prescribing for astigmatism
Correcting Astigmatism With Hybrid Lenses
BY JOHN MARK JACKSON, OD, MS, FAAO
Today we have better options than ever for correcting refractive error, especially for astigmatism correction. GP materials and designs are great and soft torics are usually very stable, even with high prescriptions. However, our usual bag of tricks doesn't always work, and a third option may come to the rescue — hybrid lenses.
Hybrid lenses, with a GP center and hydrogel periphery, are hardly new. The SoftPerm lens (CIBA Vision) has long been available, but its low Dk has limited its use. SynergEyes lenses (SynergEyes, Inc.) offer a higher-Dk option. Although practitioners use these lenses most often for irregular astigmatism (keratoconus, post-surgery, etc.), they can be a great choice for regular astigmatism, too.
When All Else Failed
My patient, a 32-year-old male, wanted to try a different approach for correcting his astigmatism. His spectacle Rx was OD –5.50 –4.25 ×180 and OS –4.75 –3.75 ×177. His K readings were OD 44.00/48.00 @ 090 and OS 43.75/47.00 @ 090. Bitoric GP lenses provided a good fit on his highly toric corneas and his vision was excellent, but he couldn't adapt to the lenses.
The comfort improved when he tried toric hydrogels, but his vision was very unstable. With this much refractive astigmatism, every little bit of rotation was evident to the patient; sometimes he saw 20/20, other times as bad as 20/50.
Figure 1. A SynergEyes lens centered well over the patient's pupil.
Enter the hybrid lens. Because his refractive and corneal astigmatism are a close match, the spherical GP center of the SynergEyes A lens could provide a good visual correction. Lens stability, which would be problematic with a spherical GP by itself, is not a problem with a hybrid lens because the soft skirt keeps the lens centered over the pupil (Figure 1).
We applied a pair of SynergEyes A lenses to test the comfort and vision. He found the initial comfort similar to a hydrogel lens. With a spherical over-refraction, his acuity was OD 20/20 and OS 20/25 and, most importantly, very stable. He was pleased with the initial results. The lenses provided a good fit according the fitting guide, and we ordered SynergEyes A OD 7.4mm (GP)/8.7mm (skirt)/ –4.25D, OS 7.4mm/8.7mm/ –4.00D. At the dispensing visit we experienced similar results with the ordered lenses: good vision and good initial comfort.
Alas, even in case reports things don't always work perfectly; at the follow-up visit we found that after a few hours of wear, the lenses became tight and uncomfortable. We plan to order a second pair with a looser fit. We will likely steepen the GP or the skirt curve, or both. Note that this is opposite to what you would do for standard GP or soft lenses. Hybrid lenses have unique fitting characteristics and you should follow the fitting guide carefully for best results.
Hybrid lenses have great potential for a wide variety of visual needs. Although they're used mostly for difficult fits such as keratoconus, they have great potential to make life better for our regular astigmats as well. CLS
Dr. Jackson is an assistant professor at Southern College of Optometry where he works in the Advanced Contact Lens Service, teaches courses in contact lenses and performs clinical research.