Home testing technology is proving to be a key advancement in monitoring and screening glaucoma patients.
Reviewed by Dr Oluwatosin U. Smith.
With the onset of the COVID-19 pandemic, glaucoma specialists had to make marked changes to their well-established clinical practice routines on the fly to ensure patient follow-up. “We had to make changes to several aspects of clinical flow and patient interaction, especially regarding diagnostic testing and disease monitoring, with the emphasis on visual field (VF) testing,” said Dr Oluwatosin U. Smith, Glaucoma Associates of Texas, Dallas, United States.
Before the pandemic, long clinic waiting times for patients were commonplace for routine follow-up visits. Because of the pandemic, Dr Smith pointed out, testing and visits were separated and testing centres were designated in some facilities.
Regarding VF testing, new requirements for cleaning equipment and ensuring adequate time between patients after each VF test resulted in prolonged delays in the clinic. In an effort to reduce the waiting times, virtual VF testing and home VF tests were implemented.
“When considering perimetry needs,” Dr Smith said, “a number of factors are considered that include the reliability, reproducibility and quantitativeness of the test; the efficiency and safety for physicians and patients; affordability; comfort; and ease of both use and cleaning. Virtual reality and home VF tests meet some of those criteria.”
Various devices are available commercially. They include head-mounted devices, referred to as virtual reality perimetry, such as the VisuALL S for clinic use and the VisuALL H for home use (both from Olleyes), IMO (Crewt Medical Systems) and the C3 Field Analyzer (Remidio).
The visual acuity assessment is usually included in most available VF testing systems, as is threshold/suprathresold testing. However, the size V stimulus test is not currently available. Specific devices can administer both adult and paediatric tests, depending on requirements.
The VisuALL system, a head-mounted device that can be bought or rented, has the advantages of being lightweight and portable; it offers goggle technology, with each eye stimulated by an individual flat screen, and threshold and suprathreshold strategies. The web-based test included with the system is similar to the in-clinic test. Patient instruction and training are required.
Dr Smith referred to a recent study that compared this system with standard automated perimetry.1 The study included 102 eyes of 25 healthy patients and 26 patients with mild-to-moderate glaucoma. All participants were evaluated with both tests.
The authors reported that the test time was longer than with the Humphrey Field Analyzer (HFA) for both the normal subjects (6.13 minutes) and the patients (9.28 minutes) (P = 0.02 and P < 0.001, respectively). The investigators found a significant correlation in the global mean sensitivity of the HFA and VisuALL in normal subjects (P = 0.001) and patients (P < 0.001). The VisuALL mean sensitivity had a greater receiver operating characteristic curve than the HFA mean sensitivity for discriminating normal eyes from glaucomatous eyes (P = 0.06).
Dr Smith said the VisuALL system had lower peak brightness and background illumination than the HFA and an eye tracker that was similar in technology to the Octopus 600 (Haag-Streit). It provided full threshold testing versus standard automated perimetry testing but required more time than the HFA because of the absence of a normal database and a frequency-of-seeing curve.
The print-out of the VisuALL system is formatted like that of the HFA print-outs. Using the system, either one eye alone or both eyes simultaneously can be tested. The system provides a full threshold test, which the IMO does not; the IMO has a special algorithm that helps improve the accuracy and speed of testing.
The important advantages of virtual reality field tests are efficiency (the devices are easy to clean after each use and multiple devices can be used at the same time), safety and the ability for devices to be worn over glasses. Ease of use is another draw since it facilitates more frequent testing, which can rapidly detect VF progression.
In addition, it is not necessary for a technician to monitor use of the devices, although someone can be available if needed. The testing can be performed in any position and location.
The major disadvantages include the potential for patient disorientation when wearing the goggle headset, preference for standard perimetry, possible high cost and the fact that further clinical studies are needed to test the device with advanced glaucoma and with size V test objects. Studies to determine patient preferences with the tests, repeat test performance, clinical utility and normal database are under way.
The Melbourne Rapid Fields (MRF) device (M&S Technologies) provides portable tablet-based perimetry. When using the MRF, patients can wear their own glasses. The software includes fixation and fast thresholding using Bayes logic. This perimetry device is available for use in the clinic and for home VF testing.
The MRF provides a printout in a similar way to the HFA, and one or both eyes can be tested at the same time. The stimulus size, ranging from the equivalent of size III to size IV depending on the degree of eccentricity, is adjustable during testing to allow for the tangent effect of a planar screen. The test requires that the patient maintains a certain distance from the screen.
A study2 that included 12 normal eyes and 78 eyes with glaucoma and compared the MRF with the HFA in glaucoma patients, found a high correlation between the two devices and comparable test-retest reliability. Another study3 that compared the MRF and the HFA in 60 patients with stable glaucoma or ocular hypertension over 6 months reported that the two were strongly correlated with each other over four visits and had good test-retest reliability.
The home-testing MRF sends a link to the patients and allows testing to be performed on the patients’ own devices. Some calibration is required, and testing is performed at a specific distance from the screen. There is a slight learning curve associated with this test.
The greatest advantage of portable tablet VF testing is that the home test can be performed on the patient’s own tablet or computer. The disadvantages are that the size V stimulus test is not available, there is some patient discomfort with the positioning required and a home test is technically more challenging to perform because of the required calibration.
Dr Smith explained that the virtual reality fields and home VFs are valuable additions to the future of office perimetry, telemedicine, remote patient monitoring and screening. “The devices have been correlated with the established perimetry method, the Humphrey VF test,” she concluded.
“There is need for improvement in the diagnostic and disease progression monitoring capabilities, and validation of use for more advanced disease is ongoing for the devices commercially in the US. Home monitoring VF devices may identify rapid VF progression.”