continuous wear colloquy
Unintended Ortho-k Effects From Silicone Hydrogel
BY LORETTA B. SZCZOTKA-FLYNN, OD, MS, FAAO
Recently, clinicians have drawn attention to unintended orthokeratology effects caused by silicone hydrogel contact lenses. These changes are characterized by large hyperopic shifts and typically occur in extended wear patients who have high refractive errors. They're reversible if the patient discontinues lens wear or if you refit him into a lower modulus lens material.
Figure 1. Topography OD shows an
ortho-k-like oblate pattern.
A Revealing Case
In February 2003, I refit a female patient from conventional soft toric contact lenses into lotrafilcon A (Focus Night & Day, CIBA Vision) lenses for daily wear because I noted significant neovascularization and hypoxia with her
low-Dk lenses. Her initial clinical data were:
- Manifest Refraction: OD 10.25 D, OS 9.75 2.50 x180
- Keratometry: OD 45.87 @ 090/46.50 @ 180; OS 46.75 @ 010/48.87 @ 100
After 14 months of wearing 8.4mm base curve, 9.00D Focus Night & Day lenses in each eye, the neovascularization had completely regressed. However, she complained of poor distance vision, which she could improve by wearing reading glasses over her contact lenses. Her refraction was now OD 7.50 0.75 x058, OS 7.75 1.00 x030. Figures 1 and 2 show her post-fitting maps.
We can explain the refractive shifts when we review the topographic findings. Note that the right eye has an
ortho-k-like oblate topographic pattern with central flattening and midperipheral
steepening. The left eye retained a prolate shape, but has significantly flatter keratometric readings than it did at baseline.
Searching for Answers
The mechanism behind such corneal shape changes remains unknown, and clinicians have presented only anecdotal reports of this effect. However, most agree that evidence points toward a corneal molding effect. Some postulate that wearing silicone hydrogel lenses inside-out could explain this finding. In fact, a Focus Night & Day contact lens worn inside out creates an
ortho-k-like post-lens tear layer when viewed with fluorescein.
Figure 2. Topography OS shows a much flatter cornea than
A small study presented at ARVO recently by Tahhan et al clarified that some patients could wear inverted silicone hydrogel lenses without sacrificing comfort or vision.
Educating Your Patients
So, if a patient presents with similar unintended corneal flattening, should you assume it's because of incorrect lens application?
It's premature to suggest an inside-out contact lens is the only cause. However, I'd emphasize correct lens application and monitor him accordingly.
Szczotka-Flynn is an associate professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens
Service at University Hospitals of Cleveland.
Contact Lens Spectrum, Issue: August 2004