We conducted this study to assess both the success rate of a self-operable OCT device in the target population and to investigate the image quality of this new technology in a clinical setting. The image resolution was close to the reference OCT but had a poorer signal-to-noise ratio and additional artifacts. The reduced image quality is a consequence of the low-cost concept. The main disadvantage of the design is the influence of reflected and numerously scattered light. This is due to abandoning the scanning of the retina, as it is also observed with fundus cameras compared with laser scanning ophthalmoscopy (SLO). In contrast to SD-OCT, only light from one depth is measured in one exposure, which reduces the sensitivity. Current technical limitations are the limited output power of the light source and the readout frequency of the camera , which lead to a low signal-to-noise ratio and motion artifacts, respectively. In addition, the device used here suffered from spurious reflections caused by the numerous surfaces of the optical components, which cause visible background noise in the images and saturation artifacts. These reflections will be reduced in future devices through better anti-reflection coating and an optimized optical layout. We recently showed that ametropia correction can be accomplished numerically . This further simplifies the design, cuts down costs, and reduces artifacts.
Since the device is not intended for regular ophthalmic diagnosis, but only for monitoring disease activity, reduced image quality is acceptable as long as morphological changes can be detected with sufficient sensitivity and specificity. Furthermore, mere monitoring of central retinal volume has been shown to be sensitive in AMD monitoring, which could be used as a further monitoring criterion . In case of disease activity, the device would refer the patient to his doctor for a confirmatory OCT scan and possibly an immediate intravitreal injection in case of confirmed activity.
In our study, we were able to detect all common biomarkers of disease activity in AMD, DME, and RVO, including PED, SRF, IRF, intraretinal hyperreflective foci, and intraretinal hemorrhage (see Fig. 3). SRF is easily detectable since both the adjacent RPE and ellipsoid zone are hyperreflective. In contrast, IRF does not have hyperreflective borders and is therefore more challenging to detect. However, it could still be visualized with SELFF-OCT.
The technical term full field, established to describe the simultaneous illumination of the scan area as opposed to scanning OCT systems, should not be confused with the size of the scan area. Quite the contrary, our scan size (4.5 × 1.4 mm) is limited by the specifications of low-cost CMOS cameras and smaller compared with most SD-OCT scanning protocols. However, a theoretical study showed that already small central OCT scans of 2 mm have high sensitivity in detecting disease activity . However, this will need confirmation in future clinical studies.
In contrast to current OCT devices, the investigated SELFF-OCT allows unassisted OCT self-examination. To achieve correct alignment, the patient has to center the fixation target into the center of the illuminated part of the retina, which the patient sees as a red circular area. This creates a “keyhole” effect and automatically guides the patient into the correct position. Scanning OCT systems would require additional optics to achieve a similar effect for a self-alignment, which would further increase overall cost, device size, and complexity.
The keyhole alignment method proved to be very reliable even in patients with low BCVA. These patients, in general, tended to need more tries in the training and longer time to locate the fixation target, but overall success rates did not differ. However, it limits device usage to patients with some residual visual function. Especially in geographic atrophy, usability may be limited. For other patients, variations in the fixation target, e.g., a circle or star, could possibly further reduce the problem. Also, we found that the gel cushion headrest we used in our study offered too little head stability. In the future, more rigid headrest designs are expected to significantly lower motion artifacts. In-lab testing with a handheld device (Fig. 1b) showed that because of improved patient interface, less motion artifacts occurred than with the tabletop device, despite it being handheld.
Nevertheless, because of the requirement for self-alignment and the necessity of keeping still during measurements, SELFF-OCT has minimum requirements concerning cognitive function, visual function, and musculoskeletal function that are less relevant in clinical OCT systems. Therefore, we excluded patients who would definitely not meet these requirements, since they would also not be eligible patients for home monitoring. However, we did not perform further extensive pre-selection of the patients such as fixation testing, but rather included a broad real-life cross-section of AMD patients. With these givens, more than three quarters of the patients (77%) were able to acquire images that were clinically gradable. While this leaves room for improvement, we consider this success rate encouraging for a pivotal trial. In our belief, if a similar success rate as the 77% in this study could be found in a later real-world home-care scenario and 3 out of 4 presumable candidates could be monitored with home-care OCT, this success rate would indeed be very satisfactory. On top of that, we are confident that the success rate can be improved in future devices.
Motivation for home-care devices
In all diseases where regular OCT monitoring is necessary, this comes with high disease burden for the patients. For AMD, most guidelines propose monthly monitoring even when no disease activity has been present for longer periods of time [4, 18]. These frequent monitoring visits significantly stress out patients and lead to low therapy adherence [10, 19]. Not only are frequent follow-up visits time-consuming, but because the patients are mostly elderly and often physically impaired, they often require assistance from relatives or other people. A long distance between the patient home and the ophthalmologist was found to be the leading cause of therapy non-adherence . Moreover, frequent visits bind the capacities of healthcare professionals and create considerable healthcare costs.
Low patient adherence leads to significantly reduced treatment outcome . Efforts to alleviate some of the treatment burden were undertaken, e.g., with the introduction of the treat-and-extend (TAE) dosing regimen . TAE tries to predict the relapse interval and adapts treatment schedules accordingly. Additionally, it combines monitoring and treatment visits. While this can reduce the amount of overall patient visits, it can also create both disease overtreatment  and undertreatment in case of an early disease relapse.
The introduction of a sensitive home monitoring system for retinal diseases would address all these issues by allowing daily disease monitoring at a minimal additional burden to the patient. Moreover, it would allow for tailor-made individualized therapy, eliminate overtreatment or undertreatment, and guarantee the best possible treatment outcomes. Therefore, an OCT-based home monitoring system could lead to a completely new monitoring and treatment scheme for these patients.
Comparison with similar approaches
Other research groups have also addressed the question to make OCT home-care compatible [22,23,24]. Recently, a design for a low-cost spectral domain OCT (SD-OCT) with component costs of below US$6000 was published . However, self-examination was not tested, and OCT scans were acquired with a dilated pupil. Therefore, it is unknown how suitable the device would be for self-examination. Currently, a home-care OCT solution is under testing by the company Notal Vision . Their device uses conventional SD-OCT technology and is also not expected to be cheaper than the low-cost OCT published . Typically, medical devices are sold with more than twice to three times the component costs. Without technological breakthroughs, like fully integrated OCT on one optical chip , we see no further price reduction potential for SD- or SS)-OCT. However, device cost is crucial for the concept of home monitoring because in contrast to an OCT device in a clinical environment, the home device will only be used a few minutes per day.
Regardless of underlying technology, home monitoring of AMD progression by OCT requires an efficient and cost-effective image interpretation. Analyzing the recorded volumes by the care-taking ophthalmologist or some other professional seems impracticable because of the excessive number of images which are generated by daily self-examination. With the recent advancements in computer science, artificial intelligence (AI) seems to be the most promising option to solve this problem . Especially with the limited quality of home-care OCT systems, it is conceivable that AI trained on both SD- and SELFF-OCT might even outperform human readers. Consequently, we are currently developing AI algorithms for interpretation of SELFF-OCT images [27, 28].
Home monitoring OCT has huge potential to create a paradigm shift in ophthalmic healthcare with benefits for the patients, doctors, and public health. Currently, we are working on a portable low-cost version of the SELFF-OCT technology, which patients will use at home for conducting a longitudinal study on the value of home monitoring by OCT.