contact lens management

Double The Challenge

Fit the presbyopic astigmatic patient in the right lens.

DIANNE M. ANDERSON, O.D., F.A.A.O.

This month, Dr. Anderson answers a common question.

Q How do I begin the fitting process for the presbyopic astigmatic patient? - Fla.

A: First, address the patient's astigmatism. Then, choose the method of presbyopic correction. You must correct astigmatism in the following categories of presbyopic patients:

► Spherical lens wearers, in whom the spherical equivalent reduces monocular acuity.

► Those whose sphere value is less than 2x the cylinder value.

► Current toric lens wearers.

Four philosophies enable you to achieve success in fitting soft toric lenses in presbyopic patients:

1. Standard toric monovision. single vision toric O.U.; one for distance and one for near.

2. Modified toric monovision. multifocal toric on one eye; single vision toric (distance or near) on the other eye.

3. Binocular multifocal toric. multifocal toric O.U.; binocular balanced.

4. Enhanced multifocal toric. multifocal toric O.U.; one eye distance or near-enhanced.

Reasons for unsuccessful wear: Undetermined eye dominance, contact lens-induced higher-order aberrations and incompatible lens materials.

Most multifocal lens designs require a designated distance and near eye. Failure to accurately determine "eye dominance" prevents you from finding the successful lens combination.

Multifocal lenses with the near correction in their center induce large amounts of negative spherical aberrations. Near correction in the lens periphery increases positive spherical aberrations. Lens decentration off the pupil's center adds to the higher-order aberrations. Uncorrected astigmatism or excessive toric lens rotation exacerbates these higher-order aberrations.

Patients with tear film insufficiency or allergies may not be able to wear multifocal toric soft lenses due to incompatibility with the currently available lens materials. In these cases, consider monovision with a daily disposable soft toric; monovision or multifocal RGP; or monovision or multifocal hybrid lenses.

Q How do I determine the best lens option for these patients?

A: Perform a careful patient history and lifestyle evaluation. For example, a soccer coach would benefit from multifocal lenses, as they preserve his depth perception.

The currently available options:

► Monovision with soft toric lenses. The ideal patient for this lens is a current distance-only spherical lens-wearer, in whom the spherical equivalent reduces monocular acuity. He may need toric lenses to improve visual acuity (VA) and restore balance. If the spectacle refraction calls for 0.75D to 1.00D of cylinder O.U., apply the toric lens to the dominant eye to improve distance VA or to the non-dominant eye to restore near VA. If the cylinder O.U. is 1.00D or more, the patient may need toric lenses O.U. to improve his sense of balance and adaptation.

► Multifocal toric soft lenses. This option works well in astigmatic patients who have critical distance and near demands and/or who can't adapt to monovision.

► Monovision with GP lenses. Spherical and aspheric GP designs can correct up to 2.75D of cylinder and work well in patients whose cylinder is corneal as well as refractive. Cylinder values beyond 2.75D require a bitoric GP design.

► Multifocal with GP lenses. Current GP wearers do well in this option. The new aspheric multifocal designs incorporate the asphericity on the anterior surface — simplifying the fitting process and reducing corneal molding. Also, new GP materials (i.e. Optimum HR [Contamac] and Paragon HDS HI 1.54 [Paragon Vision Sciences]) with a high-refractive index help enhance the effective add power of the lens.

► Translating design. The ideal patient for this lens has very strict demands for crisp distance and near vision, though doesn't desire intermediate vision. These lenses have a distinct near segment cut into the lens' inferior front surface. Translation is vital in achieving acceptable near acuity with these designs. One caveat: Most are prism ballasted, making rotational instability a possibility.

► SynergEyes Multifocal (SynergEyes, Inc.). This hybrid lens design is ideal for patients unable to acclimate to toric lens monovision and who can't tolerate the switch to GP lenses. The SynergEyes Multifocal controls large amounts of astigmatism, provided the refractive cylinder is less than or equal to corneal cylinder. The design has a front surface near segment in the GP portion's center. Pupil size — in normal room illumination — add power and lifestyle determine the center near segment parameters. The center design allows for customized segment size and add power, while the soft skirt keeps the lens well centered. Further, the lens' spherical back surface minimizes corneal molding.

Because baby boomers comprise a major portion of our population and often require medical eye care, correctly fitting presbyopic astigmatic patients is more of a golden opportunity for your patients and practice than ever before. OM