Technological advances have led to vast improvements in soft lens materials, design and manufacturing. As a result, soft toric and multifocal lens designs can now be successfully incorporated into mainstream contact lens practice.
Recent data published on worldwide contact lens trends indicate that Australian optometrists significantly under-utilise astigmatic and presbyopic contact lenses.1
This is potentially due to the complex, time-consuming and expensive processes historically involved in fitting toric and multifocal soft contact lenses.
Improvements to toric and multi focal fits make it a great time to re-assess clinical approaches to these lens designs… and to take on board a few simple and practical clinical tips that will maximise fitting success.
Allowing patients to discuss their motivations and identifying their needs may provide the perfect opportunity for a multifocal contact lens trial
Know your Patient
To maximise success, the process of a toric fitting should commence well before a lens is applied to the eye. Asking your patient the right questions will help determine their visual needs and identify any lifestyle and/or ocular factors that require consideration. Discussing their intended visual tasks will indicate their visual demands and provide the opportunity to fulfil your patient’s expectations.
As with all contact lens fitting, fine assessment of your patient’s ocular characteristics is important. To manage any deficiencies prior to fitting, it is useful to examine the tear film quality and quantity. As many toric lens stabilisation methods rely on lid interactions, it is of great benefit to document lid tension. Poor lid tonicity, especially in older patients, may not necessarily preclude fitting, but may require the trial of different toric lens designs.
The Becherer ‘twist test’ is an invaluable screening tool that helps determine a patient’s tolerance to lens rotation.2 Using the phoropter, the patient’s cylindrical correction is slowly rotated until blur is first appreciated. Patients who notice visual degradation with less than five degrees axis rotation have high visual sensitivity, necessitating highly accurate axis alignment for success.
Good Data In: Good Data Out
As practitioners, we understand the importance of accurate baseline data for lens fitting; this is particularly imperative for soft torics. An accurate and up-to-date subjective refraction is the foundation for precise toric lens calculations. Vertex-distance correction to the corneal plane for spherical and cylindrical powers is necessary for powers exceeding four dioptres. Erring on the lowest viable astigmatic correction will reduce the visual effects of any lens rotation.
There is significant evidence to show that toric lenses enhance vision, even in low astigmats. Numerous studies have demonstrated the inadequacy of attempting to mask low levels of astigmatism (0.75 – 1.00 D) with spherical and aspheric soft lenses.3,4 The availability of well-designed soft toric lenses in modalities ranging from daily disposables to extended wear means it is not necessary for patients to tolerate significant uncorrected cylinder.
Encouraging your patients to trial a lens will allow them to experience the potential enhanced vision of these designs. Having a comprehensive range of lens designs and powers available in the practice can improve the efficiency of the fitting process and also save on time, administrative costs and inconvenience to the patient.
The Lens-Eye Relationship
Patience is a Virtue
Irrespective of the stabilisation method, all toric lenses require some time to equilibrate on the eye.5 While a 15 – 20 minute allowance was previously recommended as optimal,6,7,19 with modern silicone-hydrogel lenses, good results can be achieved within a shorter period and by manual alignment of the lens markings when first applied to the eye.8 This ‘waiting period’ is also an excellent opportunity to discuss lens cleaning protocols and to answer any patient questions.
The characteristics of an ‘ideal’ soft toric lens are well known; the lens should demonstrate axis alignment, maintain a stable orientation and provide consistent vision. However, in the instance of assessing a sub-optimal fit, it is useful to revise the differences between lens rotation versus lens stability and in doing so, perform appropriate problem-solving strategies.
Stability describes the tendency for a lens to maintain a constant axis position during blinking and eye movements. It is considered a critical predictor of success.8 One well regarded technique for assessing stability involves taking a systematic approach.9 It is recommended that lens rotation be observed initially in primary gaze following blink, with any mis-orientation of the lens scribe mark(s) documented. This assessment is then repeated for upward and lateral gaze positions. Another useful test involves manually moving the lens axis from its desired orientation and observing the time required for the lens to relocate. Accurate repositioning within 15 seconds indicates a stable fit.6 A flat fitting lens will rotate erratically post-blink,10 while a steep lens will demonstrate delayed relocation.11
Rotation describes the orientation of the lens in primary gaze. Although no rotation is desirable, a small amount may be permissible, provided that the degree and direction of the misalignment is consistent. Studies indicate that most lenses rotate between five to10 degrees off the zero rotation position.12 When a lens rotates on the eye, oblique astigmatism is induced. If this is sufficient to compromise acuity, the ordered axis can be adjusted either by visual judgment using lens scribe markings, or by the resolution of cross-cylinders with a sphero-cylindrical over-refraction. Clinical data indicate that experienced clinicians are remarkably precise at evaluating lens rotation, with rotation accurately estimated to within eight degrees in 95 per cent of assessments.13
Axis adjustment can be performed using the well-known LARS rule; if rotating left, add to the axis; if rotating right, subtract from the axis (figure 1). A common and easy way to estimate is to imagine the contact lens as a clock face, with each hour on the dial corresponding to 30 degrees of rotation. A slit lamp reticule or beam rotation can be used to improve accuracy.
While LARS is useful to yield an estimated compensation, sphero-cylindrical over-refraction is the only way to completely evaluate the sphere, cylinder and axis. This approach can be particularly useful for checking for small degrees of lens rotation for patients with larger degrees of cylinder (eg. > 2D) and for maximising acuity in high visual demanders. The availability of on-line calculators and iPhone applications enable these calculations to be performed with ease and convenience. It is important to recall that even though compensation has been made by adjusting for lens rotation, the new lens will still demonstrate the same apparent degree of on-eye rotation.
The Right Presbyope
Research indicates that presbyopic contact lens correction is best started ‘early.’14 Emerging presbyopes, that require low additions, generally have quick adaptation periods and readily appreciate the enhanced clarity at near. These patients can progress more easily into higher near additions with time, and in doing so can be retained as successful long-term contact lens wearers.
Highly motivated patients are also ideal as they are inspired to succeed. One approach that can be useful is to ask the patient whether “there are any occasions when you would prefer not to wear glasses?” Patient responses can be surprising. Take for example an 87-year-old gentleman, who enthusiastically responded “Of course, I would like not to wear my glasses when I play tennis.” Further discussion revealed he was an avid tennis player, who played three or more times per week. Allowing patients to discuss their motivations and identifying their needs may provide the perfect opportunity for a multifocal contact lens trial.
Being proactive can be beneficial; despite consumer advertising and word of mouth, many patients are unaware of multifocal contact lenses. While many practitioners are comfortable with fitting monovision corrections, multifocal lens designs can provide patients with improved stereoacuity and more usable vision when both eyes are viewing binocularly.15 Furthermore, studies indicate that when comparing monovision to multifocals, patients have a three-fold preference for multifocal lens designs.16,17
Positive Communication is Key
Confidence in the hands of the optometrist results in confidence in the eyes of the patient., The way in which you discuss the lens, the fitting process and the visual experience will all influence your patient’s perception of the likelihood of success. I tend to emphasise that modern multifocal contact lenses are high-tech, specialised lenses that use advanced optical designs to optimise vision at all distances.
Explaining the basic concepts of ‘simultaneous vision’ can also be useful. For instance, a helpful description could be: “With these lenses, light rays from both far away and up close will enter your pupil together. To allow clear vision at all distances, your brain will quickly learn to adapt to the appropriate image.” With the patient well-informed of fundamental lens design principles, they are more willing to persist with adaptation during the initial trial period.
Setting appropriate expectations for lens performance is also essential. Informing patients that multifocal contact lens correction should allow them to comfortably perform 80 to 90 per cent of their daily visual tasks is realistic.18
They may then require an enhancement spectacle correction for specific activities to achieve a further improvement in vision. When conveying any potential drawbacks, negative words such as “compromised” or “reduced vision” can be avoided by using an alternative such as “balanced” vision. It can be useful to establish some ‘visual goals’, as an indicator as to whether their expectations are being fulfilled. Being up-front about the possibility that the initial prescription may need adjustment tends to help maintain patient interest and motivation, should an adjustment be required. Communication via email is a valuable way to stay in contact with the patient and monitor their progress.
The Fitting Journey
A comprehensive preliminary examination is particularly important for presbyopic patients, due to normal ocular physiological changes that occur with age and can impact upon lens wear.19 As tear production decreases with age,20 careful tear film inspection can assist in identifying any tendency towards dry eye, prior to fitting. Evaluating pupil diameter under low and high illumination levels is also recommended to ensure normal pupil dynamics. 19
Lens manufacturers provide fitting guides that are based upon pre-launch clinical data and are designed to optimise fitting for individual products. As practitioners, we can certainly follow these guidelines to our advantage.
Many practitioners will advocate measuring visual acuity binocularly at distance and near, and to over-refract with trial lenses, rather than the phoropter, in order to provide a more natural viewing environment.21,22 Industry-based studies on the performance of multifocal lenses also emphasise the need to ‘push-plus’ in the subjective refraction. Appropriate lens centration is also critical due to the optical design of these lenses. When administering contact lens training for a new presbyopic wearer, it is important to keep in mind that patience and positive reinforcement are invaluable in overcoming any difficulties with lens handling, due to reduced unaided near vision.
Success in Sight
Experts suggest that provided adequate visual acuities are achieved at fitting, patients should be encouraged to trial the lenses in their natural environments for about one week.23 There will always be cases where the patient returns and reports a desire for clearer distance/and or near vision. For centre-near multifocal designs, this can sometimes be achieved by using sunglasses for distance and good lighting for near to optimise pupil sizes. These recommendations can be discussed in the context of simultaneous vision, as described earlier. Slight changes to the prescription can also significantly enhance a patient’s visual abilities.21 It can be useful to emphasise to the patient that as their optometrist, you will be there to help every step of the way; and that with each trial of a lens design, you are a step closer to ending the journey successfully.
Contact lenses for astigmatic and presbyopic patients can deliver superior options for vision correction. By actively promoting and educating patients about contact lenses and accommodating their specific visual needs, optometrists can distinguish their unique services and earn patient loyalty. Successful utilisation of toric and presbyopic contact lens modalities will not only assist in patient retention, but also act as an area for practice growth.
Dr. Laura Downie BOptom, PhD(Melb), PGCertOcTher, DipMus(Prac), AMusA is an optometrist who specialises in contact lenses. She has been sponsored by Ciba Vision to write this article.