prescribing for presbyopia
Multifocals for Keratoconus and Those "Other" Corneas
BY DAVID W. HANSEN, OD, FAAO
I have maintained that presbyopic patients who have corneal or optical conditions should have the advantage of wearing bifocal and multifocal contact lens designs. New diagnostic procedures including corneal topography and wavefront technology have helped us identify keratoconus and other corneal abnormalities. The contact lens manufacturers have also made improvements with bifocal contact lenses.
Getting Topographical Help
Most corneal topographers provide useful data for determining shape factors, corneal irregularity measurements, simulated central and peripheral keratometric readings, apex of the cornea and comparison studies for assisting the fit of these unusual corneal shapes.
These instruments are increasingly a necessity for all contact lens practitioners. In my opinion, you can't fit and prescribe special lens designs without using topographical devices. They can predict the designs you should use, assist in fitting the unusual cornea and help you to configure, manage and modify the contact lens.
Figuring Out Where to Start
The evolution of fitting keratoconus, pellucid marginal degeneration, warped corneas, irregular corneas, post keratoplasty and post refractive surgery patients has advanced significantly in the past few years. Combined with new manufacturing techniques and space-age materials, special designs have provided new comfort and precise visual acuity for patients who have compromised corneas.
The Rose K contact lens design, which is distributed now throughout the United States by Blanchard Contact Lens, Inc., was a welcome relief to practitioners who struggled with the many options for keratoconus. This scientific philosophy provides excellent comfort and sharper clarity for patients and is reproducible because of computerized manufacturing technology.
Lens Dynamics, Inc. now manufactures the newest generation of GP lens designs for abnormal corneas using a family of lenses called the Dyna Intra-Limbal series. The designs allow you to fit most special corneas, from "nipple" keratoconus to traumatic injuries and post-refractive corneas that involve the entire corneal surface.
The computerized peripheral system and the various contact lens diameters available provide improved comfort and more accurate acuity.
Once you've successfully fit these "challenged corneal conditions" with single-vision contact lenses, you should consider the presbyope's reading requirements. If the posterior surface of the contact lens fits comfortably, have the lab polish the anterior surface with an aspheric curve. With the appropriate asphericity you can generate up to +2.00D of add power. Combined with the posterior peripheral curve system, it's common to achieve excellent success for most presbyopes -- even those over the age of 50.
Hyper-Dk materials provide the maximum physiological protection for the cornea. Wettability and hydrophilic properties are other considerations when selecting appropriate materials. Therefore, I suggest using the Menicon Z material (Menicon), which is the only GP material that is FDA approved for 30 days of continuous wear. The Intra-Limbal series, with this material, will be another addition for fitting patient who have unusual corneas.
Keep Forging Ahead
We should continue to provide excellent binocularity with multifocal designs for all patients, including those who have unusual corneal malformations such as keratoconus, and never compromise our goals and strategies.
Dr. Hansen, a diplomate and fellow of the American Academy of Optometry, is in private practice in Des Moines, Iowa.