Correcting Presbyopia With Soft Contact Lenses

A comprehensive review of the designs, products and fitting techniques that yield new opportunities for success.

THOMAS G. QUINN, OD, MS
JUNE 1998

Why get involved with fitting presbyopic patients with contact lenses? The answer is that they want contact lenses and that many of them can be successful with them. Those who have enjoyed single-vision contact lens correction for years appreciate the multitude of benefits and don't want to give them up just because they've become presbyopic. Many of those who aren't contact lens wearers have a strong interest in contact lens correction.

As demographics continue to shift over the next decade, more patients will be in the over-40 group. We want to satisfy this population of patients who make the health care decisions for themselves, their children and sometimes their elderly parents. These gatekeepers are a valuable part of any healthy practice's patient base. If they're happy in your practice, it's likely that you will have the privilege of caring for other members of their family. Advancements in lens designs provide us with a powerful array of contact lenses for presbyopes. The challenge is to identify the viable candidates and match them with the most appropriate corrective option.

Candidate Assessment

Many patients don't realize that bifocal contact lenses exist, so it's our job to inform them about the various options. In our office, patients complete a one-page Patient Visual Needs Assessment Questionnaire when they arrive for a comprehensive examination. One question asks, "Are you interested in considering contact lenses?" The response choices are "occasionally," "every day," "haven't considered" or "not interested." Even if they choose "not interested," you've at least approached the issue in a non-offensive way. Any other response presents the opportunity to discuss the patient's suitability as a contact lens candidate.

To meet the visual needs of your presbyopic patients, it's critical that you understand their visual tasks and performance expectations. Find out what your patients' motivations, desired wearing schedules and visual tasks are. Are their goals realistic? A good history goes a long way. Ask specific questions and listen carefully to the responses, both in words and in implication. Evaluate refractive errors and visual sensitivity. Low error and high adds may be problematic, as may high sensitivity to small lens changes during refractive testing and acuity not correctable to 20/20 in each eye. Setting realistic expectations at the outset saves you time and spares you frustration and patient disappointment. Every form of vision correction for the presbyope has its compromises. Understanding the limitations and benefits helps you meet the needs of the growing presbyopic population.

General Options

Reading Glasses-- Patients who have adapted to single-vision contact lenses may prefer reading glasses over their contact lenses, especially if they're early presbyopes, where assistance with near tasks is required only occasionally (e.g., reading medicine bottles or threading a needle). As presbyopia progresses and more near tasks become challenging, the inconvenience of this form of correction may become unacceptable.

Monovision-- Many early presbyopes are well-served with over-plussing the nondominant eye by +0.50D or +0.75D. The induced imbalance is minimal and often well tolerated. A fundamental dictum to successful monovision prescribing is to demonstrate before you prescribe. The idea of monovision is a bit disconcerting to many patients, but is received better when you demonstrate it as you determine the patient's suitability. Determine the patient's dominant eye, then assess near vision by holding an appropriate power loose ophthalmic trial lens over the nondominant eye while the patient is wearing distance correction. If near vision is unacceptable, the patient is probably not a monovision candidate. If near vision is acceptable, have the patient view a distance object with the ophthalmic trial lens still in place. If vision is acceptable, the patient will probably perform well with monovision correction. When distance or near vision is unacceptable, explore bifocal options.

RGP Bifocals-- RGPs have been available for many years. Ideal candidates for RGP bifocals include those already successfully wearing single-vision RGPs, astigmats and patients with high near visual demands. Success rates have increased with newer, sophisticated RGP multifocals.

Soft Bifocal Contact Lenses

Soft bifocal lenses are simultaneous vision designs, which present distance and near optical portions within the pupil at the same time. Alternating designs are unsuccessful because translation is usually insufficient to displace one optical portion of the lens for another. Some aspheric and multi-zone designs also provide optics for intermediate distances. Simultaneous designs are classified as center near, center distance and full aperture designs (Figs. 1, 2 & 3) and use aspheric, concentric, combinations of aspheric and concentric or diffractive optics.

Aspheric Center Near Designs-- Aspheric center near designs have maximum plus power centrally. The graduated front surface curve change results in a progressive increase in minus or decrease in plus toward the periphery (Table 1).

Clinically, the Unilens and perhaps other anterior aspheric multifocals not only create a progressive power effect, but they may also reduce optical aberrations and increase depth of focus. It has been stated that the front asphericity of such lenses on the eye summates corneal asphericity and the front surface asphericity of the lens. To maximize the transfer of corneal asphericity to the front of the lenses, they should be fitted as flat as possible without compromising comfort or lens centration. Most front surface aspheric soft lenses are available in three base curves.

The Sunsoft Multifocal has a single base curve and two design profiles. Profile A provides adds up to +1.25D; Profile B provides adds up to +2.25D. Profile A can be used on the dominant eye of a mature presbyope if distance vision is compromised by wearing the Profile B design on each eye.

Even with good centration, many aspheric center near designs require more plus or less minus than expected in the nondominant eye of more mature presbyopes in order to achieve adequate near vision. If this provides unacceptable distance acuity, a concentric design on the nondominant eye and an aspheric design on the dominant eye may better balance distance and near vision.

Concentric Center Near Designs-- Pupil size assessment is critical to success with concentric center near lenses. Small pupils require small add zone diameters to provide adequate distance viewing, while larger pupils require larger add zones on each eye. With any pupil size, it's often beneficial to use smaller central near zones on the dominant eye to enhance distance viewing and larger central near zones on the nondominant eye to enhance near viewing. A significant part of fitting these designs is determining the proper add zone size for each eye to optimize visual performance. Excellent centration is important with any center near contact lens design. Patients who are exposed to a wide variety of light levels and who have extreme variations in pupil size may experience some fluctuation in vision. All concentric center near designs offer multiple near zone sizes (Table 1).

Aspheric Center Distance Designs-- Aspheric center distance designs have maximum minus or minimum plus power centrally, and the graduated back surface curve change results in a progressive increase in plus or decrease in minus toward the periphery (Table 2). Generally, they provide very good distance acuity, and adapted single-vision soft contact lens wearers convert easily to them. Near acuity is often best accepted by the early presbyope, although this differs among lenses with various degrees of asphericity. A patient with large pupils may have better near vision with these designs, as increased light rays from the more plus peripheral portion enter the pupil. Centration is also key to success with back surface aspheric multifocals. A decentered lens places a more plus peripheral portion of the lens along the line-of-sight with distance fixation. This overplussing requires more minus to compensate, which diminishes the near add effect.

Concentric Center Distance Design-- The LL-Bifocal from Lombart, formerly CIBA Vision's Bi-Soft lens, is the only widely available concentric center distance soft lens. While this lens generally provides very good near vision, the peripheral near zone may interfere with distance vision, especially in patients with large pupils. This can be particularly problematic with night driving (Table 2).

Multi-Zone Designs-- All current multi-zone designs feature distance correction in the center of the lens (Table 2). The LifeStyle 4-Vue lens has an aspheric central distance portion, followed by a spherical intermediate zone, a near zone and another distance zone (Fig. 4). The outer distance zone is designed to aid night vision through the dilated pupil by providing additional distance focused light. The LifeStyle 4-Vue High Add lens has the same design but stronger intermediate and reading zone powers.

The LifeStyle Xtra lens has the same zone relationships as the LifeStyle 4-Vue, but it has multiple spherical zones and is available for quarterly replacement. To assist in the initial diagnostic fitting of the LifeStyle Xtra, the manufacturer provides a two-pair set. One pair has an add equal or almost equal to the spectacle add power, and the second pair has an add power 0.25D to 0.50D less than that. Often, prescribing an add that's less than the add used in the spectacle correction performs quite well in this design, and the LifeStyle Company, Inc., recommends beginning with the lower add pair because it's more likely to provide optimal distance performance. The distance power in both pairs generally matches the spherical portion of the vertex-adjusted spectacle distance prescription. Once the appropriate power is determined, you can order a three-pack to finish out the first year.

Specialty UltraVision's Specialty Progressive features a central distance zone surrounded by a progressive intermediate/near zone and a peripheral distance night ring. It is available in six-packs and can be dispensed as a two-week or monthly replacement lens.

The Vistakon Acuvue Bifocal, which will probably be released by the end of the year, has significantly improved my success with presbyopes and soft bifocal lenses. This simultaneous design, two-week replacement lens is approved for daily or extended wear and has ultraviolet filtration and a light blue handling tint. Its unique design features alternating distance and near zones (Fig. 5). Contrary to most simultaneous vision designs, this lens performs quite well, even in the absence of ideal centration, and is relatively independent of pupil size. Although a large range of ametropes can achieve success with the lens, myopes with low to moderate adds are very enthusiastic wearers.

Fitting is very straightforward, but you must follow specific guidelines to achieve optimal success. Initial lens power selection is equal to the vertexed spectacle prescription. Following insertion of the lenses, verify that they are properly orientated by viewing an inversion indicator on the lens. Some patients don't feel an inverted lens, which makes the inversion indicator even more valuable in assuring proper vision. Finally, allow patients to assess their vision outside of the examining room for 10 to 15 minutes. When they return to the exam room, ask them how their vision is. Their comments guide you to which, if any, lens power adjustments to make. As with nearly all soft multifocal contact lenses, higher adds in the Vistakon Acuvue Bifocal tend to degrade distance vision. A lower add lens or possibly a single-vision distance lens on the dominant eye, combined with a higher add lens on the nondominant eye often provides an acceptable balance of distance and near vision. A large supply of Vistakon Acuvue Bifocal diagnostic lenses will be available, allowing both doctor and patient to efficiently explore the feasibility of this lens with little or no economic risk.

Full Aperture Design-- The Hydron Echelon bifocal from Ocular Sciences-American Hydron uses a diffractive phase plate which extends effectively across the entire pupil. The phase plate is formed by back surface echelettes which split the light to form the near image. The add power of an Echelon lens is determined by the number of diffractive rings. Higher adds have more rings with shorter radii. Approximately 20 percent of the light is lost to higher orders of diffraction, so lens performance is often reduced in low light conditions. Good centration is necessary to achieve adequate near acuity. I've found that the Echelon lens works best on hyperopes, and pushing plus to create a distance overrefraction of -0.50D usually enhances near vision without compromising distance vision significantly. Preparing patients for initial awareness of halos at night and a 3-D effect with near printed material helps reassure and ease them through adaptation. The Echelon lens can significantly limit oxygen transmission, particularly in higher powers, so careful slit lamp examination for striae and other signs of hypoxia is indicated.

Astigmatic Correction-- Most soft bifocals don't provide satisfactory vision if the patient has an astigmatic error exceeding 0.75D. If the patient is astigmatic in one eye only, the bifocal will probably be best tolerated in the near eye. A few soft bifocals are available in toric designs (Table 3). Most are concentric center near designs with a toric back surface.

Frequent Replacement Options-- For many years, spherical single-vision soft lens wearers have enjoyed the clarity, comfort and safety provided by replacing their lenses before they become coated enough to compromise performance in these areas. Now, presbyopic lens wearers can enjoy these same benefits (Table 4). Replacement of torn or lost conventional bifocal lenses is often delayed since many offices don't have a large enough stock of specialty designs. The convenience of having ready access to a spare from a planned replacement system is particularly attractive with presbyopic lenses.

General Fitting Guidelines

As stated, good lens centration is critical to success with most soft bifocal contact lenses, especially concentric center near and diffractive designs. Although centration is still desirable, some aspheric designs perform adequately with small decentration, especially for early presbyopes. The Vistakon Acuvue bifocal seems to be relatively independent of lens centration. With most simultaneous vision multifocals, minimal movement is desired to provide a stable optical system over the pupil. However, enough lens movement must occur to flush debris from beneath the lens and to prevent limbal binding. As with all soft lenses, it's necessary to allow the lenses to settle at least 10 minutes before assessing visual performance.

Assessing Vision-- How you assess vision during bifocal fitting has a significant impact on your success. The first golden rule is to assess vision binocularly both at far and near, which provides a better and more realistic evaluation than the monocular testing. Monocular acuity assessment does not accurately reflect what patients experience during their habitual binocular state and will often be disappointing. The second golden rule is to measure success as meeting most of the patients visual needs most of the time. Success is achieved when the patient is able to perform most of his visual tasks comfortably. If the patient is happy, you should be too. Don't get locked in to the need to achieve 20/20 vision. Many bifocal contact lens wearers are successful with binocular distance acuity 20/25 and binocular near acuity of 20/30.

Push Plus-- One of the common pitfalls in soft bifocal prescribing is over-minussing or under-plussing the patient. Designs that don't allow control over near add power, such as many of the aspheric lenses, don't provide enough plus for effective near vision. The goal is to push enough plus power in order to provide good near vision without compromising distance vision, and this is best accomplished with non-phoropter overrefraction. While the patient views a distance object, introduce increasing plus trial lenses bilaterally until the patient feels that his distance vision is unacceptable. Then take away plus power in 0.25D increments to re-establish acceptable distance vision. With this power in place, have the patient view a near object such as a magazine. If near vision is acceptable, apply contact lenses incorporating the power of the overrefraction. Reassess the vision and dispense the lenses.

Keep in mind that changes as small as 0.25D in distance lens power can have a profound effect on near vision when working with presbyopic lenses. If near vision is inadequate, add additional plus to the lens on the nondominant eye or switch designs. In some cases, you can achieve success with a different design on each eye. For example, an aspheric lens on the dominant eye and a concentric center near design on the nondominant eye may provide the proper balance needed to provide adequate vision at distance and at near. Another way to assess near vision is to have the patient move a near target in and out to locate the distance of clearest vision. If this "tromboning" locates a best vision area within the patient's habitual reading zone, the patient will likely be pleased with his near vision.

A Wealth of Options

No given bifocal lens design or brand meets the needs of all presbyopic patients. Emerging presbyopes or those requiring maximum visual performance at distance and at intermediate may do best with aspheric designs. High add patients may do best with overplussing the distance correction in the nondominant eye in order to achieve adequate near vision. High add patients with detailed distance demands may do best with a single-vision distance lens on the dominant eye and a bifocal lens on the nondominant eye. Of course, many patients, particularly those with low or intermediate add strengths, do quite well with straight monovision. The wealth of options and the development of some of the newer multi-zone multifocals affords you the opportunity to provide a higher level of visual correction to presbyopic patients today.

The ability to provide clear vision at distance and at near in a more natural binocular state is within your grasp, but it's up to you to reach out and embrace it.

Thomas Quinn, O.D.,M.S., is in private practice in Athens, Ohio, and has served as faculty member at The Ohio State University College of Optometry.