Dr Edward S Bennett University of Missouri-St Louis College of Optometry One University Boulevard St Louis, MO 63121 USA E-mail: EBennett@umsl.edu
The contact lens wearing presbyopic population is underserved worldwide. There are several available options, including single vision contact lenses and spectacle over-correction for near, monovision, rigid gas permeable (GP) multifocal and bifocal lens designs and soft bifocal lens designs. This paper presents an overview of the latest research and clinical experience as it pertains to these forms of correction. Recent comparative studies concluded that contact lens multifocals perform better in many different forms of visual measurements, in some cases performing similar to best spectacle correction, than monovision wearers. The future appears to be very promising for multifocal GP and soft lens modalities.
The presbyopic population is both seriously underserved, as it pertains to contact lens correction and an outstanding opportunity for the contact lens practitioner. It has been reported both in the United Kingdom and in the United States that this patient population represents the largest growing segment as well as the largest relatively untapped segment of the contact lens market.1–4
Options for contact lens correction of presbyopia include the following:
1Single-vision contact lenses worn in combination with reading glasses.
2Monovision: one eye is corrected optimally for distance vision and one eye for near vision. There are several modifications of this option that will be discussed later in this paper.
3Bifocal soft and rigid gas permeable (GP) contact lenses, in which separate corrections for distance and near vision are provided.
4Multifocal soft and GP contact lenses in which corrections for greater than two distances are provided (that is, distance, intermediate and near corrections).
It is reported that monovision and multifocal contact lens fitting represent only nine per cent of the fittings worldwide.5 This could result from practitioner apprehension of a perceived complexity of and increased time involvement with presbyopic contact lens correction. If provided with the opportunity to wear contact lenses, the presbyopic patient is often successful. Jones and colleagues6 divided 160 non-contact lens-wearing subjects into ‘reactive’ and ‘proactive’ groups. The reactive group was not presented with contact lenses unless the discussion was initiated by the patient. With the proactive group, contact lenses were actively discussed as a viable option. Whereas only nine of 80 patients were fitted with contact lenses in the reactive group, 46 of 80 patients, including 21 of 33 presbyopic patients, were fitted from the proactive group.
It is predicted that the contact lens market will increase in the next 10 to 20 years.1,7,8 Contact lenses are a desirable option for presbyopic baby-boomers in whom vanity is an important factor. This population is more active than its predecessors, making spectacle correction a less desirable option for visual freedom. Likewise, progressive addition spectacle lenses (PAL) often require numerous head movements to find the optimum position for intermediate tasks, such as computer use, due to the varying corrective powers present during any eye movement.9–11
Prior to making the decision that a presbyopic patient is a good candidate and with the knowledge that there are normal ocular physiological changes that occur with age that can impact contact lens wear, it is important to perform a comprehensive preliminary evaluation. This evaluation should include a thorough history, tear film testing, anatomical measurements, eyelid assessment, refraction and corneal curvature evaluation. If the patient is then deemed to be a good candidate, the contact lens options should be presented and discussed, along with their possible compromises and, based on the patient's responses and perceived motivation, a decision pertaining to the presbyopic contact lens option that is most likely to be successful can be made.
Patients should be asked about their previous contact lens history, if any, and reasons for discontinuing lens wear, if pertinent. Any history of eye surgery should be noted. It is especially important to be aware of cosmetic lid surgery as the resulting tautness or rigidity in lid anatomy can cause excessive lifting in segmented, translating GP designs as well as possible increased rotation in soft toric lens patients. It is important to record all currently prescribed medications, and to be aware that numerous medications can reduce tear volume, including ibuprofen, oestrogen, antihypertensives, tricyclic antidepressants, anticholinergics, antihistamines and the scopolamine patch.12
Tear film evaluation
The most important physiological change that impacts the presbyopic patient is the progressive reduction in tear volume that occurs with age. This results from a reduction in both the goblet cells of the conjunctiva and the mass of the lacrimal glands. Discomfort due to dryness has been found to be the primary reason for patients discontinuing contact lens wear.13 Du Toit and co-workers12 found that, whereas 28 per cent of presbyopic patients reported dryness prior to contact lens wear, 68 per cent reported dryness after six months of lens wear.
Assessment of both tear quality and volume are important. A tear break-up time (tear BUT) of 10 seconds or greater has been recommended for successful all-day wear14 whereas less than 10 seconds suggests potential difficulties with lens wear.15 If the tear BUT is between six and nine seconds, patients should be instructed that all-day wear cannot be guaranteed.16 These individuals tend to benefit most from disposable or GP lens wear, with regular cleaning and frequent use of rewetting drops. A five-second or less tear BUT typically contraindicates contact lens wear, especially if the measurement is repeatable.17 It is important to emphasise that the blink interval should be considered. A normal blink occurs after every four to five seconds; if a patient blinks less frequently it can impact successful contact lens wear for a borderline dry eye patient. Tear volume can be assessed with either the Schirmer tear test or the phenol red threat test (PRTT, Zone-Quick from Menicon/Allergan). The latter test is very reliable, more comfortable and repeatable with a value less than nine millimetres of wetting in a 15-second testing period being indicative of dry eye.18,19 In addition, if the patient manifests meibomian gland dysfunction or blepharitis, tear quality can be impacted and these conditions must first be managed prior to fitting the presbyopic patient with contact lenses.
Careful measurements of the horizontal visible iris diameter and the vertical fissure size should be performed. Pupil diameter should be evaluated both in normal room illumination and with the lights dimmed. A large pupil diameter (that is, greater than five millimetres in normal room illumination) is not very common in the presbyopic population. If present, aspheric lens designs, notably GP lenses, would be contraindicated due to the glare and ghosting of images under low illumination conditions.
The lid-to-limbus position of both lids should be evaluated. A low lower lid (that is, greater than one millimetre below the limbus) would essentially rule out a segmented, translating GP design. Likewise, if the patient has very flaccid lids, this same design will likely not be successful due to the inability of the lower lid to assist in translation.
Presbyopic patients exhibiting a significant amount of ametropia (that is, greater than 1.25 D myopia or one or more dioptre of hyperopia) are the best candidates for contact lens correction.20 Very low ametropic or even emmetropic patients should be considered for contact lens wear if they are motivated. In fact, these individuals may appreciate wearing one distance lens only (if exhibiting low myopia), or either one near lens or a soft bifocal lens on one eye, if emmetropic. If the patient is amblyopic, it is imperative that, if contact lens correction is desired, the eye exhibiting the better visual acuity is not compromised.
Evaluation of corneal curvature is especially important when fitting GP lenses. Although corneal topographic evaluation is not essential when fitting the presbyopic patient into contact lenses, it is beneficial in determining the size and location of the apex, the eccentricity of the cornea and, in some cases, assisting with the design parameters. When GP lenses are the preferred option, a centrally positioned apex lends itself to an aspheric design, whereas an inferior positioned apex would be desirable when fitting a segmented, translating design. Corneal topographic evaluation also assists in diagnosing patients who have irregular cornea, notably keratoconus. Typically, these individuals are not good candidates for contact lens presbyopic designs due to the potential for further visual compromise.
At the conclusion of the preliminary evaluation, if the patient is deemed a candidate for contact lens wear, it is important to discuss the goals and available options, and determine the motivation for contact lens wear. Determine which distances are most important. Patients should be asked how they spend their time during the day and which visual tasks are especially important and time-consuming (for example, computer use, driving, reading et cetera). Patients should not be guaranteed that, if they are fitted with a presbyopic contact lens correction, spectacles will not be necessary. They should have a spectacle correction to use as a back-up for contact lenses, perhaps for morning or evening wear or to have available if lens loss or an eye infection occurs. Monovision wearers should be encouraged to wear over-spectacles for critical distance tasks, especially driving, and some aspheric multifocal wearers appreciate additional plus power when reading fine print, especially in dim illumination, or perhaps some additional minus power when driving at night.
It is particularly important to ‘under-promise and over-deliver’ to presbyopic patients being fitted with contact lenses. They should be informed of all of the available options (that is, spherical lenses and reading glasses, monovision, soft bifocal/multifocals, and GP bifocal/multifocals). Patients should be told the benefits and possible limitations of each modality. They should be aware that some visual compromise may result depending on the option selected and with the contact lens bifocal and multifocal lens options, it may be necessary to make lens changes to optimise both the fitting relationship and the quality of vision at their preferred distance(s).
The presbyopic patient who has never worn contact lenses and is unwilling to accept the possibility of visual compromise is not a good candidate. First-time wearers who are motivated should be considered seriously for presbyopic contact lens correction. The practitioner needs to be empathetic to the fact that this individual has never experienced and may be apprehensive about adaptation to lens wear. In addition, patients have to adapt to the multiple imagery of bifocal/multifocal contact lenses or the blur resulting from monovision and to be able to exhibit mastery of lens care and handling.21 The latter factor is especially important to assess during the preliminary evaluation. Nevertheless, the benefits of visual freedom from spectacles should be presented and by offering and providing the contact lens option, the resulting benefit to patients can be an improvement in their quality of life. A summary of factors to consider for presbyopic contact lens success is provided in Table 1.
Table 1. Important factors for presbyopic patient selection
High probability for success
• Definite need for a visual correction
• Current contact lens wearer
• Tear BUT ≥ 10 seconds
• Good ocular health
• History of successful contact lens wear
Moderate probability for success
• Very low ametropia or emmetropia
• New wearer but motivated; aware of possible vision compromise
• Tear BUT between 6 and 9 seconds
• Large pupil size (>5 mm in room illumination): limits available choices for correction
• Low lower lid and/or flaccid lids: rules out segmented lens designs
Low probability for success
• New wearer with very low ametropia or emmetropia; unwilling to accept vision compromise
• Unrealistic expectations
• Tear BUT ≤ 5 seconds (repeated measurements) and/or PRTT ≤ 9 mm
• Poor hygiene
• Poor manual dexterity
• Irregular corneas
CONTACT LENS CORRECTION OPTIONS
Single-vision contact lens wear and reading glasses
The combination of reading spectacles and single vision GP or soft contact lenses provides the benefits of optimum vision at distance and near, ease of fit and limited expense. Typically, this option consists of plus power reading spectacles, although progressive addition lenses, to be worn over distance power contact lenses, may be indicated in older patients who require intermediate correction. Many patients feel inconvenienced by the frequent application and removal of spectacles for their intermediate and near tasks. In addition, an important motivating factor for contact lens wear, especially with current lens wearers, is the minimal or non-use of spectacles. Therefore, the disadvantages of this option, in combination with the ongoing introduction of improved contact lens multifocal designs, makes this a less popular and less desirable option for the presbyopic patient.
Monovision was first reported as a form of presbyopic contact lens correction in the late 1950s by Westsmith22 and represents the most popular form of contact lens correction for presbyopia.20,23 The success rate for monovision is between 70 and 76 per cent24,25 and is dependent on the ability of the brain to suppress blur from the defocused eye.26
• avoidance of some of the problems present in multifocal contact lenses, including ghost images and fluctuating vision due to change of pupil size.
A major problem with monovision is a decrease in stereopsis. Jain, Arora and Azar25 found that stereopsis changed from 87 to 124 seconds of arc. Kirschen, Hung and Nakano28 found that stereopsis changed from 50 seconds of arc with bifocal contact lenses to 200 with monovision. Richdale, Mitchell and Zadnik29 found 79 seconds of arc difference between monovision and multifocal contact lenses. Several studies have demonstrated that stereoacuity loss increases with increasing monocular addition.30,31 Some monocular suppression of blur also occurs as the addition increases.32 Essentially, a deliberate impairment of binocularity occurs with monovision correction. Subjects with this modality have also demonstrated contrast sensitivity loss and sometimes compromise on critical distance vision tasks.33–35 An increase in anisometropia of 0.50 D or more and as much as 1.25 D has been found in 29 per cent of monovision wearers.36
Driving with monovision has been a controversial topic, in part resulting from the ocular physiological changes that occur with age. Older individuals pose the largest threat to road safety, having the highest crash rate per distance travelled.37 It could be concluded that monovision should add to the problems that presbyopic patients have while driving, especially at night and, in fact, as many as 80 per cent of monovision patients have reported problems with night driving.38 This would be especially true with glare. Johannsdottir and Stelmach39 found that under low light levels, monovision patients will experience glare from a point source of light. In addition, monovision wearers have a very difficult time suppressing headlights while driving at night, with one-third of the subjects experiencing glare while night driving.40 Interestingly, Wood and associates41 assessed 13 habitual monovision wearers on several simulated driving tasks under daytime conditions and found no difference in driving performance between monovision and their habitual distance correction. Nevertheless, monovision patients are advised to avoid driving or operating dangerous machinery during the first two to three weeks of adaptation.42
There is a report of an aviation accident in which three passengers were injured when the pilot was wearing a monovision correction.43 This accident greatly heightened consumer awareness of possible compromises with this form of correction.
The age and near addition of the patient are predictive of success, with lower addition patients (+1.25 to +2.00 D) being more successful than higher addition power patients.25,44 The lifestyle and visual needs of the patient must be evaluated when considering monovision. If prolonged and critical distance vision is desirable, monovision is not a good option. Likewise, if depth perception is important to a given occupation, for example, with construction workers, monovision would not be recommended.45 Individuals who desire the benefit of being able to change viewing distances constantly and still remain focused, such as those in occupations like teaching, the performing arts, public speaking and sales, could benefit from monovision lens wear.
Esophoria at distance and a reduction in nearpoint visual acuity and stereopsis have also been shown to indicate a poor prognosis as monovision has resulted in an esophoric shift in eye posture.44,46 McAlister and Woods47 found that a patient's personality, expectations, attitudes and tolerance to blur and discomfort are important for success in monovision. Du Toit, Ferreira and Nel48 reported a significant correlation between initial negative response and unsuccessful monovision wear. In addition, introverted males tend to reject monovision most frequently, whereas the most successful patients were laid-back and optimistic.49
LENS SELECTION AND FITTING CONSIDERATIONS
Both GP lenses, due to their resultant visual performance, wettability and oxygen permeability, and silicone hydrogel lens materials lend themselves to monovision. As a result of the greater tendency for dryness and surface deposition with hydrogel lenses, a disposable (daily to monthly) lens is essential for long-term success. If handling is challenging to the new monovision wearer, the rigidity of GP lenses would make them a preferable option.
The eye to be selected for near depends on several factors. In a review of the literature it has been found that in 95 per cent of the cases it has been the non-dominant eye.25 The most popular method for establishing ocular dominance is to have the patient extend both of their arms in front of them, forming an aperture with the fingers from both hands. The patient is then instructed to centre a distant target in the opening of their hands. Whichever eye is found to be in alignment with the object when they are alternatively closed is the dominant eye. A ‘swinging plus’ test has also been advocated,50 in which the patient walks around the room holding a plus power trial lens equal to the required add over one eye, repeating the procedure over the other eye. This is also beneficial for simulating the potential impact of monovision on the quality of vision. The eye that the patient deems more comfortable with the over-plus correction will be the eye corrected for near. Typically, the full distance and near powers are prescribed. It is possible that by ‘over-plussing’ the power of the distance lens and/or ‘under-plussing’ the power of the near lens, not only is the patient's vision compromised at one or both distances but also it may reduce the interocular suppression of blur that is important for monovision to be successful.4
It is recommended to perform tests of binocular vision to determine the effect of monovision on stereopsis. As indicated previously, it is important to strongly encourage—if not require—the patient to have over-spectacles for use while driving and for any other critical distance visual tasks. Although full adaptation to monovision may take two to three weeks,25 patients should be told that it may take as long as four to six weeks. If difficulty in adapting is experienced (that is, headaches, eyestrain, blurred vision), switching the near and distance-corrected eyes should be considered. If this is not successful, a bifocal or multifocal lens should be recommended. Important factors for successful monovision lens wear are provided in Table 2.
Table 2. Important factors for monovision fitting and prescribing, modified from Bennett and Jurkus4
• Monovision is most successful in early presbyopic patients; those individuals who are optimistic in nature; people who are realistic about the visual limitations and anyone who does not require long periods of critical distance vision.
• The proper eye for near vision should be selected. Often, this is the non-dominant eye and/or the eye in which vision is reduced relative to the other eye. If anisometropia is present, the eye with higher myopia should be considered for near, all other factors being equal.
• The indicated addition power should be demonstrated to patients so that they can obtain a realistic impression of the resulting blur.
• Binocular vision testing should be performed to determine the effect of monovision on stereopsis.
• It is recommended to prescribe the full amount of correction and avoid the temptation of prescribing less plus power in the near-corrected eye and/or prescribing more plus power in the distance-corrected contact lens.
• Patients should be strongly encouraged, if not required, to obtain a pair of driving spectacles (that is, minus correction in the lens over the near-corrected eye) to wear for driving or any other critical distance tasks.
Although most individuals adapt within two weeks, patients should be instructed that it could take up to several weeks to fully adapt to monovision.
Bifocal and multifocal contact lenses
Bifocal and multifocal contact lenses may represent the most underserved and potentially the largest growing and profitable modality for contact lens practice. In a 2006 Contact Lens Spectrum reader profile survey, most respondents indicated that this lens modality will be one of those most likely to exhibit growth.51 Nevertheless, there is reluctance by practitioners to fit bifocal and multifocal contact lenses. This appears to pertain to several factors including expense and perceived complexity of the designs, as well as the ultimate chair time involved if multiple fittings and refittings are necessary. As a result, patients are often unaware that this option exists. Consumers responding to a popular contact lens website (http://www.contactlenses.org) often comment that either they are not aware of the existence of bifocal contact lens wear or they have been told by their practitioner that bifocal contact lenses are not very successful.52 The visual performance provided at multiple distances by many of these designs is an important benefit to patients who have been provided with this option by practitioners willing to fit it.
Numerous terms have been ascribed for the definition of different bifocal/multifocal lens designs. The most common terms in use today are ‘simultaneous vision’ and ‘alternating vision’.
Simultaneous vision lenses have multiple powers positioned within the pupil at the same time. Therefore, light rays from both distance and near targets are imaged on the retina. Many popular hydrogel and GP multifocal designs are based on this principle. To be successful, the patient will selectively suppress the most blurred images that are not desirable for a given task. Therefore, this concept functions on the basis of blur interpretation and/or blur tolerance of superimposed multiple images on the retina formed by the various powers of the lens. For true simultaneous vision, the primary vision-correcting regions must remain within the pupillary boundary in all positions of gaze and, to provide equally bright images, the distance and near areas of the lens should cover nearly equal areas of the pupil.4
There are three designs available that use the simultaneous vision principle:
Aspheric lens designs have a gradual change of curvature along one of their surfaces (anterior or posterior) based on the geometry of conic sections. The rate of flattening (or eccentricity) is greater (and sometimes much greater) than with single-vision lens designs, thereby creating an increase in plus power toward the periphery of the lens. Some designs are centre-near, such that the highest plus power is in the geometrical centre and decreases in power toward the periphery.
Concentric or annular designs are structured with a small (typically two-thirds to three-fourths the size of the pupil in normal room illumination) central annular zone that, in most cases, provides the distance power with the near power present on the annulus that surrounds the distance zone. There are also several centre-near designs available. Both aspheric and concentric designs tend to shift up naturally or translate during near gaze. Therefore, a greater near power effect is achieved. Both designs are available in GP and soft lens materials.
Diffractive designs are the only simultaneous vision lenses that exhibit true equality of near and distance powers. These designs function through a central zone that focuses images at distance by refraction of light and at near through diffraction principles created by the zone echelettes. As equal amounts of light pass through both the distance and near elements of the lens, diffractive designs are truly pupil-independent. This design is available only in hydrogel lenses and is not currently being marketed in the United States of America. To be successful, it is important for all simultaneous vision lens designs to exhibit good centration with little movement on blinking.
Alternating vision pertains to lens designs in which translation or vertical movement of the lens results in only one zone of vision in front of the pupil at any given time. Therefore, ideally the distance zone will be in front of the pupil in straight ahead gaze and the near section will be in front of the pupil in near gaze. This consists of an intentional shifting of the lens from distance to near gaze and vice versa. These designs are typically prism ballasted to weight the lens to keep the various powers in the proper position on the eye. Some of these designs are also truncated to assist in lens stability. The intent of these designs is to rely on the lids to push the lens upward with inferior gaze. There are several forms of these designs in GP lens materials, including crescent, executive and decentred concentric shapes. As translation is much easier to obtain with a GP design due to the smaller diameter and thicker inferior edge profile, all commonly used translating designs are available in GP materials.
MULTIFOCAL AND BIFOCAL PRESCRIBING AND FITTING CONSIDERATIONS
It is recommended to fit initially patients who have a high probability of success with contact lens bifocal and multifocal lens designs. This includes current lens wearers who are motivated not to wear spectacles. It is important that the patient's initial experience is good visually. Therefore, if lenses can be fitted from inventory, which is often possible with hydrogel lenses, or empirically with aspheric GP lenses, patients can experience good vision at all distances from the beginning. Once the lenses are fitted, they should be allowed to adapt for a minimum of 15 to 20 minutes prior to evaluating the lens-to-cornea fitting relationship. At that time, the patient can be encouraged to walk around the office and perform normal everyday visual tasks, such as looking at a computer, reading a magazine and looking at a distance. Vision should be checked binocularly and the over-refraction should be performed with loose lenses or a flipper bar to provide for a more natural and normal environment. It is also important to be willing to use different approaches. This could include two different soft lens bifocals, a bifocal on one eye and a spherical lens on the other eye, bifocals with different additions on each eye or ‘over-plussing’ one eye slightly (that is, ‘modified monovision’). An overview of fitting considerations is provided in Table 3.
Table 3. Important fitting considerations for bifocal and multifocal contact lenses4,21
• Initially, mention the multifocal/bifocal option prior to the patient entering presbyopia.
• When discussing correction options with the presbyopic patient, multifocal and bifocal lenses should be emphasised. Likewise, patients should be aware that some compromise may exist and lens exchanges may be necessary to provide for a successful fit and vision.
• Initially fit individuals who have great potential to be successful, such as highly motivated existing contact lens wearers, before fitting more challenging patients.
• Use loose trial lenses or flipper bars for over-refracting to provide a more natural environment.
• Check vision binocularly to simulate a real world environment.
• Allow sufficient time to allow the lenses to settle prior to evaluating the lens-to-cornea fitting relationship—usually 15 to 20 minutes is sufficient.
• When the lenses have been dispensed (and/or with the diagnostic lenses in combination with the over-refraction), patients should walk around the office and perform common visual tasks (look at a computer, read a magazine, look at distance et cetera) and indicate the visual tasks that they are pleased with and those that they feel could be improved.
• Always attempt to satisfy the patient's primary visual goals but also indicate to them that occasional spectacle use may be necessary to meet all of their visual demands.
• Do not hesitate to prescribe unequal additions to obtain satisfactory vision at all distances. Likewise, a ‘modified multifocal’ approach in which one eye is slightly over-plussed at distance may allow the patient to obtain all of their visual goals.
• Have available multiple GP and soft lens diagnostic sets/inventories and be willing to try different types of lenses on a given patient to achieve success.
GP MULTIFOCAL AND BIFOCAL LENS DESIGNS
There are many aspheric progressive designs currently in use and reports of high success rates have been claimed, often greater than 75 per cent.53–57 These designs typically have a posterior surface with high eccentricity and a spherical anterior surface although several anterior surface designs have been introduced recently. As indicated previously, these lenses use simultaneous vision although some translation in downward gaze is desirable.
Aspheric lens designs are recommended for patients with early presbyopia who do not have a critical distance visual demand. Most designs have a nominal addition of approximately 1.00 to 1.25 D (depending on pupil diameter) but newer designs have also been introduced with ‘multiple additions’, often consisting of increasing the eccentricity of the back surface by varying amounts and effectively decreasing the distance optical zone. In addition, some designs provide higher additions via the ability to add near power on the front surface in a concentric ring in the mid-periphery of the lens. As the patient views inferiorly to read, these designs rely on the mild translation that should occur naturally with downward gaze.
Patients who have been single vision GP wearers and have recently entered presbyopia are excellent candidates for aspheric multifocal lenses. They tend to observe improvement in their near vision immediately with little compromise to their distance vision. As these are thin lens designs, the comfort level and fitting relationship should be similar to those of their previous lenses. Patients with a high intermediate lens demand benefit from these lenses; they include accountants, electricians, plumbers and those with mechanical responsibilities.58 Likewise, if they spend, at minimum, 35 per cent of their waking hours at a computer, an aspheric lens design has been recommended.59 The presbyopic athlete would benefit from the fact that these lenses typically exhibit a tight-fitting relationship and do not easily dislodge from the eye.
Patients who have either flaccid lids or a low lower lid and are, therefore, not good candidates for an alternating design would be good candidates for an aspheric multifocal. Patients who have a large pupil diameter (typically five or more millimetres in normal room illumination) are not good candidates for an aspheric multifocal as a result of the glare and ghost images they will experience at distance under low illumination, notably when driving at night.
Fitting an aspheric multifocal lens design should be as easy as or easier than fitting a spherical GP lens. Typically, the lenses have a standard material (often a low-medium Dk fluoro-silicone/acrylate), a standard centre thickness, a standard periphery and a limited number of lens total diameters. In initially acquiring experience with these designs, it is recommended to use diagnostic lenses and to order the lenses from the laboratory. With experience, it is possible to order these lenses empirically. Therefore, the patient's first experience with this design should be a good one visually.59 A reorder or exchange rate of 50 to 100 per cent per eye has been reported.59,60
Aspheric lens designs should exhibit good centration with limited (approximately 1 mm) lens movement with the blink to maintain the optical centre, and in most designs the optimum power for distance, in front of the pupil for distance viewing. Early aspheric designs had very high eccentricity and were fitted approximately 3.00 D steeper than ‘K’. Most of the designs in common use today have lower eccentricities than their predecessors and are often fitted 0.75 to 1.50 D steeper than ‘K’. As a result of the back surface geometry of these designs, the fluorescein pattern typically appears to be uniform (Figure 1).
Possible problems with these lenses include decentration and poor vision at near. If the lens moves excessively, resulting in inferior decentration, the back optic zone radius of the lens should be steepened, typically by 0.50 D.17 Whereas slight superior decentration is acceptable if the lens exhibits moderate superior decentration, lens adherence and possibly corneal distortion can result. Again, the selection of a steeper back optic zone radius may result in a more centred fitting relationship, however, if there is no improvement, the patient should be refitted into a front surface aspheric design (power change is on the front surface with a spherical back surface). If lateral decentration occurs, increasing the total diameter may be beneficial; if not, an alternating design would be indicated.
Some patients experience blur at near due to insufficient addition with these designs. As indicated previously, higher addition aspheric lens designs are available. One such design is the Essential GP Multifocal (Blanchard), which has three series of additions, with the increase in addition resulting from an effective decrease in the central distance power zone.61 The ability of the higher addition series has resulted in a high success rate with this design.62 The introduction of the Essential CSA design allows for more addition to be placed on a concentric ring surrounding the central distance zone (4.0 to 4.6 mm in diameter) on the front surface of the lens (Figure 2). Other approaches for patients with these symptoms would include a ‘modified multifocal’ approach, a pair of reading spectacles for fine print or an alternating design.
Alternating lens designs
Alternating or translating lens designs are successful, if the lower near section shifts upward during downward gaze, allowing most or all of the pupil to view through the near section of the lens. As a result of the prism ballast necessary with these designs, a high or hyper Dk lens material is customarily used.
With good translation, these lenses will provide excellent vision at distance and near and therefore, represent the lens of choice for patients who have critical visual demands. In addition, patients who do not have excessive intermediate visual demands or have a large pupil and therefore, are not good aspheric multifocal wearers would be good candidates.
The lower lid tonicity must be average-to-tight for these designs to be successful. In addition, the lower lid needs to be positioned within one millimetre of the lower limbus, as it acts as a support system to move the lens vertically.58 If the lower lid is positioned greater than 1.5 mm above the lower limbus, it may be difficult to provide a sufficient segment height for acceptable near vision.17
The alternating vision lens designs available today are segmented (that is, crescent, executive and straight-top) and concentric (or annular).
• Segmented alternating designs
These lens designs have monocentric optics, which result in the elimination of the image jump problems that existed with first generation segmented alternating GP designs. Diagnostic fitting is important and typically diagnostic sets provide average lens parameters to allow the practitioner to approximate the final lens design (that is, -2.00 and +2.00 D distance powers, +2.00 D addition, 9.4 to 9.6 mm overall diameter, average segment height and prism). Typically, alternating designs are fitted slightly flatter than ‘K’ to allow for a rapid descent of the lens to the lower lid. When evaluating the lens on the eye, the segment line (or crescent) should be positioned at or within one millimetre below the lower pupil margin. The lens should be picked up slightly with blinking but the segment line should not move more than one millimetre into the pupil. It is important to evaluate the segment position with the patient viewing straight ahead in normal room illumination to minimise errors pertaining to incorrect segment height determination. Patients with a slightly low lower lid would benefit from both a larger overall diameter and segment height, and vice versa for patients exhibiting a lower lid above the lower limbus. If the lenses are truncated, the RALS (right add, left subtract) acronym can be used to determine the axis. For example, if both lenses rotate 15 degrees toward the nose, the prism can be ordered at 105 degrees R and 75 degrees L.
It is also important to assess translation. While at the slitlamp, the patient should be advised to view inferiorly and, by pulling up the upper lid it can be observed whether the lens has shifted up (that is, translated). The segment line should be at least bisecting the pupil, as the practitioner views it in straight ahead gaze. Alternatively, the ophthalmoscope can be used from an inferior position to simulate reading, in which case the segment should appear to be predominantly in front of the pupil.
• Concentric (annular) alternating designs
These are also prism ballasted designs with a central distance zone of approximately four millimetres in diameter, which is decentred slightly superiorly in an attempt to be positioned directly in front of the pupil during distance gaze but in close proximity to the lower lid, such that translation can occur with inferior gaze.63 This is surrounded by a near concentric periphery. Increasing the central distance zone can result in improved distance vision but degraded near vision and vice versa. Like segmented designs, these designs are often fitted slightly flatter than ‘K’.
Five problems can occur with these designs, all of which can often be managed successfully. They are excessive lens rotation, excessive lifting of the lens, poor lens translation, poor intermediate vision and comfort.
Whereas some rotation of the lens toward the nose can be beneficial when converging to read, excessive rotation is often the result of a back optic zone radius that is too steep, especially on a with-the-rule astigmatic cornea. The tear layer will assist in promoting centration when, in fact, it is desirable to promote inferior displacement. Therefore, a flatter back optic zone radius should be refitted on these patients.
If the segment is pulled excessively into the pupillary zone during the blink, resulting in fluctuating vision at distance, the prism ballast should be increased, typically by 0.50Δ.
Poor lens translation is often the result of insufficient edge clearance, with the lens falling under the lower lid with inferior gaze.27,64 This can be corrected by flattening the peripheral curve radius or more easily by flattening the back optic zone radius by 0.50 D. It must be confirmed that patients drop their eyes, not their head, to read. If these strategies are unsuccessful, it is likely that the patient has flaccid lids and another lens design would be indicated.
If the patient is wearing an alternating bifocal lens design, over-spectacles with the appropriate correction for intermediate tasks (often at the computer) can be prescribed. There are numerous alternating designs that provide an intermediate correction, including executive and aspheric corrections. In addition, one design (Essential Solution from X-Cel) has an aspheric back surface and a crescent segmented front surface.
Due to the thickness of these designs and the need for lower lid interaction, the misperception often exists that it is more difficult to adapt to these lenses. In fact, the reverse is often the case.65 As both aspheric multifocal and alternating designs must exhibit little movement with a blink to be successful, the initial comfort can be better than with a spherical lens design. As many practitioners are apprehensive about being in a ‘comfort zone’ with these lenses, it must be remembered that the primary differences with segmented designs pertain only to segment height determination and prism and that patient satisfaction with these designs is often unparalleled. The laboratory consultant can be an invaluable resource in assisting with gaining expertise and confidence with these designs. In addition, there are numerous resources available, including several programs and guides available from the GP Lens Institute (http://www.gpli.info).
SOFT BIFOCAL AND MULTIFOCAL LENSES
Numerous soft bifocal and multifocal lens designs have been introduced in recent years. They do have some limitations compared with GP designs. The quality of vision is somewhat compromised as a result of relying exclusively on simultaneous vision and as a result of the water content of the lens. In fact, the term ‘20/Happy’ has been associated with these lenses because their corrected vision may be reduced compared with their spectacle acuity but the patient is satisfied. There appears to be a degradation of vision at high spatial frequencies.35 In addition, any demonstrated improvement in near vision may be, in part, the result of an increased depth of focus not from the bifocal powers per se.66 It is apparent that some individuals are so motivated not to wear spectacles that they are satisfied with a multiple-line Snellen acuity reduction; however, this presents potential liability concerns for the practitioner. Several improvements in lens materials, designs and replacement schedules have resulted in greater use and success in recent years. The introduction of silicone hydrogel multifocals provides increased oxygen transmission and the opportunity for overnight wear. The fact that most bifocal and multifocal lenses are provided to patients using anywhere from a monthly to a daily disposable regimen is beneficial to a patient population more prone to dryness and surface deposits. This also allows the practitioner to provide trial lenses directly from an inventory to patients on weekly intervals and then make changes as necessary once the patients have adapted to lens wear.
Designs in common use on the market today are either centre-distance or centre-near designs.
Most of the currently available centre-distance lenses are concentric, although they can be aspheric as well. Representative examples of concentric designs are the Acuvue Bifocal (Vistakon) and the Frequency 55 Multifocal and Proclear Multifocal DW (both from CooperVision). The Acuvue Bifocal is a multizone design with five alternating distance and near zones. With multiple additions (+1.00 to +2.50 D in 0.50 D steps), it lends itself well to providing unequal additions. It has been found that 51 per cent are successful when prescribing the full binocular prescription; 32 per cent with a modified bifocal approach (adding plus power to the distance prescription of the non-dominant eye) and 17 per cent when fitted with an enhanced monovision approach, which consisted of fitting the non-dominant eye with a single-vision lens for near and reducing the addition of the bifocal lens in the dominant eye.67 Other options that have been recommended include using a distance single-vision lens on the dominant eye and the Acuvue Bifocal on the non-dominant eye for patients with critical distance vision demands and using less addition on the Acuvue Bifocal on the dominant eye for patients needing intermediate distance correction.68 In higher addition powers, subjects have reported a reduction in the quality of distance vision exhibiting symptoms of fluctuating vision, ghosting/shadows and haloes around lights.69 It has also been found that the Acuvue Bifocal offers similar near performance to progressive addition (spectacle) lenses at varying illumination levels.70
The Frequency 55 Multifocal and, most recently, the Proclear Multifocal DW designs combine multifocal optics with monovision. A centre-distance lens, which transitions through an aspheric intermediate to the outer near zone, is placed on the dominant eye. A centre-near lens, which transitions through an aspheric intermediate to a spherical peripheral distance zone, is placed on the non-dominant eye71–73 (Figure 3). Binocular summation is expected, providing acceptable vision at all distances under binocular conditions. The central zone is 2.3 mm for the distance lens and 1.7 mm for the near lens and +1.50, +2.00 and +2.50 D additions are available. To determine if the visual acuity will satisfy the patient, CooperVision recommends the following fitting matrix:74
D Lens 6/6
N Lens 6/6
N Lens 6/12
D Lens 6/12
The patients should be advised about possible shadowing and ghost images, to which they may adapt, and to return in four to seven days.73
Several lenses are available in a centre-near aspheric design. The Soflens Multifocal (Bausch & Lomb) is an aspheric design that is available in two back optic zone radii and two addition powers. If there is blur at distance with a myopic patient, it is recommended to increase minus power in the dominant eye first, then in both eyes if necessary.74 If there is a complaint with distance vision and both lenses have the higher additions, it is recommended to change to a lower addition on the dominant eye. When near blur is present, it is recommended to increase the plus power in the non-dominant eye. More recently, the silicone hydrogel PureVision Multi-Focal has been introduced. This centre-near aspheric design has spherical aberration-control optics and the benefits of hyper-oxygen transmissibility (Dk = 112), including the opportunity for up to 30 days of extended wear.
The Focus progressive design (CIBA Vision) is a centre-near aspheric design with a two-week to one-month replacement schedule.75,76 It can be worn for up to six nights extended wear and has two back optic zone radii. The addition is nominal and patients with advanced presbyopia often need to add +0.50 to +0.75 D over the non-dominant eye for best success at near.77 It also exhibits good handling capabilities.9
Translating soft bifocal design
There is one translating design currently available, the Triton Translating Bifocal (Gelflex). The back surface design with truncation and prism allows for lens stability and location.78 When the lens translates, which is more challenging in a hydrogel lens, the vision is excellent although there is more potential for lens awareness due to the inferior thickness.27 The horizontal diameters are 14.5 and 15.0 mm with vertical diameters ranging from 11.4 to 13.9 mm. It is not a frequent replacement lens but it is a viable option for patients motivated for hydrogel lens wear but unsatisfied with the vision from other designs.
Soft toric multifocals
There are several commercially available soft toric multifocal lenses, although they are custom lenses and not currently available in a planned replacement modality. This should change soon and, ultimately, these designs should be available in a silicone hydrogel lens material. A hybrid design, the SynergEyes M lens (SynergEyes) should be available soon. This is concentric with a rigid centre and soft surround.79 This design holds promise for patients who need an astigmatic correction but have not been able to achieve either a good fitting relationship or comfort with a GP design. A summary of lens selection criteria is provided in Table 4.
Table 4. Lens selection
Type of patient
Spherical refractive error; current soft lens wearer
Low-to-high add requirement with high visual demand at near, distance or both
Translating GP bifocal
Low lower lid
a. Critical vision demand
Aspheric GP multifocal
b. Non-critical vision demand
Less than 5 mm pupil diameter
a. Critical vision demand
Translating GP multi(bi)focal
b. Non-critical vision demand
High intermediate (computer) demands
Aspheric GP or soft multifocal
Early presbyopia; successful single vision lens wearer
Occasional lens wear preferable
Spherical silicone hydrogel or monovision silicone hydrogel lens wear
As indicated earlier, monovision has resulted in a success rate of more than 70 per cent and aspheric GP multifocals have resulted in similar success, with one study reporting 86 per cent success.61 Alternating GP bifocals have achieved a similar, if not higher, success rate.80,81 The success rate of soft bifocal lenses is lower but appears to be increasing with new lens designs and replacement schedules.69 Some interesting trends have resulted when these modalities are compared directly.
Monovision versus bifocal and multifocal contact lens designs
Some early studies in which monovision was compared with a diffractive design82 and both a diffractive and a centre-near design83 found monovision to be more successful visually. More recent studies with newer designs have resulted in different outcomes. Kirschen, Hung and Nakano28 found that not only was stereoacuity significantly better with the Acuvue Bifocal when compared to monovision, but the soft bifocal resulted in a statistically significant decrease in the interocular difference in visual acuity at distance and near and improved binocularity. In several comparative studies in which patients had to make a forced choice between the two modalities, the bifocal/multifocal was preferred to monovision. Situ and associates84 refitted 50 monovision wearers into the Acuvue Bifocal. Forty completed the six-month study and although the low and high contrast visual performance did not particularly favour one modality over the other, 68 per cent preferred the bifocal whereas 28 per cent preferred monovision. Richdale, Mitchell and Zadnik29 fitted 38 presbyopes with no experience in presbyopic contact lens correction. They were randomised into either the SofLens Multifocal (Bausch & Lomb) or monovision for one month, at which time they switched modalities and the study was repeated. Vision was equal at distance and near out of both modalities but 76 per cent preferred the bifocal lenses, whereas 24 per cent preferred monovision. Johnson and co-workers85 performed a similar study, in which patients wore GP monovision lenses for six weeks followed by six weeks in a GP aspheric multifocal (or vice versa). At the conclusion of the study, 75 per cent preferred the multifocal design.
Spectacle correction versus bifocal and multifocal contact lens designs
Recent studies have concluded that spectacle lens acuity differed little from bifocal and multifocal contact lens acuities. Fisher, Bauman and Schwallie9 found that distance and near acuity as well as stereoacuity and visuomotor task performance were better with the best spectacle correction than with either an annular soft bifocal design or an aspheric soft multifocal design. Jimenez, Durban and Anera70 found similar visual performance between progressive addition lenses and an annular soft bifocal under varying conditions of illumination. Woods and colleagues61 reported no statistical difference in near and distance acuities for subjects wearing a GP aspheric design versus their spectacle corrections.
Monovision correction versus soft bifocal lenses, GP multifocal lenses and spectacles
Rajagopalan, Bennett and Lakshminarayanan35 compared the visual performance of subjects wearing GP monovision lenses, soft bifocal lenses, GP aspheric multifocal lenses and progressive addition spectacle lens (PAL) wearers. There was relative parity for the binocular high and low contrast acuities between PAL wearers and GP aspheric multifocal wearers followed by soft bifocal wearers and then monovision. The difference between monovision and the other three groups was most evident with high contrast acuity. In the contact lens groups, GP multifocal lens wearers had the highest binocular contrast sensitivity at all spatial frequencies, on parity with PAL wearers, except at the highest spatial frequency (18 cpd) in which PAL wearers performed superiorly (Figure 4).
LENS CARE AND PATIENT EDUCATION
The keys to successful management of the presbyopic patient include patience and reassurance. They may exhibit apprehension (if a new wearer) about both their ability to wear lenses and their ability to handle them. The instructions should be provided slowly and on a one-by-one basis.
Proper manipulation of the lids is important to successful handling of the lenses. The middle finger of the contralateral hand should be positioned underneath the upper eyelashes to pin them back, while the middle finger of the ipsilateral hand is positioned over the lower lashes and the lens, positioned on the forefinger of same hand (as eye) places the lens directly on the cornea. For removal of soft lenses, the same procedure as with spherical lenses can be used (that is, pinching the lenses off the cornea). Alternatively, GP lenses are removed easily by pulling the lid at the lateral canthus. GP aspheric lenses fit tightly and for removal, the fingers should be positioned similar to insertion, ensuring that the lid margin is directly against eye. The lids can then be pulled laterally to eject the lens.
It is important to emphasise proper care instructions. Patients should be provided with verbal instructions on how to care for the lenses, including solution use, and then be asked to repeat the instructions for proper care. These lens care instructions should be reinforced at follow-up visits to help ensure compliance. Patients should be asked about their lens handling and cleaning as well as wearing schedule and solutions being used. Due to the potential for dryness, emphasis must be placed on proper replacement, cleaning as prescribed and supplemental use of rewetting/relubricating drops.
Contact lens correction of presbyopia continues to evolve and improve. In particular, the new GP and soft multifocal designs have resulted in increased success rates and patient satisfaction versus monovision. With the improved GP multifocal designs, the introduction of silicone-hydrogel multifocals and the future introduction of soft disposable toric multifocal designs, the future should be promising for this underserved and ever-growing segment of the population.