HYBRID LENSES

Myopic Shift Secondary to Hybrid Lens Wear

This case report presents an unexpected result of hybrid lens wear that may be worth a second look.

By Dustin Gardner, OD, & Aaron Zimmerman, OD, MS, FAAO

	Dr. Gardner is the Cornea and Contact Lens Fellow at The Ohio State University College of Optometry. He can be reached at dgardner@optometry.osu.edu.
	Dr. Zimmerman is an assistant clinical professor of optometry at The Ohio University College of Optometry and associate chief of the contact lens clinic. He can be reached at azimmerman@optometry.osu.edu.

Hybrid contact lenses have been around for well over 20 years and historically have been indicated for corneal ectasias such as keratoconus (Little, 1971; Rubinstein and Sud, 1999). These lenses consist of a GP center surrounded by a soft skirt. The GP center allows for lacrimal lens correction of corneal irregularity, while the soft skirt encourages lens stability and typically provides better comfort compared to corneal GP contact lenses.

Recent material enhancements have allowed hybrid lenses to be manufactured with much higher oxygen transmissibility profiles, and new lens design features have helped to prevent these lenses from tightening up on the ocular surface. SynergEyes, Inc. introduced its Duette hybrid lens design in late 2010 for individuals who have astigmatism in which the corneal cylinder power closely matches the spectacle power.

An unintended complication of contact lens wear is corneal warpage, affecting approximately 12 percent of all lens wearers (Wang, 2002). Ideally, corneal warpage would occur in a controlled manner such as with orthokeratology (Barr et al, 2003). The following is a case report in which midperipheral corneal flattening has occurred secondary to wearing the Duette hybrid lens, causing a myopic shift.

Case Report

A 25-year-old Caucasian male with a history of moderate myopia and low astigmatism presented to the contact lens clinic specifically for a Duette fitting. History and ocular health evaluation were unremarkable. Entering visual acuity was 20/20 OD and OS, but the patient reported some issues with glare/halos, especially at night. Manifest refraction was –5.25 –1.25 x 164 OD and –5.50 –0.50 x 022 OS. Best-corrected visual acuities were 20/15 OD and OS. Simulated K values were 42.0D/43.2D @ 82 OD and 41.9D/43.0D @ 108 OS. Figures 1 and 2 show the patient's topography maps prior to the hybrid lens fitting.

Figure 1. Right corneal topography prior to hybrid lens fitting.

Figure 2. Left corneal topography prior to hybrid lens fitting.

The fitting guide indicated that we should use a 7.9mm base curve with a medium skirt OD and OS. Evaluation of the fluorescein pattern OD showed proper alignment and good centration; the patient reported good comfort, and with over-refraction he was able to see a clear 20/15. Evaluation of the fluorescein pattern OS showed proper alignment as well, but the lens decentered inferior-temporally. With over-refraction the patient was correctable to 20/20, but due to the lens decentration the patient reported haze and slight lens awareness. To improve lens centration, we fit a 7.9mm base curve with the steep skirt. This lens centered much better, provided better comfort, and eliminated the halos. With over-refraction the patient's visual acuity was 20/15. Slight central pooling was noted, but the pupil was still visible. We ordered these contact lenses with the appropriate lens powers and then dispensed.

Two months later, the patient returned to the clinic with a complaint about blurred vision through his glasses following end-of-day lens removal. However, the patient did not have any visual complaints while wearing the Duette lenses. Entering visual acuities with the lenses were 20/15– OD and 20/15 OS. We removed the lenses and performed manifest refraction. For the right eye the manifest refraction was now –6.25 –0.50 x 155 and for the left eye it was –6.50DS, which achieved a best-corrected acuity of 20/15 OD and OS. Taking the previous manifest refraction and comparing spherical equivalents to that day's end point revealed a –0.50D OD and –0.75D OS myopic shift in refractive error over the two months. Figures 3 and 4 show the topography results from that visit.

Figure 3. Topography of the right eye following two months of wearing the Duette lens on a daily wear schedule.

Figure 4. Topography of the left eye following two months of wearing the Duette lens on a daily wear schedule.

Central simulated K values were similar to pre-lens values at this visit, but a clear ring of midperipheral flattening was evident on each ocular surface. The pattern was the opposite of what you would expect to see with a myopic orthokeratology treatment. Moving the measuring curser to the midperipheral area in question in both the initial topography maps and the new topography maps showed approximately 4.00D of flattening. With the lenses removed, Figures 5 and 6 show clear corneal impression rings on each eye.

Figure 5. Retro-illumination of the corneal impression ring for the left eye.

Figure 6. Retro-illumination of the corneal impression ring for the right eye.

We then reapplied the Duette lenses for fluorescein evaluation. The central alignment seemed to be a little steep OD and OS, but not significantly different from the fitting guide's suggested ideal fit photo, and lens movement was reduced to less than 0.25mm OD and OS. Figures 7 and 8 were taken of the fit at the follow-up visit. It was evident that the lens was fitting tightly just beyond the GP-soft skirt junction. This possibly occurred as the lenses settled into the conjunctival tissue.

Figure 7. Fluorescein pattern of the right lens at the two-month visit. Notice minimal fluorescein in the periphery (arrow) of the GP portion of the lens.

Figure 8. Fluorescein pattern of the left lens at the two-month visit. Although more fluorescein was present peripherally, there is evidence of slight bearing (arrow).

We educated the patient on the nature of the blurred vision that occurred following lens removal. The lenses clearly were not causing physiological harm to the cornea, but the blurred vision without the contact lenses was a concern for the patient. Therefore it was decided that he should temporarily discontinue lens wear. The patient returned two weeks following lens wear cessation, at which time the topography maps (Figures 9 and 10) showed a noticeable decrease in the midperipheral flattening, and the manifest refraction was returning to baseline.

Figure 9. Two weeks following lens cessation of the right eye. There is noticeably less midperipheral flattening.

Figure 10. Two weeks following lens cessation of the left eye. There is noticeably less midperipheral flattening.

Conclusion

The Duette fitting guide states that the central GP portion should be lifted off the cornea by the silicone hydrogel skirt and never interact with the surface of the eye. At the initial fit, the fluorescein pattern closely reflected what was described in the fitting guide. Following the dispensing visit, the lenses showed good fluorescein patterns and appropriate lens movement. Over the next two months the lenses began to settle into the conjunctiva, and this settling seemed to be the cause of the midperipheral corneal flattening.

If this is a recurring issue with the Duette hybrid lens design, discussions of how to manage the midperipheral flattening should occur. It is also possible that the Duette design could be utilized for off-label applications such as orthokeratology for low hyperopia. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #199.