Vision Testing That's Less Black and White
Most of us likely remember having our vision tested as kids. We went to the doctor, stood behind a duct-tape line, covered one eye, and read what we saw. The gigantic “E” at the top was pretty simple for most of us to make out. Those of us who were lucky, however, continued to read down the list well enough to be told that we had “perfect” 20/20 vision. We were then sent on our merry ways, relieved that we had avoided the embarrassment and indignation of — gasp — having to wear glasses.
As adults, most of us continue to have our vision tested in this fashion. Now, however, many of us know our vision is barely sufficient, if that, even though the test may tell us it’s still “perfect” after all these years. So what’s the problem?
Here’s the thing: the chart we all know so well— the Snellen chart— is the oldest diagnostic test still widely used in the 21st century. It was developed in 1862 by a Dutch doctor, Herman Snellen. That’s right. With all of the advances in eye care, the way your vision is tested is still decidedly old school.
It’s fair enough to wonder why that matters. Sure, the Snellen chart is an oldie, but can’t it also be a goodie? Many people, including an increasing number of reputable medical professionals, believe the answer is no.
Sorry, Dr. Snellen.
Many eye care professionals are now testing not only the ability of patients to focus on objects like that big “E” on the Snellen chart, but also their visual functioning in situations that are less black and white, as it were. This new method is called contrast sensitivity testing.
Contrast sensitivity refers to a person’s ability to discern the differences in brightness that separate objects from their background. Using contrast sensitivity testing, physicians are better able to measure — and ultimately treat — visual errors. These errors are not identified by the Snellen chart, but ultimately prevent a person from seeing properly.
“The bottom line is that 20/20 is not enough,” says Dr. Arthur P. Ginsburg, a pioneer of vision testing technologies since the late 1970s and the developer of the Functional Acuity Contrast Test (F.A.C.T.™), which measures contrast sensitivity.
Dr. Ginsburg compares vision to an orchestra. Like an orchestra, he says, vision is multilayered and dynamic; one could never fully understand an orchestra’s talents by evaluating only a single instrument. Likewise, one cannot understand one’s visual ability by measuring only the ability to distinguish black letters on a white background. Most of the objects we see every day are much larger and don’t have the same dramatic contrast with their environment as the letters on the Snellen chart.
Measuring contrast sensitivity is thought to be especially important for cataract patients who are going to have their natural lenses replaced with intraocular lens implants, as well as LASIK and other refractive surgery patients. When contrast sensitivity is tested, physicians gain a deeper, more detailed understanding of a patient’s vision. Patients, meanwhile, develop a better understanding of their visual difficulties and post-surgical results.
“There is so much press these days assessing the quality of vision after refractive surgery,” says Dr. Jim Lewis, who tests his patients’ contrast sensitivity with a device incorporating Dr. Ginsburg’s F.A.C.T.™ method. “It is very difficult to tell the science from the hype. This [device] will allow us to tell who is telling the truth.”
The philosophy behind this form of vision testing arises from what is known in ophthalmology circles as the channel model. In this model, the eye uses several different methods to create a cohesive image from a variety of visual data. Testing how the elements of a person’s vision combine in both high and low light situations is the key to contrast sensitivity testing.
“Your refraction is one number — 20/20 or 20/30, for example,” says Dr. Ginsburg. “The problem with that number is that it is only measuring one size of cell in the eye that is processing what we see.”
Using objects of varying size and contrast, as well as different glare levels to replicate both daytime and nighttime conditions, contrast sensitivity testing allows Dr. Lewis and others to more accurately measure the degree to which a patient’s vision helps — or hinders — their everyday functioning. He believes that this form of testing provides diagnoses that are much more refined than standard testing allows.
I think Dr. Snellen would approve.
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