letters to the editor
Don't Forget UVR Protection for Aphakes I read with great interest the January Pediatric and Teen CL Care column, "Key Strategies to Manage Pediatric Aphakes," by Jeff Walline, OD, PhD, and Marjorie Rah, OD, PhD. This is an important and timely topic because the very young members of our society must have their refractive error corrected to develop their vision to its full potential.
It also brings to mind that there are instances in cataract surgery when an intraocular lens (IOL) is contraindicated. The contact lens options described in this column were informative and helpful to practitioners engaged in vision care of this kind. However, one important omission precipitated this letter, and this omission was protection from ultraviolet radiation (UVR).
The crystalline lens is the main UVR filter in the eye, and when this organ is removed a suitable filter must be introduced to protect the retina. The unprotected retina of an aphake is very vulnerable to the UV band and, if exposed to a suprathreshold dose, solar retinitis will ensue. Such an overdose of UVR is possible by simply being outdoors.
The other ocular UVR filter, the cornea, is transparent to the complete UVA band and filters out 50 percent of the UVR only at 315nm. The cornea becomes opaque to UVR at 290nm. The UVB band (315nm to 290nm) that will thus reach the retina is toxic. In contrast, the crystalline lens blocks 50 percent of the UVR at 390nm and 100 percent at 360nm. It follows that when we remove the most effective ocular UVR filter, it must be replaced by a man-made one — either a spectacle lens or a contact lens with appropriate UV blocking.
Unfortunately, there are no UVR-blocking soft contact lenses in the high-plus range suitable for correcting aphakes. Therefore, aphakes will need some form of spectacle correction. In adult aphakes I generally prefer a UVR-blocking spherical soft contact lens in the plus range, and I correct residual spherical and astigmatic error with a progressive ophthalmic lens. GP lenses that feature a UVR blocker do not cover the entire cornea and, therefore, are not sufficient as the only UVR filter.
The ocular light and UVR transmission curve is not new knowledge and is available in textbooks such as Environmental Vision (Pitts and Kleinstein, 1993) and Clinical Ocular Anatomy and Physiology, 16th Edition (Bergmanson, 2009). A supplement to the November 2007 issue of Contact Lens Spectrum titled, "Raising Awareness of the Ocular Dangers of UV Radiation Exposure and the Need for Protection," also discusses this topic.
We at the Texas Eye Research and Technology Center have established with greater precision the transmission curve for each of the ocular media components and the intact eye. This work is published in Physiological Measurement (Walsh, Bergmanson, Koehler, Harmey, 2008).
Over the last few years I have seen aphakic patients in our clinics who did not undergo IOL implantation for a variety of reasons. Without exception, these patients had not been prescribed UVR protection in any form despite living in Texas, a UVR-intense region of the United States. What is perhaps worse, all of them had been seen by multiple practitioners — both optometrists and ophthalmologists — who all had failed to provide UVR protection of any kind. In addition, these patients had not been informed of or counseled about their vulnerability. I can only conclude that there is widespread ignorance about this important aspect of eye care.
Jan Bergmanson, OD, PhD, PhD h.c., DSc
Director, Texas Eye Research and
University of Houston College of
For references, please visit www.clspectrum.com/references.asp and click on document #161.
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Contact Lens Spectrum, Issue: April 2009