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Since the introduction of multifocal contact lenses (MFCLs), manufacturers have worked hard to improve their design with materials that are better suited to the age group for which they are intended. Nowadays all disposable modalities are catered for in both hydrogel and silicone hydrogel materials (see Part 1).
Early designs of multifocal lenses often proved tricky to fit, but the latest generation of lenses available in a range of modalities are easy to fit, and offer both patient and practitioner much more flexibility. Although the take up of MFCLs is increasing, it is still low when considering the age profile of the population in the UK.
The authors believe that eye care practitioners (ECPs) who are nervous or lack confidence in fitting MFCLs may find it initially much easier to fit emerging presbyopes with multifocal lenses. Then, as their confidence increases, more challenging cases may be successfully managed.
Different designs of MFCLs
Alternating, simultaneous, annular, concentric, aspheric and segmented are the many, various terms associated with multifocal lens design. No wonder practitioners get confused. Although an understanding of the mechanics and optics of MFCLs is useful, the key to fitting success is to manage the patient’s expectations from the very start and fit according to his or her individual needs.
A positive attitude on the part of the ECP goes a long way, and it often reaps rewards. When developing a fitting philosophy and strategy for MFCLs, the first consideration should be to hone your communication skills and then focus on your fitting skills.
Communication
As covered in detail in Part 1, the first step to success with multifocals requires the ECP to believe they work. Patients sense our level of enthusiasm and anything less than full engagement will condemn the fitting process to a waste of time. An important factor in presbyopic CL fitting is to listen to the patient’s needs and make sure the critical ones are met. In some instances it may be difficult to uncover a patient’s visual priorities until trial wear has begun and the patient comments upon distance or near vision. It is important to elicit as much information about a patient’s work/lifestyle prior to fitting them with MFs to ensure that the first MFCLs, once settled on eye, tick most of the boxes. This means going into a little more depth than just asking ‘What do you do for a living?’ When we use open question techniques we get more honest and richer replies that help us to guide the patient to the right products. ‘What does it involve? How many hours are you in that environment? How detailed is the
work on the screen?’ are all relevant.
Having established the patient needs, the next step will be to link those needs to the features and benefits of the contact lenses. The authors would strongly advise against using such terminology as ‘giving you back your vision of 10 years ago’ or ‘this will solve all your problems’. These phrases and similar may set the patient’s expectations far too high. It is a good idea to give the patient an idea of what to expect. For an existing CL wearer it could be useful to ask them to score subjectively their distance and near vision with the current lenses. This usually reveals something like 10/10 and 4/10. We can then offer them lenses that will give them about 8-9/10 for both – most patients are very satisfied with these levels.
So the aim for our MFCL patients is not necessarily acuities of 6/4 and N5 for each eye, but the ability to go shopping without specs on and still be able to read the price labels and to drive home; being able to play cards with your peers and be the only one without specs on; lunching with friends and be the only one able to read the menu without borrowing some reading specs. The possibilities are endless, but importantly all relate to the real world situation.
Fitting
Preparation – pre-fitting assessment
When considering refitting an existing contact lens wearer into MFCLs, it is important the patient has an updated spectacle prescription. If you are fitting from another practice’s prescription it is well worth re-refracting the patient to ensure that the spectacle correction is both current and accurate.
Binocularly balancing the prescription will ensure that the maximum plus is taken into consideration, and is always worth checking.
As always, it is important to consider the back vertex distance for prescriptions over ±4.00DS. Another important consideration is the patient’s habitual working distance; this should be taken into account when fine-tuning the near addition.
The next step is to determine the best vision sphere (BVS) and again binocularly balance. When binocularly balancing the BVS, pay particular attention to any indication that the patient may be uncomfortable having vision fogged in one eye, or that the quality of binocular vision has deteriorated when the fogging lens is removed. This is especially appropriate where astigmatism is to be masked by the best sphere.
Eye dominance
One definition of ocular dominance is ‘the superiority of one eye over the other in some perceptual or motor task. The term is usually applied to those ‘superiorities’ in function which are not based on a difference in visual acuity between the two eyes, or on a dysfunction of the neuromuscular apparatus of one of the eyes’.1
Ocular dominance can be measured in two ways: motor dominance (such as established by a hole in a card and relies on physical movement and alignment), and sensory dominance (as found by the fogging technique, which relies on subjective response to changes in visual image).
Motor dominance (or ‘sighting’) of one eye over the other is suggested by three consistent results from the ‘hole-in-the-card’ test. With both eyes open, the patient holds (with both hands, and comfortably at arm’s length) a card with a hole cut at its centre. The patient then views a letter on a distance logMAR chart. The examiner then occludes each eye alternately and the dominant eye is recorded as the one that continues to see the letter when its companion is occluded.2
Sensory dominance is assessed differently. After determining the distance prescription, using a trial frame and with consulting room lights on, the patient is asked to view a letter on the distance test chart as a +1.50 trial lens (or similar but related to the predicted addition) is introduced over one eye and then the other. The patient is asked if they notice any difference in the clarity of the letters, viewed binocularly, when either right or left eye is blurred. The dominant eye is considered to be the one that suffers the most noticed blur when viewing the letter binocularly.
When considering fitting monovision or MFCLs it may also be of benefit determining near sensory dominance. In this instance the patient observes a near chart with the full near prescription in a trial frame and with room lights on. A -1.50 trial lens is introduced before each eye while the patient views a near object or line of print. The dominant eye at near will be the one that results in most noticed binocular blur when the -1.50D trial lens is introduced before it.
What is the significance of measuring near sensory dominance? If distance and near sensory dominance differ it can be considered that the patient may be a good candidate for MFCLs or monovision.
It is important to consider these two measures of ocular dominance separately. Depending on the clinical requirement, either sighting or sensory test may be appropriate, but they do not appear to be equivalent.3
Measuring dominance is not just useful in fitting monovision or multifocals; there could be an argument to say that ocular dominance should be measured in anybody being fitted with contact lenses. In the case of low astigmats, if the dominant eye has a small degree of astigmatism, the justification for fitting toric lens in that eye becomes increasingly important. Some new personalised spectacle lenses also recommend assessing dominance when dispensing.
In many of the MFCL fitting guides that are available, the importance of ocular dominance is specified and it is important that this information is available before fitting commences. However, dominance may only become an issue when picking the initial trial lens for patients who have a moderate or high reading addition.
Other considerations
As well as carefully reviewing refraction and dominance, a full slit-lamp assessment must be undertaken.
Recent research has estimated that the dropout rates for MFCLs are 15.9 per cent in the US, 31 per cent in Asia and 30.4 per cent in Asia.4 The biggest reason for CL dropout after 40 years of age is poor comfort, followed by inconvenience and reduced vision.5
The increased number of dropouts in the presbyopic population underlines the importance of managing lid-related pathology to improve both the comfort and wetting of contact lenses. Blepharitis is a common cause of contact lens intolerance and subsequent discontinuation. If not appropriately managed it can lead to a worsening of signs and symptoms; disrupted preocular tear film, discomfort and changes in visual function.6
Meibomian gland dysfunction (MGD) is a major cause of evaporative dry eye and it has been shown that contact lens wear is associated with a decrease in the number of functional meibomian glands.7 Symptoms of MGD include foreign-body sensation, burning, itching, watering and fluctuating or decreased vision. The diagnosis of MGD is sometimes difficult because many of the symptoms mirror the everyday complaints of contact lens wearers.
It is important to assess the stability of the tear film by performing a tear break-up test (TBUT). A TBUT can be performed non-invasively using a Keeler tearscope, keratometer, or a topographer, or it can be performed invasively using fluorescein and a cobalt blue filter at the slit lamp. A TBUT greater than 10 seconds is considered normal and anything less than 10 seconds may indicate tear film instability.
Nowadays, there are many treatment and management options for both available for both blepharitis and MGD which can increase the comfort of contact lens wear as well as reduce and manage the symptoms of dry-eye.
Initial trial
The fitting characteristics of soft multifocals differ significantly between manufacturers, as well as, in situ, between wearers. Due to their relative design complexity, MFCLs should not be issued to patients without them first having a proper trial fitting.
All manufacturers provide fitting guides for their products. Most of these guides are available in PDF form and the authors strongly suggest keeping these guides on the consulting room computer. In all cases the initial trial lenses should be chosen according to the manufacturer’s fitting guide.
Allow the initial trial lenses to settle for at least 15 minutes before evaluating them. Encourage the patient to have a browse around outside of the practice. Many manufacturers suggest that initial evaluation of vision with MFCLs should be subjective. Ask the patient how they feel their vision is with the lenses. If your practice is equipped with a computerised test chart it is a good idea to adjust the bottom line to correspond to 6/6. Distance and reading vision should be assessed binocularly.
If the patient returns from their initial trial and report they are happy with both distance and near vision, then dispense the trial lenses and review a week later. In general, try to keep using test charts to a minimum and use real-life objects. For example, have a poster at the end of the consulting room or ask the patient to view an email, text or perform a task on their smartphone or tablet. Binocular distance and near vision should be recorded along with the fitting characteristics. Measurement of monocular VAs with MFCLs should be avoided.
If the patient reports dissatisfaction with vision then over-refraction can commence to improve vision. Again, this should be done monocularly with both eyes open, using a trial frame, with the room lights on. Improvements to distance vision should start with small ±0.25 changes, to the dominant eye. In some instances and, where possible, an over-refraction should be confirmed outside the consulting room looking at a distance target. Better still, take the patient outside and confirm any distance over-refraction.
Improvements to near vision should also be performed using ±0.25 steps, ideally while performing a task on a smart phone or tablet. Most patients who attend for a fitting for MFCLs are likely to have a smartphone and most will mention their frustration at not being able to use read their phone without some optical assistance.
Keep changes to distance and reading to a minimum and always confirm any change to prescription for both distance and reading to ensure that correcting one does not have a detrimental effect on the other. It is also worth remembering, as mentioned in Part 1, that MFCLs are adaptive. It will take a few days before the patient is fully adapted to their new visual environment and things that seemed difficult to see on day one may be much easier by the end of a week. So don’t rush into early changes when, given time to adapt, the patient may well be happy with that first prescription. Subjective scoring can be very useful when assessing when to change or not. As a useful rule, when asked to score their DV and NV out of 10 after the initial walk about with the lenses, anything less than seven needs working on before they leave the practice.
As a guide, it is useful to determine what tasks the patient performs in an ordinary day and to fit the lenses accordingly. Success in soft multifocals is seldom a matter of achieving 6/6, as it typically is with soft spheres or torics. Even when the Snellen acuity is not what it would be in spectacles, multifocal contact lenses allow patients to function well without having to wear spectacles. People vary hugely in their adaptation to and tolerance of blur. It is important to remember that one person’s good 6/7.5 could be another’s poor 6/5.
The fitting of a multifocal lens should appear the same as any other soft contact lens. The lenses should centre well, show good post-blink movement and have a smooth return on push-up. The wettability of the lenses should also be noted. Topography may be useful (Figure 1).
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As a part of the discussion with patients regarding multifocal lenses, it may be wise to point out that there may be limitations to what can be achieved. The mantra is that multifocal lenses will fulfil most of a patient’s visual needs most of the time. As practitioners we should never underestimate what may deemed as successful by any patient as it is both a subjective and patient-specific decision.
In most cases, maintaining comfortable distance vision is paramount, especially for critical distance tasks such as driving. In these instances it may be necessary to consider a small reading prescription over MFCLs for very small print or prolonged reading. As mentioned earlier it is important to consider what tasks the patient is performing when wearing MFCLs.
Conclusion
The fitting of MFCLs is very rewarding, creates positive patient perception that may result in referrals, and is a great practice builder. The latest generation of MFCLs are much easier to fit than their predecessors and the first time success rate is very high.
Confidence in fitting increases with practice and inevitably there are going to be a number of failures. It is important to remember that not all patients will be suitable for MFCLs. However, don’t give up at the first hurdle. In the same way opticians have access to many varifocal designs of spectacle lenses and these are dispensed based on patient need, there are now a number of both daily and re-useable MFCLs available. If one design doesn’t work try another. The fitting guides produced by each manufacturer have been produced after extensive research and it is important that, as well ensuring a good baseline refraction, these guides are followed. With increasing success and confidence will come more challenging fits such as toric MFCLs, amblyopic patient fitting, specialised RGP, hybrid and scleral lens types.
In the final part in this series we will look at aftercare management.
Model answers
(The correct answer is shown in bold text)
1 Which of the following does not describe a multifocal contact lens design?
A Simultaneous
B Bioptic
C Aspheric
D Alternating
2 Which of the following best describes ocular dominance as assessed in relation to multifocal contact lens fitting?
A Anisometropia
B Difference in corrected acuity
C Difference in preference of superiority of function with equal acuities
D Preference of binocular viewing over monocular viewing
3 Which of the following is used to assess motor dominance?
Sighting
A Sighting
B Fogging
C Occlusion
D Stenopeic slit
4 Which of the following lenses might be employed to assess near vision sensory dominance for a 45 year old?
A Plus 1.00DS
B Minus 1.00DS
C Plus 3.00DS
D Minus 3.00DS
5 Which of the following statements about invasive tear break up time (BUT) is false?
A BUT varies with age
B Non-invasive BUTs are expected to be greater
C BUT indicates tear volume
D BUT would be expected to be greater than 10 seconds
6 Which of the following best describes enhanced monovision?
A A distance lens before the non-dominant eye, a near lens before the dominant eye
B Multifocal lenses in each eye with the lens before the non-dominant eye overcorrected
C A single vision lens in one eye, a multifocal lens before the other
D A combination of two different multifocal designs
References
1 Dictionary of Visual Science 4th Edn By David Cline, Henry W Hofstetter, John R Griffin, pp 820. Chilton Trade Book Publishing: Radnor, Pennsylvania, 1989.
2 Pointer, JS – Sighting versus sensory Ocular Dominance – Journal of Optometry (2012) 5, 52-55.
3 Toelkes S, Buset, N – Ocular dominance: A comparison of tests Optometry & visual science, Dec 2000, Vol 77 – issue 12 – p 288.
4 DEWS report. The definition and classification of dry eye disease; report of the Definition and Classification Subcommittee of the International Dry Eye Workshop. Ocul Surf, 2007; 5:75.
5 Akerman, Dwight – 40 is the new 20/20 - Presbyopia equals opportunity, CL Spectrum 2010.
6 McDonald MB. The patient’s experience of blepharitis. Ocul Surf, 2009; 7 (2 Suppl): S17-S18.
7 Arita R, Itoh K, Inoue K et al. Contact lens wear is associated with decrease in meibomian glands. Ophthalmology, 2009; Mar 116; 379-84.
Indie Grewal is an optometrist and franchise partner with Leightons in St Albans. Keith Tempany owns an independent practice in Dorset and was the winner of Contact Lens Practitioner of the Year at the 2014 Optician Awards