EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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70 EW CATARACT March 2013 Determining continued from page 69 tients who have difficulty driving at night or during other low contrast circumstances, and reading charts alone cannot address those quality of vision issues. "A number of my early cataract and dysfunctional lens syndrome patients have stopped driving at night because of difficulty with vision in this low contrast circumstance, but they may still have very good best corrected Snellen acuity," he said. Contrast sensitivity has become Dr. Donnenfeld's "gold standard" for vision testing "because it measures vision under adverse circumstances such as glare and scotopic conditions." He noted almost all of the current laser and IOL evaluation studies are incorporating contrast sensitivity testing to evaluate quality of vision. "There are plenty of situations that can affect contrast sensitivity— a really bad ocular surface, irregular cornea, cataract, the rings in a multifocal lens, higher order aberrations, etc. There are all kinds of layers of what could happen," Dr. Devgan said. "We are working on advanced functional vision testing modalities and more widespread acceptance of the other objective measures of quality of vision and functionality," Dr. Waring said. Evaluating the ocular surface "can also be a strong indicator of contrast sensitivity," Dr. Donnenfeld said. "I use topography on these patients to look for dropout or significant irregularity." What to use Dr. Colenbrander has designed a series of mixed contrast sensitivity charts that mix letter chart acuity with contrast sensitivity. Other tests are "useful to find some of the many causes of contrast loss," but his cards can measure the consequence of contrast loss. "These allow clinicians and researchers to compare low contrast performance with high contrast performance in the patient's own eye," he said. He likens this to measuring a patient's blood pressure and comparing it to that same patient's blood pressure from the previous week, month, or year, which is more informative than the traditional tests, which compare it only to the general population's average. Dr. Devgan uses an OPD Scan III (Nidek, Fremont, Calif.) to more fully evaluate the patient's vision including higher order aberrations, which can reduce image quality. The aberrometer can produce a simulated eye chart or image that simulates what the patient sees in terms of acuity, contrast, and aberrations such as ghosting. 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"But if the patient has bad aberrations from decentered LASIK or corneal scarring, the system will print out an eye chart with ghosting and distorted letters. The clinician is able to see what the patient is seeing." Dr. Donnenfeld uses the WaveScan (Abbott Medical Optics, Santa Ana, Calif.) to determine higher and lower order aberrations and point spread function. "It gives you a way to verify objectively what the patient's subjective complaints are," he said. Dr. Waring believes the quantification of light scatter "is an emerging field of interest as another ancillary measurement for visual quality," he said. The Visiometrics OQAS (Optical Quality Analysis System, Terrassa, Spain) is a double-pass wavefront device that produces an "objective measurement of forward light scatter and resultant point spread function based," Dr. Waring said. "It's a great tool to pick up on a dysfunctional lens. It will find the light scatter that results from nuclear sclerosis or cortical changes in a patient with snellen acuity of 20/20." "We are also working on objective measurements of reading speed —another real world assessment of functional vision. The Salzburg Reading Desk (SRD Vision, New York) is an emerging technology where we can compare reading speed pre- and post-surgical treatments of presbyopia," he said. Dr. Waring uses Scheimpflug imaging and densitometry graphs generated from light scatter (Figure 1). "Even something as simple as a slit lamp photo can document lens changes that affect vision," he said. "I educate my patients by showing them these qualitative and quantitative findings, and they more readily understand why their vision has changed." The bottom line? If patients note they can read the Snellen letters but the letters aren't sharp or clear, "you have to move to something else," Dr. Devgan said. "What we now know about visual acuity means simple measures like Snellen don't tell the whole story," Dr. Donnenfeld said. "I recommend clinicians don't tell patients that they should be happy with 20/20 vision. The best indicator of vision is the patient's subjective perception of vision. Snellen doesn't determine happiness." EW Editors' note: Drs. Colenbrander and Devgan have no financial interests related to this article. Dr. Donnenfeld has financial interests with Abbott Medical Optics, Alcon (Fort Worth, Texas), Allergan (Irvine, Calif.), and Bausch + Lomb (Rochester, N.Y.). Dr. Waring has financial interests with SRD. Contact information Colenbrander: gus@ski.org Devgan: Devgan@gmail.com Donnenfeld: ericdonnenfeld@gmail.com Waring: georgewaring@me.com