor point, it can be very frustrating removing lenses from trial frames simply to orientate the lens in the correct position. The auxiliary lenses have also been designed for practicality. For example, there are two occluders, two pinholes, a plano lens (for those malingerers), a stenopaic slit, a translucent Maddox rod (red is thought to induce accommodation and therefore a clear colour is a welcome change), a frosted lens and red and green dissociation filters.
All reduced aperture metal sets have lenses secured using a crimping process. As a result of this process, thick lenses are more difficult to secure, therefore, most reduced aperture metal sets are made with an aperture less than 24mm. This has the disadvantage of reducing the patient's binocular field and also not allowing the practitioner to view the patient's eye easily. An interesting feature of the Optimed reduced aperture sets was that rather than have a single reduced aperture for all lenses, two variable apertures were present. Low power lenses (below +/-6.50D) had a lens aperture of 24mm, whereas powers above this had lens apertures of 20mm. This means that for the majority of prescriptions the practitioner can enjoy part of the benefit a full-aperture trial lens offers.
All cylinder lenses were marked both on the lens and the mount. Marking the lenses in this fashion provides two key advantages:

Optical centres are set at the geometric centre of the lens
Any axis rotation of the lens from the mount can easily be detected.

According to the ISO standard all complete lenses (lens and mount) must meet a required diameter of 38mm and specific widths. All the trial lenses met this specification. The issue of diameter and width is an important one if one requires ease of fitting into the very latest trial frames.

Methodology
All lenses were measured using the Topcon CL2500 laser autofocimeter, with a resolution of 0.01D for power and 1¡ for lens axis. The autofocimeter lens was cleaned prior to measurement. Each reading was performed after centring the lens with respect to its geometric centre. Cylindrical lenses were carefully aligned along their axis marking in order to measure the cylindrical power and axis.
The spherical lenses from all trial lens set types are clearly very accurate, with only 5 per cent of the lenses greater than ±0.08D from the stated value (Figure 3 and Table 1). Furthermore, as expected, larger errors were only found in lenses of higher power, for example, the maximum error of -0.21D was found in a lens of stated power +20D! Figure 3 shows the error of each trial lens with respect to the magnitude of lens power measured. A cylindrical component is present in few lenses and is generally small in magnitude.
The cylindrical lenses from all trial lens set types are again clearly very accurate, with only 5 per cent of the lenses greater than ±0.10D from the stated value (Figure 4 and Table 2). The axis is also very precise with respect to the lens markings.
The prismatic lens powers from all trial lens set types were very accurate (Table 3). All lenses were within 0.25Æ of the stated value. The axis of the prismatic component was more variable than the cylindrical power trial lenses, but this has little clinical significance.
In conclusion, the new trial lens sets by Optimed are well presented and accurate enough to use in clinical practice with confidence.

Acknowledgement
The author would like to thank Dr. Trusit Dave and Olivia Hunt for their help in compiling this article.

Proprietary interest
This study for funded by Optimed Ophthalmic Medical Instruments Ltd as a independently conducted evaluation of trial lens sets OM232PD, OM232MD and OM232FD.
The author has no financial interest in this or any other product manufactured by Optimed Ophthalmic Medical Instruments.

Dr James Wolffsohn is a senior lecturer in optometry and vision sciences, Aston UniversityOne of the core functions in an eye examination is to refract. Also, whether we like it or not, refraction is indirectly responsible for the success of our practices.
Therefore, there is a need to place emphasis on the importance of trial lens sets within the consulting room. Practitioners must have confidence in the accuracy of lenses within their trial lens sets, so how accurate are they? The question of accuracy is important Ð particularly when one invests a reasonably large amount of money (approximately £600-£1,000) that they are accurate, well constructed and manufactured according to International Standards.
Few independent studies have been published regarding the accuracy of trial lenses. The present study examines three new trial lens sets recently launched onto the market by OptiMed Ophthalmic Medical Instruments (available through Topcon UK). The trial lens sets comprise of 232 lenses in the trial lens types shown in Figure 1.
The lenses are contained in a sturdy, wooden case (Figure 2). For those practitioners who prefer to mount trial lenses into their own consulting room furniture, the trays can easily be removed. The lens mounts for the reduced aperture metal lenses are made of a light, strong alloy and the plastic mount of a rigid polymer. All lenses are colour coded (red for minus, black for plus and white for prisms and auxiliary lenses) and marked according to the BS ISO 9801:1997. A very useful aspect of all three trial lens types was that all the lenses had markings on both sides of the lens, although this is a minor point, it can be very frustrating removing lenses from trial frames simply to orientate the lens in the correct position. The auxiliary lenses have also been designed for practicality. For example, there are two occluders, two pinholes, a plano lens (for those malingerers), a stenopaic slit, a translucent Maddox rod (red is thought to induce accommodation and therefore a clear colour is a welcome change), a frosted lens and red and green dissociation filters.
All reduced aperture metal sets have lenses secured using a crimping process. As a result of this process, thick lenses are more difficult to secure, therefore, most reduced aperture metal sets are made with an aperture less than 24mm. This has the disadvantage of reducing the patient's binocular field and also not allowing the practitioner to view the patient's eye easily. An interesting feature of the Optimed reduced aperture sets was that rather than have a single reduced aperture for all lenses, two variable apertures were present. Low power lenses (below +/-6.50D) had a lens aperture of 24mm, whereas powers above this had lens apertures of 20mm. This means that for the majority of prescriptions the practitioner can enjoy part of the benefit a full-aperture trial lens offers.
All cylinder lenses were marked both on the lens and the mount. Marking the lenses in this fashion provides two key advantages:

Optical centres are set at the geometric centre of the lens
Any axis rotation of the lens from the mount can easily be detected.

According to the ISO standard all complete lenses (lens and mount) must meet a required diameter of 38mm and specific widths. All the trial lenses met this specification. The issue of diameter and width is an important one if one requires ease of fitting into the very latest trial frames.

Methodology
All lenses were measured using the Topcon CL2500 laser autofocimeter, with a resolution of 0.01D for power and 1¡ for lens axis. The autofocimeter lens was cleaned prior to measurement. Each reading was performed after centring the lens with respect to its geometric centre. Cylindrical lenses were carefully aligned along their axis marking in order to measure the cylindrical power and axis.
The spherical lenses from all trial lens set types are clearly very accurate, with only 5 per cent of the lenses greater than ±0.08D from the stated value (Figure 3 and Table 1). Furthermore, as expected, larger errors were only found in lenses of higher power, for example, the maximum error of -0.21D was found in a lens of stated power +20D! Figure 3 shows the error of each trial lens with respect to the magnitude of lens power measured. A cylindrical component is present in few lenses and is generally small in magnitude.
The cylindrical lenses from all trial lens set types are again clearly very accurate, with only 5 per cent of the lenses greater than ±0.10D from the stated value (Figure 4 and Table 2). The axis is also very precise with respect to the lens markings.
The prismatic lens powers from all trial lens set types were very accurate (Table 3). All lenses were within 0.25Æ of the stated value. The axis of the prismatic component was more variable than the cylindrical power trial lenses, but this has little clinical significance.
In conclusion, the new trial lens sets by Optimed are well presented and accurate enough to use in clinical practice with confidence.

Acknowledgement
The author would like to thank Dr. Trusit Dave and Olivia Hunt for their help in compiling this article.

Proprietary interest
This study for funded by Optimed Ophthalmic Medical Instruments Ltd as a independently conducted evaluation of trial lens sets OM232PD, OM232MD and OM232FD.
The author has no financial interest in this or any other product manufactured by Optimed Ophthalmic Medical Instruments.

Dr James Wolffsohn is a senior lecturer in optometry and vision sciences, Aston UniversityOne of the core functions in an eye examination is to refract. Also, whether we like it or not, refraction is indirectly responsible for the success of our practices.
Therefore, there is a need to place emphasis on the importance of trial lens sets within the consulting room. Practitioners must have confidence in the accuracy of lenses within their trial lens sets, so how accurate are they? The question of accuracy is important Ð particularly when one invests a reasonably large amount of money (approximately £600-£1,000) that they are accurate, well constructed and manufactured according to International Standards.
Few independent studies have been published regarding the accuracy of trial lenses. The present study examines three new trial lens sets recently launched onto the market by OptiMed Ophthalmic Medical Instruments (available through Topcon UK). The trial lens sets comprise of 232 lenses in the trial lens types shown in Figure 1.
The lenses are contained in a sturdy, wooden case (Figure 2). For those practitioners who prefer to mount trial lenses into their own consulting room furniture, the trays can easily be removed. The lens mounts for the reduced aperture metal lenses are made of a light, strong alloy and the plastic mount of a rigid polymer. All lenses are colour coded (red for minus, black for plus and white for prisms and auxiliary lenses) and marked according to the BS ISO 9801:1997. A very useful aspect of all three trial lens types was that all the lenses had markings on both sides of the lens, although this is a minor point, it can be very frustrating removing lenses from trial frames simply to orientate the lens in the correct position. The auxiliary lenses have also been designed for practicality. For example, there are two occluders, two pinholes, a plano lens (for those malingerers), a stenopaic slit, a translucent Maddox rod (red is thought to induce accommodation and therefore a clear colour is a welcome change), a frosted lens and red and green dissociation filters.
All reduced aperture metal sets have lenses secured using a crimping process. As a result of this process, thick lenses are more difficult to secure, therefore, most reduced aperture metal sets are made with an aperture less than 24mm. This has the disadvantage of reducing the patient's binocular field and also not allowing the practitioner to view the patient's eye easily. An interesting feature of the Optimed reduced aperture sets was that rather than have a single reduced aperture for all lenses, two variable apertures were present. Low power lenses (below +/-6.50D) had a lens aperture of 24mm, whereas powers above this had lens apertures of 20mm. This means that for the majority of prescriptions the practitioner can enjoy part of the benefit a full-aperture trial lens offers.
All cylinder lenses were marked both on the lens and the mount. Marking the lenses in this fashion provides two key advantages:

Optical centres are set at the geometric centre of the lens
Any axis rotation of the lens from the mount can easily be detected.

According to the ISO standard all complete lenses (lens and mount) must meet a required diameter of 38mm and specific widths. All the trial lenses met this specification. The issue of diameter and width is an important one if one requires ease of fitting into the very latest trial frames.

Methodology
All lenses were measured using the Topcon CL2500 laser autofocimeter, with a resolution of 0.01D for power and 1¡ for lens axis. The autofocimeter lens was cleaned prior to measurement. Each reading was performed after centring the lens with respect to its geometric centre. Cylindrical lenses were carefully aligned along their axis marking in order to measure the cylindrical power and axis.
The spherical lenses from all trial lens set types are clearly very accurate, with only 5 per cent of the lenses greater than ±0.08D from the stated value (Figure 3 and Table 1). Furthermore, as expected, larger errors were only found in lenses of higher power, for example, the maximum error of -0.21D was found in a lens of stated power +20D! Figure 3 shows the error of each trial lens with respect to the magnitude of lens power measured. A cylindrical component is present in few lenses and is generally small in magnitude.
The cylindrical lenses from all trial lens set types are again clearly very accurate, with only 5 per cent of the lenses greater than ±0.10D from the stated value (Figure 4 and Table 2). The axis is also very precise with respect to the lens markings.
The prismatic lens powers from all trial lens set types were very accurate (Table 3). All lenses were within 0.25Æ of the stated value. The axis of the prismatic component was more variable than the cylindrical power trial lenses, but this has little clinical significance.
In conclusion, the new trial lens sets by Optimed are well presented and accurate enough to use in clinical practice with confidence.

Acknowledgement
The author would like to thank Dr. Trusit Dave and Olivia Hunt for their help in compiling this article.

Proprietary interest
This study for funded by Optimed Ophthalmic Medical Instruments Ltd as a independently conducted evaluation of trial lens sets OM232PD, OM232MD and OM232FD.
The author has no financial interest in this or any other product manufactured by Optimed Ophthalmic Medical Instruments.

Dr James Wolffsohn is a senior lecturer in optometry and vision sciences, Aston UniversityOne of the core functions in an eye examination is to refract. Also, whether we like it or not, refraction is indirectly responsible for the success of our practices.
Therefore, there is a need to place emphasis on the importance of trial lens sets within the consulting room. Practitioners must have confidence in the accuracy of lenses within their trial lens sets, so how accurate are they? The question of accuracy is important Ð particularly when one invests a reasonably large amount of money (approximately £600-£1,000) that they are accurate, well constructed and manufactured according to International Standards.
Few independent studies have been published regarding the accuracy of trial lenses. The present study examines three new trial lens sets recently launched onto the market by OptiMed Ophthalmic Medical Instruments (available through Topcon UK). The trial lens sets comprise of 232 lenses in the trial lens types shown in Figure 1.
The lenses are contained in a sturdy, wooden case (Figure 2). For those practitioners who prefer to mount trial lenses into their own consulting room furniture, the trays can easily be removed. The lens mounts for the reduced aperture metal lenses are made of a light, strong alloy and the plastic mount of a rigid polymer. All lenses are colour coded (red for minus, black for plus and white for prisms and auxiliary lenses) and marked according to the BS ISO 9801:1997. A very useful aspect of all three trial lens types was that all the lenses had markings on both sides of the lens, although this is a minor point, it can be very frustrating removing lenses from trial frames simply to orientate the lens in the correct position. The auxiliary lenses have also been designed for practicality. For example, there are two occluders, two pinholes, a plano lens (for those malingerers), a stenopaic slit, a translucent Maddox rod (red is thought to induce accommodation and therefore a clear colour is a welcome change), a frosted lens and red and green dissociation filters.
All reduced aperture metal sets have lenses secured using a crimping process. As a result of this process, thick lenses are more difficult to secure, therefore, most reduced aperture metal sets are made with an aperture less than 24mm. This has the disadvantage of reducing the patient's binocular field and also not allowing the practitioner to view the patient's eye easily. An interesting feature of the Optimed reduced aperture sets was that rather than have a single reduced aperture for all lenses, two variable apertures were present. Low power lenses (below +/-6.50D) had a lens aperture of 24mm, whereas powers above this had lens apertures of 20mm. This means that for the majority of prescriptions the practitioner can enjoy part of the benefit a full-aperture trial lens offers.
All cylinder lenses were marked both on the lens and the mount. Marking the lenses in this fashion provides two key advantages:

Optical centres are set at the geometric centre of the lens
Any axis rotation of the lens from the mount can easily be detected.

According to the ISO standard all complete lenses (lens and mount) must meet a required diameter of 38mm and specific widths. All the trial lenses met this specification. The issue of diameter and width is an important one if one requires ease of fitting into the very latest trial frames.

Methodology
All lenses were measured using the Topcon CL2500 laser autofocimeter, with a resolution of 0.01D for power and 1¡ for lens axis. The autofocimeter lens was cleaned prior to measurement. Each reading was performed after centring the lens with respect to its geometric centre. Cylindrical lenses were carefully aligned along their axis marking in order to measure the cylindrical power and axis.
The spherical lenses from all trial lens set types are clearly very accurate, with only 5 per cent of the lenses greater than ±0.08D from the stated value (Figure 3 and Table 1). Furthermore, as expected, larger errors were only found in lenses of higher power, for example, the maximum error of -0.21D was found in a lens of stated power +20D! Figure 3 shows the error of each trial lens with respect to the magnitude of lens power measured. A cylindrical component is present in few lenses and is generally small in magnitude.
The cylindrical lenses from all trial lens set types are again clearly very accurate, with only 5 per cent of the lenses greater than ±0.10D from the stated value (Figure 4 and Table 2). The axis is also very precise with respect to the lens markings.
The prismatic lens powers from all trial lens set types were very accurate (Table 3). All lenses were within 0.25Æ of the stated value. The axis of the prismatic component was more variable than the cylindrical power trial lenses, but this has little clinical significance.
In conclusion, the new trial lens sets by Optimed are well presented and accurate enough to use in clinical practice with confidence.

Acknowledgement
The author would like to thank Dr. Trusit Dave and Olivia Hunt for their help in compiling this article.

Proprietary interest
This study for funded by Optimed Ophthalmic Medical Instruments Ltd as a independently conducted evaluation of trial lens sets OM232PD, OM232MD and OM232FD.
The author has no financial interest in this or any other product manufactured by Optimed Ophthalmic Medical Instruments.

Dr James Wolffsohn is a senior lecturer in optometry and vision sciences, Aston UniversityOne of the core functions in an eye examination is to refract. Also, whether we like it or not, refraction is indirectly responsible for the success of our practices.
Therefore, there is a need to place emphasis on the importance of trial lens sets within the consulting room. Practitioners must have confidence in the accuracy of lenses within their trial lens sets, so how accurate are they? The question of accuracy is important Ð particularly when one invests a reasonably large amount of money (approximately £600-£1,000) that they are accurate, well constructed and manufactured according to International Standards.
Few independent studies have been published regarding the accuracy of trial lenses. The present study examines three new trial lens sets recently launched onto the market by OptiMed Ophthalmic Medical Instruments (available through Topcon UK). The trial lens sets comprise of 232 lenses in the trial lens types shown in Figure 1.
The lenses are contained in a sturdy, wooden case (Figure 2). For those practitioners who prefer to mount trial lenses into their own consulting room furniture, the trays can easily be removed. The lens mounts for the reduced aperture metal lenses are made of a light, strong alloy and the plastic mount of a rigid polymer. All lenses are colour coded (red for minus, black for plus and white for prisms and auxiliary lenses) and marked according to the BS ISO 9801:1997. A very useful aspect of all three trial lens types was that all the lenses had markings on both sides of the lens, although this is a minor point, it can be very frustrating removing lenses from trial frames simply to orientate the lens in the correct position. The auxiliary lenses have also been designed for practicality. For example, there are two occluders, two pinholes, a plano lens (for those malingerers), a stenopaic slit, a translucent Maddox rod (red is thought to induce accommodation and therefore a clear colour is a welcome change), a frosted lens and red and green dissociation filters.
All reduced aperture metal sets have lenses secured using a crimping process. As a result of this process, thick lenses are more difficult to secure, therefore, most reduced aperture metal sets are made with an aperture less than 24mm. This has the disadvantage of reducing the patient's binocular field and also not allowing the practitioner to view the patient's eye easily. An interesting feature of the Optimed reduced aperture sets was that rather than have a single reduced aperture for all lenses, two variable apertures were present. Low power lenses (below +/-6.50D) had a lens aperture of 24mm, whereas powers above this had lens apertures of 20mm. This means that for the majority of prescriptions the practitioner can enjoy part of the benefit a full-aperture trial lens offers.
All cylinder lenses were marked both on the lens and the mount. Marking the lenses in this fashion provides two key advantages:

Optical centres are set at the geometric centre of the lens
Any axis rotation of the lens from the mount can easily be detected.

According to the ISO standard all complete lenses (lens and mount) must meet a required diameter of 38mm and specific widths. All the trial lenses met this specification. The issue of diameter and width is an important one if one requires ease of fitting into the very latest trial frames.

Methodology
All lenses were measured using the Topcon CL2500 laser autofocimeter, with a resolution of 0.01D for power and 1¡ for lens axis. The autofocimeter lens was cleaned prior to measurement. Each reading was performed after centring the lens with respect to its geometric centre. Cylindrical lenses were carefully aligned along their axis marking in order to measure the cylindrical power and axis.
The spherical lenses from all trial lens set types are clearly very accurate, with only 5 per cent of the lenses greater than ±0.08D from the stated value (Figure 3 and Table 1). Furthermore, as expected, larger errors were only found in lenses of higher power, for example, the maximum error of -0.21D was found in a lens of stated power +20D! Figure 3 shows the error of each trial lens with respect to the magnitude of lens power measured. A cylindrical component is present in few lenses and is generally small in magnitude.
The cylindrical lenses from all trial lens set types are again clearly very accurate, with only 5 per cent of the lenses greater than ±0.10D from the stated value (Figure 4 and Table 2). The axis is also very precise with respect to the lens markings.
The prismatic lens powers from all trial lens set types were very accurate (Table 3). All lenses were within 0.25Æ of the stated value. The axis of the prismatic component was more variable than the cylindrical power trial lenses, but this has little clinical significance.
In conclusion, the new trial lens sets by Optimed are well presented and accurate enough to use in clinical practice with confidence.

Acknowledgement
The author would like to thank Dr. Trusit Dave and Olivia Hunt for their help in compiling this article.

Proprietary interest
This study for funded by Optimed Ophthalmic Medical Instruments Ltd as a independently conducted evaluation of trial lens sets OM232PD, OM232MD and OM232FD.
The author has no financial interest in this or any other product manufactured by Optimed Ophthalmic Medical Instruments.

Dr James Wolffsohn is a senior lecturer in optometry and vision sciences, Aston University