Essential Contact Lens Practice Managing the Presbyope As the number of patients wearing contact KEY POINTS lenses around the world grows, so does the The number of presbyopic patients requiring contact lens number requiring presbyopic correction. Many correction is increasing and is predicted to continue to patients fitted with lenses are now beginning to do so over the next five years KEY POINTS experience presbyopia and demand satisfactory In fitting the presbyope, the practitioner should correction without recourse to spectacles. have access to a number of different lens designs and be aware of alternative There is also the demand from presbyopic fitting approaches hyperopes who, on reaching presbyopia, now The availability of single use need full-time correction for distance and disposable trial lenses allows ease of trial for both patients near and, with more active lifestyles and and practitioners increased awareness of contact lenses, are Lens power adjustments should not be based on asking for contact lens correction. The number objective visual acuity alone of presbyopic patients in Europe is on a steady Subjective visual performance assessment is most effectively incline and is forecast to grow further over the achieved by experiencing lens wear in both the work and next five years. Practitioners can therefore home environment expect to see an increase in the number of There is a significant untapped opportunity for contact lens presbyopes attending for contact lens fittings correction of presbyopes over the next few years. 91 Managing the Presbyope s the size of the presbyopic market increases, so too does the number of options of correcting presbyopia with A contact lenses. The history of contact lens correction of presbyopia has been one of products being launched onto the market with claims that have not always been realised in practice. This has led to scepticism by some practitioners and a reluctance to fully embrace fitting presbyopes with multifocal contact lenses. Before looking at the techniques required to correct presbyopia with contact lenses, we should be aware of the available options as shown in Figure 1. Spectacles One of the most common methods of correcting the contact lens-wearing presbyope is with a pair of reading spectacles worn over the distance contact lens correction. These may either be a full-frame single vision, multifocal or a half-eye depending on the needs of the individual. Such correction puts the presbyopic contact lens wearer in the same category as the presbyopic emmetrope. The advantage of this technique is that the contact lens correction requires no modifications. The obvious disadvantage is, of course, that the principal reason for contact lens wear is being ignored and as the near addition increases, clear intermediate vision is reduced. Presbyopia and Contact Lenses Over-spectacles Multifocal CLs Monovision FIGURE 1 RGP Soft Alternating Simultaneous Simultaneous Alternating Solid Fused Aspheric Multi-zone Zonal Aspheric Aspheric Centre Near Centre Distance 92 Essential Contact Lens Practice Contact lens patients do not want to wear spectacles, because, if they did, they would be doing so already. Consequently pure contact lens options should be explained first to the presbyopic contact lens wearers followed by spectacle correction option if appropriate. Monovision Monovision is the correction of one eye with the distance prescription and the contra-lateral eye with the near prescription. It works on the principle that the visual system can suppress the central focus image and, thus, enable the object of interest to be seen clearly. Monovision remains an effective means of correcting presbyopia with contact lenses, especially in lower adds, and an understanding of its indications and contraindications is essential to the practitioner dealing with presbyopic patients. Monovision clearly disrupts a patient’s stereopsis and, for some patients who have either little tolerance for visual disruption or who are engaged in detailed visual tasks, this disruption might prove too great. While some investigators have tried to develop predictive tests to assess which patients might prove suitable for monovision, these have not proved to be as valuable as simply allowing the patient to try the lenses. An advantage of monovision is that it allows the practitioner more flexibility to choose the most suitable lens for the patient (such as the material type and design) compared to specific multifocal designs. Whenever monovision has been compared directly with previous bifocal or multifocal contact lens designs in controlled clinical trials that have been published, monovision designs have had a success rate equal to or above that of the bifocal in question (Figure 2). However, since these studies were carried out, many newer simultaneous designs have been made available to practitioners. A more recent study by 7 Dutoit et al has shown that adapted monovision wearers rated many aspects of subjective vision performance higher with simultaneous vision bifocal contact lenses. These included distance vision in good and poor lighting, driving at night and depth perception. Near vision in poor lighting was rated higher during monovision wear. In addition, existing successful monovision wearers when refitted with simultaneous vision bifocal contact lenses preferred the bifocal contact lens correction (68 per cent) compared to monovison (25 per cent) after a six-month trial.8 In general, less compromised near visual acuity performance in all illuminations provided by monovision is an indication for consideration of this type of fitting option for presbyopes with strong near vision demands. Whereas when critical 93 Managing the Presbyope Relative success rate of monovision vs historical bifocal contact lens designs Monovision 90% Diff ractive FIGURE 2 80% Other No diff erence 70% 60% 50% 40% 30% Percentage of success rate 20% 10% 0% Papas Back Harris Molinari4 Saunders5 Macalister6 et al1 et al2 et al3 FIGURE 2 Comparison of success rates of monovision with a variety of historical bifocal contact lenses or sustained tasks requiring good distance binocularity predominate, it is advisable to avoid monovision or to consider supplementary correction. Alternating bifocals The alternating, or translating, bifocal was one of the fi rst types of bifocal contact lenses to be produced. The patient looks through the distance portion of the optic zone in primary gaze (Figure 3). On down gaze, the lens is held up against the lower eyelid, so the visual axis looks through the near portion. The advantage is that visual quality will remain high as long as the visual axis is directed through the appropriate part of the lens. The disadvantage is that for this to occur signifi cant eyelid/lens interaction needs to occur, which can lead to decreased patient comfort through increased lens bulk and mobility. The majority of alternating designs are available as rigid gas-permeable lenses. However, more recently a number of soft alternating vision designs have become available FIGURE 3 The principle of the translating bifocal contact lens 94 Essential Contact Lens Practice (Figure 4). The challenge is to produce a lens that produces (a) significant consistent translation in a manner that minimizes patient discomfort. The two distinct portions that make up an alternating lens may be either fused or solid portions with a range of alternative segment shapes (Figure 5). Prism, truncation or both controls lens stability, position and translation in rigid designs. Soft lens designs use prism and other design features used in soft toric lenses to stabilise the lens. Simultaneous vision designs Simultaneous vision bifocals rely on an optical system that (b) places two images on the retina simultaneously and then relies on the visual system to ‘select’ the clearer picture (versus monovision in which a clear image is placed on each retina, the confusion occurring at a higher part of the visual pathway). Early simultaneous vision bifocals had discrete zones of distance and near vision (Figure 6). In more recent designs, the power distribution across the lens surface has been variable and lenses have been described as multifocal, aspheric or progressive (Figure 7) and are available in both soft and rigid materials. FIGURE 4 Other lens types use a ‘modified monovision’ approach by using (a) Triangle shape seg design different bifocal designs in each eye. Alternatively lens designs (b) Triangle shape seg in primary position of gaze can consist of a number of concentric zones to control visual performance in varying illumination levels (Figure 8) or involve a combination of diffractive and refractive optics to achieve bifocal correction (Figure 9). There is potential for some confusion in using the term multifocal or progressive because it implies a similar mechanism to a multifocal spectacle lens. In simultaneous vision contact lens systems, the basic principle of the system remains the same irrespective of whether the power varies in a discrete or progressive manner across the surface. Simultaneous vision contact lenses may be further subdivided according to whether the power distribution across the surface is either centre- distance or centre-near. The availability of single-use disposable soft trial lenses in newer designs, daily disposable multifocals and silicone hydrogel multifocals, as well as empirically ordered aspheric RGP lenses, has resulted in an increased prescribing of this form of lens correction. However it still represents only 7 percent of new fits 9 (soft multifocal) in the UK, suggesting it is not yet an integral part of contact lens practice. Aspheric design Centre distance A centre-distance lens usually has a back surface aspheric curve resulting in the central portion of its optical zone for distance vision, which is surrounded by an area containing the power of 95 Managing the Presbyope the lens required for near work. This is achieved by the aspheric curve inducing positive spherical aberration. Rays of light from a distant object are focused by the central zone on the retina a b c and compete with the out-of-focus rays being formed by the surround (Figure 10).