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Bifocal and Multifocal Contact Lenses
Introduction
Presbyopia, resulting from a gradual decrement in visual function at near, is one of the most prevalent ocular conditions resulting in patient complaints and dissatisfaction in the 40 and older age group. Nevertheless, it also represents an outstanding opportunity for potential contact lens wearers. Presbyopic patients represent the largest growing segment of the population and the largest untapped section of the contact lens market ( ):
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There were 78 million so-called ‘baby boomers’ born in the United States between 1946 and 1964 ( ).
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Only 3% of presbyopes currently wear some form of presbyopic contact lens correction ( , ). This is consistent with a survey that concluded that there has been a significant under-prescribing of contact lenses for the correction of presbyopia ( ).
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In the United Kingdom, it has been found that the presbyopic market has greater potential for growth than the normal younger contact lens market ( , ).
The low use of presbyopic contact lenses is most likely the result of several factors ( ):
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They are often perceived by practitioners as being complicated or challenging to fit, resulting in the selection of easier options such as monovision or single-vision contact lenses in combination with reading glasses and multifocal spectacles ( ).
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It is common for patients to be told that bifocal contact lenses are not likely to be successful.
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Multifocal contact lenses will not be successful if they are never presented as an option to presbyopic patients.
(For further information about multifocal contact lens prescribing, see Section 9 , Addendum, available at:
https://expertconsult.inkling.com/ .)
Multifocal and monovision contact lens prescribing increased from 30% of fits in 2003 to 50% in 2010, although after that, it appeared to plateau ( ). Increases are likely because:
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Many baby boomers who have never worn corrective eyewear may choose contact lenses over spectacles because of vanity.
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Current emerging presbyopes are more active than their predecessors and appear to be more determined to maintain their youthful appearance and active lifestyle.
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More than 90% of contact lens wearers in the 35- to 55-year-old age category have worn contact lenses for a large period of their lives and are committed to continuing contact lens wear ( ).
The benefits of multifocal contact lenses compared with spectacles include the following:
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One can avoid numerous head and gaze requirements associated with spectacle wear during computer use and other activities which require near vision at a level above primary gaze ( , ).
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Tasks involving numerous dynamic eye movements are more challenging for the multifocal spectacle wearer as a result of viewing into the varying corrective powers with eye movement ( ).
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Multifocal contact lenses move with the eye, minimising possible problems, as the wearer is typically looking through the lens centre.
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Progressive addition spectacles can result in distortions in the size and shape of objects whose images extend beyond the limited intermediate and near zones ( ).
The visual freedom that multifocal lenses provide is a powerful benefit, and presbyopic individuals can be among the most satisfied patients. Also, this cohort of patients represents the high end of earnings potential; therefore practice income generated from these patients – and their referrals – can build a contact lens practice. As manufacturing technology continues to improve, success rates increase and both practitioner and consumer confidence continues to grow. The purpose of this chapter is to review important clinical considerations in fitting the presbyope, including patient selection, lens designs, fitting and problem-solving.
History
See Section 8 , History, available at: https://expertconsult.inkling.com/ , for the development of the various designs of lenses.
How to Achieve Bifocal Vision
There are two ways to achieve bifocal vision:
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Translation (see p. 272 ) refers simply to the shifting upward of the lens during downward gaze to allow the wearer to view through the near optics. These can be annular or concentric, or they can have separate powers similar to a bifocal spectacle lens.
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Simultaneous or bivision (see p. 271 ) refers to lens designs in which multiple powers (i.e. near, distance and possibly intermediate) are in front of the eye at the same time. While the patient is looking at a distant object, the light entering the pupil from the near zone forms a very blurred image. The near image blur circle then covers a large area of the retina and is essentially ignored by the lens wearer. These can be:
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annular or concentric
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aspheric, where the back surface flattens at a particular rate, generating a gradual increase in plus power away from the centre of the lens.
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Back surface aspheric multifocal rigid gas permeable (RGP) lenses are popular today due to advances in manufacturing technology that result in better optical quality and the ability to incorporate higher add powers.
Soft Lenses
Early soft bifocal or multifocal lenses gave poor optical quality. Manufacturing innovations provide better optical quality, variable add powers and the availability of weekly-to-monthly disposability which:
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reduces cost to the patient
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allows for replacement lenses
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reduces dry eye–induced complications – more prevalent in the older patient base
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allows the practitioner to try different lenses on a trial basis for limited time periods in an effort to achieve satisfactory vision.
The presbyopic ‘toolbox’ now includes:
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hydrogel and silicone/hydrogel multifocal lenses
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daily disposable multifocals in both spherical and toric powers
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RGP standard and high-add lens designs
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hyper-oxygen-permeable (Dk) hybrid lenses
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scleral multifocal designs.
Preliminary Evaluation and Patient Selection
Physiological changes in the presbyopic population
Tear Volume and Quality (see Chapter 5 )
A reduction in tear volume is the most important change occurring over time. This can result in dry eye symptoms and can impact on contact lens wear. A progressive reduction in tear production results from a reduction in both the goblet cells of the conjunctiva and the mass of the lacrimal glands ( ). Caution is needed if an extended-wear schedule is prescribed, due to tear physiology and also the thickness of many presbyopic lens designs, making daily wear a preferable option for these patients. Clinical signs of dry eye must be ruled out ( ) with careful evaluation of tear film quality and volume, as these are reduced with contact lens wear ( ). The appropriate lens material and lens replacement schedule must also be carefully considered in presbyopic patients.
Reduced tear flow results in:
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increased lens surface deposition
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blurred vision
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discomfort
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possible papillary hypertrophy.
Eyelid Tonicity
This is reduced, making it challenging for a translating RGP lens to be successful, as these designs depend on lid tonicity to move the lens upward with downward gaze.
Crystalline Lens
Changes in the crystalline lens can affect the contact lens prescription and best corrected visual acuity. If reduced, the presbyopic contact lens option will result in a further compromise, especially for distance.
Pingueculae and Pterygia
These can result in a decrease in comfortable lens wear.
Dexterity
Handling of lenses must be considered since presbyopes find near tasks – such as checking whether the lens is inside out – more difficult. Handling tints and lenses that are less ‘floppy’ help with lens insertion.
Examination procedures
The following procedures are required in addition to those for any new contact lens wearer (see Chapters 6 and 15 ).
Patient Requirements
The primary goals of presbyopic contact lens patients differ from those of pre-presbyopes in various aspects:
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what they expect from contact lens wear
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what distance(s) are important to them
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their occupational/avocational vision requirements.
Several extra details and measurements are needed prior to fitting bifocal lenses.
History and Symptoms (see Chapter 15 )
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History of eye surgery. Cosmetic lid surgery, in particular, can affect RGP translation and aspheric multifocal lens success by causing excessive lifting and superior decentration on blinking.
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Medication. Check whether the patient is taking any medications that would reduce tear volume. This can include ibuprofen, oestrogen, antihypertensives, tricyclic antidepressants, anticholinergics and the scopolamine patch ( ).
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Dry eye problems – see ‘ Tears ’.
Tears (see also Chapter 4 and Section 9 , Addendum, available at: 
https://expertconsult.inkling.com/ )
As tear volume decreases with age, it is especially important to evaluate whether the patient is a good candidate for contact lenses in general. A tear break-up time (TBUT) of:
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less than 10 seconds indicates that the patient may not be a good candidate ( )
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6–9 seconds should limit the patient to a daily wear schedule
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5 seconds or less typically contraindicates contact lens wear, especially if performed multiple times with a consistently low value ( ).
If the patient has blepharitis or meibomian gland dysfunction, tear quality can be reduced, so the condition needs to be managed prior to reassessing tear quality for possible contact lens wear. Tear volume can be assessed either with the Schirmer tear test or with a phenol red thread test (Zone-Quick from Menicon/Allergan), although in routine practice, these are rarely done. In the latter test a value of less than 9 mm of wetting in a 15-second time period should contraindicate contact lens wear ( , ).
Pupil Size
Pupil size ( Fig. 13.1 ), should be recorded both in room illumination and with the room lights dimmed such that the millimetre rule readings are barely visible. A pupil gauge may be preferable for measuring, and these are available either as a pen-torch ( Fig. 13.2 ) or a card. The presence of a large pupil in normal room illumination (i.e. >5 mm) – although not highly common in the presbyopic population – would contraindicate an aspheric RGP multifocal lens design because of the ghost images and glare the patient would experience under low-illumination conditions. Pupil size is also critical for soft multifocal designs, as almost every design relies on simultaneous vision and is therefore pupil dependent ( , ). A high intersubject variability was found in pupil diameter, working distance and illumination conditions while conducting the same task. It was concluded that eye-care practitioners should always assess pupil diameter in real-life conditions where possible ( ).
Lid Position
The lid-to-limbus relationship should be observed; in particular, the position of the lower lid and the palpebral aperture should be measured. Individuals with a low-positioned lower lid (i.e. >1 mm below the inferior limbus) will not be good candidates for translating RGP lens designs.
Corneal Topography (see also Chapter 8 )
Whereas keratometry is acceptable in providing an estimate of the paracentral curvature, and thus can assist in selecting the back optic zone radius (BOZR) of the lens to be fitted diagnostically, videokeratography (VKG) does have several benefits:
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The location of the corneal apex can be determined.
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A centrally located apex lends itself to aspheric multifocal lens designs.
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An inferior-positioned apex lends itself to translating designs where an inferior position is desirable ( ).
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Patients with irregular corneas (e.g. keratoconus, trauma, postsurgical) typically are poor candidates for bifocal, multifocal or monovision contact lens correction, with the possible exceptions of hybrid and scleral lens options.
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Topography also provides information on corneal diameter and pupil size ( ).
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Measuring corneal topography over soft lenses can assist in determining where the optics are in relation to the line of sight, which, in turn, may assist in identifying and solving their complaints ( , ).
Visual Status
The best candidates for bifocal/multifocal contact lenses should have greater than 1.25 D of myopia or 1.00 D of hyperopia (Josephson & Caffery 1991). Emmetropes or near-emmetropic patients should not be dismissed, however, if they are well-motivated. Even with the advancements in the quality of lens design, if the patient is amblyopic, monovision and soft bifocal contact lens wear are not advisable due to the potential for further compromise in distance vision. Procedures to perform on the potential presbyopic contact lens wearer are summarised in Table 13.1 .
Table 13.1
Recommended Examination Procedures for the Potential Presbyopic Contact Lens Patient
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recommend discussing presbyopic options before the patient becomes presbyopic.
Key Point
A pre-presbyopic high myope who is close to exhibiting presbyopic symptoms (for example, the 40-year-old 6.0 D myope) will experience an increase in accommodative demand when changing to contact lenses and should be advised that a presbyopic contact lens correction may then be necessary.
Patient characteristics
Personality qualities that have been found to more likely result in success in presbyopic contact lens wear include agreeableness, openness and conscientiousness ( ).
Occupational and recreational information required includes:
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Their goals with the lenses
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The distance(s) they want to see most clearly – for example:
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If they use a computer 30% of the time or more in a normal day, then a multifocal lens design would be indicated to help optimise the intermediate vision. Sit the patient in front of a computer to determine the working distance.
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If critical distance vision is expected, a translating RGP lens should be considered.
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Perfect vision is not possible at all distances, and some compromise is necessary. Patients not prepared to accept this are not good candidates.
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A description of the work environment. Excessive wind or dust, poor air quality or prolonged computer use lead to dryness necessitating frequent application of rewetting drops.
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Do they play sports?
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A daily disposable soft lens is often the preferred option with these patients.
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If optimum vision is important, an aspheric, hybrid or scleral multifocal is likely to result in minimal decentration or loss.
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The goal is to achieve a satisfactory balance between the vision at the distances most important to them ( ). If patients feel that spectacles interfere in any way with their lifestyle, they are often willing to accept a compromise, if present. The goal of presbyopic contact lens wear should be to satisfy ‘most of the visual needs, most of the time, or essentially to reduce, rather than eliminate the need for supplemental near correction’ ( , ). For example, a +1.00 D supplementary spectacle correction may be necessary for reading small print under low illumination for the moderate presbyope, particularly if they have small pupils and are wearing an aspheric multifocal contact lens correction. Fortunately, this is the exception to the rule. However, the practitioner is more likely to be successful and the patient's confidence maintained if practitioners ‘underpromise and overdeliver’ ( ).
A realistic approach about the time needed to achieve the final fit should be discussed. With all multifocal designs, lens exchange(s) may be necessary, and patients should be informed that the first lens may not be the final lens and that the fit or lens power may need to be fine-tuned at subsequent visits. Increased illumination and magnification can be beneficial, and magnifying apps can help mobile phone users. Candidates suitable for presbyopic contact lens correction are shown in Table 13.2 .
Table 13.2
Candidates for Presbyopic Contact Lens Correction
High likelihood for success:
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Moderate likelihood for success:
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Low likelihood for success:
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Presbyopic Contact Lens Options: Single Vision Contact Lenses With Reading Glasses
The use of single-vision lenses (RGP or soft) in combination with reading glasses provides the following benefits ( ):
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good bilateral vision at both distance and near
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simplicity of fit
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low cost.
The over-spectacles are typically single-power plus lenses but may be a progressive addition, particularly to assist with intermediate correction. In some cases, minimal add powers are used to enhance the reading ability of emerging presbyopes. However, patients with varied near and distance tasks will complain of the inconvenience and poor cosmesis of spectacles. Nevertheless, it is important to present this option to all potential presbyopic contact lens wearers, and some patients will prefer to begin with this option, but they are likely to change to an alternative presbyopic contact lens system later.
Monovision
Monovision is an optical means of correction for presbyopia in which one eye is optimally corrected for distance vision and the other eye optimally corrected for near. This is typically accomplished with contact lenses, although monovision refractive surgical procedures can also be applied ( ).
The origin of monovision is unclear, although the use of the monocle in the 1800s certainly was an early method of monovision correction. Using a contact lens in this fashion was first attributed to Westsmith in the 1960s ( ). The advantages of the monovision system include the following ( , ):
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Conventional lenses are used which do not require special lens designs.
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The professional time required is decreased.
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It is less expensive to the patient.
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Thin, non-prism-ballasted lenses are used.
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Only one lens is changed for current contact lens wearers.
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The patient can usually determine soon after initiating lens wear if they are going to be successful.
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Avoidance of many of the symptoms/compromises associated with multifocal contact lenses, including ghost images, reduced contrast sensitivity, and fluctuating vision related to pupil size changes.
However, the primary limitation to monovision pertains to concerns about the lack of balanced binocular vision. A literature review by indicates that monovision may:
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stress the visual system
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impair stereoscopic depth perception
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affect performance in complex spatial-motor tasks such as driving.
Patient selection
Trying to explain the concept of monovision to a patient can be challenging, and it is often easier to actually demonstrate the system. Cerebral cortex binocular cells have identical receptive fields for detection of size, orientation, motion sensitivity and directionality. The inputs from the two eyes, however, do not produce identical influences on the cortical cells. One eye is dominant (see p. 270 and , ). Ninety-five percent of the monovision papers reviewed by had the dominant eye corrected for distance vision. Good and poor candidates for monovision are shown in Table 13.3 .
Table 13.3
Good and Poor Candidates for Monovision
(Modified from Bennett, E.S., Jurkus, J.M., 2005. Presbyopic correction. In Bennett, E.S., Weissman, B.A.: Clinical Contact Lens Practice (2nd ed.). Philadelphia: Lippincott Williams & Wilkins: 27-1 to 27-18.)
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Other considerations include:
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lifestyle
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motivation
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visual needs equally distributed between far and near distances ( )
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personality – various studies have evaluated personality and psychological factors predictive of successful monovision wear ( , , , ). Cattell's 16 Personality Factor (16PF) test showed that patients with realistic expectations and the willingness to persevere, the ‘Factor G superego strength score’, could predict monovision success ( ). Adaptable, holistic people with an optimistic attitude towards treatment had high potential for success. also found that a person's expectation of self-efficacy, or belief in succeeding, was a predictor of success.
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age – younger presbyopes are more successful than older presbyopes; add powers of +1.00 to +2.00 D are more readily accepted than higher adds ( , , ).
recommends monovision screening criteria that evaluate:
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age
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add power
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distance prescription
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prior use of contact lenses
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motivation
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pupil size
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occupational and avocational needs
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apprehension of handling lenses.
Once the initial screening has been completed, the best predictor of success with monovision is a trial period using the appropriately selected lens powers.
Lens Selection and Type
The criteria for lens fitting are the same for rigid or soft lenses in monovision, and the lens powers must be carefully selected.
Ocular Dominance
Assumptions about dominance can be misleading ( ). The patient's declared writing hand is not necessarily associated with the same sighting or ‘dominant’ eye; nor is the apparently better-sighted eye. If dominance is not tested for and the wrong eye is assumed to be dominant, monovision may ultimately fail.
Tests for Ocular Dominance
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Hole in the hand test – specifically, ask the patient to keep both eyes open and to centre an object, such as a letter on the vision chart, through the opening formed by his linked hands held out at arm's length ( ). The eye that aligns the target in the centre of the opening is the dominant eye. If one eye instinctively closes, this is most likely the nondominant eye.
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Ask which eye the person uses to sight a camera or telescope.
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Introduce a +1.00 to +2.00 D plus lens over each eye individually and ask which eye experiences the greater blur. This indicates the dominant eye ( ). If the patient reports blurred vision at a distance, regardless of which eye is covered by the plus lens, it is likely that monovision will not be successful.
The full distance and near powers are generally prescribed. Reducing the add power to minimise the dioptric difference between the two eyes may alter the suppression pattern. Patients with strong sighting preferences have reduced interocular blur suppression and decreased binocular depth of focus. This strong dominance may make it difficult for the patient to learn to ignore the out-of-focus monovision image ( ).
Fitting the lenses (for lens fitting in monovision, see Section 9 , Addendum, available at: https://expertconsult.inkling.com/ )
Full adaptation to the monovision system can take as long as 8 weeks, with most subjects adapting in 2–3 weeks and about one-half in 1 week ( , , ). If a patient does not appear to be coping, it may be beneficial to switch the eye powers before discarding the monovision concept, but if the initial acceptance of monovision is lacking, it may not be successful.
Problems With Monovision
Monovision may present some visual challenges. Identifiable visual changes with monovision include a small reduction in high-contrast visual acuity such as reading or viewing a vision chart. There is also a loss of contrast sensitivity function that is proportional to amount of add ( ).
One of the biggest concerns with monovision is the change in depth perception due to the anisometropic correction. Monocular clues and binocular clues are used to judge depth and distance. The monocular clues are unchanged with monovision. These include:
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object interposition hiding parts of an object
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judging the customary object size, colour and clarity of objects
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lines converging to a vanishing point
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shadows.
Binocularly, although monocular clues for depth perception are present, monovision can reduce stereoacuity. The normal ageing process reduces the mean angle of stereopsis from 20 to 58 arcseconds. Monovision further reduces stereoacuity; stereopsis in monovision ranges from 50 to 113 arcseconds for near; found in all the papers they reviewed that stereoacuity was affected adversely. Although there is generally no significant effect on peripheral visual acuity, low-contrast binocular distance acuity may be reduced with monovision.
For further information on the visual effects, see Section 9 , Addendum, available at: https://expertconsult.inkling.com/ .
Patient Education
It is possible that a practitioner could be liable for any injury in which a monovision scenario could be a contributing factor ( ). The report of an aviation accident with a pilot wearing a monovision correction heightened consumer awareness of possible compromise with this form of correction ( ). The monovision wearer must be particularly aware of the induced vision change and its possible effect on their perception. Patients need to be carefully selected, have a demonstration of vision with monovision and be aware of the adaptation period ( ).
Monovision does not tend to improve beyond the initial adaptation period, which, as mentioned previously, can take as long as 8 weeks, and patients should be told not to expect an increase in the quality of their vision after that ( ). Alternative vision correction options should be presented, and the patient should participate in the modality selection. Risks and benefits of correcting the presbyope with all types of lenses must be considered (see also Chapter 31 ).
Success
Despite the compromises present with this modality, monovision is still in common use, although it is not the preferred mode for many practitioners. Internationally, whereas multifocal and monovision lenses accounted for 56% of soft lenses prescribed for individuals 45 years of age or older, the breakdown is 48% multifocal and only 8% monovision ( ). Likewise, in the United States, 71% of practitioners rate D multifocals as their preferred correction in presbyopia compared with 19% monovision and 10% overcorrection with reading glasses ( ). in a review of 19 studies found an average success rate of 76%, although other reviews have found 59–67% ( ). concluded that visual performance of monovision patients is comparable to that of patients with balanced binocular corrections, provided that the reading add does not exceed +2.50 D, the stimuli are supra-threshold and the illumination is photopic.
For a review of monovision, see , and for papers discussing the comparison of monovision and multifocals, see Section 9 , Addendum, available at: https://expertconsult.inkling.com/ .
Fitting and prescribing guidelines for monovision are provided in Table 13A.1 Section 9 , Addendum, available at: 
https://expertconsult.inkling.com/ .
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