The majority of multifocal soft lenses currently available to the practitioner utilise the principle of simultaneous vision and this article will concern itself with currently available simultaneous vision designs.
The simultaneous vision soft lenses on the market employ centre near aspheric correction, centre distance aspheric correction or centre distance multizone optics. The strength of these designs lies in their success in providing intermediate vision, as well as distance and near. Intermediate vision is critical in the computer-based workplace and is frequently employed in social occasions.
The exception in the multifocal soft lens market is the Triton lens, a soft translating bifocal from Gelflex Laboratories in Perth, Australia. While translating bifocals are historically less successful in soft lens material than in RGP material, this may be a design which overcomes some of the visual compromise associated with simultaneous vision.
Equally, however, translating bifocals present problems when near targets are not positioned in the lower half of the visual field, and as they have no intermediate portion, tasks such as computer use may be problematic.
Managing patient expectations
When we present the patient with simultaneous vision, we know that some will perceive their quality of vision has been degraded compared to spectacles. Indeed some patients will perceive this problem with single-vision lenses and there have been papers which ably explain reasons why vision with soft lenses may disappoint.1-3
Some patients are happy to accept this situation and some are not. Acceptance will depend not only on ability to adapt to such vision but also on expectation, motivation and visual requirements. It is, therefore, very important for the practitioner to address all these points, this process is just as important as the over-refraction process.
Careful questioning of the patient is essential to establish the above in addition to normal suitability criteria for any potential contact lens wearer. We must prepare our patients for the possibility of visual compromise. The quality may not be equal to spectacles although measured acuity often is.
One challenge for the practitioner is to convey this to the patient without off-putting negativity. It may help to explain how the lenses work, how that differs from spectacles and therefore the challenge of achieving good vision at all distances. If the patient accepts this scenario then it is a measure of their motivation and if they experience little or no compromise then they are extremely satisfied.
It is also worth addressing our expectations as the practitioner. We are normally seeking the best possible acuities for our patients when prescribing spectacles or contact lenses.
It may be necessary to rethink this ideology. This is not to say we should lower our standards in any way but if we can meet the needs and expectations of our patients then we have definitely succeeded.
We need to allow the patient to judge whether the outcome is successful, with the proviso that they are able, or legal, to attain the desired standard for any required task, such as driving.
Motivation
This is in common with any type of contact lens. As well as the visual aspect of multifocals, patients need to consider adaptation, handling, aftercare and cost issues before proceeding. A well informed patient will be less likely to feel disappointed.
Visual requirements
We must be sure that a multifocal is the optimum choice. Some occupations and hobbies may indicate a different choice for the presbyope. We need to know what our patient needs to see, before we can judge if these lenses will meet their requirements. Also we need to learn which is their priority, be it distance or near, in order to offer the best balance of prescription to suit their needs.
Listening skills are key here as well as communication skills and a sense of what is achievable. Predicting success is very difficult and it is suggested that the practitioner offers a trial if the patient fulfils the above criteria. Being flexible and keeping an open mind are helpful.
Prescribing commonalities
Despite the variety of products available, there are several commonalities in fitting procedure for today's soft multifocal lenses. Remembering these key points can greatly simplify lens fitting.
Always use binocular viewing during over-refraction
This is a departure from the single-vision lens over-refraction technique we are used to because neither eye is occluded or fogged during over refraction. With simultaneous vision lenses, the patient is making a mental selection between the near or distance vision image in each eye at any given time. Binocular over-refraction allows us to assess the patient's ability to combine the images from both eyes, and gives us a better idea of their functional vision.
Chart selection
As well as recording acuities, it may be useful to use a 'real life' scenario to judge power changes, rather than a conventional, high contrast chart. If you can use the view out of a window, even better. A disappointing trial after a 'successful' fitting can often be pre-empted that way. Often +0.25DS change will have minimal or no effect in a consulting room but will be more noticeable when 'true' distance is viewed. When over-refracting, use a large target such as a 6/9 letter on the Snellen chart. This will help prevent over minus in the final lens power, but this does not represent best acuity. This is measured at the end.
Equipment for over-refraction
The use of a phoropter is not advised as this may alter the level of light on the eye, therefore affecting the pupil size. A phoropter can also hinder quick assessment of power changes between distance and near. It also obscures facial expressions that can be quite informative. The suggested option is using a ± 0.25DS twirl. This is a simple, versatile and quick method. As most cases will only require a power modification of 0.25DS, it is recommended that each 0.25DS power change is tried before making further adjustments. Hand-held trial lenses could be used if a twirl is not available.
Settling time
A minimum of 20 minutes is recommended. There does appear to be some neurological adaptation in that short time and many patients give a much more positive response even after 20 minutes. This time is also important for a subjective assessment of the vision to be made.
Small changes
Most final prescriptions should be within 0.25DS of the initial trial lens selection. This minimum change can have a significant effect on acuity, considerably more than would be expected with a single-vision lens. Therefore, making larger changes may well 'over-shoot' the optimum power.
Assess effect of each power change
After each suggested or demonstrated power change, the effect of that change must be checked at both distance and near. Only make a change if there is significant improvement of distance vision without compromise at near, and vice versa.
We are trying to achieve the best balance of distance and near vision, according to the patient's priorities.
When to stop power adjustments
It is recommended that two changes should be sufficient if a design is going to be successful. Further changes are unlikely to succeed and will not only waste chair time but will be disheartening to both patient and practitioner.
Trial period
The purpose of the trial is to reach a point where our patient feels comfortable with their vision and confident enough to try an extended trial. A two to four day supply should suffice and allow the patient to try the lenses in a variety of situations. It is important not to allow the trial period to go for more than four days in case a further power adjustment proves necessary.
Fitting
Normal soft lens fitting criteria apply. With these designs good centration is particularly important.
TWO SOFT LENS DESIGNS
The parameters of two soft lenses designed for correction of presbyopia are listed in Table 1. Of note are the differences in material, diameter and the style of addition between each lens type.
Binocular over-refraction
An example of the binocular over-refraction method applied to Focus Dailies Progressives (Figure 1) is detailed.
Select a trial lens using the spherical equivalent of the spectacle prescription plus half the addition, remembering to adjust for vertex distance. Alternatively, use the trial lens selection table provided by the manufacturer, this allows for vertex distance. It is not necessary to specify the addition separately as this is a progressive design and will correct spectacle reading additions up to +3.00DS. So only one power is specified for each lens.
After inserting the trial lenses, allow a minimum of 20 minutes to settle. There does appear to be some acceptance of simultaneous vision even in that short time. Ideally, this short trial would take place out of the practice so that the patient experiences a familiar environment in which to assess the vision.
The author strongly recommends you ask the patient to score the quality of vision out of 10 for both distance and near vision. This exercise tells you whether the patient is comfortable with this design of lens. Scores of 7 and over would indicate likely acceptance of simultaneous vision.
Secondly, these scores indicate where the problem area is and therefore the likely over-refraction (Table 3). A typical response may be 8 for distance and 6 for near, so for that case we would know we have to improve near vision. If they give 8 for both distance and near, then record visual acuities and discuss a two to four-day trial. Scores of 5 or less for both distances represents a challenge. If this is the case, enhanced monovision is often successful (see later).
It is recommended to record binocular scores first and then Snellen acuity. Patients occasionally wish to change their scores after being presented with a chart but the grading of vision in a familiar environment rather than a consulting room is more relevant and therefore more useful for trouble-shooting.
Refining the vision with Focus Progressive lenses
Case 1 Ð Poor distance vision
Show -0.25DS binocularly, to keep the binocular vision balanced. If distance vision is measurably better with the additional power, check that the near vision is still acceptable; if so, then trial the new powers.
It is not normally necessary for the patient to take another 20 minutes to evaluate and report revised scores.
If the -0.25DS change in both eyes results in poor near vision, show -0.25DS in the distance to each eye in turn, and ask the patient to make a choice between the right or left eye. This approach offers the flexibility that using dominance does not. Evaluate which eye is preferred and now check that the change would be accepted for near. If so, change that one lens, re-evaluate distance and near vision binocularly then trial the new powers. If the patient has no preference between right or left eye in distance viewing, then check if they have a preference for near viewing and adjust the powers accordingly.
Case 2: Poor near vision
Show +0.25DS for near vision. If this improves near vision, ensure that change is tolerated in the distance and then proceed to a trial with new power.
If the +0.25DS change in both eyes causes blur of distance vision, show +0.25DS to each eye in turn for near and evaluate which eye improves more. Now ensure that this monocular change would be accepted for distance, if so then proceed to a trial with the new power.
If the patient shows no preference when offered 0.25 to each eye in turn, repeat the exercise at 'the other distance' to determine which lens to change.
If there is still no preference, then use your judgement relating to the dominant eye. Otherwise, dominance is not relevant in the above procedure.
Either of these over refraction routines should take no longer than a couple of minutes. Multifocal fitting does not have to be time consuming as the above steps have hopefully demonstrated.
Please note that Dailies Progressive trials should not be used to prescribe monthly progressives and vice versa. There will occasionally be power differences due to material and manufacturing differences.
Case 3: Modified monovision
If the above does not yield a satisfactory result, it may be worth trying modified multifocal monovision. Now it is necessary to determine dominance. This would entail fitting a progressive lens biased towards distance in the dominant eye with a progressive lens biased towards near in the other (Figure 1).
Case 4: Enhanced monovision
This has the advantage over monovision with single-vision lenses by maintaining stereopsis at distance or near (Figure 2).
The dominant eye is fitted with a single-vision lens biased for distance or near vision, depending on the individual's requirements. The non-dominant eye is fitted with a multifocal lens.
Consider using a toric lens (either daily, twice weekly or monthly disposable, depending on the modality prescribed) in the dominant eye with the multifocal in the other if the patient has more than 0.75 cylinder in their prescription.
Remember, after each power modification, obtain revised scores from the patient to ensure improvement achieved (this will reassure and motivate the patient).
FREQUENCY 55 MULTIFOCAL
Refining the vision with Frequency 55 Multifocal (Figure 4)
Case 1: Poor distance vision
Show -0.25 for distance to D (dominant eye) lens and check reading not compromised, and make the change without changing the add power. If more than -0.25 is required to improve distance and is not tolerated for near, then consider reducing the add of the D lens instead. Otherwise it is possible to reduce the add on both lenses, add -0.25 to the distance power of both or use D lenses for both eyes
Case 2: Poor near vision
Show +0.25 for near viewing and adjust the distance power of N (non-dominant) lens. If more plus power required, increase add in N lens. Otherwise, add +0.25 to the distance powers of both lenses, increase add in both, or use two N lenses. Enhanced monovision may be used if a successful outcome not achieved with the above procedure.
Conclusion
A review of population trends in the UK indicate that people in the age group 50-65 currently constitute a significant market of about 10 million. This is set to grow over the next 20 years to some 13.5 million. This is a growing market with a higher than average disposable income in many cases. Our responsibility, as eye care practitioners, is to fully inform our patients of the range of options available to the presbyope. Success with these lenses is very rewarding for you and your patients, and a considerable practice builder. The author encourages you to be adventurous and enjoy the challenge.
References
1 Port M. Why can't I see in my CLs? optician, 2002; November 1, 5875: 224.
2 Harvey W and Long W. The optics of soft toric fitting: Vision through contact lenses. optician, 203; October 3, 5921: 226.
3 Hough A. Soft bifocal contact lenses: the limits of performance. Contact Lens & Anterior Eye, 2002; 25: 161-175.
Acknowledgements
Thanks to Dr Vicki Evans and Margaret Richmond of Ciba Vision and John Rogers of CooperVision for their help in the writing of this article.
Jayne Schofield is a contact lens consultant with Ciba Vision and visiting clinician at City UniversityThe majority of multifocal soft lenses currently available to the practitioner utilise the principle of simultaneous vision and this article will concern itself with currently available simultaneous vision designs.
The simultaneous vision soft lenses on the market employ centre near aspheric correction, centre distance aspheric correction or centre distance multizone optics. The strength of these designs lies in their success in providing intermediate vision, as well as distance and near. Intermediate vision is critical in the computer-based workplace and is frequently employed in social occasions.
The exception in the multifocal soft lens market is the Triton lens, a soft translating bifocal from Gelflex Laboratories in Perth, Australia. While translating bifocals are historically less successful in soft lens material than in RGP material, this may be a design which overcomes some of the visual compromise associated with simultaneous vision.
Equally, however, translating bifocals present problems when near targets are not positioned in the lower half of the visual field, and as they have no intermediate portion, tasks such as computer use may be problematic.
Managing patient expectations
When we present the patient with simultaneous vision, we know that some will perceive their quality of vision has been degraded compared to spectacles. Indeed some patients will perceive this problem with single-vision lenses and there have been papers which ably explain reasons why vision with soft lenses may disappoint.1-3
Some patients are happy to accept this situation and some are not. Acceptance will depend not only on ability to adapt to such vision but also on expectation, motivation and visual requirements. It is, therefore, very important for the practitioner to address all these points, this process is just as important as the over-refraction process.
Careful questioning of the patient is essential to establish the above in addition to normal suitability criteria for any potential contact lens wearer. We must prepare our patients for the possibility of visual compromise. The quality may not be equal to spectacles although measured acuity often is.
One challenge for the practitioner is to convey this to the patient without off-putting negativity. It may help to explain how the lenses work, how that differs from spectacles and therefore the challenge of achieving good vision at all distances. If the patient accepts this scenario then it is a measure of their motivation and if they experience little or no compromise then they are extremely satisfied.
It is also worth addressing our expectations as the practitioner. We are normally seeking the best possible acuities for our patients when prescribing spectacles or contact lenses.
It may be necessary to rethink this ideology. This is not to say we should lower our standards in any way but if we can meet the needs and expectations of our patients then we have definitely succeeded.
We need to allow the patient to judge whether the outcome is successful, with the proviso that they are able, or legal, to attain the desired standard for any required task, such as driving.
Motivation
This is in common with any type of contact lens. As well as the visual aspect of multifocals, patients need to consider adaptation, handling, aftercare and cost issues before proceeding. A well informed patient will be less likely to feel disappointed.
Visual requirements
We must be sure that a multifocal is the optimum choice. Some occupations and hobbies may indicate a different choice for the presbyope. We need to know what our patient needs to see, before we can judge if these lenses will meet their requirements. Also we need to learn which is their priority, be it distance or near, in order to offer the best balance of prescription to suit their needs.
Listening skills are key here as well as communication skills and a sense of what is achievable. Predicting success is very difficult and it is suggested that the practitioner offers a trial if the patient fulfils the above criteria. Being flexible and keeping an open mind are helpful.
Prescribing commonalities
Despite the variety of products available, there are several commonalities in fitting procedure for today's soft multifocal lenses. Remembering these key points can greatly simplify lens fitting.
Always use binocular viewing during over-refraction
This is a departure from the single-vision lens over-refraction technique we are used to because neither eye is occluded or fogged during over refraction. With simultaneous vision lenses, the patient is making a mental selection between the near or distance vision image in each eye at any given time. Binocular over-refraction allows us to assess the patient's ability to combine the images from both eyes, and gives us a better idea of their functional vision.
Chart selection
As well as recording acuities, it may be useful to use a 'real life' scenario to judge power changes, rather than a conventional, high contrast chart. If you can use the view out of a window, even better. A disappointing trial after a 'successful' fitting can often be pre-empted that way. Often +0.25DS change will have minimal or no effect in a consulting room but will be more noticeable when 'true' distance is viewed. When over-refracting, use a large target such as a 6/9 letter on the Snellen chart. This will help prevent over minus in the final lens power, but this does not represent best acuity. This is measured at the end.
Equipment for over-refraction
The use of a phoropter is not advised as this may alter the level of light on the eye, therefore affecting the pupil size. A phoropter can also hinder quick assessment of power changes between distance and near. It also obscures facial expressions that can be quite informative. The suggested option is using a ± 0.25DS twirl. This is a simple, versatile and quick method. As most cases will only require a power modification of 0.25DS, it is recommended that each 0.25DS power change is tried before making further adjustments. Hand-held trial lenses could be used if a twirl is not available.
Settling time
A minimum of 20 minutes is recommended. There does appear to be some neurological adaptation in that short time and many patients give a much more positive response even after 20 minutes. This time is also important for a subjective assessment of the vision to be made.
Small changes
Most final prescriptions should be within 0.25DS of the initial trial lens selection. This minimum change can have a significant effect on acuity, considerably more than would be expected with a single-vision lens. Therefore, making larger changes may well 'over-shoot' the optimum power.
Assess effect of each power change
After each suggested or demonstrated power change, the effect of that change must be checked at both distance and near. Only make a change if there is significant improvement of distance vision without compromise at near, and vice versa.
We are trying to achieve the best balance of distance and near vision, according to the patient's priorities.
When to stop power adjustments
It is recommended that two changes should be sufficient if a design is going to be successful. Further changes are unlikely to succeed and will not only waste chair time but will be disheartening to both patient and practitioner.
Trial period
The purpose of the trial is to reach a point where our patient feels comfortable with their vision and confident enough to try an extended trial. A two to four day supply should suffice and allow the patient to try the lenses in a variety of situations. It is important not to allow the trial period to go for more than four days in case a further power adjustment proves necessary.
Fitting
Normal soft lens fitting criteria apply. With these designs good centration is particularly important.
TWO SOFT LENS DESIGNS
The parameters of two soft lenses designed for correction of presbyopia are listed in Table 1. Of note are the differences in material, diameter and the style of addition between each lens type.
Binocular over-refraction
An example of the binocular over-refraction method applied to Focus Dailies Progressives (Figure 1) is detailed.
Select a trial lens using the spherical equivalent of the spectacle prescription plus half the addition, remembering to adjust for vertex distance. Alternatively, use the trial lens selection table provided by the manufacturer, this allows for vertex distance. It is not necessary to specify the addition separately as this is a progressive design and will correct spectacle reading additions up to +3.00DS. So only one power is specified for each lens.
After inserting the trial lenses, allow a minimum of 20 minutes to settle. There does appear to be some acceptance of simultaneous vision even in that short time. Ideally, this short trial would take place out of the practice so that the patient experiences a familiar environment in which to assess the vision.
The author strongly recommends you ask the patient to score the quality of vision out of 10 for both distance and near vision. This exercise tells you whether the patient is comfortable with this design of lens. Scores of 7 and over would indicate likely acceptance of simultaneous vision.
Secondly, these scores indicate where the problem area is and therefore the likely over-refraction (Table 3). A typical response may be 8 for distance and 6 for near, so for that case we would know we have to improve near vision. If they give 8 for both distance and near, then record visual acuities and discuss a two to four-day trial. Scores of 5 or less for both distances represents a challenge. If this is the case, enhanced monovision is often successful (see later).
It is recommended to record binocular scores first and then Snellen acuity. Patients occasionally wish to change their scores after being presented with a chart but the grading of vision in a familiar environment rather than a consulting room is more relevant and therefore more useful for trouble-shooting.
Refining the vision with Focus Progressive lenses
Case 1 Ð Poor distance vision
Show -0.25DS binocularly, to keep the binocular vision balanced. If distance vision is measurably better with the additional power, check that the near vision is still acceptable; if so, then trial the new powers.
It is not normally necessary for the patient to take another 20 minutes to evaluate and report revised scores.
If the -0.25DS change in both eyes results in poor near vision, show -0.25DS in the distance to each eye in turn, and ask the patient to make a choice between the right or left eye. This approach offers the flexibility that using dominance does not. Evaluate which eye is preferred and now check that the change would be accepted for near. If so, change that one lens, re-evaluate distance and near vision binocularly then trial the new powers. If the patient has no preference between right or left eye in distance viewing, then check if they have a preference for near viewing and adjust the powers accordingly.
Case 2: Poor near vision
Show +0.25DS for near vision. If this improves near vision, ensure that change is tolerated in the distance and then proceed to a trial with new power.
If the +0.25DS change in both eyes causes blur of distance vision, show +0.25DS to each eye in turn for near and evaluate which eye improves more. Now ensure that this monocular change would be accepted for distance, if so then proceed to a trial with the new power.
If the patient shows no preference when offered 0.25 to each eye in turn, repeat the exercise at 'the other distance' to determine which lens to change.
If there is still no preference, then use your judgement relating to the dominant eye. Otherwise, dominance is not relevant in the above procedure.
Either of these over refraction routines should take no longer than a couple of minutes. Multifocal fitting does not have to be time consuming as the above steps have hopefully demonstrated.
Please note that Dailies Progressive trials should not be used to prescribe monthly progressives and vice versa. There will occasionally be power differences due to material and manufacturing differences.
Case 3: Modified monovision
If the above does not yield a satisfactory result, it may be worth trying modified multifocal monovision. Now it is necessary to determine dominance. This would entail fitting a progressive lens biased towards distance in the dominant eye with a progressive lens biased towards near in the other (Figure 1).
Case 4: Enhanced monovision
This has the advantage over monovision with single-vision lenses by maintaining stereopsis at distance or near (Figure 2).
The dominant eye is fitted with a single-vision lens biased for distance or near vision, depending on the individual's requirements. The non-dominant eye is fitted with a multifocal lens.
Consider using a toric lens (either daily, twice weekly or monthly disposable, depending on the modality prescribed) in the dominant eye with the multifocal in the other if the patient has more than 0.75 cylinder in their prescription.
Remember, after each power modification, obtain revised scores from the patient to ensure improvement achieved (this will reassure and motivate the patient).
FREQUENCY 55 MULTIFOCAL
Refining the vision with Frequency 55 Multifocal (Figure 4)
Case 1: Poor distance vision
Show -0.25 for distance to D (dominant eye) lens and check reading not compromised, and make the change without changing the add power. If more than -0.25 is required to improve distance and is not tolerated for near, then consider reducing the add of the D lens instead. Otherwise it is possible to reduce the add on both lenses, add -0.25 to the distance power of both or use D lenses for both eyes
Case 2: Poor near vision
Show +0.25 for near viewing and adjust the distance power of N (non-dominant) lens. If more plus power required, increase add in N lens. Otherwise, add +0.25 to the distance powers of both lenses, increase add in both, or use two N lenses. Enhanced monovision may be used if a successful outcome not achieved with the above procedure.
Conclusion
A review of population trends in the UK indicate that people in the age group 50-65 currently constitute a significant market of about 10 million. This is set to grow over the next 20 years to some 13.5 million. This is a growing market with a higher than average disposable income in many cases. Our responsibility, as eye care practitioners, is to fully inform our patients of the range of options available to the presbyope. Success with these lenses is very rewarding for you and your patients, and a considerable practice builder. The author encourages you to be adventurous and enjoy the challenge.
References
1 Port M. Why can't I see in my CLs? optician, 2002; November 1, 5875: 224.
2 Harvey W and Long W. The optics of soft toric fitting: Vision through contact lenses. optician, 203; October 3, 5921: 226.
3 Hough A. Soft bifocal contact lenses: the limits of performance. Contact Lens & Anterior Eye, 2002; 25: 161-175.
Acknowledgements
Thanks to Dr Vicki Evans and Margaret Richmond of Ciba Vision and John Rogers of CooperVision for their help in the writing of this article.
Jayne Schofield is a contact lens consultant with Ciba Vision and visiting clinician at City UniversityThe majority of multifocal soft lenses currently available to the practitioner utilise the principle of simultaneous vision and this article will concern itself with currently available simultaneous vision designs.
The simultaneous vision soft lenses on the market employ centre near aspheric correction, centre distance aspheric correction or centre distance multizone optics. The strength of these designs lies in their success in providing intermediate vision, as well as distance and near. Intermediate vision is critical in the computer-based workplace and is frequently employed in social occasions.
The exception in the multifocal soft lens market is the Triton lens, a soft translating bifocal from Gelflex Laboratories in Perth, Australia. While translating bifocals are historically less successful in soft lens material than in RGP material, this may be a design which overcomes some of the visual compromise associated with simultaneous vision.
Equally, however, translating bifocals present problems when near targets are not positioned in the lower half of the visual field, and as they have no intermediate portion, tasks such as computer use may be problematic.
Managing patient expectations
When we present the patient with simultaneous vision, we know that some will perceive their quality of vision has been degraded compared to spectacles. Indeed some patients will perceive this problem with single-vision lenses and there have been papers which ably explain reasons why vision with soft lenses may disappoint.1-3
Some patients are happy to accept this situation and some are not. Acceptance will depend not only on ability to adapt to such vision but also on expectation, motivation and visual requirements. It is, therefore, very important for the practitioner to address all these points, this process is just as important as the over-refraction process.
Careful questioning of the patient is essential to establish the above in addition to normal suitability criteria for any potential contact lens wearer. We must prepare our patients for the possibility of visual compromise. The quality may not be equal to spectacles although measured acuity often is.
One challenge for the practitioner is to convey this to the patient without off-putting negativity. It may help to explain how the lenses work, how that differs from spectacles and therefore the challenge of achieving good vision at all distances. If the patient accepts this scenario then it is a measure of their motivation and if they experience little or no compromise then they are extremely satisfied.
It is also worth addressing our expectations as the practitioner. We are normally seeking the best possible acuities for our patients when prescribing spectacles or contact lenses.
It may be necessary to rethink this ideology. This is not to say we should lower our standards in any way but if we can meet the needs and expectations of our patients then we have definitely succeeded.
We need to allow the patient to judge whether the outcome is successful, with the proviso that they are able, or legal, to attain the desired standard for any required task, such as driving.
Motivation
This is in common with any type of contact lens. As well as the visual aspect of multifocals, patients need to consider adaptation, handling, aftercare and cost issues before proceeding. A well informed patient will be less likely to feel disappointed.
Visual requirements
We must be sure that a multifocal is the optimum choice. Some occupations and hobbies may indicate a different choice for the presbyope. We need to know what our patient needs to see, before we can judge if these lenses will meet their requirements. Also we need to learn which is their priority, be it distance or near, in order to offer the best balance of prescription to suit their needs.
Listening skills are key here as well as communication skills and a sense of what is achievable. Predicting success is very difficult and it is suggested that the practitioner offers a trial if the patient fulfils the above criteria. Being flexible and keeping an open mind are helpful.
Prescribing commonalities
Despite the variety of products available, there are several commonalities in fitting procedure for today's soft multifocal lenses. Remembering these key points can greatly simplify lens fitting.
Always use binocular viewing during over-refraction
This is a departure from the single-vision lens over-refraction technique we are used to because neither eye is occluded or fogged during over refraction. With simultaneous vision lenses, the patient is making a mental selection between the near or distance vision image in each eye at any given time. Binocular over-refraction allows us to assess the patient's ability to combine the images from both eyes, and gives us a better idea of their functional vision.
Chart selection
As well as recording acuities, it may be useful to use a 'real life' scenario to judge power changes, rather than a conventional, high contrast chart. If you can use the view out of a window, even better. A disappointing trial after a 'successful' fitting can often be pre-empted that way. Often +0.25DS change will have minimal or no effect in a consulting room but will be more noticeable when 'true' distance is viewed. When over-refracting, use a large target such as a 6/9 letter on the Snellen chart. This will help prevent over minus in the final lens power, but this does not represent best acuity. This is measured at the end.
Equipment for over-refraction
The use of a phoropter is not advised as this may alter the level of light on the eye, therefore affecting the pupil size. A phoropter can also hinder quick assessment of power changes between distance and near. It also obscures facial expressions that can be quite informative. The suggested option is using a ± 0.25DS twirl. This is a simple, versatile and quick method. As most cases will only require a power modification of 0.25DS, it is recommended that each 0.25DS power change is tried before making further adjustments. Hand-held trial lenses could be used if a twirl is not available.
Settling time
A minimum of 20 minutes is recommended. There does appear to be some neurological adaptation in that short time and many patients give a much more positive response even after 20 minutes. This time is also important for a subjective assessment of the vision to be made.
Small changes
Most final prescriptions should be within 0.25DS of the initial trial lens selection. This minimum change can have a significant effect on acuity, considerably more than would be expected with a single-vision lens. Therefore, making larger changes may well 'over-shoot' the optimum power.
Assess effect of each power change
After each suggested or demonstrated power change, the effect of that change must be checked at both distance and near. Only make a change if there is significant improvement of distance vision without compromise at near, and vice versa.
We are trying to achieve the best balance of distance and near vision, according to the patient's priorities.
When to stop power adjustments
It is recommended that two changes should be sufficient if a design is going to be successful. Further changes are unlikely to succeed and will not only waste chair time but will be disheartening to both patient and practitioner.
Trial period
The purpose of the trial is to reach a point where our patient feels comfortable with their vision and confident enough to try an extended trial. A two to four day supply should suffice and allow the patient to try the lenses in a variety of situations. It is important not to allow the trial period to go for more than four days in case a further power adjustment proves necessary.
Fitting
Normal soft lens fitting criteria apply. With these designs good centration is particularly important.
TWO SOFT LENS DESIGNS
The parameters of two soft lenses designed for correction of presbyopia are listed in Table 1. Of note are the differences in material, diameter and the style of addition between each lens type.
Binocular over-refraction
An example of the binocular over-refraction method applied to Focus Dailies Progressives (Figure 1) is detailed.
Select a trial lens using the spherical equivalent of the spectacle prescription plus half the addition, remembering to adjust for vertex distance. Alternatively, use the trial lens selection table provided by the manufacturer, this allows for vertex distance. It is not necessary to specify the addition separately as this is a progressive design and will correct spectacle reading additions up to +3.00DS. So only one power is specified for each lens.
After inserting the trial lenses, allow a minimum of 20 minutes to settle. There does appear to be some acceptance of simultaneous vision even in that short time. Ideally, this short trial would take place out of the practice so that the patient experiences a familiar environment in which to assess the vision.
The author strongly recommends you ask the patient to score the quality of vision out of 10 for both distance and near vision. This exercise tells you whether the patient is comfortable with this design of lens. Scores of 7 and over would indicate likely acceptance of simultaneous vision.
Secondly, these scores indicate where the problem area is and therefore the likely over-refraction (Table 3). A typical response may be 8 for distance and 6 for near, so for that case we would know we have to improve near vision. If they give 8 for both distance and near, then record visual acuities and discuss a two to four-day trial. Scores of 5 or less for both distances represents a challenge. If this is the case, enhanced monovision is often successful (see later).
It is recommended to record binocular scores first and then Snellen acuity. Patients occasionally wish to change their scores after being presented with a chart but the grading of vision in a familiar environment rather than a consulting room is more relevant and therefore more useful for trouble-shooting.
Refining the vision with Focus Progressive lenses
Case 1 Ð Poor distance vision
Show -0.25DS binocularly, to keep the binocular vision balanced. If distance vision is measurably better with the additional power, check that the near vision is still acceptable; if so, then trial the new powers.
It is not normally necessary for the patient to take another 20 minutes to evaluate and report revised scores.
If the -0.25DS change in both eyes results in poor near vision, show -0.25DS in the distance to each eye in turn, and ask the patient to make a choice between the right or left eye. This approach offers the flexibility that using dominance does not. Evaluate which eye is preferred and now check that the change would be accepted for near. If so, change that one lens, re-evaluate distance and near vision binocularly then trial the new powers. If the patient has no preference between right or left eye in distance viewing, then check if they have a preference for near viewing and adjust the powers accordingly.
Case 2: Poor near vision
Show +0.25DS for near vision. If this improves near vision, ensure that change is tolerated in the distance and then proceed to a trial with new power.
If the +0.25DS change in both eyes causes blur of distance vision, show +0.25DS to each eye in turn for near and evaluate which eye improves more. Now ensure that this monocular change would be accepted for distance, if so then proceed to a trial with the new power.
If the patient shows no preference when offered 0.25 to each eye in turn, repeat the exercise at 'the other distance' to determine which lens to change.
If there is still no preference, then use your judgement relating to the dominant eye. Otherwise, dominance is not relevant in the above procedure.
Either of these over refraction routines should take no longer than a couple of minutes. Multifocal fitting does not have to be time consuming as the above steps have hopefully demonstrated.
Please note that Dailies Progressive trials should not be used to prescribe monthly progressives and vice versa. There will occasionally be power differences due to material and manufacturing differences.
Case 3: Modified monovision
If the above does not yield a satisfactory result, it may be worth trying modified multifocal monovision. Now it is necessary to determine dominance. This would entail fitting a progressive lens biased towards distance in the dominant eye with a progressive lens biased towards near in the other (Figure 1).
Case 4: Enhanced monovision
This has the advantage over monovision with single-vision lenses by maintaining stereopsis at distance or near (Figure 2).
The dominant eye is fitted with a single-vision lens biased for distance or near vision, depending on the individual's requirements. The non-dominant eye is fitted with a multifocal lens.
Consider using a toric lens (either daily, twice weekly or monthly disposable, depending on the modality prescribed) in the dominant eye with the multifocal in the other if the patient has more than 0.75 cylinder in their prescription.
Remember, after each power modification, obtain revised scores from the patient to ensure improvement achieved (this will reassure and motivate the patient).
FREQUENCY 55 MULTIFOCAL
Refining the vision with Frequency 55 Multifocal (Figure 4)
Case 1: Poor distance vision
Show -0.25 for distance to D (dominant eye) lens and check reading not compromised, and make the change without changing the add power. If more than -0.25 is required to improve distance and is not tolerated for near, then consider reducing the add of the D lens instead. Otherwise it is possible to reduce the add on both lenses, add -0.25 to the distance power of both or use D lenses for both eyes
Case 2: Poor near vision
Show +0.25 for near viewing and adjust the distance power of N (non-dominant) lens. If more plus power required, increase add in N lens. Otherwise, add +0.25 to the distance powers of both lenses, increase add in both, or use two N lenses. Enhanced monovision may be used if a successful outcome not achieved with the above procedure.
Conclusion
A review of population trends in the UK indicate that people in the age group 50-65 currently constitute a significant market of about 10 million. This is set to grow over the next 20 years to some 13.5 million. This is a growing market with a higher than average disposable income in many cases. Our responsibility, as eye care practitioners, is to fully inform our patients of the range of options available to the presbyope. Success with these lenses is very rewarding for you and your patients, and a considerable practice builder. The author encourages you to be adventurous and enjoy the challenge.
References
1 Port M. Why can't I see in my CLs? optician, 2002; November 1, 5875: 224.
2 Harvey W and Long W. The optics of soft toric fitting: Vision through contact lenses. optician, 203; October 3, 5921: 226.
3 Hough A. Soft bifocal contact lenses: the limits of performance. Contact Lens & Anterior Eye, 2002; 25: 161-175.
Acknowledgements
Thanks to Dr Vicki Evans and Margaret Richmond of Ciba Vision and John Rogers of CooperVision for their help in the writing of this article.
Jayne Schofield is a contact lens consultant with Ciba Vision and visiting clinician at City UniversityThe majority of multifocal soft lenses currently available to the practitioner utilise the principle of simultaneous vision and this article will concern itself with currently available simultaneous vision designs.
The simultaneous vision soft lenses on the market employ centre near aspheric correction, centre distance aspheric correction or centre distance multizone optics. The strength of these designs lies in their success in providing intermediate vision, as well as distance and near. Intermediate vision is critical in the computer-based workplace and is frequently employed in social occasions.
The exception in the multifocal soft lens market is the Triton lens, a soft translating bifocal from Gelflex Laboratories in Perth, Australia. While translating bifocals are historically less successful in soft lens material than in RGP material, this may be a design which overcomes some of the visual compromise associated with simultaneous vision.
Equally, however, translating bifocals present problems when near targets are not positioned in the lower half of the visual field, and as they have no intermediate portion, tasks such as computer use may be problematic.
Managing patient expectations
When we present the patient with simultaneous vision, we know that some will perceive their quality of vision has been degraded compared to spectacles. Indeed some patients will perceive this problem with single-vision lenses and there have been papers which ably explain reasons why vision with soft lenses may disappoint.1-3
Some patients are happy to accept this situation and some are not. Acceptance will depend not only on ability to adapt to such vision but also on expectation, motivation and visual requirements. It is, therefore, very important for the practitioner to address all these points, this process is just as important as the over-refraction process.
Careful questioning of the patient is essential to establish the above in addition to normal suitability criteria for any potential contact lens wearer. We must prepare our patients for the possibility of visual compromise. The quality may not be equal to spectacles although measured acuity often is.
One challenge for the practitioner is to convey this to the patient without off-putting negativity. It may help to explain how the lenses work, how that differs from spectacles and therefore the challenge of achieving good vision at all distances. If the patient accepts this scenario then it is a measure of their motivation and if they experience little or no compromise then they are extremely satisfied.
It is also worth addressing our expectations as the practitioner. We are normally seeking the best possible acuities for our patients when prescribing spectacles or contact lenses.
It may be necessary to rethink this ideology. This is not to say we should lower our standards in any way but if we can meet the needs and expectations of our patients then we have definitely succeeded.
We need to allow the patient to judge whether the outcome is successful, with the proviso that they are able, or legal, to attain the desired standard for any required task, such as driving.
Motivation
This is in common with any type of contact lens. As well as the visual aspect of multifocals, patients need to consider adaptation, handling, aftercare and cost issues before proceeding. A well informed patient will be less likely to feel disappointed.
Visual requirements
We must be sure that a multifocal is the optimum choice. Some occupations and hobbies may indicate a different choice for the presbyope. We need to know what our patient needs to see, before we can judge if these lenses will meet their requirements. Also we need to learn which is their priority, be it distance or near, in order to offer the best balance of prescription to suit their needs.
Listening skills are key here as well as communication skills and a sense of what is achievable. Predicting success is very difficult and it is suggested that the practitioner offers a trial if the patient fulfils the above criteria. Being flexible and keeping an open mind are helpful.
Prescribing commonalities
Despite the variety of products available, there are several commonalities in fitting procedure for today's soft multifocal lenses. Remembering these key points can greatly simplify lens fitting.
Always use binocular viewing during over-refraction
This is a departure from the single-vision lens over-refraction technique we are used to because neither eye is occluded or fogged during over refraction. With simultaneous vision lenses, the patient is making a mental selection between the near or distance vision image in each eye at any given time. Binocular over-refraction allows us to assess the patient's ability to combine the images from both eyes, and gives us a better idea of their functional vision.
Chart selection
As well as recording acuities, it may be useful to use a 'real life' scenario to judge power changes, rather than a conventional, high contrast chart. If you can use the view out of a window, even better. A disappointing trial after a 'successful' fitting can often be pre-empted that way. Often +0.25DS change will have minimal or no effect in a consulting room but will be more noticeable when 'true' distance is viewed. When over-refracting, use a large target such as a 6/9 letter on the Snellen chart. This will help prevent over minus in the final lens power, but this does not represent best acuity. This is measured at the end.
Equipment for over-refraction
The use of a phoropter is not advised as this may alter the level of light on the eye, therefore affecting the pupil size. A phoropter can also hinder quick assessment of power changes between distance and near. It also obscures facial expressions that can be quite informative. The suggested option is using a ± 0.25DS twirl. This is a simple, versatile and quick method. As most cases will only require a power modification of 0.25DS, it is recommended that each 0.25DS power change is tried before making further adjustments. Hand-held trial lenses could be used if a twirl is not available.
Settling time
A minimum of 20 minutes is recommended. There does appear to be some neurological adaptation in that short time and many patients give a much more positive response even after 20 minutes. This time is also important for a subjective assessment of the vision to be made.
Small changes
Most final prescriptions should be within 0.25DS of the initial trial lens selection. This minimum change can have a significant effect on acuity, considerably more than would be expected with a single-vision lens. Therefore, making larger changes may well 'over-shoot' the optimum power.
Assess effect of each power change
After each suggested or demonstrated power change, the effect of that change must be checked at both distance and near. Only make a change if there is significant improvement of distance vision without compromise at near, and vice versa.
We are trying to achieve the best balance of distance and near vision, according to the patient's priorities.
When to stop power adjustments
It is recommended that two changes should be sufficient if a design is going to be successful. Further changes are unlikely to succeed and will not only waste chair time but will be disheartening to both patient and practitioner.
Trial period
The purpose of the trial is to reach a point where our patient feels comfortable with their vision and confident enough to try an extended trial. A two to four day supply should suffice and allow the patient to try the lenses in a variety of situations. It is important not to allow the trial period to go for more than four days in case a further power adjustment proves necessary.
Fitting
Normal soft lens fitting criteria apply. With these designs good centration is particularly important.
TWO SOFT LENS DESIGNS
The parameters of two soft lenses designed for correction of presbyopia are listed in Table 1. Of note are the differences in material, diameter and the style of addition between each lens type.
Binocular over-refraction
An example of the binocular over-refraction method applied to Focus Dailies Progressives (Figure 1) is detailed.
Select a trial lens using the spherical equivalent of the spectacle prescription plus half the addition, remembering to adjust for vertex distance. Alternatively, use the trial lens selection table provided by the manufacturer, this allows for vertex distance. It is not necessary to specify the addition separately as this is a progressive design and will correct spectacle reading additions up to +3.00DS. So only one power is specified for each lens.
After inserting the trial lenses, allow a minimum of 20 minutes to settle. There does appear to be some acceptance of simultaneous vision even in that short time. Ideally, this short trial would take place out of the practice so that the patient experiences a familiar environment in which to assess the vision.
The author strongly recommends you ask the patient to score the quality of vision out of 10 for both distance and near vision. This exercise tells you whether the patient is comfortable with this design of lens. Scores of 7 and over would indicate likely acceptance of simultaneous vision.
Secondly, these scores indicate where the problem area is and therefore the likely over-refraction (Table 3). A typical response may be 8 for distance and 6 for near, so for that case we would know we have to improve near vision. If they give 8 for both distance and near, then record visual acuities and discuss a two to four-day trial. Scores of 5 or less for both distances represents a challenge. If this is the case, enhanced monovision is often successful (see later).
It is recommended to record binocular scores first and then Snellen acuity. Patients occasionally wish to change their scores after being presented with a chart but the grading of vision in a familiar environment rather than a consulting room is more relevant and therefore more useful for trouble-shooting.
Refining the vision with Focus Progressive lenses
Case 1 Ð Poor distance vision
Show -0.25DS binocularly, to keep the binocular vision balanced. If distance vision is measurably better with the additional power, check that the near vision is still acceptable; if so, then trial the new powers.
It is not normally necessary for the patient to take another 20 minutes to evaluate and report revised scores.
If the -0.25DS change in both eyes results in poor near vision, show -0.25DS in the distance to each eye in turn, and ask the patient to make a choice between the right or left eye. This approach offers the flexibility that using dominance does not. Evaluate which eye is preferred and now check that the change would be accepted for near. If so, change that one lens, re-evaluate distance and near vision binocularly then trial the new powers. If the patient has no preference between right or left eye in distance viewing, then check if they have a preference for near viewing and adjust the powers accordingly.
Case 2: Poor near vision
Show +0.25DS for near vision. If this improves near vision, ensure that change is tolerated in the distance and then proceed to a trial with new power.
If the +0.25DS change in both eyes causes blur of distance vision, show +0.25DS to each eye in turn for near and evaluate which eye improves more. Now ensure that this monocular change would be accepted for distance, if so then proceed to a trial with the new power.
If the patient shows no preference when offered 0.25 to each eye in turn, repeat the exercise at 'the other distance' to determine which lens to change.
If there is still no preference, then use your judgement relating to the dominant eye. Otherwise, dominance is not relevant in the above procedure.
Either of these over refraction routines should take no longer than a couple of minutes. Multifocal fitting does not have to be time consuming as the above steps have hopefully demonstrated.
Please note that Dailies Progressive trials should not be used to prescribe monthly progressives and vice versa. There will occasionally be power differences due to material and manufacturing differences.
Case 3: Modified monovision
If the above does not yield a satisfactory result, it may be worth trying modified multifocal monovision. Now it is necessary to determine dominance. This would entail fitting a progressive lens biased towards distance in the dominant eye with a progressive lens biased towards near in the other (Figure 1).
Case 4: Enhanced monovision
This has the advantage over monovision with single-vision lenses by maintaining stereopsis at distance or near (Figure 2).
The dominant eye is fitted with a single-vision lens biased for distance or near vision, depending on the individual's requirements. The non-dominant eye is fitted with a multifocal lens.
Consider using a toric lens (either daily, twice weekly or monthly disposable, depending on the modality prescribed) in the dominant eye with the multifocal in the other if the patient has more than 0.75 cylinder in their prescription.
Remember, after each power modification, obtain revised scores from the patient to ensure improvement achieved (this will reassure and motivate the patient).
FREQUENCY 55 MULTIFOCAL
Refining the vision with Frequency 55 Multifocal (Figure 4)
Case 1: Poor distance vision
Show -0.25 for distance to D (dominant eye) lens and check reading not compromised, and make the change without changing the add power. If more than -0.25 is required to improve distance and is not tolerated for near, then consider reducing the add of the D lens instead. Otherwise it is possible to reduce the add on both lenses, add -0.25 to the distance power of both or use D lenses for both eyes
Case 2: Poor near vision
Show +0.25 for near viewing and adjust the distance power of N (non-dominant) lens. If more plus power required, increase add in N lens. Otherwise, add +0.25 to the distance powers of both lenses, increase add in both, or use two N lenses. Enhanced monovision may be used if a successful outcome not achieved with the above procedure.
Conclusion
A review of population trends in the UK indicate that people in the age group 50-65 currently constitute a significant market of about 10 million. This is set to grow over the next 20 years to some 13.5 million. This is a growing market with a higher than average disposable income in many cases. Our responsibility, as eye care practitioners, is to fully inform our patients of the range of options available to the presbyope. Success with these lenses is very rewarding for you and your patients, and a considerable practice builder. The author encourages you to be adventurous and enjoy the challenge.
References
1 Port M. Why can't I see in my CLs? optician, 2002; November 1, 5875: 224.
2 Harvey W and Long W. The optics of soft toric fitting: Vision through contact lenses. optician, 203; October 3, 5921: 226.
3 Hough A. Soft bifocal contact lenses: the limits of performance. Contact Lens & Anterior Eye, 2002; 25: 161-175.
Acknowledgements
Thanks to Dr Vicki Evans and Margaret Richmond of Ciba Vision and John Rogers of CooperVision for their help in the writing of this article.
Jayne Schofield is a contact lens consultant with Ciba Vision and visiting clinician at City UniversityThe majority of multifocal soft lenses currently available to the practitioner utilise the principle of simultaneous vision and this article will concern itself with currently available simultaneous vision designs.
The simultaneous vision soft lenses on the market employ centre near aspheric correction, centre distance aspheric correction or centre distance multizone optics. The strength of these designs lies in their success in providing intermediate vision, as well as distance and near. Intermediate vision is critical in the computer-based workplace and is frequently employed in social occasions.
The exception in the multifocal soft lens market is the Triton lens, a soft translating bifocal from Gelflex Laboratories in Perth, Australia. While translating bifocals are historically less successful in soft lens material than in RGP material, this may be a design which overcomes some of the visual compromise associated with simultaneous vision.
Equally, however, translating bifocals present problems when near targets are n
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