Article Date: 4/1/2004

presbyopia
Contact Lens Options for Presbyopes
Satisfying your presbyopic patients has never been easier. Here's a review of some of the options that are available to this patient demographic.
BY ROBERT L. DAVIS, O.D., F.A.A.O, Oak Lawn, Ill.

Presbyopia has swept the vision correction market. New patients represent 46% of the bifocal-eligible patients between -0.50 and +1.00. This is a motivated and influential group that seeks correction for its near point dilemma. Their options include refractive surgery, monovision, soft bifocals, rigid bifocals and reading glasses. This article will cover the soft lens options.

Starting the search

The inherent characteristics of the soft lens design limit lens movement necessary for the alternating fitting concept. The remaining soft lens options include monovision, aspheric and annular lens designs. Each design has advantages, dispelling the notion that one best design exists.

The practitioner doesn't always arrive at a simple solution. Trial lenses are necessary to reach a successful outcome. We test the patient in real-life scenarios -- in the office, at the computer for intermediate distance, reading for near vision and looking outside down the street for distance vision. Modifying the prescription in 0.25D increments outside the confines of the phoropter will help you reach success quickly.

Once you and the patient agree on a lens design, dispense the lenses and schedule the patient for a mandatory, one-week follow-up appointment. It's important to note that you shouldn't determine a final prescription until the patient goes out into his visual world and reports back.

Let's review the options

The following is an analysis of the contact lens options for the presbyopic patient:

The Focus Progressive (CIBA Vision) is a near center aspheric lens design with an add prescription (+1.25) used for beginning presbyope patients who require better distant vision than near. Most of the time you must add +0.50D to the manifest sphero-equivalent prescription to arrive at the appropriate distance prescription. This prescription alteration will take advantage of the full bifocal power but won't degrade far vision. The fitting manual suggests selecting the initial lens power by adding one half of the add power to the distant spherical equivalent.

You can also fit this lens design by offsetting the distance prescription by another half diopter to integrate additional add power. You can also use the CIBA Focus Progressive as the distant lens with one of the other bifocal lens designs to improve near vision.

The C-VUE lens (Unilens Corp.) is a near centered aspheric design with two base curves (8.5 and 8.8) and two strengths of add powers. It's manufactured in a lathed polymacon and methafilcon material. You can prescribe a planned quarterly replacement schedule for this lens.

The C-VUE also is available in a molded, polymacon two-week disposable replacement schedule. The EMA lens is a six-month replacement lens made from the polymacon material. These lenses, as well as the disposable Bausch & Lomb soft lens bifocal, have the same optics, which you can interchange. The low add design has excellent distance optics for the beginning and moderate presbyope. The high add design has greater add power and degrades the distant acuity in comparison; distant and add zones in front of the pupil effect the patient's ability to resolve the image.

The advantage of the two add fitting lenses is that you can interchange them to either gain greater distance vision with both eyes fitted with the low add design, or greater near vision with both eyes fitted with the high add design or using one high add on the nondominant eye and a low add on the dominant eye.

Incorporating the monovision philosophy, I've used a spherical near lens on the nondominant eye and a low add design on the dominant eye to satisfy the visual requirements for a college English professor.

The power ranges of these lenses (-10.00 to +6.00) have expanded the patient pool that can enjoy binocular vision without the need for reading glasses.

The Frequency 55 Multifocal (CooperVision) is a methafilcon A material designed in both a near-centered and distant-centered lens. It incorporates a spherical center zone surrounded by an aspheric intermediate zone with an additional spherical zone in the periphery. It's a flexible wear lens, with 55% water content and light blue handling tint.

The real advantage to this lens design involves the clever integration of a distance-centered lens for the dominant eye and near-centered lens for the non-dominant eye. The distance-centered lens integrates a 2.3 mm spherical distance prescription, whereas the near-centered lens has a 1.7 mm spherical near prescription in the center. The distance center lens design usually needs a +0.50 added to the distance prescription while the near-centered lens requires -0.50 added to the distance prescription. The bifocal options include +1.00, +1.50, +2.00 and +2.50.

The manufacturer suggests an initial lens selection of a D lens for the dominate eye and an N lens for the non-dominant eye. Initially, I select two D lenses and check the quality of the near vision. If the patient requires improvement in the near vision, replacing the non-dominant lens with the N lens usually solves the inadequacy. If the patient still needs improvement in the near vision, then I replace the D lens in the dominant eye with an additional N lens. The higher add prescriptions usually have a detrimental effect on the quality of the distance vision. The real advantage of this lens design is the flexibility of lens parameters to fit your patients with this one modality.

The Acuvue Bifocal (Vistakon) is a flexible lens design that you can use with the entire spectrum of presbyopic prescriptions. Configure the bifocal add powers with a +1.00, +1.50, +2.00 or +2.50. You can fit this two-power lens design in a bifocal arrangement or a modified multifocal monovision lens design by offsetting the add powers.

The alternating distance and near-concentric annular power strategy reduces the problems encountered at night or in dim illumination. In low levels of light when the pupil dilates, light falls on an adjacent zone of distance power, aiding the ability for distance vision in conditions such as night driving. Typically, you need to increase the distance prescription by -0.50D for optimal distance viewing.

This simultaneous lens design incorporates alternating distance and near powers inside the pupillary zone. Increasing the bifocal power reduces the quality of vision in the distance because of the near prescription affecting alternating power separation within the pupil. Offsetting the bifocal powers creates a modified multifocal monovision approach, resulting in an improved distance, near and intermediate visual range as compared to the straight bifocal fitting strategy. The easy fitting approach allows the trial lens to quickly demonstrate the patient's acceptability.

The Quattro lens (Blanchard) is another simultaneous multifocal design. The multifocal effect comes from opposing a unique anterior aspheric curve (S curve) to a spherical back curve. The S curve travels from center to periphery, a constant controlled flattening that results in a power modification moving progressively toward more minus. Base initial lens selection on the near power visual requirement.

Within a central area of 3.00 mm, referred to as a power block, the lens contains all the powers the patient needs for vision at any distance. The brain is accommodative and interprets only those impulses relevant to the object under observation. When reading, the central near design, combined with the normally smaller pupil, creates a sharper image and good contrast. As the pupil enlarges when looking from near to far, a greater portion of the power is devoted to distance. The Quattro lens is a quarterly replacement modality made out of hioxifilcon B, 48% water, blue handling tint material designed as an anterior surface aspheric multifocal.

Fitting fine points

The refraction only gives you the absolute distant and near prescription. Some designs require an addition or subtraction of 0.25D. Some patients will tolerate over plus, aiding in the near prescription, and others will require over minus to arrive at acceptable distant vision with a bifocal design.

Always investigate the visual ranges monocularly with each contact lens design. This allows you to understand the improvement or deterioration of adding or subtracting 0.50D. Always adjust the contact lens design quality under binocular conditions. Patients who have 20/30 vision monocularly will frequently achieve 20/20 vision binocularly after summation.

What time is it?

A successful lens design in the daytime might be crippling at night. The pupil size can cause flare/glare and destroy the image quality without any solution except selecting a different lens design. Each lens design incorporates a different zone size. Instead of becoming discouraged with the patient's symptoms, attempt a different fitting concept.

Each lens design has a unique zone configuration that provides you with different options. Some designs have a near prescription in the center and distance in the periphery, which aids night vision during scotopic conditions. Some designs are aspheric in nature, reducing the flare and glare. Investigating light and dark lighting conditions will reduce chair time and narrow lens selection.

It never ends

The most important facet in the fitting procedure involves pushing and pulling the prescription by +/- 0.25D to arrive at the optimal lens power. Changing the bifocal power will always alter the way your patient perceives distance. It's this fragile balance between distance and near that provides a comfortable bifocal lens design. You'll need to continuously tweak and refine this bifocal arrangement as your patient ages. This is why the presbyopic patient is truly a practice builder as long as he remains a loyal patient.

Dr. Davis is in private practice and conducts clinical research. He's a diplomate in the Cornea and Contact Lens Section of the American Academy of Optometry.

 

 

 



Optometric Management, Issue: April 2004