This article is more than 5 years old. Information may no longer be current.
ODs recognize clinical value of color vision testing
The advanced technology is reimbursable and provides an additional piece to the diagnostic puzzle.
Click Here to Manage Email Alerts
Testing for acquired color vision deficiencies is underutilized throughout optometry, practitioners say, despite the fact that it can provide valuable diagnostic information. Cone function loss may be caused by retinal, optic nerve or neurological disorders, in addition to trauma, cataracts and hundreds of common medications and substances.
Two computerized vision tests that provide eye care practitioners with high-tech diagnostic information for children through the elderly are Innova System’s Rabin Cone Test and Konan Medical’s ColorDx.
RCCT
The Rabin Cone Contrast Test (RCCT) is available on two platforms, a 23-inch all-in-one unit and a Microsoft Surface Pro 4 tablet that allows for mobility, Cheryl Nordstrom, Innova president, told Primary Care Optometry News.
She explained how the test works. Patients are presented with a series of letters that isolate the red, blue and green cone cell function, with the colors decreasing in intensity to establish threshold. A threshold value is attained for each cone type and each eye.
“By isolating the function of the three cone types and detecting threshold levels, the RCCT is able to quickly detect degradation in sensitivity,” she said. “Test results are saved and compared to subsequent results to observe progression.”
John A. McCall Jr., OD, a private practitioner and senior vice president of Vision Source, has been using the system since 2014. He explained in an interview with Primary Care Optometry News that the patient is presented with a letter of one color embedded within other colors. “If you see an ‘L’ you push the ‘L’ and the system provides auditory feedback.”
He has his technicians push the buttons for older patients, he noted.
“I am absolutely amazed at the depth and breadth of information it gives you about color vision,” McCall said.
Jerome Sherman, OD, FAAO, who runs a private practice in New York and teaches at the State University of New York College of Optometry, told PCON, “I was intrigued by the concept of combining two important psychophysical tests – color vision and contrast sensitivity – with the hope that additional information about early deficits in the eye, optic nerve and visual pathway can be revealed with this novel device. The emphasis in common disease is for earlier detection and possible intervention, such as in age-related macular degeneration with nonprescription supplements or in glaucoma with topical medications or selective laser trabeculoplasty. The value of the Rabin Cone Contrast Test is its broad-based approach at identifying pathology early.
“Years ago, I examined patients with early damage to their photoreceptors by observing the loss, attenuation or disorganization of the so-called PIL or photoreceptor integrity line, with spectral domain optical coherence tomography (SD-OCT),” Sherman continued. “Such patients nowadays can also be followed with the RCCT, which measures functional degradation of cone cells and of the cone visual pathway. I recommend performing both SD-OCT for structural assessment and the RCCT for functional assessment.”
“We are able to get a baseline with RCCT, like drusen distortion or macular edema...You are better able to chart the progression of disease with this test,” McCall added.
He shared a case where the patient progressed from dry to wet AMD, with visual acuity of 20/200. The patient’s macular threshold was “completely blacked out” on OCT and he had no color vision. After anti-VEGF injections were begun, the swelling improved and vision returned to 20/25. Color vision went back to 40%.
McCall said his clinic screens all patients 30 years and older.
If color dropout exists “you may be missing a disease process,” McCall said. He suspects the ganglion cell complex (GCC) may be affected, which is the first depression in many cases of glaucoma.
A study from Kim and colleagues confirms this link. Researchers found that macular GCC thickness may be an alternative option to retinal nerve fiber layer thickness to evaluate glaucoma.
Another study by Niwa and colleagues concluded that RCCT may be useful in determining color vision deficiency in glaucoma and advancing the understanding of the pathophysiology of damage from glaucoma.
The test, which takes about 3 minutes per eye, picks up small changes to the cones – such as a distortion or disability at a very early stage – that would not be detected by other means, according to McCall.
“If the instrument is used as part of normal patient screening,” Sherman said, “cone and cone pathway deficiencies can be detected, and abnormalities can then be confirmed with other technologies such as OCT, autofluorescence, central fields, micro-perimetry, pattern electroretinograms (pERGs) and visual-evoked potentials (VEPs).”
Sherman said that patients can “easily identify” with this functional test. Those testing positive may be motivated to become more compliant with their recommended nutraceutical program.
“We are especially interested in pointing out to our patients who still insist on smoking that this behavior is often inconsistent with normal color vision,” he added.
Nordstrom added that RCCT testing may also identify patients taking Plaquenil (hydroxychloroquine sulfate, Sanofi-Aventis) doses that are toxic to the macula. However, lenticular changes may degrade the red portion of the spectrum.
McCall said that milky nuclear sclerotic opacity primarily affects blue, and bull’s eye maculopathy affects all three colors.
“To measure the cataract impact specific to each patient,” Nordstrom said, “doctors may use the contrast sensitivity test included in the Rabin cone system.”
She stated that the U.S. Air Force, U.S. Army, U.S. Navy and the Federal Aviation Administration all incorporate RCCT screening into their diagnostics. The RCCT is billed under CPT code 92283, extended color vision, anomaloscope or equivalent.
“I don’t see any reason why the average practice would not want to incorporate the Rabin system for all the information it provides,” McCall said.
ColorDx
ColorDx by Konan is another option for testing color vision.
“We are having to educate the market about the value of testing for acquired vision color deficiencies...as it’s really not taught in many optometry schools,” Ian McMillan, vice president, North American sales and marketing, Konan Medical, told PCON.
He explained that tritan deficiencies are rarely genetic and yet 15% of the population may have this deficiency.
“There is a much lower concentration of ‘S’ cone cells (blue) compared to ‘M’ and ‘L’ cone cells (green and red), so when S cones are affected, for example, due to Plaquenil toxicity or degenerative pathology, the patient may experience a tritan deficiency. It can be a very important sign, and it’s another piece of information in the puzzle,” McMillan explained.
In 2011, Craig Thomas, OD, who has offices in Dallas, began testing with ColorDx. That year Medicare paid for 5,000 color vision tests, according to Thomas. He billed for 50 of them, which represents 1% of the national total.
“I’ve been on a mission, because I felt that I should not be doing 1% for the total of anything. There are 55,000 eye doctors in the country,” Thomas said in an interview. “That told me that most optometrists and ophthalmologists did not understand the clinical value they can get from this test.”
He noted that the ColorDx can be completed on a computer or tablet.
“When you’re trying to diagnose disease, unfortunately, the way we’ve been trained is that the threshold visual field is the go-to test,” Thomas said. “But we know now that visual field, color vision, VEP and ERG are all functional tests, not just visual field. If you really understand that everyone is different, then who is to say that if the visual field is normal that there is nothing wrong with a patient? They could have abnormal color vision, which could be the first sign [of pathology].”
In his practice, rather than performing one function test, Thomas now performs three or four on a patient. Color vision testing has become a component of his overall functional testing. The test has allowed him to make the diagnosis of disease much earlier for some patients, he said.
Thomas highlighted the case of a patient with 20/20 vision and a normal visual field, but elevated pressures. After conducting an OCT, he found a small defect on one eye, and a small defect was also indicated by ColorDx testing. By combining those results with the elevated pressures, he made the diagnosis of glaucoma. “And I didn’t have to wait for a visual field defect to make that diagnosis,” he said.
“I perform this test on anyone that I suspect of potential eye disease,” he continued. “I say that whoever you’d want to run a visual field or OCT scan on you should consider a color vision test. Why wouldn’t you want more information that you cannot get in any other way?”
The test has been accepted for use in the Special Olympics, for Navy pilots and other armed forces, McMillan said. – by Abigail Sutton
- References:
- Kim NR, et al. Br J Ophthalmol. 2010;doi:10.1136/bjo.2010.182493.
- Niwa Y, et al. IOVS. 2014;doi:10.1167/iovs.14-14079.
- For more information:
- John A. McCall Jr., OD, is a PCON Editorial Board member. He can be reached at vsourcejam@aol.com.
- Ian McMillan can be reached at imcmillan@konanmedical.com.
- Cheryl Nordstrom can be reached at cheryl@innovasystemsusa.com.
- Jerome Sherman, OD, FAAO, is a PCON Editorial Board member. He can be reached at j.sherman@sunyopt.edu.
- Craig Thomas, OD, can be reached at thpckc@yahoo.com.
Disclosures: McCall is senior vice president of vendor relations for Vision Source. McMillan is an employee of Konan Medical. Nordstrom is the owner of Innova Systems. Sherman is a consultant to Innova. Thomas is a paid consultant for Konan Medical USA.