One of the more perceived challenging areas within contact lens practice is fitting presbyopic patients with contact lenses to allow the majority of their visual requirements to be met through the development of their presbyopia. However, the availability of newer optical designs, daily disposability and lens designs in enhanced hydrogel, silicone hydrogel and high-permeability rigid lens materials mean that there is less restriction to the modality of wear or physiological compromise when correcting presbyopia with contact lenses, resulting in better success rates than previously.
More recently we have also seen disposable toric multifocal options introduced allowing reading and astigmatic correction giving a significant benefit in visual performance for low to medium astigmats. Yet despite the introduction of new multifocal contact lens designs by virtually every major manufacturer in recent years, the percentage of multifocal lenses – fitted to those in the presbyopia age range – in practices globally remains low, notwithstanding a gradual increase in presbyopia fitting over time ( Fig. 22.1 ) ( ).
As shown in Fig. 22.2 , the use of contact lenses drops sharply at the same time vision correction needs to increase in the presbyopic population. Interestingly, as many as 4 in 10 contact lens wearers are ≥40 years old, yet according to a poll conducted by Gallup in 2015, only 9% of adults requiring multifocal correction in that age group received a recommendation for contact lenses as a means of correction ( ). This is a significant untapped opportunity for contact lens practitioners not currently engaged in the multifocal fitting.
Today’s presbyopes, Generation X (Gen Xers), born between 1965 and 1980, and Baby Boomers (born 1946–1964) enjoy more affluent and active lifestyles than ever before. Gen Xers are in their prime earning years, and Baby Boomers are just beginning to retire and enjoy life outside of work. Both groups are regular users of digital devices ( ), which add to their visual demands; have significant disposable income ( ); over two-thirds value looking younger ( ); and they are willing to spend money on products and procedures to maintain a youthful appearance ranging from hair colouring and teeth whitening to cosmetic surgery ( ).
Offering contact lens correction to this group should now be considered an integral, routine part of contact lens practice and represents a very significant opportunity for practice growth and increased patient satisfaction.
The options for the correction of presbyopia to both existing and new contact lens wearers include:
Distance-powered contact lenses and near reading spectacles.
Bifocal or multifocal contact lenses:
Simultaneous image contact lenses.
Alternating image contact lenses.
The contact lens options for presbyopic correction are shown in Fig. 22.3 with some examples of the different brands available. Each option has advantages and disadvantages, which vary with the lens type, the fitting approach used and the degree of presbyopia present. A systematic approach to lens selection can be used depending on the stage of presbyopia, as shown in Box 22.1 ( ).
Emerging Presbyope (Up To +1.00 DS)
Simultaneous: full correction in both eyes
Monovision: distance and full near
Mid-Presbyope (+1.25 to +2.00 DS)
Simultaneous: full correction to both eyes
Translating: full correction to both eyes (do not overcorrect add)
Monovision: distance and full near
Late Presbyope (+2.25 to +3.00 DS)
Simultaneous: modified monovision; enhanced monovision
Translating: full correction to both eyes
Monovision: distance and partial near; consider top-up spectacles to provide additional plus
Distance-powered contact lenses combined with near reading spectacles may be the simplest and least expensive option. However, it does not address the problem for the patient who does not wish to wear spectacles, and it may even demotivate an existing lens wearer. Many contact lens wearers becoming presbyopic want to continue to wear contact lenses as their primary correction option for their vision correction needs and not being given this option is a very significant reason for ceasing contact lens wear. It should be remembered that intermittent use of spectacles is often far more inconvenient than constant use.
Patient motivation plays an important role in any form of contact lens fitting. However, this motivation is often restricted to those patients who are aware of the various contact lens options, which they are then keen to explore further. Perhaps more important is an informed choice based on the advantages and disadvantages of the various options available, as the majority of patients are not aware that contact lenses are a possibility for the correction of presbyopia. This more ‘proactive’ approach may result in somewhat lower success rates but inevitably, in a larger contact lens patient base. and have shown that a significant proportion of an unselected presbyopic population can achieve success with simultaneous image multifocal contact lenses.
Caution should prevail when considering patients with compromised binocular vision, amblyopia, distance acuity <6/12, or exacting critical vision needs for either distance or near vision. High- and low-contrast visual acuity charts ( Fig. 22.4 ) give more information about acuity. In particular, the difference in low-contrast acuity between spectacles and contact lenses may give some indication of possible success.
It is more important, however, to have access to trial lenses to obtain an idea of potential success for any particular type of multifocal lens or fitting technique based on both patient subjective feedback and objective measurement. As with any contact lens preassessment, careful attention should be paid to tear quality and quantity, which are often reduced in this age group, as well as eyelid tone and position. The selection of a lens material that offers high wettability and low coefficient of friction may be especially relevant in the presbyopic age group. When getting started with this form of lens fitting, it may help to start with selecting patients that are generally accepted as being ‘better’ candidates versus choosing those who might be considered as ‘more challenging’ to fit successfully. Table 22.1 summarizes the different patient types when considering a fitting simultaneous image, alternating image and monovision ( ).
|Good candidates (getting started)||Existing soft lens wearers who are emerging presbyopes||Moderate and advanced presbyopes||Significant astigmatic refractive error|
|Moderate intermediate-vision requirements||Lower lid above, tangent to, or no more than 1 mm below the limbus||Reading positions other than standard downward gaze|
|Spherical or near-spherical refractive errors, unless toric multifocal is available||Myopic or low hyperopic powers||Current contact lens wearers|
|Willing to accept some limited compromise in distance vision||Normal to large palpebral apertures||Motivated and realistic expectations|
|Normal to tight lid tension|
|More challenging candidates (experience required)||Do not desire any compromise in distance vision||High hyperopes||Low myopes|
|Emmetropic or near-emmetropic distance refractive error||Small palpebral apertures||Concentrated specific visual needs|
|Would benefit from a toric correction||Loose lower lids||High reading addition|
|Small pupil size (<3 mm)||High visual demands and expectations|
It is important that patients are given realistic expectations about the likely level of vision, as with any type of vision correction for presbyopia. It is necessary to ensure that patients fully understand the basis of presbyopia and their expectations should be set out in a positive but informative manner. This involves discussing the benefits of combined distance/near correction without the need for spectacles (less head movement, no peripheral distortion, more natural image formation) as well as likely differences between the visual performance of monovision, simultaneous image or alternating image lenses.
When compared to spectacles or single-vision contact lenses, visual decrements may be noticed, such as reductions in visual acuity (especially in low luminance) and possibly stereopsis, and reduced intermediate vision depending on the type of lens fitted. It should also be explained to the patient that it is quite normal for fitting to require more than one appointment in order to try out alternative lens powers and fitting approaches, depending on their assessment of lens performance in their everyday visual environment.
It is worth establishing what a successful outcome for the patient would be in advance of the fitting. Is it being able to read their phone with no reading glasses, a restaurant menu, using their laptop computer? By establishing their overarching needs and being orientated in the fitting process to achieving them patient satisfaction is more likely and, when there are gripes, the fitter can revert to the primary objective and ask if it was achieved.
Measurement of the ocular dominance or sighting preference is useful in establishing which eye to correct for distance vision during monovision fitting, or while making adjustments during simultaneous lens fitting. Ocular dominance can be determined using preferential looking tests or alternatively by the +1.00D sensory test. The former is carried out by sitting opposite the patient and asking the patient to look through a hole in a piece of card at an open eye of the practitioner. Whichever eye the patient lines up with the open eye of the practitioner is the dominant one. The latter test involves placing the best binocular distance refraction in the trial frame and, while patients look at the lowest line they can read, a +1.00D lens is placed alternatively in front of each eye. Patients indicate when the vision is clearest, by viewing the distance chart. If the +1.00D lens is in front of the left eye when the image is reported as clearest, then the right eye is considered distance-dominant, and vice versa .
It has been found that unsuccessful wearers became successful after switching near and distance corrections contrary to the dominance as measured by traditional methods, but rarely contrary to the +1.00D sensory test ( ). Nowadays most manufacturers recommend the +1.00D sensory test to assess dominance. Historically, pupil size measurements were useful when fitting bi-concentric designs; however, this procedure is less relevant with more recent designs. Nevertheless, clinical experience reveals larger pupils can be more challenging when fitting alternating image lenses and very small pupils may be less successful when fitting simultaneous image lenses.
Bifocal and Multifocal Contact Lenses
Bifocal and multifocal contact lenses can be simultaneous or alternating image designs. Simultaneous designs generally require the lens to be relatively stable on the eye and will be associated with some form of visual compromise because objects at both distance and near are imaged simultaneously on the retina. Alternating image lenses require significant lens movement so that the distance and near portions of the lens can be positioned over the pupil by interaction with the lids.
Relatively recent comparative studies have concluded that multifocal contact lenses perform better, in many different forms of visual measurements than monovision correction ( ). However, reported that multifocal contact lens wearers were significantly less satisfied with aspects of their vision during nighttime than daytime driving, particularly regarding disturbances from glare and haloes.
Simultaneous Image Designs
A variety of simultaneous lens designs are available in both rigid and soft materials. The availability of single-use disposable soft trial lenses and soft lens designs that also fully correct astigmatism and empirically ordered individually based aspheric rigid lenses has resulted in an increased prescribing of this form of lens correction ( ).
In simultaneous image designs, the distance, intermediate and near correction zones are both positioned in front of the pupil in every direction of gaze so that light from either a distant or near object passes through all zones. As fixation is directed to either a distant or a near object, one zone produces a focused image while the others produce a blurred image that overlaps the same retinal elements as the focused one ( ) ( Fig. 22.5 ).
The placing of simultaneous images on the retina by any optical system relies on the visual system being able to select the clearer picture and to ignore the out-of-focus image, whether a distant or near object is being viewed. The phenomenon of binocular summation improves the end result by improving the monocular images and generating a binocular image that offers improved contrast and acuity. Care needs to be exerted to remain in the zone of summation versus extending into the zone of inhibition. Summation is thought to occur when the amount of optical disparity is less than 1.00 D.
The spread of light from the defocused image reduces the contrast of the focused image ( ). As a result, the fitting of a simultaneous image lens is likely to result in some level of reduction in image quality in comparison with that resulting from a single-vision correction. The extent of contrast loss will depend upon the relative amounts of in-focus to out-of-focus light striking the retina. If equal contrast is to be achieved for both near and far viewing, the refractive system should allow approximate equality of the areas of the two portions of the lens transmitting to the pupil. Lens performance may be affected by many factors, which include pupil size, lens design and centration of optics relative to the pupil. If the optics are decentred with regard to the visual axis then ‘shadowing’ effects are produced by virtue of induced asymmetrical aberration, principally coma ( ). The theoretical retinal intensity of different lens designs and the effect of variations in pupil size can be investigated by measuring their modular transfer function ( ).
Regardless of the different optical principles and designs available, large well-controlled independent studies are required to determine whether patient acceptance is more successful with any one design. Comparing patient acceptance success rates from different studies is difficult due to differences in success criteria, patient profile and length of study. showed that existing successful monovision wearers could be successfully fitted with bifocal contact lenses and that after a 6-month period 68% preferred bifocal lenses compared to a 25% preference for monovision.
With aspheric designs, the refractive power gradually changes from the geometric centre of the lens to the more peripheral area of the optic zone. Such lenses are best described as ‘multifocal’ enhancing or extending the depth of focus ( ) due to the progression of powers but can also be considered as a type of concentric design as the power distributions are concentric around the centre of the lens. By the nature of their design, lens function will vary somewhat with changes in pupil size. This can lead to variations in distance and near-vision image contrast which can be minimised if the lens design takes into account pupil size variation.
Power distribution is produced by the use of a continuous aspheric surface of fixed, or more typically, variable eccentricity. Aspheric lens designs can be subdivided according to whether the power distribution is the most plus (least minus) centrally, resulting in a centre-near design ( Fig. 22.6A ), or most minus (least plus) centrally resulting in a centre-distance design ( Fig. 22.6B ). While both options are available in soft and rigid materials, centre near front surface aspheric designs are much more prevalent amongst soft modern aspheric multifocals.
Front Surface Aspheric Designs
Front surface-soft aspheric designs generally generate negative spherical aberration, resulting in decreasing plus power from the geometric centre of the lens. This in essence creates a centre-near design. The aspheric curve is calculated to increase the overall spherical aberrations of the eye and, if necessary, of the lens itself. The increase in depth of focus can be effective at correcting the early presbyopic patient (up to +1.50 D). As presbyopia increases, the front surface curve must have a greater degree of asphericity to allow more plus refractive power within the overall optical system. This often involves more complex surface geometry of varying eccentricity to allow stabilized distance and near power zones within a specified area.
Apart from the visual demands of the presbyopic patient, it would also be expected that visual performance would depend upon the interaction of the optical characteristics of the particular lens design with the aberrations of the eyes of the wearer. Ocular spherical aberration is unique to the individual and can vary from patient to patient. Consequently, variations in ocular aberration between individuals may explain in part why lenses of this type meet the needs of some wearers but sometimes not others ( ).
Eyes with greater positive spherical aberration effectively work against negative spherical aberration generated by a centre near aspheric design resulting in a less multifocal add effect. Whilst the patient may demonstrate improved intermediate acuity, they may require a higher reading add than their spectacle add to effectively improve their near vision. Different centre near aspheric soft lenses do have different distributions of optical power on their surfaces ( Fig. 22.7 ) and thus it may be possible to improve performance by changing to a different design.
An alternative approach is to use a high asphericity front curve combined with a centre distance design. This will generate negative spherical aberration and thus increase the depth of focus of the lens/eye optical system.
Pupil size is known to decrease with age, as well as when looking at near objects and, of course, under photopic conditions ( Fig. 22.8 ). If a centre-near multifocal contact lens design is not optimised and has a fixed design for all reading additions, visual performance can be reduced as the pupil size diminishes with age. Most, but not all, current multifocal designs ( Fig. 22.9 ) are adapted to reflect this age change as the reading addition increases assuming that higher reading adds will be required for older patients.
A more recent finding is that not only does pupil size vary with age but refractive error can also influence pupil size with myopes tending to have larger pupil sizes than hyperopes, particularly in mesopic light conditions ( ) ( Fig. 22.10 ). confirmed this finding and discussed the implications for multifocal design.
Whilst these pupil size differences may be relatively small, when considered as an area this can have a significant impact on visual performance. Guillon’s data indicates the difference in pupil size area from a -8.00-D myope to a +6.00-D hyperope is 24%. If not considered in the lens design, this can result in differences in success between myopes and hyperopes. A more recent lens design ( Fig. 22.11 ) varies the optic profile both across the prescription and the reading addition range to optimize optics and visual performance.
The optical performance and patient satisfaction with front surface aspheric simultaneous image soft lenses have improved significantly in recent years and they form a very significant part of the recent growth of presbyopic contact lens correction with multifocal ( Fig. 22.1 ).
Back Surface Aspheric Designs
Back surface aspheric surfaces that generate the reading addition are mostly found in RGP lens designs and result in power changes from the central distance correction to that required for near vision by inducing positive spherical aberration. The greater the eccentricity (or rate of flattening), the higher the reading power in relation to distance power. However, the higher the reading addition, the more likely that distance vision will be affected adversely, especially in low-contrast and/or low-light conditions. Back surface centre distance aspheric soft lens designs are limited in the amount of positive spherical aberration they can generate and are therefore only suitable for early presbyopia of up to +1.25 D.
However, in rigid lenses, the back surface geometry may depart significantly from corneal topography with the ‘higher-eccentricity’ designs. This is due to rapidly flattening back surface aspheric geometry. Such lenses will need to be fitted fairly steep to allow for appropriate lens centration ( ). Back surface aspheric rigid lens designs can now be based on corneal topography and ocular prescription to create an individual lens design for correcting presbyopia ( ). The aim is to modify the combined optical system of the lens, tears and cornea to provide a predictable varifocal effect.
Multizonal Aspheric Designs
The approach with zonal designs is to use a modified monovision strategy with the first pair of lenses trialled. The lens used for the dominant eye is a centre-distance lens design whilst the lens for the other eye is centre-near in design. Lens designs can use aspheric surfaces, spherical surfaces or a combination of both with unique zone sizes to produce two complementary but inverse-geometry lenses ( Fig. 22.12 ). Each lens is a multifocal and the intention is that some binocular summation will still occur, with the intention of providing acceptable vision at all distances under binocular conditions. Both centre-near and centre-distance designs have fixed optical zones regardless of added power ( Fig. 22.13 ). This could have the effect of biasing the optical performance towards pure monovision in older wearers. Once again caution is needed to not exceed the level of disparity to cause inhibition.