prescribing for presbyopia
Managing the Post-Refractive Surgery Presbyope
BY DAVID W. HANSEN, OD
As refractive surgery procedures become more frequently utilized by the presbyopic population, we will be faced with accommodating their postoperative needs. And even though new technologies will be at our fingertips, it's important that we don't forget the previous workhorse designs that have worked well for us in the past.
Post-Refractive Surgery Options
Once a cornea is altered by refractive surgery, analyze it carefully before prescribing any new presbyopic alternatives.
Corneal topography -- Ideally, corneal topography should be a standard clinical procedure used both pre- and postoperatively to assist you in your evaluation of patients who require contact lenses to supplement their visual requirements. As refractive procedures become more accurate, new multifocal designs will also surface.
Multifocal lens designs -- Corneal topographers equipped with software to simulate the contact lens on the cornea with fluorescein can be utilized to fit multifocal designs before applying a diagnostic contact lens to the eye. This saves chair time for these unusual corneas, and by changing parameters in the simulation software, it helps foster communication with the laboratory when designing the lens.
Currently, aspheric multifocal contact lenses offer a unique option for post-LASIK presbyopes. Many of these lenses have been fit steeper than "flat K" by 2.00D to 4.00D. The fluorescein pattern on these corneas produces a central pooling that looks exaggerated due to the flattening of the central cornea. Vaulting the central zone without causing a "seal-off" of oxygen to the cornea is of prime concern.
It may be necessary to design the lens utilizing the preoperative corneal data to establish a reference central "K."
If the pre- and postoperative astigmatism is similar, use the original corneal measurements as your baseline data for fitting the lens. Pay special attention to the peripheral corneal topography to assure a good lens-to-cornea relationship with good vertical excursion movements.
Reverse geometry designs -- To accommodate the plateau contour of the cornea resulting from refractive surgery, try fitting a reverse geometry contact lens. Reverse geometry designs are ideal because the secondary curve is steeper than the base curve, thus facilitating lens centration.
To determine the base curve of the lens, select the average corneal curve over the 6.0mm -7.0mm plateau cap caused by the "surgery zone."
Corneal topography using the numerical map is helpful in determining the initial "secondary curves" that will parallel the cornea to give a good cornea-lens relationship. A concentric bifocal lens design is indicated for these situations. Translation of the bifocal lens across the center "cap" is crucial for success, and it may be necessary to alter the overall lens diameter or secondary curves to assist the movement.
New Designs and Technology
The contact lens industry will continue to provide us with new options for the "I don't want to wear eyeglasses" generation. Therefore, you must always be prepared to assist your presbyopic patients by staying aware of all the options available to them.
Dr. Hansen, a diplomate and fellow of the American Academy of Optometry, is in private practice in Des Moines, Iowa.