Contact Lens Monthly CET Essential contact lens practice Part 8 — Managing the presbyope Practitioners can expect a rise in presbyopic patients attending for contact lens fitting over the next few years. Jane Veys, John Meyler and Ian Davies continue their series by outlining the options and techniques available to correct presbyopia with contact lenses. C7603, three contact lens points suitable for optometrists, DOs and CLOs
s the number of patients the same category as the presbyopic Key Points wearing contact lenses emmetrope. The advantage of this around the world grows, technique is that the contact lens correc- ● The number of presbyopic patients so does the number requir- tion requires no modifications which, requiring contact lens correction is ing presbyopic correction. assuming that it is optimum at the time increasing and is predicted to continue AMany patients fitted with lenses are now of fitting, remains the case. to do so over the next five years ● In fitting the presbyope, the beginning to experience presbyopia and The obvious disadvantage is, of course, practitioner should have access to demand satisfactory correction without that the principal reason for contact lens a number of different lens designs recourse to spectacles. wear is being ignored. Contact lens and be aware of alternative fitting There is also the demand from presby- patients do not want to wear spectacles, approaches opic hyperopes who, on reaching presby- because, if they did, they would be doing ● The availability of single use opia, now need full-time correction for so already. Consequently pure contact disposable trial lenses allows distance and near and, with more active lens options should be explained first ease of trial for both patients and lifestyles and increased awareness of to the presbyopic contact lens wearers practitioners contact lenses, are asking for contact followed by spectacle correction option ● Lens power adjustments should lens correction. The number of presby- if appropriate. not be based on objective visual opic patients in Europe is on a steady acuity alone incline and is forecast to grow further Monovision ● Subjective visual performance over the next five years. Practitioners Monovision is the correction of one eye assessment is most effectively can therefore expect to see an increase with the distance prescription and the achieved by experiencing lens in the number of presbyopes attending contra-lateral eye with the near prescrip- wear in both the work and home for contact lens fittings over the next tion. It works on the principle that the environment few years. visual system can suppress the central ● There is a significant untapped As the size of the presbyopic market focus image and, thus, enable the object opportunity for contact lens correc- increases so to does the number of of interest to be seen clearly. Monovision tion of presbyopes options of correcting presbyopia with remains an effective means of correct- contact lenses. The history of contact lens ing presbyopia with contact lenses, and, correction of presbyopia has been one of products being launched onto the market with claims that have not always been Presbyopia and contact lenses realised in practice. This has led to scepti- cism by some practitioners and a reluc- Over-spectacles Bifocal CLs Monovision tance to fully embrace fitting presbyopes with multifocal contact lenses. Before RGP Soft looking at the techniques required to correct presbyopia with contact lenses, Alternating Simultaneous Simultaneous Alternating we should be aware of the available options as shown in Figure 1. eg Gelflex Triton Solid Fused Aspheric Multi-zone Aspheric Procornea Royal Spectacles Probably the most common method eg Acuvue Bifocal eg eg Frequency 55 of correcting the contact lens-wearing Centre distance Centre near Centre distance Tangent Streak Presbylite 2 Proclear Multifocal presbyope is with a pair of reading MagniVue spectacles worn over the distance contact lens correction. These may either eg eg be a full-frame single vision, multifocal Astrocom MF Focus Progressive or a half-eye depending on the needs Figure 1 Contact Quasar plus PureVision Multifocal Occasions of the individual. Such correction puts lens options for Aqualine MF 200 Biomedics 73 Menifocal Z Dailies Progressive the presbyopic contact lens wearer in presbyopes
24 | Optician | 05.10.07 opticianonline.net CET Contact Lens Monthly
Relative success rate of monovision vs bifocal contact lenses
90% Monovision 80% Di ractive Other 70% No di erence te ra 60% Figure 3 The principle of the translating bifocal contact lens ss
cce 50% su (a) (b) of 40% tage
en 30% rc
Pe 20%
10%
0% Papas Back Harris Molinari Saunders Macalister et al1 et al2 et al3
Figure 2 Comparison of success rates of monovision with a variety of different Figure 4 (a) Triangle shape seg design (b) Triangle shape seg in primary position bifocal contact lenses of gaze as such, an understanding of its indica- In general, less compromised near lenses to stabilise the lens. tions and contraindications is essential to visual acuity performance in all illumi- the practitioner dealing with presbyopic nations provided by monovision is an Simultaneous vision designs patients. indication for consideration of this type Simultaneous vision bifocals rely on an Monovision clearly disrupts a patient’s of fitting option for presbyopes with optical system that places two images on stereopsis and, for some patients who strong near vision demands. Whereas the retina simultaneously and then relies have either little tolerance for visual when critical or sustained tasks requiring on the visual system to ‘select’ the clearer disruption or who are engaged in detailed good distance binocularity predominate, picture (versus monovision in which a visual tasks, this disruption might prove it is advisable to avoid monovision or to clear image is placed on each retina, the too great. While some investigators have consider supplementary correction. confusion occurring at a higher part of tried to develop predictive tests to assess the visual pathway). Early simultane- which patients might prove suitable Alternating bifocals ous vision bifocals had discrete zones of for monovision, these have not proved The alternating, or translating, bifocal distance and near vision (Figure 6). In to be as valuable as simply allowing was one of the first types of bifocal more recent designs, the power distri- the patient to try the lenses. An advan- contact lenses to be produced. The bution across the lens surface has been tage of monovision is that it allows the patient looks through the distance variable and lenses have been described practitioner to choose the most suitable portion of the optic zone in primary as multifocal, aspheric or progressive lens for the patient (such as the material gaze (Figure 3). On down gaze, the lens (Figure 7) and are available in both soft type and design) without having to add is held up against the lower eyelid, so and rigid materials. Other lens types the compromise that might exist with a the visual axis looks through the near use a ‘modified monovision’ approach particular bifocal design. portion. The advantage is that visual by using different bifocal designs in Whenever monovision has been quality will remain high as long as each eye. Alternatively lens designs can compared directly with current bifocal the visual axis is directed through the consist of a number of concentric zones or multifocal contact lens in controlled appropriate part of the lens. The disad- to control visual performance in varying clinical trials that have been published, vantage is that for this to occur signifi- illumination levels (Figure 8) or involve monovision has had a success rate equal cant eyelid/lens interaction needs to a combination of diffractive and refrac- to or above that of the bifocal in question occur, which can lead to decreased tive optics to achieve bifocal correction (Figure 2). However, since these studies patient comfort through increased (Figure 9). were carried out, many newer simulta- lens bulk and mobility. The majority There is potential for some confu- neous designs have been made available of alternating designs are available as sion in using the term multifocal or to practitioners. A more recent study rigid gas-permeable lenses. However, progressive because it implies a similar by Dutoit et al7 has shown that adapted more recently a number of soft alter- mechanism to a multifocal spectacle monovision wearers rated many aspects nating vision designs have become lens. In simultaneous vision contact of subjective vision performance higher available (Figure 4). The challenge lens systems, the basic principle of the with simultaneous vision bifocal contact is to produce a lens with a different- system remains the same irrespective of lenses. These included distance vision in powered near portion while maintain- whether the power varies in a discrete good and poor lighting, driving at night ing a smooth passage of the upper or progressive manner across the surface. and depth perception. Near vision in eyelid over the anterior surface. The Simultaneous vision contact lenses may poor lighting was rated higher during two distinct portions that make up an be further subdivided according to monovision wear. In addition, existing alternating lens may be either fused or whether the power distribution across successful monovision wearers when solid portions with a range of alterna- the surface is either centre-distance or refitted with simultaneous vision bifocal tive segment shapes (Figure 5). Prism, centre-near. contact lenses preferred the bifocal truncation or both controls lens stabil- The availability of single-use dispos- contact lens correction (68 per cent) ity, position and translation in rigid able soft trial lenses in newer designs, compared to monovison (25 per cent) designs. Soft lens designs use prism and daily disposable multifocals and silicone after a six-month trial.8 other design features used in soft toric hydrogel bifocals, as well as empiri- opticianonline.net 05.10.07 | Optician | 25 Contact Lens Monthly CET
cally ordered aspheric RGP lenses, ope (up to +1.50D). Apart from the visual has resulted in an increased prescribing demands of the presbyope, it would also of this form of lens correction. However be expected that visual performance it still represents only 4-14 per cent of would depend upon the interaction of new fits in the UK,9 suggesting it is the optical characteristics of the particu- not yet an integral part of contact lens a b c lar lens design with the aberrations of practice. the eyes of the wearer. Consequently, variations in ocular aberration between Aspheric individuals may explain in part why lenses of this type meet the needs of some Centre distance wearers but not others.12 As presbyopia A centre-distance lens usually has a back d e f increases, correcting the wearers spheri- surface aspheric curve resulting in the Figure 5 Bifocal segment shapes. Fused, A=straight top, B = cal aberration alone will not be sufficient central portion of its optical zone for solid one-piece, C=straight top, D= reversed crescent, and the front surface curve must have distance vision, which is surrounded by E=crescent, F= triangular a greater degree of asphericity to allow an area containing the power of the lens more plus refractive power within the required for near work. This is achieved optical system. This often involves more by the aspheric curve inducing positive N D complex surface geometry of varying spherical aberration. Rays of light from eccentricity to allow stabilised distance a distant object are focused by the central and near power zones within a specified zone on the retina and compete with the D N area which is design dependent. out-of-focus rays being formed by the As the pupil constricts, the distance surround (Figure 10). When regarding vision becomes progressively blurred, a near object, the reverse occurs, and this which could lead to significant problems, time it is the light rays from the periph- such as when driving a car in bright eral zone that come into focus. The visual Figure 6 Left: bi-concentric centre distance design; sunlight. These lenses can be fitted with system then picks out the clearer of the Right: bi-concentric centre near design a view to reducing the add power in two images. one or other of the eyes to help address Centre Centre The greater the eccentricity (or rate of D N this problem – a ‘modified monovision’ flattening) of the back surface aspheric near distance technique. curve the higher the reading power in relation to distance power. However, Multi-zone concentric the higher the reading addition, the N D more likely that distance vision will Centre distance be affected adversely, especially in low It became clear that with future designs, contrast and/or low light conditions. Distance power greater attention should be paid to Current back surface aspheric soft Near power minimising the dependency of lens lenses are therefore recommended for Figure 7 Left: front surface centre near design; function on pupil size, especially in early presbyopia only (up to +1.25D). Right: back surface centre distance design relation to different lighting condi- In soft lenses, the aspheric back surface tions. One approach is to increase the will not normally have any significant number of concentric zones alterna- D impact on fit, but in RGP lenses the back D tively powered for distance and near surface geometry may depart signifi- D vision. This concept resulted in a centre- cantly from corneal topography. This is distance multi-zone design consisting due to rapidly flattening back surface N N D of five alternating distance and near aspheric geometry and will be fitted N powered zones (Figure 8). The width and significantly steeper to allow appro- spacing of the zones is based on the varia- priate lens centration.10 Back surface tion of pupil size in different illumina- aspheric RGP lens designs can now be Distance power Near power tions within the presbyopic population. based on corneal topography and ocular Figure 8 Multi-zone concentric Figure 9 Diffractive design Theoretically, the lens design favours prescription to create an individual lens centre distance design distance vision in extreme high and low design for correcting presbyopia.11 lighting conditions and provides a more The aim is to modify the combined of pupil constriction for close work. The equal ratio of light division in ambient optical system of the lens, tears and optical principle is the same as for the illumination conditions.13 The multiple cornea to provide a predictable multi- centre-distance lens, although reversed, ring configuration is designed to provide focal effect. so this time it is the central portion of vision which is more specific to the Probably the most fundamental the lens that forms the light from close available lighting conditions. Transition concern with a centre distance system is objects and is surrounded by the required curves between the concentric zones are in its dependency on the pupil size. The distance power (Figure 11). Front such that the zones are not readily visible near pupil reactions means that as a near surface soft aspheric designs promote on the slit-lamp biomicroscope. object is brought into view proportion- negative spherical aberration and the ally, less of the pupil allows light in from aspheric curve can be calculated to limit Modified monovision the near zone of the lens. the spherical aberrations of the eye These lens designs use a modified and, if necessary, of the lens itself. The monovision approach in that the lens Centre near improvement of retinal image quality used for the dominant eye is a centre Centre-near bifocal and aspheric designs and increase in depth of focus can be distance lens design while the lens for the were introduced to address the problem effective at correcting the early presby- other eye is centre near in design. Lens
26 | Optician | 05.10.07 opticianonline.net CET Contact Lens Monthly
Near Distance Distance Near
Figure 10 Principle of a simultaneous vision centre-distance Figure 11 Principle of a simultaneous vision centre-near design design designs can use aspheric surfaces, spher- provide useful visual props in helping to ical surfaces or a combination of both Distance lens: dominant eye assess visual performance. with unique zone sizes to produce two Spherical/ N aspheric/ I complementary but inverse geometry spherical Lighting design lenses (Figure 12). Each lens is a multi- D Lighting plays an important part in focal and the intention is that binocular seeing, particularly in assessing vision summation will still occur, providing for the presbyope. Ideally, the consulting acceptable vision at all distances under Distance power room should have a wide range of light- binocular conditions. This type of lens Intermediate power ing possibilities. These should range from design results in a modified monovision Near lens: non-dominant eye bright, direct illumination on targets to approach with the first pair of lenses D maximise the chances of a patient first trialled. I seeing the in-focus image, through to the ability to decrease the level of illumina- Diffractive bifocals N tion so visual performance at, or near, Diffractive lenses work on the principle darkness can be assessed. It might also of placing a phase plate on the rear surface be valuable to have a glare source on or of the lens, which is able to split the light Intermediate power near visual tasks to help in assessing the passing through into two discrete focal Near power effect of glare on vision. points, one for distance and the other for Figure 12 Distance lens: dominant eye near vision. This design was available in spherical/aspheric/spherical design Techniques both soft and rigid materials but neither The techniques for correcting presby- products are currently available. High contrast chart Low contrast chart opia with contact lenses will vary from lens type to lens type. There are, Instrumentation however, certain fundamental princi- The basic instrumentation required for FNPRZ FNPRZ ples in presbyopic correction that will presbyopic contact lens fitting is the be discussed in detail in this article, same as that needed to fit a regular RGP EZHPV EZHPV with reference to the type of correction or soft contact lenses. DPNFR DPNFR being made. The reader is referred to individual manufacturers’ fitting guides Lens trial RDFUV RDFUV for more details. As with all contact lens It is essential to be able to trial a lens, URZVH URZVH fitting, the practitioner must ensure the regardless of the design, which is as HNDRU HNDRU patient is suitable to wear lenses. As the ZVUDN ZVUDN close as possible to the patient’s refrac- VPHDE VPHDE eye ages, a number of conditions might tive needs. This can be ordered empiri- PVEHR PVEHR affect this suitability that have to be cally or, ideally, be made available from EMYDF EMYDF taken into account – in particular, tear in-practice single-use fitting banks. This Figure 13 quality, quantity as well as eyelid tone allows a more realistic assessment by High and low available to help both themselves and and position. It is also important that the patient and practitioner as well as contrast patients judge the visual performance. the patient is given realistic expecta- allowing vision assessment in the work visual acuity High and low-contrast visual acuity tions about the likely level of vision and home environment. To assess the chart charts (Figure 13) give more informa- and the compromises that are inherent outcome of a fit, the patient has to experi- tion about acuity, and, in particular, the in this type of contact lens correction. ence vision as it will be in the final lens. difference in low-contrast acuity between This involves discussing the benefits Judging success simply by measuring spectacles and contact lenses gives some of combined distance/near correction acuity alone will not provide an effec- indication of possible success. without the need for spectacles, as well tive predictor of outcome. As well as the visual acuity charts, the as likely differences between the vision practitioner should have access to other performance of monovision, simultane- Visual assessment near tasks, such as the opportunity to sit ous or alternating vision lenses. When As indicated above, the assessment of patients at an office desk viewing a VDU compared to spectacles or single-vision visual acuity alone is a poor indicator of screen (possibly in the reception area) contact lenses, this may take the form of success with presbyopic – and indeed and a wide variety of different coloured reductions in visual quality, especially in much non-presbyopic – contact lens paper and contrasts of type. Needles, low luminance, stereopsis and reduced practice. Practitioners must have tools threads, screws, nuts and bolts can also intermediate vision depending on the opticianonline.net 05.10.07 | Optician | 27 Contact Lens Monthly CET
type of lens fitted. It is also an oppor- Table 1 tunity to explain to the patient that a Patient selection for presbyopic contact lens correction14 period of adaptation is required (just as with bifocal or progressive specta- Patient selection cle lenses) and it is normal that fitting Monovision Simultaneous Alternating requires more than one appointment to Good candidates Significant refractive Existing soft lens Early and advanced trial alternative lens powers and fitting (getting started) error wearers who are presbyopes approaches. When getting started with emerging presbyopes this form of lens fitting, it may help Reading postions Moderate inter- Lower lid above, tangent to start with selecting patients that are other than standard mediate vision to, or no more that 1mm generally accepted as being ‘better candi- downward gaze requirements below the limbus dates’ versus choosing what might be Current contact lens Spherical or near Myopic or low hyperopic considered a more challenging patient wearers spherical refractive powers to fit successfully. Table 1 summarises errors one approach for different patient types Motivated and realistic Willing to accept Normal to large palpebral when considering monovision fitting, expectations some compromise in apertures simultaneous vision and alternating distance vision 14 vision fitting. Normal to tight lid tension Monovision ● Physical fit – the physical and physi- More Emmetropes, previ- Do not desire any High hyperopes ological fit of a contact lens required challenging ously uncorrected compromise in to correct presbyopes by the monovi- candidates hyperope, low myopes distance vision (more experi- Concentrated specific Moderate hyperopic Small palpebral apertures sion technique will be the same as ence required) the fit required by one used without visual needs refractive correction modification. Dry eye symptoms or Emmetropic or near Loose lower lids ● Ocular dominance – monovision clinical signs emmetropic distance works because the visual system is able refractive error to suppress the blurred foveal image in High visual demands Would benefit from a an eye. In general, the visual system is and expectations toric correction better able to suppress an image in the Small pupil size non-dominant rather than the dominant (<3mm eye, and it is for this reason that ocular Adapted from Bennett E S 2007 dominance should be assessed. An empirical means of assessing ocular dominance is to ask patients if they are the lowest line they can read, a +2.00D scious level, so the practitioner should right or left handed and assume that is placed alternatively in front of each not immediately explain how the vision ocular follows motor dominance. While eye. The patient indicates when the has been corrected. Under binocular this is true in many cases, there are some vision is clearest. If the +2.00D lens is viewing, looking at a high-contrast, well- in which the reverse is true and others in front of the left eye when the image illuminated distance chart, the patient for which there is no strong dominance, is reported as clearest then the right eye should be asked to read as far down the a valuable finding in itself. is considered as distance dominant and chart as possible without comment on Alternative and preferred means of vice versa. It has been found that that visual quality. The patient should then assessing ocular dominance include unsuccessful wearers became success- be directed towards a high-contrast near ‘pointing’ and ‘sighting’. In the former, ful after switching near and distance type, with illumination again being high patients are asked to clasp their hands corrections contrary to the dominance to maximise the chances of seeing the together with forefingers pointing out as measured by traditional methods but image. Once again, the patient should be like a child pretending to fire a gun. They rarely contrary to the +2.00D test.15 asked to read as far as possible. If they are are then asked to keep their eyes open ● Trial lens power selection – for the unable to read with the distance or the and to point the fingers at one of the majority of patients, a good starting point near type, the practitioner should not, at practitioner’s eyes, with the practitioner in selecting appropriate lens power is to this stage, occlude either eye. Instead, the sitting at the opposite end of the room. fit the dominant eye with the distance ‘non viewing eye’ in the one that has the The practitioner then looks to see which correction and then the non-dominant out-of-focus image should be progres- of the patient’s eyes the fingers are lined eye with the full-near correction. It is sively blurred with spherical lenses until up with – this is the dominant eye. also recommended that the practitioner the image comes into view. In sighting, the patient holds a card should, at this stage, avoid going into the When the distance or near type is with a hole at arms length, with the detailed mechanics of how the vision is seen clearly, the amount of blur should practitioner asking him or her to view a being corrected. It is important to correct be progressively reduced while asking distant object. Once the object is sighted, any astigmatism equal to greater than the patient to continue to read. Once the the practitioner again looks to see which 0.75D in either or both eyes which, if left full extent of the blur has been removed, of the patient’s eyes is lined up with the uncorrected, can result in reduced visual the patient should be asked to view a object. This is the dominant eye. performance, asthenopic symptoms and distant object (if it was the near test that An alternative approach to preferen- poor tolerance. was causing problems before) and then tial looking is termed the +2.00D blur ● Visual assessment – the first task return to reading. This technique will test. This involves placing the best for the practitioner is to encourage the demonstrate the ability of the patient to binocular distance refraction in the trial patient to suppress each eye to see clearly. suppress the ‘non-viewing’ eye. frame and, while the patient looks at The ability to do this occurs at a subcon- Once the ability to suppress has been
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demonstrated, the practitioner should optimise the refraction, again binocularly to check that the optimum correction for distance and near has been achieved. It is only then that the practitioner should explain to the patient how the vision has been corrected. The maxim ‘show then tell’ is probably one of the key factors behind success in monovision fitting. After static visual acuity has been assessed, the patient should be encour- aged to walk around the practice wearing the full monovision correction. It is here that single use trial lenses or frequent replacement lenses are of value Figure 14a Segment position in primary Figure 14b Segment position positioned over in allowing the exact prescription to be position of gaze pupil in down gaze due to successful lens fitted and trialled. The dynamic visual translation assessment should start with an appre- ciation of the effect of suppression on Enhanced monovision fitting to the refractor head as it allows a more peripheral acuity before allowing the Enhanced monovision involves fitting natural head posture, which is critical patient to carry out other tasks, such as one eye with a bifocal lens and the in fitting this type of lens. The practi- judging distance. These assessments are other with a single-vision lens. A variety tioner should avoid any consideration important, both clinically and ethically, of options exist. The more frequent of over-plusing the prescription during in showing the patient the advantages approach involves fitting the dominant the refraction. Alternating bifocals are and limitations of the correction. eye with a single-vision distance designed to function by having two Ideally, an extended trial period is lens (spherical or toric) and the non- discrete focal lengths for distance and preferred in monovision correction dominant eye with a bifocal lens. This near. If the only way of achieving a satis- so that the patient can fully assess the improves binocular summation and factory result is to dramatically alter the benefits of the correction. Before this offers some level of stereo-acuity to the binocular refractive state, the lenses are occurs, the onus is on the practitioner to monovision wearer that is experiencing not being allowed to work in this way explain fully the type of correction fitted increasing blur with a higher reading and lens translation should be improved and to make sure the patient understands add. Alternatively the same approach or the practitioner should try a straight that the adaptation period may involve can be used when fitting patients that monovision correction. problems in close work and a ‘learning require sharper distance vision than ● Visual assessment – the static visual curve’ in driving, especially at night. bilateral simultaneous vision can offer. assessment is carried out in a similar way For most road users, monovision still The bifocal lens in the non-dominant eye to monovision. It is, however, probable provides adequate visual performance usually needs more bias for near. This that a trial frame will have to be worn to to meet regulatory standards, although modification can be achieved effectively provide the correct near refraction. Once the EU directive on driving licences by increasing the distance power of the again, visual contrast and illumination requires that a driver of a Grade 2 vehicle bifocal lens by +0.50D to +0.75D while should remain high to assist the patient (greater than 750 kilograms) must have reducing the add power accordingly. in visualising the two images. When a minimum of 6/12 vision in the worst assessing dynamic visual performance, eye. When fitting monovision, and Alternating vision bifocals the practitioner should demonstrate to indeed all presbyopic contact lens correc- ● Physical fit – an alternating vision the patient the effect of the near addition tions, the practitioner has an obligation rigid bifocal must be fitted to allow trans- leading to an area of blur inferiority. As a to inform patients of the adaptation that lation between the distance and near patient new to bifocal or varifocal specta- may be required. If a patient is unable to zone to occur. The lens should, there- cles would be instructed, so the alternat- adapt to any visual disturbance caused fore, be mobile and supported by the ing vision bifocal contact lens wearer by monovision in specific situations, a lower eyelid. This is normally achieved should be aware of this, although this practitioner may consider prescribing a by fitting on alignment or with minimal effect will be less than with a spectacle spectacle over-refraction. apical clearance. In primary gaze, the lens due to the reduced vertex distance. lower pupil margin should be in line Partial monovision with the top of the near segment (Figure Simultaneous vision bifocals Generally, the acceptance and there- 14a). On near vision, the pupil should ● Physical fit – in contrast to the fore the success of monovision falls as look through the near segment (Figure alternating vision lens, the refractive the reading add increases.16,17 As the 14b). The fit is most effectively assessed optic simultaneous vision bifocal should indicated add exceeds +2.00D, toler- by using a hand-held Burton lamp and be fitted with minimum, rather than ance can often be improved if a reduced fluorescein. The hand-held Burton lamp maximum, movement. It is critical that reading addition is given. The patient may is preferable to the slit lamp as it encour- the lens is well centred over the visual need ‘top up’ glasses for small print and ages a more natural head posture. If the axis to enable the correct portion of possibly additional glasses for driving or lens does not centre adequately, the fit light to pass through each part of the a secondary distance correcting contact should be modified. lens. As the lens decentres, the aberra- lens. This form of monovision is ideal for ● Trial lens power selection – once tions increase, to the detriment of vision. social users whose near vision demands the lens fit has been optimised, a normal The optimum centration should not be will be lower than full-time wearers. It is binocular over-refraction should be achieved to the detriment of the physio- also useful for patients who have greater carried out at both distance and near. The logical fit of the lens, and the fit should be intermediate vision needs. use of a trial frame and lenses is preferred sufficient to allow tear exchange to occur. opticianonline.net 05.10.07 | Optician | 31 Contact Lens Monthly CET
● Trial lens power selection – it is in Table 2 power selection that simultaneous vision Visual quality assessment scale bifocals differ to the greatest extent, with different manufacturers recommending Grade Descriptor Description different strategies for varying designs. 5 Excellent Sharp and clear at all times The basic principle in achieving correc- 4 Good Occasional periods of blur tion is to provide a full binocular correc- 3 Satisfactory Acceptable but slight blur/haze tion at distance and near. If the lens is 2 Fair Blur/haze noticeable at all times working as a true bifocal, the distance 1 Poor Significant blur, unacceptable correction should be determined first and the different near additions tested in turn. When assessing distance correc- tion, care should be taken to maximise the assessment of ocular dominance and Troubleshooting: poor vision the plus power of the lens to fully relax binocular variation to the prescription, as The most common problem in presby- binocular accommodation. Although in monovision. The modified approach opic lens correction is inadequate vision. the most effective adjustment options can be achieved by adjusting the refractive Although the visual acuity might be may vary with the lens design being power of the lens or selecting alterna- excellent, the patient could still complain used, most designs are sensitive to 0.25 tive lens designs for each eye to delib- of unacceptable vision because visual dioptre adjustments to the distance lens erately improve distance vision in one quality is not the same as visual acuity, power which can have a profound effect eye, at the expense of near performance and with many correction options it is on distance or near visual performance. while improving near in the other. This unlikely that objective and subjective Lens power adjustments are best inves- can be achieved by increasing the minus/ visual performance will be the same tigated by using +/-0.25D twirls/flippers decreasing the plus on the dominant eye as that experienced through a specta- or trial lenses during binocular vision in to enhance distance vision while decreas- cle correction. Subjective assessment of ambient illumination or the illumination ing the minus/increasing the plus in the visual quality, such as a 0-5 scale (Table where problems are being experienced non-dominant eye. A similar bias can be 2) might help in recording this. If the by the wearer. The use of phoropters obtained by using different add powers visual quality is unacceptable, the first should be avoided during over-refrac- in each, the lower add power being fitted step should be to modify the refraction, tion as the resulting light reduction to the dominant eye to improve distance which is most effectively achieved by will increase pupil size and alter optical vision. Similarly, one eye may be fitted placing trial lenses over the patient’s eyes performance. Any distance minus with a centre distance simultaneous and ensuring that whatever improve- power adjustment should only be made design and the other with a centre near ment is made at one distance is not offset if it has been demonstrated to make a design. Some designs use the lens design by significant degradation at another. If significant impact on distance visual itself to deliver a ‘modified monovision’ a lens type is to be changed, the practi- acuity (ie half to one line of Snellen fitting approach as the starting point tioner should only consider switching visual acuity) combined with a subjec- (Figure 12). from one basic principle to another and tive improvement. ● Visual assessment – visual assess- avoid changing to another design which If a satisfactory distance and near ment, both static and dynamic, should is based on the same optical principle. correction cannot be achieved, many be carried out as previously described. manufacturers recommend moving Particular note should be made of the Conclusions towards a ‘modified monovision’ effect of pupil size on visual performance, Presbyopes are increasing throughout technique by over-correcting one eye and which should be adequately explained to Europe and the demand for presbyopic under-correcting the other. This requires the patient. contact lens correction will inevita-
Table 3 Table 4 Clinical pearls for presbyopia fitting18 Fitting approach depending on degree of presbyopia18 Set realistic expectations up- Always assess vision performance Emerging presbyope (up to +1.00DS) front. Success is what is right with both eyes open. Let patient trial Simultaneous: full correction in both eyes for the patient and remember lens performance at home and work Monovision: distance and full near the 20/happy rule and have them return in a week for follow-up assessment Decide your clinical strategy Avoid phoropters for over-refraction. Mid presbyope (+1.25DS to +2.00DS) with each patient and avoid Trial frame or flippers are best and Simultaneous: full correction to both eyes trying different designs based look for an improvement in overall Translation: full correction to both eyes (do not overcor- on the same optical principle. vision. Use th Snellen letter chart rect add) Consider different approaches only to record visual acuity for legal Monovision: distance and full near including modified monovision purposes and as a benchmark for and enhanced monovision future lens changes Study and follow the manufac- Always look for the optimal balance Late presbyope (+2.25DS to +3.00DS) turer’s fitting advice for any between near and distance vision Translating: full correction to both eyes one particular design of lens as that meets the patient’s visual needs Simultaneous: modified monovision; enhanced they all differ slightly in design monovision characteristics and optimal Monovision: distance and partial near; consider top-up fitting spectacles to provide additional plus Adapted from Christie C and Beerten R 2007 Adapted from Christie, C and Beerten R, 2007
32 | Optician | 05.10.07 opticianonline.net CET Contact Lens Monthly
bly continue to increase. There is an meeting the patient’s particular visual availability of single-use diagnostic trial enormous untapped interest in contact needs. There are now more lens options lenses allows effective trials to help lens wear among presbyopes. Being than ever to offer our presbyopic eliminate failures prior to dispensing. aware of the different lens designs, patients and the lack of the ‘perfect’ Daily disposable multi-focal lenses are fitting approaches and the associated contact lens solution for the presby- also available for patients offering even advantages and disadvantages, along ope shouldn’t discourage practitioners greater levels of patient convenience as with the patients personality, occupa- from fitting this ever-increasing patient well as lens designs available in silicone tion and previous lens wearing history, base. New simultaneous designs with hydrogel materials. helps in understanding which is the improved optical performance are now If the initial lens powers selected fails more appropriate starting point in relatively easy to fit and the increasing to provide adequate visual performance,
Multiple-choice questions – take part at www.opticianonline.net
If a +2.00 blur test results in the What is usually meant by the term Which of the following is true for 1patient reporting that the image is 6‘modified monovision’? 11assessing ocular dominance? clearest when the +2.00D lens is held in A Alternating the distance and near lens in A A +2.00D lens held before the non- front of the left eye then: each eye with every use dominant eye will be reported as more A The patient is left eye dominant B Having a reduced addition in one eye blurry than when held before the other eye B No strong dominance is present C Having the near lens before the dominant B The visual system can more easily suppress C The patient is right eye dominant eye the image from the dominant eye D The patient is left handed D Using bifocal lenses adapted to bias one C The patient is more likely to align the eye to near vision fingers with the sight from the dominant Which of the following statements eye if asked to simulate shooting the 2regarding alternating bifocal lenses is For whom might a back surface practitioner false? 7aspheric soft lens be most appropriate? D Right-handed people are right eye dominant A Fused and solid designs are available A The pre-presbyope with high-order B They are usually fitted steeper than flattest K aberrations When selecting the power of the C Visual quality is high with successful fits B Early presbyopia (+1.25 D or less) 12trial lens, which of the following is D Prism is used to control lens stability and C Established presbyopia (+2.00 D or more) true? position D Presbyope with low grade astigmatism A Fit the near lens to the dominant eye B It is best to explain the mechanics of Which of the following statements is Modified monovision fitting approach presbyopic lens design 3false in relation to simultaneous vision 8involves: C Phoropter heads are useful lens fitting? A Reducing the add power during monovision D Astigmatism should be corrected A Lens centration is important fitting B 0.25D adjustments can have a profound B Fitting one eye with a single-vision lens and What is the vision requirement for effect on visual performance the other with a bifocal 13the worse eye of a Grade 2 vehicle C Over-refraction using a phoropter is C Ensuring both eyes are fitted with driver? preferred alternative centre-near designs A >6/9 D Objective vision measurement alone is not D Altering distance or near power to enhance B 6/12 or more a good predictor of success distance vision in one eye and near in the C 6/24 or more other D >6/60 Which of the following statements 4regarding the success of monovision Which of the following is least useful The use of partial presbyopic compared to other presbyopia strategies is 9when assessing the vision through a 14correction with multifocal lenses correct? trial presbyopic lens? and spectacles over the top is described as A Monovision is less successful than bifocal A A glare source what? contact lenses B A sample of near task object A Modified monovision B There is no evidence that monovision is C A low contrast chart B Partial monovision more successful than bifocal lenses D A retinoscope C Enhanced monovision C Monovision is shown in most studies so far D Alternating monovision published to equal or better the success Which of the following modalities rates of bifocal lenses 10might be the preferred option for Why is a Burton lamp preferable to D There are no comparative studies yet significant refractive error presbyopes? 15a slit lamp for assessing the fit of published in this area A Monovision an alternating bifocal lens? B Diffractive bifocals A A more natural head posture may be What is the main disadvantage of a C Simultaneous bifocals maintained by the patient 5translating bifocal contact lens? D Alternating bifocals B The light is closer to ultraviolet so better A Poor vision shows up fluorescein B Poor comfort due to lid interaction C The edge of the segment is more clearly C Unavailable in soft material defined D Only avaiable as a fused lens design D It has less effect on pupil size
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alternative fitting approaches such as Vision Sci, 1992; 69:8 609-614. with three types of presbyopic contact lens enhanced and modified monovision 4 Molinari J F. A clinical comparison of correction. J Brit Contact Lens Assoc, 1995; can be explored. Key fitting tips are subjective effectiveness of monovision, 18, 119-125. summarised in Table 2.18 With experi- aperture-dependent and independent 13 Meyler J, Veys J. A new ‘pupil-intelligent’ ence, alternating lens designs can be bifocal hydrogel lens fittings. Trans Brit lens for presbyopic correction. Optician, added to the lens choice to offer patients Contact Lens Assoc, 1988; 58-59. 1999; 217, (5687), 18-23. bifocal correction if more exacting visual 5 Saunders B D. The optical performance of 14 Bennett ES. Bifocal and multifocal performance is required. In addition the bifocal contact lenses. Trans Brit Contact contact lenses. In Contact Lenses, 5th edn simplicity of monovision remains an Lens Assoc, 1989; 71-74. (AJ Phillips and L Speedwell, eds) 2007 pp effective solution for many presbyopes. 6 Macalister G O, and Woods C A. Monovision 311-331. A more systematic approach can be used versus RGP translating bifocals. JBCLA, 15 Michaud L, Tchang JP, Baril C, Gresset J. depending on the stage of presbyopia as 1991; 14:4 173-178. New perspectives in monovision: a study shown in Table 3.18 It is recommended 7 Du Toit R, Situ P, Simpson T and Fonn D. comparing aspheric with disposable lenses. that practitioners select and use two or Results of a one year clinical trial comparing ICLC, 1995; 22, 203-208. three alternative lens designs so that a monovision and bifocal contact lenses. 16 Schor C, Landsman L, Erickson P. Ocular sound clinical approach can be devel- Optom Vis Sci, 2000; 77, S18. dominance and the interocular suppression oped and used with confidence, with the 8 Situ P, du Toit R, Donn D and Simpson T. () of blur in monovision. Am J Optom, 1987; 64, result that this form of fitting becomes an Successful monovision contact lens wearers 723-730. integral part of contact lens practice. ● refitted with bifocal contact lenses. Eye 17 Erikson P. Potential range of clear vision Cont Lens, 2003; 29(3), 181-184. in monovision. J Am Opt Assoc, 1988; 59, References 9 Morgan P, Efron N. Trends in UK contact 203-205. 1 Papas E, Young G and Hearn K. Monovision lens prescribing 2006. Optician, 2006; 231, 18 Christie C and Beertren R. The correction versus soft diffractive bifocal contact (6054), 16-17. of presbyopia with contact lenses. Optom In lenses: a crossover study. ICLC, 1990; 17: 10 Edwards K. Progressive power contact Pract, 2007; 8, 19-30. 181-186. lens problem-solving. Optician, 2000; 219 2 Back A P, Woods R and Holden B A. (5749), 16-20. ● Jane Veys is education director, The The comparative visual performance of 11 Woods C. Ruston D, Hough T, Efron N. Vision Care Institute, Johnson & Johnson monovision and various concentric bifocals. Clinical performance of an innovative back Vision Care. John Meyler is senior director, Trans Brit Contact Lens Assoc, 1987; 46-47. surface multifocal contact lens in correcting professional affairs, Europe, Middle East & 3 Harris M G, Sheeny J E and Gan C M. Vision presbyopia. CLAO J, 1999; 25, 176-181. Africa, Johnson & Johnson Vision Care. Ian and task performance with monovision and 12 Plakitsi A, Charman WN. Comparison Davies is vice president, The Vision Care diffractive bifocal contact lenses. Optom of the depths of focus with the naked eye Institute, Johnson & Johnson Vision Care SUBSCRIBE TODAY and get 4 extra FREE issues
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