Presbyopic Contact Lens Care
PAUL WHITE, O.D., & RONALD WATANABE, O.D.
Today's presbyopic contact lens care is most effective when historical lessons are understood and applied to clinical practice. This review of significant research over the past 10 years will help.
About 60 years ago Feinbloom patented translating and alternating vision, scleral bifocal contact lenses, segmented with an upper distance and a lower near correction. Soon after this, Williamson and Noble developed a simultaneous vision, concentric, scleral bifocal contact lens with a central near and surrounding annular distance correction.
The concepts of alternating and simultaneous vision are still the basis of bifocal contact lenses. Simultaneous vision was first used with single-vision monovision about 1930. The subsequent six decades have produced only refinements of the major theme, including so-called progressive power changes accomplished by aspheric curves on the back or front of the contact lens.
Ten years ago the principle of diffraction was applied to simultaneous bifocal contact lenses. Diffractive bifocal contact lenses have not fulfilled expectations, nor have the many bifocal/multifocal contact lenses based upon the principles of refraction. Why? Because there are many deficiencies related to the rules of demand and supply.
There are about 70,000,000 presbyopes in the United States, but most are not interested in contact lenses, especially those who are emmetropic, have low distance refractive errors or who need an add of less than one diopter. These people have an intermittent need for optical correction, which is often insufficient for them to want contact lenses, especially if contact lenses degrade their vision.
Improved cosmesis is the primary motivation for pre-presbyopes to wear contact lenses. Although this is still a consideration for some presbyopes, it's not so much a factor after age 50, particularly with the availability of 'invisible' multifocal spectacles. The demand for contact lens correction for presbyopia is probably greatest among people from age 40 to about 50, especially those who need constant correction for distance and those who presently wear contact lenses. This latter group comprises a small but significant minority -- about 10 percent -- of the estimated 27,000,000 contact lens wearers in the United States. Many presbyopic contact lens wearers or prospective wearers are satisfied with distance single-vision contact lenses and reading glasses or with single-vision monovision contact lenses, which further reduces the demand for multifocal contact lenses.
DEMANDS OF THE AGING EYE
Contact lens wear places a demand on the ocular surface, which is not always accepted even with pre-presbyopes. The aging eye with its many changes of anatomy and physiology is even less likely to accept this demand. With aging, there is typically a reduction of the quantity and quality of the precorneal fluid due to decreased aqueous production of the lacrimal glands and lipid production of the meibomian glands. Eyelid tonus decreases, which decreases spreading of precorneal fluid and may cause various degrees of ectropion. Pupil diameters decrease and their response to stimuli becomes sluggish. The crystalline lens loses transparency, the retina becomes thinner and denser, some optic nerve fibers atrophy and the macula may degenerate. These internal ocular changes simultaneously decrease the quantity and quality of light reaching the retina and its ability to properly receive and transmit images (Fig. 2).
FIG. 2: OLDER EYES WITH DECREASED PRECORNEAL FLUID AND FLACCID EYELIDS
MEETING THE DEMAND
The best retinal imagery occurs when the pupil of each eye is constantly and fully covered by only the appropriate spherical and cylindrical refractive power for a given viewing distance. By definition, simultaneous vision bifocals or multifocals do not accomplish this. In different ways and to different degrees, this applies to concentric and annular designs, aspheric lenses, and single-vision monovision.
In theory, alternating vision designs would produce better retinal imagery if the pupil of each eye were constantly and fully covered by only the appropriate refractive power for a given viewing distance. This would mandate exact position, movement and translation of segmented and alternating vision designs. In practice, this is usually impossible to accomplish. Alternating vision designs often have a simultaneous vision component during some phases of wear, and bifocal or multifocal simultaneous vision designs often exhibit an alternating vision component during some phases of wear (Fig. 3).
FIG. 3: AN ALTERNATING RGP LENS POSITIONED AFTER A BLINK SO THAT THE PUPIL IS SIMULTANEOUSLY COVERED WITH PORTIONS OF BOTH DISTANCE AND NEAR OPTIC ZONES.
Most simultaneous vision, soft bifocal or multifocal contact lenses are not available in toric form. Uncorrected residual astigmatism with them or with rigid non-toric lenses degrades retinal imagery and visual acuity. There are, however, many toric soft or rigid single-vision contact lenses that can be used in monovision correction.
A properly fitted soft contact lens usually has good centration and about one to two millimeters of movement. While this is somewhat conducive for simultaneous vision designs, it reduces the translation necessary for alternating designs.
The reverse is true for rigid lenses. Alternating rigid contact lens designs have the distance power in the upper portion and the near power in the lower portion of the optic zone. To maintain this on the eye and to neutralize lens rotation, prism is incorporated which usually causes an inferior-positioning lens. Rigid corneal lenses should position centrally in the vertical palpebral aperture or slightly superior with a portion of the upper edge of the lens under the upper eyelid. Most practitioners avoid fitting single-vision, non-prismatic lenses with inferior positioning because of an increased occurrence of desiccation staining, decreased lens wetting and cleaning, decreased comfort, and increased visual flare and visual degradation. Soft lenses produce better physiologic tissue response when they move adequately. Fitting a soft lens too tightly to attain better position of bifocal or multifocal optic zones will produce limbal and scleral compression, reduced debris removal, and negative corneal and conjunctival responses. Contact lenses should first provide good physical relationships and only if this can be achieved, should the optical factors be evaluated.
Compared to spectacles and even to single-vision contact lenses, the optic zone diameters of both concentric, annular simultaneous vision and segmented, alternating vision designs are quite small, often about two to four millimeters. This exacerbates the problem of maintaining the correct zone or zones in front of the pupil both because of lens movement factors and because of the varying size of the pupil as it adjusts to different levels of illumination and to stimuli from accommodation and convergence.
Multifocal aspheric designs not only suffer from the same problems, but as the eccentricity, or rate of flattening, of the conic curve is increased to produce increased add effects, there is a concurrent increase of undesired induced astigmatism and aberrations. We are all familiar with these effects in progressive addition spectacle lenses. This occurs because the centers of curvature of various points on the typical conic section aspherics do not lie on a common axis. This type of aspheric produces an increased plus or decreased minus power from the vertex to the periphery of the back surface (central distance and peripheral near, i.e., centrad), and conversely a decreased plus or an increased minus on the front surface (central near and peripheral distance, i.e., reverse-centrad).
A DECADE OF STUDIES
There have been very few well-designed and controlled clinical studies related to contact lens care of presbyopes which have stood the test of time. Following are abstracts of one of the better studies published each year over the past decade.
McGill, et al., compared comfort, fitting characteristics and visual performance among CIBA Bisoft, Bausch & Lomb PA1, Barnes Hind Hydrocurve II and University Optical Alges simultaneous vision bifocal contact lenses for 10 presbyopic patients. There were no significant differences in comfort or fitting characteristics. All lenses compromised distance and near visual performance relative to best corrected spectacle visual performance.
Overall, the PA1 lenses performed best at distance, the Alges lenses performed best at near, and the Bisoft and Hydrocurve lenses fell somewhere in between. The extent and relative direction of the compromises on distance and/or near vision were related to lens design features such as zone positioning, zone diameter and zone powers.
McGill, et al., evaluated near-point stereopsis for 10 presbyopic patients to determine if bifocal contact lenses impair binocular function less than monovision. Testing was done with monovision and binocular correction with each of four simultaneous bifocal contact lenses used in the 1987 study. Simultaneous vision bifocals produced at least as much reduction in stereopsis as monovision compared to baseline spectacle correction. Repeat testing of bifocal stereopsis with best near overrefraction suggested that a portion of the stereo reduction could be attributed to insufficient effective adds with the bifocal contact lenses.
Back, et al., designed a study to compare subjective success rates of three presbyopic contact lens systems. Two hundred presbyopes were prescribed monovision (MV), a pair of concentric center-near lenses (CN pair), or a combination of center-near on one eye, center-distance on the other eye concentric lenses (CNCD).
Overall, 112 subjects (56% successfully wore at least one lens system for a minimum of three months. MV was the most successful system (67% success); disrupted stereopsis was not a significant reason for failure with this system. The lower success rates with the two concentric bifocal systems (CN pair 42%, CNCD 37%) could be attributed to the greater visual compromise required with these lenses.
Erickson and Schor reviewed the literature and reported that most visual functions are affected by contact lens bifocals and single-vision monovision (MV) departures from the conventional optical correction strategies used on non-presbyopes. Sensory functions such as contrast sensitivity and stereo-acuity are affected most, whereas motor functions such as convergence and accommodation are not noticeably impaired. They concluded that MV appears to produce a more widely acceptable visual compromise than bifocal contact lenses for most patients.
Sheedy, et al., evaluated the effects of concentric, simultaneous vision, bifocal contact lenses on task performance, visual acuity and stereopsis. Forty presbyopes were prescribed CIBA Spectrum center-near bifocal contact lenses (BCL) and also distance contact lenses combined with reading spectacles (DCL) which served as the control. Thirty-two subjects completed the 8-week study. At dispensing and after eight weeks of regular BCL wear, performance with BCLs was significantly poorer than with DCLs for all three near tasks. Subjects wearing BCLs generally had more errors per trial. Visual acuities with BCLs were reduced significantly by 0.8 to 1.4 acuity lines compared to DCLs. Stereopsis was reduced compared to DCLs at both measurement sessions. It is likely that the decreased task performance with the simultaneous vision BCL is caused by the decreased visual acuity with these lenses. Nonetheless, 27 patients chose to wear the BCL on a regular basis at the conclusion of the study.
Kuhl, et al., did a clinical investigation to determine the success of using a flow chart system to fit presbyopic patients with contact lenses. This type of system provides practitioners with a simple, step-by-step approach to fitting presbyopic patients. Patients were prescribed monovision, simultaneous vision bifocal, alternating vision bifocal or diffractive bifocal contact lenses. The patients were fit first with monovision and about 55 percent were successful. Those who were not successful proceeded to the next stages. Stage 2 used the simultaneous lens design, stage 3, the alternating lens design and stage 4, the diffractive lens design. Of the 22 patients enrolled in the study, 17 (77.3%) were successful through Stage 3 and 18 (81.8%) were successful through Stage 4.
Cox, et al., tested the visual acuities of 13 pre-presbyopic subjects using high- and low-contrast logMAR charts under high- and low-illumination conditions. Subjects were alternatively corrected with simultaneous, monocentric, soft, bifocal contact lenses with add powers of +1.25, +2.00, and +2.75 D. The results revealed significantly poorer low-contrast and low-illumination visual acuities for the higher add power lenses.
This study suggests that simultaneous vision bifocal soft contact lenses may not be the optimum form of correction for the older presbyopic contact lens patient.
Collins, et al., studied the objective and subjective characteristics of adaptation to monovision over a period of eight weeks. Sixty presbyopic subjects wore high water content hydrogel lenses in the study. During the eight weeks of monovision wear, there were no significant changes in the subjects' visual acuities (distance, intermediate or near) in high- and low-illuminance conditions, near stereopsis or interocular blur suppression. Nevertheless, the subjects reported significant improvement in various aspects of visual performance during the same period. Forty-eight percent of the subjects reported complete tolerance to the vision with their correction within the first week of monovision and 78 percent were completely satisfied with the monovision correction at the end of eight weeks.
The improved tolerance to monovision may be related to changes in aspects of vision other than those measured in this study, or it may reflect a psychological adjustment.
Michaud, et al., evaluated monovision for patients wearing spherical, single-vision soft lenses compared to those wearing single-vision soft lenses whose front surface had a mild asphericity (SV-38). They hypothesized that the aspheric front surface might reduce aberrations and improve visual acuity and contrast sensitivity. There was no difference in tested stereopsis between the spherical and aspherical designs. Patients did not have a visual preference for either lens design even though testing demonstrated some slightly improved visual acuity at near and high frequency contrast sensitivity with the aspheric design.
Smiley, et al., compared three popular RGP, back-surface aspheric, multifocal designs (VFL-3, LifeStyle Gp and Multifocal 19) in terms of vision, comfort and patient satisfaction. All subjects were successful RGP wearers, so comfort was not a factor. The average visual acuities for Multifocal 19 were 20/22 D and 20/34 N, for LifeStyle Gp 20/28 D and 20/31 N, and for VFL-3 20/27 D and 20/34 N. Patients also rated their subjective vision satisfaction on a scale of 0 to 100. Multifocal 19 was rated 67 percent D and 65 percent N, LifeStyle Gp, 51 percent D and 65 percent N, and VFL-3, 50 percent D and 53 percent N.
Scores for subjective satisfaction were from the mid-40s to the mid-60s. A score of 40 indicates mildly blurred vision most of the time with some clear vision, while 60 indicates clear vision most of the time with some visual disturbance.
THE CLINICAL APPROACH
Despite the inherent problems associated with presbyopic contact lens care, many patients can be successful when fitted properly. This necessitates a systematic yet flexible approach incorporating the current knowledge on monovision and multifocal contact lenses.
Assess the prospective contact lens wearer -- Careful patient selection is the first step toward success with multifocal contact lenses. While taking the patient's history and discussing contact lens options, determine his or her expectations for vision, visual demands at work and elsewhere, previous contact lens history and motivation.
Motivation is the most crucial factor in determining patient success. How much does the patient dislike wearing eyeglasses? Do eyeglasses interfere with his lifestyle? Is the patient a current contact lens wearer who wants to continue wear after becoming presbyopic?
Bifocal contact lens wearers must be willing to accept some blur, ghosting, cloudiness or lens awareness. If patients are willing to accept these compromises to eliminate or reduce spectacle wear, motivation is appropriate.
When describing potential vision with multifocal contact lenses, inform patients that their vision will not be as clear as it is with spectacles at either distance or near. Explain that they may notice ghost images, some cloudiness and even a three-dimensional effect when reading, and that they may not be able to wear multifocals for as many hours as they wore their single-vision lenses. By setting realistic expectations at the beginning, you will minimize visual complaints later.
Visual demands should be moderate when patients wear multifocal contact lenses. Rule out those who require detailed near vision for extended periods, e.g., architects, accountants or seamstresses. Patients who require accurate and consistent distance vision correction, e.g., professional drivers, are also poor candidates. Also, consider patients' recreational activities and hobbies. Needlepoint, model-building, target shooting and even golf may be too visually demanding for multifocal contact lenses. Part-time contact lens wear for less visually demanding social or recreational activities is a positive factor (Table 1).
Patients who wear contact lenses for binocular distance correction, particularly rigid lenses, have an advantage when adapting to their new optical correction. If the patient has never worn contact lenses, you should factor general adaptation into the total adaptation time.
Assess ocular surface health, particularly the cornea, pre-corneal tear fluid and eyelid integrity. Age-related changes in these tissues may contraindicate contact lens wear, especially multifocal designs with thick contact lens profiles.
Select the best lens option -- Once you've determined that your patient is a good presbyopic contact lens candidate, you must select the best contact lens option: single-vision lenses for distance with reading spectacles; single-vision lenses for close with distance spectacles; monovision or multifocal contact lenses. If the patient wants to eliminate spectacles, the first two are not options. Although monovision can be successful, as indicated in the studies of Back, Erickson, Kuhl, Collins and Michaud, many patients cannot adapt to the induced anisometropia and may be better suited to multifocals.
Kuhl describes an approach to fitting multifocals that can increase your success rate. Begin with monovision, a simple, cost- and time-effective system that can be trialed in-office with single-vision contact lenses. An initial 30-minute trial with lenses of the appropriate powers can often weed out those who will not be able to adapt. Those who tolerate the initial one-week wearing period should continue for another one to two months as satisfaction often improves over time. If the patient is still unable to tolerate the inter-eye disparity, try multifocal lenses. Because there are similar designs for both rigid and hydrogel contact lenses, you can use this system for either. Figure 4 shows a strategy for fitting multifocal contact lenses.
For adds of 1.75 or less, an aspheric simultaneous design is often the first choice. One brand each of soft and rigid lenses should suffice for a simple fitting system. If the patient has a high spherical refractive error, try an RGP design, especially when this would result in less residual astigmatism. If the aspheric design does not provide satisfactory distance and near vision, try a concentric simultaneous design. In general, the center-near design is better than the center-distance design because the pupil size decreases during near viewing and increases during night driving. Also, higher add powers increase the flexibility to improve distance and near vision through power and add changes. If the concentric design is not successful, try a diffractive design in a higher add power. However, ghost images, 3-D effects and reduced illumination often negate this option, which performs better for patients with spherical refractive errors who work under high illuminance.
Patients with add requirements of 2.00 or more are less likely to be successful with an aspheric design and may also have more difficulty in general as indicated in the Cox study. Begin with a concentric or diffractive design, but be prepared to go to an alternating design. Due to the difficulties previously described, alternating designs are usually reserved as the final option, but when fit properly, they provide the best vision of any multifocal design.
Assess the lens -- Fit and vision assessments of monovision and multifocal contact lenses are more critical than for single-vision lenses. Small changes in power or base curve may result in significant improvements or degradations in visual clarity. The effect of binocular summation is also important in maximizing vision.
Simultaneous designs usually perform better when the lens is centered on the cornea. An exception is RGP moderate aspheric back surface lenses, which perform better with superior positioning, as shown in the Smiley study. Adjust your fit criteria if the manufacturer recommends a lens position other than central. Lens movement on blink should be optimal for corneal health, but the return to a central position should be quick and accurate.
Alternating design RGP lenses, on the other hand, must sit on the lower lid and maintain this position. Use a Burton UV lamp or an ophthalmoscope to assess movement in primary gaze and in down gaze to simulate eye positions when viewing at a distance and when reading. In primary gaze, the segment line should be within one to two millimeters of the lower pupil margin in normal room illumination. The segment line should be approximately horizontal, but a slight nasal tilt may be acceptable (Figs. 5 & 6).
FIG. 5: ALTERNATING VISION RGP LENS WITH SEGMENT LINE ABOUT 1MM BELOW LOWER PUPIL MARGIN WITH PRIMARY GAZE.
FIG. 6: ALTERNATING VISION RGP LENS WHOSE SEGMENT LINE HAS A SLIGHT UPWARD NASAL TILT.
As the patient looks down, the lens should translate upward so that the patient views through a sufficient portion of the near segment of the lens; usually at least 60 percent of the pupil must be covered by the near segment. Upward translation should be quick and without significant lens rotation. The return to primary position should also be quick. Often, a full blink will allow the lens to realign properly.
Fluorescein patterns for aspheric RGP lenses are generally mild to moderate apical clearance with mid-peripheral alignment and peripheral clearance. The slightly steep fit is necessary for an aspheric lens with higher back surface eccentricity to remain stable on the eye.
Conversely, alternating design RGP lenses should fit slightly flat with mild apical touch, mild mid-peripheral clearance and moderate peripheral clearance to enhance translation and inferior position. Vary the amount of prism ballast and the axis and base curves to improve the balance between orientation stability and translation.
Once you've achieved optimal fit, overrefract with spectacle trial lenses. This better simulates natural viewing, especially for simultaneous designs where the small aperture of the phoropter may interfere with light entering through the peripheral zones. A monocular overrefraction should be followed by a binocular overrefraction to determine if binocular summation allows acceptance of an extra +0.25 or +0.50 to enhance near vision without degrading distance vision. If near vision is not acceptable with aspheric lenses, an extra +0.25 over the nondominant eye may improve near acuity. If this is not successful, try another design.
With all bifocal or multifocal contact lenses, particularly simultaneous designs, best corrected visual acuity is often 20/25 to 20/30 as shown in the McGill, Erickson and Smiley studies. Final lens specifications should provide acceptable visual acuity at distance and near, as well as good comfort and good corneal physiology. CLS
References are available from: Dr. Paul White, The New England College of Optometry, 424 Beacon Street, Boston, MA 02115.
Dr. White is a professor and Dr. Watanabe is an assistant professor at The New England College of Optometry, Boston
1. About how long ago was the first bifocal contact lens patented?
a. 80 years
b. 60 years
c. 40 years
d. 20 years
2. Monovision was first used about:
3. With aging:
a. pupil diameter increases
b. ocular surface becomes drier
c. eyelid tonus increases
d. both "b" and "c"
4. To provide optimum vision, segmented and alternating vision bifocals require exact:
d. all of the above
5. An inferior positioning rigid contact lens increases:
a. desiccation staining
b. lens wetting
c. lens cleaning
6. As the eccentricity of aspheric curves becomes greater:
a. add effect is decreased
b. add effect is increased
c. induced astigmatism is
d. none of the above
7. In the 1987 McGill study, which lens type performed best at distance?
b. Hydrocurve II
8. In the 1988 McGill study, stereopsis with simultaneous vision bifocals was:
a. not affected
b. better than with monovision
c. equal or less than with monovision
d. none of the above
9. In the 1989 Back study, which was the most successful system?
d. all equal
10. In the 1990 Erickson and Schor study, MV most affects:
b. contrast sensitivity
d. both "a" and "b"
11. In the 1991 Sheedy, study, bifocal contact lenses reduced:
a. task performance
b. visual acuity
d. all of the above
12. In the 1992 Kuhl study, about what percent of the patients were successful with monovision?
13. In the 1993 Cox study, as the add power increased there was poorer:
a. low-contrast sensitivity
b. low-illumination acuity
c. "a" and "b"
d. neither "a" nor "b"
14. In the 1994 Collins study, from the first to the eighth week about what was the percent increase of complete acceptance:
15. In the 1995 Michaud study, the aspheric design used for monovision slightly improved:
a. near visual acuity
b. low frequency contrast sensitivity
c. high frequency contrast sensitivity
d. both "a" and "c"
16. In the 1996 Smiley study, the back surface aspheric RGP lenses produced near visual acuities of about:
17. With prospective presbyopic contact lens patients, what is the most crucial factor to assess?
b. refractive error
c. visual demands
d. contact lens history
18. What approach should be tried first with presbyopes?
a. monovision lenses
b. aspheric lenses
c. concentric lenses
d. segmented lenses
19. Problems of diffractive designs include:
a. ghost images
b. 3-D effects
c. reduced illumination
d. all of above
20. Alternating design RGP segmented lenses should often be fit with:
a. slight apical touch
b. mid-peripheral clearance
c. peripheral clearance
d. all of the above