EyeWorld India June 2013 Issue

33 EWAP CAtArACt/IOL June 2013 “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., USA) 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. “So, for instance, if someone has a totally normal optical system, the OPD will print what that eye chart looks like for the patient (which is crisp and clear),” he said. “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., USA) 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, NY, USA) is an emerging technology where we can compare reading speed pre- and post-surgical treatments of FAM Han Bor, MD Senior Consultant & Head, Cataract & Implant Service The Eye Institute @Tan Tock Seng Hospital 11 Jalan Tan Tock Seng, Singapore 308411 Tel. no. +65-6357-7726 Fax no. +65-6357-7718 famhb@singnet.com.sg S nellen acuity has been and still is the gold standard of vision tests. It is a well-established test that is simple to carry out. Minimal instruction is required and it is simple for the patient to be tested. However, real-life vision is a complex process involving the dynamic interplay between our eyes, various structures and the illumination and contrast of objects under diverse environmental conditions. Snellen acuity alone is insufficient to quantify our vision in such broad dynamics. Patients who do badly under Snellen testing would obviously have either refractive errors or other forms of compromised vision. However, patients who score well on the Snellen acuity test may still have visual complaints. Other tests are required to provide an insight into some of these patients’ visual problems. Some of these tests are interactive in nature and measure the patient’s subjective inputs. Low contrast acuity tests and contrast sensitivity tests are useful tests. These measure the resolution (frequency) as well as the contrast acuity of the eye. It provides us with some insight into the patient’s vision under low-light conditions. Some other tests measure glare or straylight in the eye and its impact on vision. Straylight information gives us an idea about the patient’s visual clarity, glare and haloes. Evaluating the ocular wavefront is objective and fast. It provides indirect evidence on visual quality. The visual image can usually be simulated with the acquired aberrations. However, it usually requires the acquisition of sophisticated equipment. I routinely do Snellen acuity tests. It provides an overview of the patient’s vision. A good manifest refraction is essential to exclude refractive errors. If the patient is still unhappy with their vision despite scoring well on Snellen charts, I would carry on to perform the other tests. I would perform Scheimpflug imaging of the cornea followed by an ocular wavefront assessment on a dilated eye. This is to isolate cornea aberrations from ocular aberrations. I would perform low-contrast Snellen acuity or a contrast sensitivity test, with or without glare to assess the patient’s quality of vision. With improved technology and more advanced forms of refractive or vision correction procedures, we need to understand the finer details of vision and develop better ways to analyze and understand the visual process. Editors’ note: Dr. Fam has no financial interests related to his comments. Views from Asia-Pacific 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.” EWAP 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, USA/Hünenberg, Switzerland), Allergan (Irvine, Calif., USA), and Bausch + Lomb (Rochester, NY, USA). 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