An investigational virtual reality oculokinetic perimetry (VR-OKP) platform is showing promise for overcoming many of the limitations that accompany standard perimetry.
Yvonne Ou, MD, associate professor of ophthalmology and co-director, Glaucoma Service, University of California San Francisco (UCSF), outlined the new platform at the 23rd annual Glaucoma Symposium, held during the 2019 Glaucoma 360 meeting in San Francisco.
“The virtual reality test has a built-in lighting environment and utilizes the foveation reflex,” explained Dr. Ou. “In addition, it can facilitate more frequent testing because it is low cost, eliminates the need for a highly skilled examiner, avoids some of the ergo-nomics issues that can make conventional testing difficult, and may eventually be available for home testing.”
OKP was first described in the 1980s by Bertil Damato, MD, whose motivation was to create a method of visual field examination that could be done by a patient without supervision, using only a paper test chart, a record sheet, and a pencil. His inspiration was to develop a test that would be analogous to the Amsler Grid Test for macular degeneration in terms of allowing at-risk patients to perform at-home functional testing, said Dr. Ou.
OKP utilizes eye movement rather than a moving test target to map out blind spots. It was first created as a paper test, but later it was developed as a computerized version, a web-based version, and a pediatric version.
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The VR version was developed in collaboration with Vivid Vision as an industry partner and is done using a wireless head-mounted device. Subjects learn to do the test-ing using self-paced automated instructions.
Because the test is done in a virtual environment, it eliminates the need to control for lighting and distractions from the surrounding environment.
Because the patient’s eye is moving, the testing utilizes the foveation reflex, and compared with standard perimetry, it potentially reduces user fatigue.
The current VR-OKP test uses suprathreshold testing, but a threshold testing module is also under development.
To perform the test, the patient uses head movements to translocate a “head cursor” so that it lies within a circular fixation target. Once that is done, another stimulus appears, and the patient is tasked to move the head cursor to the new stimulus. These steps are repeated until the test is completed.
The testing software allows on-the-fly customization of various features, such as the layout (e.g., 30-2 or 24-2); number of times to retest all spots, missed spots, or blind spots; fixation target size; test duration; and stimulus wait time. It generates a report that graphically illustrates the missed test locations.
A study conducted at UCSF found that the VR-OKP test had 98.3% sensitivity for de-tecting the physiologic blindspot, Dr. Ou reported. The study included 18 males and 12 females (mean age 31 years, range 19 to 50 years of age) who did unilateral testing with both the left and right eyes.
Mean test duration was 5.3 minutes, and a survey completed by the participants showed they experienced little-to-no discomfort or fatigue taking the test. There were no adverse events.
“An ongoing study is designed to determine how well the VR-OKP test outcomes match the results of Humphrey visual field testing in patients with glaucoma,” Dr. Ou said.
Discussing a 78-year-old patient enrolled in the comparative study, Dr. Ou noted that the results of the VR-OKP were reasonably concordant with the Humphrey visual field test, even though the VR-OKP is a suprathreshold test. Outcomes from two VR-OKP tests performed with a 30-minute intertest interval showed good repeatability.
“In addition, the patient stated that she loved the VR format because it did not require eye covering,” Dr. Ou added. “She said it caused no discomfort and was less frustrat-ing than the traditional Humphrey visual field,”
Perspective on impact
Discussing the potential role of the VR-OKP test, Dr. Ou referred to an excerpt from a chapter by R. Rand Allingham, MD, in the fourth edition of Chandler & Grant’s Glaucoma textbook.
“Areas of existing damage are far more likely to demonstrate progressive loss, either by scotomatous enlargement or deepening, than undamaged areas,” Dr. Allingham wrote. “Therefore, it is useful to examine these areas more carefully when examining a series of visual fields.”
“The future is exciting,” Dr. Ou said. “We can design smart algorithms that test areas of previous scotomas in more detail, and we can do threshold testing and home testing so that we can overcome intertest variability.
“In addition, my laboratory research group is interested in determining if there are certain retinal ganglion cell types that are particularly vulnerable in early disease,” she concluded. “Perhaps we might be able to design test stimuli to look for those.”