New Options for Patients Who Have Astigmatism and Presbyopia

How to successfully fit toric multifocal contact lenses.

By Deepak Gupta, O.D.

Goal Statement:

We have seen many changes in multifocal contact lenses during the past decade. Some practitioners have realized the growth potential with our aging population, while others still avoid multifocal contact lenses due to past negative experiences or the increased chair time required to fit complex designs. This course will review the epidemiology of patients with astigmatism and presbyopia, discuss contact lens options for these patients, and offer clinical pearls to assist in fitting these patients.

Faculty/Editorial Board:

Deepak Gupta, O.D.

Credit Statement:

This course is COPE qualified for 1 hour of CE Credit. COPE ID 20698-CL. Please check with your state licensing board to see if this approval counts toward your CE requirement for relicensure.

Joint-Sponsorship Statement:

This continuing education course is joint-sponsored by the University of Alabama School of Optometry.

This course is sponsored by an unrestricted educational grant from CooperVision.

Disclosure Statement:

Dr. Gupta has no financial relationships to disclose.

We have seen many changes in multifocal contact lenses in the past decade. Some forward-looking practitioners realize the growth potential with our aging population. Others avoid multifocal contact lenses due to negative experiences, fear of failure, or the extra chair time required. This is especially true when trying to correct astigmatic patients who also have problems with their near vision.

In the past, we would have told them to wear reading glasses over their contact lenses or prescribed monovision. In a recent study, however, most patients preferred multi-focals to monovision because multifocals offered better intermediate vision and better stereopsis than monovision.1 We now have a lens that lets astigmatic presbyopes decrease their dependence on reading glasses: toric multifocal contact lenses.

When we fit multifocal lenses in the past, particularly for those with higher adds, the typical result was a modification of monovision. Newer lenses, such as those based on the Balanced Progressive Technology design from CooperVision, allow both eyes to be corrected more closely to the desired distance and near prescriptions.

As of 2000, there were more than 100 million presbyopes in the United States.1 About one-third of them have more than -0.75D of astigmatism. Not all of them are appropriate candidates for toric multifocal contact lenses, though. So, how do you find out which individuals you will be able to fit with these contacts?

Multifocal Candidates

To screen for potential multifocal candidates, consider the patient’s ocular health and refractive status. Also, assess the patient’s level of motivation to determine whether he or she will diligently come in for visits, and will have patience and accept lens changes should they be necessary. Finally, consider your patient’s expectations. If he demands precise crisp vision all the time, your patient may end up disappointed.

Before the fitting process begins, your role is to make sure that the patient realizes that most correction for presbyopia requires some compromise depending on personal preference and visual needs. No one option—whether it is contact lenses, eyeglasses or refractive surgery—works in all situations. In short, the patient should understand that there is nothing that you can do to completely restore his or her vision to pre-presbyopic levels. Once your patient accepts this notion, you can then proceed.

O.D.s should not avoid fitting multifocal contact lenses out of fear of material costs. Today’s design and parameter availability, plus the exchange or refund policies of most manufacturers, allow for multifocal fitting with virtually no risk. For example, CooperVision offers an “It’s Okay Guarantee,” in which you can return lenses within 100 days for a full refund. Other manufacturers have similar return and exchange policies.

In terms of the extra chair time, set your fitting fees accordingly. Patients will pay as long as they perceive value in the rendered service.

Stabilizing Design

Soft toric lenses require rotational stability. To achieve this, most toric designs employ one or more of these methods:

  • Prism ballasting. This method entails adding more lens mass to the inferior portion of the lens, making that part thicker and heavier. This prevents the lens from rotating without being too uncomfortable for the patient. Prism ballasting is one of the most common methods of lens stabilization, as it offers a reasonable balance between comfort and good stability. A minor drawback is the introduction of base-down prism into the lens.

  • Lens truncation. This involves cutting off the bottom portion of the lens, leaving it flat, or truncated. The flat edge usually rests on the lower lid, and the bottom “corners” help hold the lens in place. Lens truncation is an effective stabilization system, but it tends to make the lens less comfortable. The only soft contact lens that has this design is the Triton translating lens (GelFlex). This design is usually more common with gas permeable (GP) lenses.

  • Thin zones. This design, also called “dynamic stabilization” and/or “double slab-off,” involves removing lens material at the apex and base of the lens, thus creating thin zones at the top and bottom. These zones allow the eyelids to exert pressure on the lens and hinder its rotation. I have found that this design offers the greatest comfort of the three stabilization methods. The two basic multifocal design concepts are translating (alternating) and simultaneous vision. With the alternating design, the top of the lens usually has the distance correction, while the bottom contains the near correction. When the patient looks straight ahead, he or she will see well at distance. When the patient looks down, the lens translates so that the near correction covers the visual axis. This design generally does not translate well with soft contact lenses, so it is mostly available in GP materials.

    Simultaneous vision is the most common design employed with soft multifocal lenses. The retina receives input from multiple distances at different levels of clarity. Depending on where the patient looks, the visual system and brain determine which image is clearest and learn to ignore the blurred images.

    Simultaneous-vision multifocal lenses can be concentric, aspheric or diffractive. With a concentric design, the central zone contains the distance or near power focus and is surrounded by one or more rings that contain the opposite power. Some lens types alternate distance and near in a repeating pattern; this helps improve pupil coverage and visual input with variations of illumination and pupil size.

Fitting Approaches

Many options exist for achieving a successful multifocal fit. With the “total bifocal fit,” each eye gets the maximum vision for distance and near. This works best for patients who require low adds. As the add increases, attempts to correct both eyes perfectly for distance and near often result in more compromised vision at both distances.

Another consideration: the concept of visual system dominance. When fitting a patient with multifocal lenses, determine the dominant eye, using such methods as the “hole in the hand” test. Another simple method is the “fogging” technique, in which you overcorrect plus power to each eye; the non-dominant eye accepts the most plus.

Monovision vs. Multivision

Monovision once was the preferred method of correcting many presbyopes. It offers good vision at various distances, is less time consuming and is less expensive for patients. The success rate of monovision in adapted contact lens wearers is 59% to 67%.2 Monovision may work for an emerging presbyope, in whom an effective add of +0.50D or +0.75D in the non-dominant eye enhances reading ability.

But, as the patient gets older and needs more add power, monovision has two drawbacks. It diminishes depth perception and stereopsis, often leading to unsatisfactory vision, especially for nighttime driving. And, it offers no intermediate correction, which is especially important for computer users.

Multifocal contact lenses generally allow a more equal image size and quality between the two eyes, cause less disruption in depth perception, and offer better overall quality of vision.

Practitioner prescribing appears to be shifting to multifocals. Also, one study found that among 40 subjects, after six months of wear, 68% preferred bifocal lenses, and 25% preferred monovision.3 One year later, 53% of subjects were still wearing bifocal lenses.

A new addition to multifocal designs is CooperVision’s Biomedics EP, a two-week disposable lens designed for emerging presbyopes. Biomedics EP offers binocular visual acuity at far, intermediate and near distances. The lens is specifically intended for patients who require up to a +1.25D add. The design features a center spherical distance zone with a progressive aspheric zone that provides excellent intermediate and near vision.

To fit this lens, you need only the vertex-corrected manifest refraction. There is no need to compensate for add power or determine eye dominance. Parameters include sphere powers of +4.00D to -6.00D (0.25D steps), an 8.7mm base curve and a 14.4mm diameter. The lenses are made of omafilcon A, a lens material frequently used for patients with dry eye symptoms.

Modified multivision can help solve the dominance issue. In modified multivision, the dominant eye receives the better correction for distance, and the non-dominant eye receives a slightly greater add power. Unlike monovision, both eyes are fit with multifocal lenses and can see relatively well at distance and near. This gives patients better overall vision and is easier to adapt to. Many manufacturers have used this approach in their designs and fitting nomograms to simplify and enhance fitting success.

Factors For Success

An important indicator for a successful multifocal fit is the patient’s motivation. The fitting process may be longer than with spherical lenses, and more than three follow-up visits may be needed to

hone vision. Educate patients up front about this. Sometimes, apparent failures turns into successful fits with a few minor adjustments. If they think one visit will result in ideal vision at all distances, they will likely fail.

Also, make sure patients understand multifocal lens capabilities. I often employ the 80/20 analogy: The patient can expect multifocal contact lenses to meet his or her needs about 80% percent of the time; however, the patient will need to supplement the lenses for the remaining 20%. This may be reading glasses to enhance very fine print, distance glasses to enhance nighttime vision, or even eyeglasses alone. As long as patients know what to expect, they can adjust.

As with all contact lens fittings, make sure that the patient’s external ocular health is sound. Resolve issues with the lids, cornea and conjunctiva to ensure a successful physiological result. Ocular surface dryness is a common complaint in the presbyopic patient and should be addressed at the onset of the fitting process. I tell patients at the beginning that contact lens wear may necessitate the periodic use of rewetting drops. Lenses, such as those in the Proclear family, can help minimize dryness symptoms.

Also, take into account conditions, such as cataracts and macular degeneration, which can negatively impact best-corrected visual correction and toric multifocal fitting.

Patients with very small pupils often have difficulty using anything but the central portion of a contact lens. This can be problematic for an aging patient with increasingly miotic pupils. Determine pupil size at the beginning of the fitting process to see if your patient is a suitable candidate. I have found that patients with a pupil diameter of less than 4.0mm are poor candidates. While these patients have greater depth of field, they usually don’t get the full benefit of the outer concentric portion of the lens. A quick way to check for pupil size vs. concentration of the lens is to observe the red reflex through a retinascope or direct ophthalmoscope.

Aside from multifocal GPs, there are many soft multifocal contact lenses with excellent success rates. For example, Bausch & Lomb’s PureVision multifocal lenses feature a monthly modality with excellent optics and a high Dk value. Vistakon’s Acuvue Bifocal was one of the first commercially available soft multifocal lenses. CIBA Vision offers Focus Progressives and Focus DAILIES Progressives.

Proclear Multifocal

This is my lens design of choice for any presbyopic patient. For patients with -0.75D or less astigmatism, I prescribe the Proclear Multifocal. For patients with more than -0.75D, I prescribe the Proclear Toric Multifocal. It features a monthly disposable replacement schedule, which is easy for patients to remember.

CooperVision describes the design of this lens as “Balanced Progressive Technology.” This concentric design lens system employs a center-distance design lens (D lens) for the dominant eye and a center-near lens (N lens) for the non-dominant eye. Both lenses feature a spherical central zone surrounded by an aspheric annular zone, which is then surrounded by a spherical peripheral annular zone. It is important to note the D and N designation when fitting and ordering lenses.

The Proclear Multifocal Toric is available in a wide range of parameters. Adds range from +1.00D to +4.00D in 0.50D steps. Sphere powers range from +20.00D to -20.00D, and cylinder powers are available up to -5.75D. The lens is available in base curves of 8.4mm and 8.8mm. The axis is available at 5° intervals around the clock. The lens features an inverse prism ballast to help stabilization.

There is no charge for the diagnostic lenses. For the Proclear Multifocal Toric and Proclear Multifocal XR, diagnostic lenses can be ordered directly through CooperVision. This is a made-to-order lens and takes about 10 working days to arrive.

Proclear is made of omafilcon A. PC Technology creates a material containing molecules of phosphorylcholine, a substance found naturally in human cell membranes. These molecules, which resist deposits, attract and surround themselves with water, keeping Proclear lenses moist and comfortable.

The recommended fitting protocol for Proclear Multifocal and Proclear Multifocal Toric lenses is as follows: Determine the refractive status and dominant eye, and order the diagnostic lenses. After receiving the lenses, insert the appropriate D lens in the dominant eye and appropriate N lens in the non-dominant eye. After allowing the lenses to settle, assess the rotation and compensate using the LARS rule (reviewed later).

Next, evaluate lens performance in normal lighting conditions—first binocularly, then monocularly, if necessary. By checking the visual acuity of each eye separately, it will be easy to determine which lens power may need to be changed and greatly increase the success rate.

CooperVision suggests the following matrix for acceptable vision in each eye: The eye with the D lens should be 20/20 at distance and 20/40 at near. The eye with the N lens should be 20/20 at near and 20/40 or better at distance. If the patient’s acuity does not match this matrix, refine the powers on the appropriate lens. While this sounds similar to monovision, this design allows each eye to see at distance, intermediate and near, creating an additive effect to the binocular visual acuity and thus, clearer, more balanced vision at all distances.

At follow-up, make the smallest adjustment possible. A 0.25D change in a multifocal toric lens can make a major subjective difference.

Fine-Tuning Your Fits

When fine-tuning your fit:

  • Use available resources, namely fitting guides and consultation services that can save you time, money and frustration. Consider using software or online fitting calculators. For example, CooperVision’s Multi-Track fitting software, available on the company’s Web site, takes you through the three-step fitting process. It works with all their multifocal lenses, lets you order directly from your calculator, and comes in Palm and PC software.

  • Assess rotation. This is no different for toric multifocals than conventional torics. Toric lenses have specific markings to assess rotation, often at 6 o’clock but sometimes at 3 and 9 o’clock. When the markings are ideally aligned, the cylinder axis is located as marked on the diagnostic lens. If the markings are rotated, so is the cylinder axis. To compensate for rotation, visualize the rotation as clock hours; each hour equals 30º. When a lens does not align properly, use the LARS rule: Left Add, Right Subtract. If rotation is clockwise, the bottom portion of the lens has rotated to the left. So, we add those degree increments to the lens axis when ordering the diagnostic lens.

    Counterclockwise rotation means that the bottom portion of the lens has rotated to the right; this value is subtracted when ordering the diagnostic contact lens. For example, for a refraction of -3.25D -1.75D x 90 and a diagnostic lens rotation 20º clockwise, we would order a contact lens Rx of -3.00D -1.25D x 110. This assumes that when the new lens is placed on the eye, the lens will again rotate 20º clockwise.


  • Allow lenses to settle for 10 to 15 minutes before assessment. The wait is worthwhile; vision improves during this time (usually near vision before distance vision). Tell the patient that vision will become clearer during an adaptation period, which may last several weeks.

    The Proclear Multifocal Toric features a simultaneous-vision design in which distance and near light enter the pupil simultaneously. The brain learns to selectively choose the clearer image (such as the distance image while driving). Pupil size influences the amount of light exposed to the retina. When measuring acuity and performing an over-refraction, try simulating lighting conditions the patient commonly uses. I generally use illumination that is slightly brighter than that found in a fine restaurant during dinner.


  • Think outside the box. A patient may want better distance vision, and two D lenses may work better than the conventional D and N combination. I start with this method for patients who want crisp distance and intermediate vision and don’t mind occasionally wearing reading glasses over their contact lenses.

    Similarly, two N lenses may be necessary for an older presbyope who requires a higher add, is exacting about near work, and is not as critical about distance vision. These patients generally wear their lenses all day at work and put eyeglasses on over their contact lenses for driving or watching television. Work with patients to determine their most important consideration.


  • Think outside the box. A patient may want better distance vision, and two D lenses may work better than the conventional D and N combination. I start with this method for patients who want crisp distance and intermediate vision and don’t mind occasionally wearing reading glasses over their contact lenses.

    Similarly, two N lenses may be necessary for an older presbyope who requires a higher add, is exacting about near work, and is not as critical about distance vision. These patients generally wear their lenses all day at work and put eyeglasses on over their contact lenses for driving or watching television. Work with patients to determine their most important consideration.

Dr. Gupta is the clinical director for The Center for Keratoconus at Stamford Ophthalmology in Stamford, Conn. His clinical experience includes heavy emphasis on specialty contact lenses, and glaucoma diagnosis and management.

References

  1. Richdale K, Mitchell GL, Zadnik K. Comparison of multifocal and monovision soft contact lens corrections in patients with low-astigmatic presbyopia. Optom Vis Sci 2006 May;83(5):266-73.
  2. Evans BJ. Monovision: a review. Ophthalmic Physiol Opt 2007 Sep;27(5):417-39.
  3. Situ P, Du Toit R, Fonn D, Simpson T. Successful monovision contact lens wearers refitted with bifocal contact lenses. Eye Contact Lens 2003 Jul;29(3):181-4.


Category: Astigmatism

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