Glaucoma is one of the major causes of irreversible blindness worldwide, and when compounded with cataract, it is almost visually debilitating. Pre-existing visual field defects are a cause of suboptimal outcomes following cataract surgery. In the crusade for the prevention of blindness, virtual reality, or VR, perimetry takes a leap forward to help serve patients in both the developed and developing countries of the world.
Currently, various VR headset perimeters have been described that enable performing perimetry in a VR setup with the added advantage of performing it in even incapacitated patients who cannot sit for long duration on the standardized perimeters. The newly introduced VR eCloud perimeter by Elisar is lightweight and portable and has an added advantage of an infrared eye tracking system that limits fixation losses and increases the predictability of the test. It also allows binocular visual field testing and does not necessitate occlusion of the eyes. The eCloud perimeter has an integrated head-mounted device that houses a flat screen and an optical system that comprises a convex lens that forms a virtual image, infrared cameras for detection of pupil movement or eye tracking, background illumination stimuli, interpupillary distance set-up and a lens holder for placing the corrective lens for refractive error. The monocular field of view achieved at each eye is 95° diagonally, which allows a 24-2 standard threshold test to be performed with a central fixation target. The size and brightness of the stimuli are changed to measure the dynamic light sensitivity of patients.
The patient holds the response button and presses it whenever the stimulus is appreciated. The test control unit is paired with the headset through Bluetooth, and the test is initiated. The administrator can visualize the details of the test on the test control unit, which is a smartphone. At the end of the test, the results are stored on the backend server, known as eCloud, which facilitates retrieval of data as and when necessary along with the regular updates that can be applied to the network and the apparatus for upgradability of the system.
The device incorporates a modified ZEST algorithm for visual field analysis. The initial trials conducted for test-retest variability and its comparison with Humphrey field analyzer show there is an agreement of test. However, a detailed analysis with long-term results and its comparison with other established modes of perimetry is essential to put it forward as a newer modality that helps to diagnose patients with field defects.
Disclosure: Agarwal reports financial interest in the eCloud Perimeter.