Prescribing for Astigmatism

Contact Lenses for Astigmatic Presbyopes

By Thomas G. Quinn, OD, MS, FAAO

When I give presentations on multifocal contact lenses, the most common question I'm asked is: What do you do for astigmatic presbyopes? Here's how I manage this growing population.

If a patient is already accustomed to wearing toric soft lenses, your first impulse may be to prescribe toric soft monovision, but numerous studies have demonstrated that patients prefer multifocal vision over monovision (Johnson et al, 2000; Rajagopalan et al, 2006; Richdale et al, 2006; Situ et al, 2003). In fact, as noted in the May Contact Lens Design & Materials column, a number of toric soft multifocals in hydrogel and silicone hydrogel materials are available today (Watanabe, 2012).

Fitting toric soft multifocals can be time-consuming, mostly because fitting sets are not generally available, and we must order diagnostic lenses. I have found the following process efficient.

Start With Astigmatism

A key first step in fitting toric soft multifocals is to ensure proper astigmatic correction. To save time, I often order initial diagnostic lenses with the astigmatic axis equal to and 10 degrees to either side of the spectacle cylinder axis. At dispensing, if I note that lens rotation is consistently in the same direction and the same degree, I can dispense one of the alternative axes. Of course, if the lens rotates more than 10 degrees, I order a new diagnostic lens with the appropriate axis. If the rotation is not stable, a different base curve or lens design is necessary.

Conclude With Presbyopia

If visual complaints persist after the astigmatic error is properly corrected, I focus on modifying the presbyopic powers. In general, to solve distance-vision complaints, increase distance minus or decrease the add in the dominant eye. To solve near-vision complaints, do the opposite: decrease distance minus (increase plus) or increase the add in the nondominant eye. Be sure to follow the manufacturer's fitting guide, as some designs employ other problem-solving strategies.

When Refractive Cylinder Equals Corneal Cylinder

When the vertexed refractive astigmatism matches the corneal cylinder, GP optics will correct astigmatism, presbyopia, and any distance spherical error. Such optics are available in corneal and scleral GPs and hybrid lenses.

• Corneal GP Multifocals These lenses perform exceptionally well compared to soft multifocals and progressive-addition spectacle lenses (Rajagopalan et al, 2006). Manufacturing advances allow for fabrication of center-distance and center-near designs by using both spherical and aspheric optics on the front and/or back surfaces of lenses. Manipulation of these curves, combined with adjustable zone sizes, offers a wide range of designs.
• Scleral GP Lenses Some patients find it difficult to adapt to a corneal GP lens, particularly if they are already wearing soft lenses (Michaud et al, 2009). Scleral GP lenses offer GP optics with exceptional comfort. These designs are increasingly available with multifocal optics. See the February issue (Potter, 2012) for what is currently available.
• Hybrid Multifocals These designs have great potential to meet patients' visual and comfort needs. In my November 2012 Prescribing for Presbyopia column, I will discuss the nuances of fitting the Duette Multifocal (SynergEyes). CLS

For references, please visit www.clspectrum.com/references.asp and click on document #201.