prescribing for astigmatism
When Soft Toric Lens Wearers Become Presbyopic
BY JULIE A. SCHORNACK, OD, MED
The number of choices available to us for our patients who have visually significant amounts of refractive astigmatism is amazing. For the vast majority of patients, we don't have significant restrictions in the spherical power, cylinder power or cylinder axis parameters available to meet their needs.
However, the emergence of presbyopia can present an added complication to satisfying the needs of soft toric lens patients.
In presbyopic patients who have low refractive cylinder (>1.00D), monovision with toric contact lenses may address their needs nicely. With the loss of stereopsis and the decreased visual overlap that occurs with monovision, all attempts should be made to achieve the best monocular vision possible in each eye.
That being said, don't overlook the value of using monovision with aspheric soft lenses to correct low amounts of astigmatism. Recent studies have concluded that many of the more recent entries into the aspheric soft lens market have an increased capacity for correcting low amounts of refractive cylinder.
In soft toric lens patients who have higher amounts of refractive cylinder, entering into a monovision correction may prove more challenging. With increasing amounts of refractive cylinder, the precision required to match the axis and power is amplified. It's important to ensure that the soft toric lens corrects the cylinder power adequately.
When assessing the soft toric lens performance, check the positioning of the lenses. Any rotational instability or excessive movement on blinking will result in undue fluctuations of visual acuity. This instability combined with the monovision correction could lead to an unsatisfactory visual outcome.
Soft Toric Multifocals
Although many practitioners select monovision as their first mode of correction for soft toric lens-wearing presbyopes, soft toric multifocal contact lenses should not be ignored as an option. Several soft toric multifocal options are available from multiple manufacturers. Although current parameters are somewhat limited, you can obtain the prescriptions of most of your presbyopic soft toric lens patients.
Patients who have an oblique cylinder correcting axis may have the most limited choices. At this time, current parameters limit us from the benefits of more breathable silicone hydrogel materials and more frequent disposability with this lens type. However, careful selection of appropriate patients can make this category of lenses rewarding.
We also need to recognize that a large portion of our soft toric presbyopic contact lens patients have significant intermediate distance demands including computer tasks. A creative approach may be necessary to address intermediate needs. Consider a modified monovision fitting by placing a distance lens on one eye and an intermediate and near multifocal lens on the other eye. Sometimes something as simple as under-minusing the near eye and providing adequate patient education concerning the compromised power can be a great solution.
Ultimately, in our soft toric presbyopic contact lens patients it's important to realize that there's no one right answer. When approaching this patient population, keeping your ears open to individual patient needs and your options as flexible and creative as possible will lead to the most satisfactory outcome for you and your patients. CLS
Dr. Schornack is the associate dean of Clinical Education and serves in the Cornea and Contact Lens Service at the Southern California College of Optometry.