DALLAS – A battery of smartphone tests have been developed to help clinicians detect and monitor eye changes in MS patients.
At a meeting of the Americas Committee for Treatment and Research in Multiple Sclerosis,, said that there are two main high priority gaps to fill when it comes to better understanding the effects of MS on vision. “One, I think we need a way for early detection of visual pathway disturbances after either an acute clinical event or a subclinical event,” said Dr. Kardon, professor of neuro-ophthalmology at the University of Iowa, Iowa City. “Two, we need to monitor changes in the visual pathway over time in MS patients and capture variations due to changes in nerve conduction. The idea is, can we have a suite of smartphone tests that you can use in the clinic, but the patient can also use at home unsupervised, to get a time domain, so if there are fluctuations of core body temperature due to myelination, or subclinical changes going on, could we detect it earlier and monitor these patients? That’s the motivation.”
Although use of smartphone technology and mobile devices are emerging in health care settings, most of this technology is used sparingly in vision testing, mostly due to a lack of rigorous calibration of instruments and validation, said Dr. Kardon, who also directs the Iowa City VA Center for Prevention and Treatment of Visual Loss. To make a visual smartphone test viable, he continued, the visual output of the device must match the intended input in terms of multiple parameters (technical validation). Important parameters for vision tests include brightness, luminance, spatial resolution, and temporal resolution. Confounding variables include ambient lighting and viewing distance.
In his work with researchers fromin Denmark, Dr. Kardon has developed four smartphone visual tests intended to be intuitive for patients. “We didn’t want something that was going to take more than 15 seconds,” he said. The visual tests include:
1. Critical flicker fusion, a test of optic nerve conduction. “This tests how well you can see a light flickering at a given temporal frequency at different levels of contrast, or how fast it can flicker before you don’t see a flicker anymore,” Dr. Kardon said. “The user sees spots that are flickering and just touches the ones they perceive to be flickering; they eliminate them by touching them.” When the test ends, the software “brackets what they did to a finer scale, and it finds the contrast at which that flicker wasn’t perceived anymore.”
2. The Landolt C visual acuity test. For this, the user must indicate the direction of the gap in the ring in a forced-choice task. “The user touches which arrow on the screen is pointing to where the location of the break in the Landolt C is perceived,” Dr. Kardon said. The Landolt C becomes progressively smaller until the location of the break can no longer be seen. “It’s pretty simple, and it finds the smallest size of the ‘C’ at which you’re making mistakes about 50% of the time, which is the threshold value for visual acuity,” he said.
3. Contrast sensitivity test at a fixed spatial frequency. “In this test, we fix the size of the letter to a large size, so spatial frequency is not at play, and we vary the contrast,” he said. “Users push the arrow wherever they see the break.” The contrast between the “C” and the background is sequentially reduced until a threshold is determined for the lowest contrast at which the location of the break in the “C” can still be observed.
4. Contrast sensitivity test at different spatial frequencies. This measure, also known as a vanishing optotype, is a line drawing of an object on a smooth, diffuse grayscale background. By altering the line properties used to define the shape of the vanishing optotype, one can vary its spatial frequency and contrast independent of target size. “This makes it an easy test because what the patient is asked to do is to touch wherever they see an object on the screen to eliminate it from the series of optotypes on the screen,” Dr. Kardon said. “The test is very fast, very intuitive.”
The researchers piloted use of these tests in aof 104 age-matched control subjects and 117 MS patients. Of the 117 MS patients, 74 had a history of optic neuritis and 43 did not. The four tests were used in conjunction with standardized assessments, including the near-contrast acuity card test at 2.5%, the distant Early Treatment Diabetic Retinopathy Study (ETDRS) acuity test, as well as optical coherence tomography (OCT) of the retinal nerve fiber layer and ganglion cell layer thickness. Dr. Kardon and his colleagues found that when clinicians used a large target and varied the contrast, the test “did very well at differentiating normal from eyes with either previous optic neuritis or no previous optic neuritis,” he said. “It also differentiated eyes with previous optic neuritis and those with no optic neuritis. The visual acuity test didn’t perform as well because this is a near test. What we discovered afterward is that even at a fixed distance, many people who are presbyopic, or don’t have their optimal near correction, don’t do so well, because you’re testing spatial acuity. That’s a warning sign for future tests. You have to be careful as to how these are interpreted if they don’t have their best correction at near.”
Results from the critical flicker fusions tests were significant, except that they didn’t differentiate eyes affected by optic neuritis from those that weren’t. “The reason is that conduction was down in all of those eyes, so the combination of using contrast sensitivity and flicker fusion may not only help you diagnose MS, but whether that eye had been involved with optic neuritis before,” Dr. Kardon said. To date, he and his colleagues have completed technical validation of temporal frequency and contrast parameters. They’ve also completed preliminary investigations for determining test-retest variability, blurring effects, binocular summation effects, and quantification of normative ranges and abnormal subject data.
“A benefit of smartphone testing in MS is that visual dysfunction can be detected, leading to earlier interventions,” Dr. Kardon concluded. “We can study this on a time scale that wasn’t previously available. Wouldn’t you like to know on a daily or even a weekly basis what the fluctuations are in a home environment for MS patients? It’s low-cost, large-scale, and enables you to study genotype-phenotype comparisons.”
Going forward, Dr. Kardon and his colleagues have developed video cameras that go around the periphery of the iPad that can assess pupil and ocular motility, as well as eyelid and facial features in real time. He disclosed that he has received funding from the National Eye Institute, the Department of Defense, and from VA Rehabilitation Research and Development. He was also a member of the Novartis steering committee for the OCTiMS study and is a cofounder of MedFace and FaceX.