Software that allows for digital recording of eye movements improves efficiency, collaboration with other professionals.

By Thomas E. Boismier, MPH

Many years ago, I learned how to perform electronystagmography (ENG) on a strip-chart recorder. The ENG lab I worked for switched to a PC-based ENG system in 1985. Since that time, I've done some 500 ENG tests per year. I've always thought the change from strip-chart to computer-based recording was a quantum leap in convenience, accuracy, test flexibility and recording quality.

State of Early Testing

Over the years, I became very comfortable using electrode-based ENG recordings. When the university vestibular lab I worked for purchased one of the earliest infrared video-ENG systems for research use, I was not very impressed. The system was cumbersome. The goggles were so heavy that their weight had to be supported by a spring assembly, the field of view through the goggles was very limited, and we had to switch to a second pair of goggles for the "vision denied" (eyes closed) tests.

Calibration consumed 15 to 30 minutes, and I had concerns about video's lower sampling rate as compared to electrode-based ENG. It was definitely not the quantum leap I experienced in the change from strip-chart to computer-based electrode ENG.

As the years passed, several vendors brought improved video ENG systems to market. I dutifully reviewed the systems at conferences and when visiting other balance centers, but none seemed to offer a huge advantage over the electrode-based system I had used for years.

New Dimensions in Care

When given the opportunity to build my own balance center, I again picked computer-based ENG and rotary chair systems by choosing those that I thought had the best software and EOG amplifiers. As our program grew, video technology made its way into the lab. Our physical therapists lobbied for a pair of video-Frenzel goggles with VCR and monitor so they could record nystagmus during Dix-Hallpike testing and canalith repositioning maneuvers.

We were very pleased with the ability to record and play back eye movements. The video recordings added a new dimension to vestibular rehabilitation treatment and patient education. Recordings also made it possible for the therapists to review with me any unusual eye movements they came across, without having to make the patient go through the provocative motions all over again.

A few years ago, I was asked to participate in a pre-release beta-test of a new video-ENG (VNG) system. At the end of that beta-test period, I realized that the resulting system was a quantum leap over electrode-based ENG. The goggles were light enough that patients didn't complain of headaches halfway through the test, and there was no need to switch from one pair of goggles to another when changing from vision-allowed to vision-denied tests. The field of view was excellent, the recordings were incredibly clean and the difference in sampling rate between video and electrode recordings produced no significant results in the ocular motility test.

VNG/ENG Combination

When these products became commercially available, we upgraded both of our ENG rooms to combined ENG/VNG systems. We now use video recordings on 77 percent of our patients.

Electrode recordings give us better results in a small number of patients (those with pupils partially obscured by ptosis, and those who cannot keep their eyes open in the dark), so we are quite happy with the ability to choose.

To duplicate our positive experience with the video Frenzels, we spent several thousand dollars on a VCR and quad monitor for each of our two VNG systems, so we could record the signals from the goggles' cameras onto videotape. This has worked very well, but definitely has disadvantages.

The monitor and VCR take up a lot of space in the test rooms. Additionally, we have to keep a drawer full of videotapes and we have to document which tape was used for which patient, and of course, we have to remember to press the "record" button at the start of the test! Sometimes, when I review a tape, it is difficult to tell what specific subtest is being performed when an eye movement pattern appears.

Digital Video Software

Recently, I was asked to beta test a new version of the ICS CHARTR VNG software, which allows the user to record and save digital video clips of eye movements directly to the computer's hard drive, with no special video recording equipment required. The new software provides high-quality recordings of the actual eye motion without the space requirements, cost and complexity of a VCR and quad-monitor setup. The video clip software records up to 40 seconds of eye movement at the press of a key or footswitch. This allows the examiner to record any unusual or unexpected eye movements seen during any of the VNG subtests.

All of our test equipment (VNG/ENG, Rotary Chair, VAT, posturography) is connected to our office network. Therefore, I can analyze the data as the test battery proceeds. The software allows me to review and analyze each subtest of the VNG battery as soon as it has been completed, while the technician and patient proceed to the next subtest. In most cases, I have the data analysis finished and the majority of the report written before the last caloric irrigation has been performed. After the last caloric test is finished, I speak with the patient to review their history and the preliminary test results, and I counsel the patient regarding results and what our recommendations to the referring physician will be.

Digital Data Applications

As part of the data analysis I routinely review eye movement recordings of all Dix-Hallpike tests for the period of time in which the patient reported symptoms, looking for torsional nystagmus. Previously, this required that I wait until the VNG test battery was completely finished, then the patient waited for their counseling session while I got the videotape from the test room, brought it to my office and searched through the tape looking for the Dix-Hallpike test. Now, as soon as the Dix-Hallpike recording is completed, the actual eye movement video is available at my desktop immediately via our office network.

Reviewing the eye movement video with the patient is often a useful tool for counseling and patient education. The video clip screen contains the patient's and test's names, providing a more professional look than the previous VCR method. The VCR and television monitor is not needed; I can simply show the video clip on the PC.

When I want to place a video clip into a slide show for a talk, I no longer have to connect a VCR to my computer and convert the video to a digital format; I can simply export it from the software.

The exported video files can easily be sent to colleagues on disk, by e-mail or other Internet transfer for an opinion.

I've found that the ability to digitally record eye movements during VNG testing represents another quantum leap in both convenience and recording quality over electrode-based ENG.

Thomas Boismier is director of the Balance Care Center, a division of Ear, Nose & Throat Associates PC, in Fort Wayne, IN. He can be reached by e-mail at TBoismier@med.web.com or by telephone at (260) 426-8117, ext. 238.