All-digital Binocular Indirect Virtual Video Ophthalmoscope

Introduction

Since the introduction of the modern self-illuminating binocular indirect ophthalmoscope (BIO) in the mid-20th century, improvements have focused mainly on improving illumination without major changes to the basic optical system.1.2 The optical principle of BIO relies on reducing the examiner’s interpupillary distance (IPD) using mirrors and/or prisms so that the examiner’s visual axes of both eyes can simultaneously receive light rays reflected back through the patient’s pupil. Light rays returning from the fundus are collimated by an indirect ophthalmoscopy lens to produce a true, inverted, side-reversed image between the patient and the examiner. Performing and anatomically interpreting BIO examinations is a skill that ophthalmology trainees acquire during their residency training programs.3 Conventional BIOs are unable to capture videos and images of examinations. Video-enabled BIO devices are commercially available at a higher price, are bulkier, and allow for 2D video and still image acquisition of ophthalmoscopic examination using an integrated digital camera4–6 Among the limitations of currently available BIO devices with video support is the possible decentration of the captured image from the examiner’s point of view, which requires frequent adjustments4 and the recordings’ lack of stereo vision, as they provide two-dimensional (2D) rather than stereoscopic 3D images. Here, we describe a novel BIO prototype design with fully digital video recording that provides stereoscopic three-dimensional (3D) ocular fundoscope image recording with the potential for real-time anatomical correction.

Methods

This prospective observational pilot study was approved by the Human Research Ethics Committee of the Research Institute of Ophthalmology, Giza, Egypt, and was conducted in compliance with all local laws and in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all study participants. The prototype used in this study consists of a general LED light source and two synchronized mini-cameras 15 mm apart. The mini cameras are connected to the processor, storage media (Samsung note-9 Android smartphone in the current prototype) and virtual reality set (VISIONHMD Bigeyes H1 3D Video Glasses, in the current prototype) (Figure 1). The synchronized dual cameras were configured to export captured video to a Samsung note-9 using a docking console (Samsung Dex Dock Station). The custom-made Android app was designed to capture investigative media from the dual camera, with the right camera projecting to the right half of the screen and the left camera projecting to the left half of the screen, creating a side-by-side image. stereogram. The software also allows for optional real-time anatomical correction of the examination view at the touch of a button on the screen or via a wired remote shutter. The examination media is then projected into the virtual reality suite such that the image from the right camera is projected onto the right side of the VR glasses and is seen by the examiner’s right eye, and the left camera image is projected onto the left side of the VR glasses and is seen by the left eye the examiner.

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Figure 1 (AND) Schematic diagram and (B) current prototype of a fully digital binocular indirect virtual video ophthalmoscope composed of two mini-cameras, a light source, a virtual reality set, a connecting console and a smartphone.

The prototype was first tested and adjusted on three different schematic eyes, including the Ocular Imaging Eye Model (Ocular Instruments inc. Bellevue, WA, USA), the RetCam Digital Retinal Camera Practice Kit (Massie Research Laboratories Inc., Pleasanton, CA, USA), and the Reti Eye Model (Gulden Ophthalmics, Elkins Park, PA, USA). The LED light has been tested for safety for the human eye in terms of light intensity and spectrum. The light intensity was 3.8 mW/cm2 (safe limits are at least 1 order of magnitude below the safety limit set by ISO15004-2.2, which is 706 mW/cm2)7,8 and the light spectrum fell entirely within the safe visible spectrum with no ultraviolet or infrared composition.

Binocular stereoscopic indirect ophthalmoscopy was then performed on 15 eyes of 15 patients in dim light after pupil dilation using 1% Tropicamide eye drops without and with real-time digital anatomical correction of the examination view. In 10 patients, collateral video output to another virtual reality set was attempted for observers, and in 5 patients to an external monitor.

Result

Binocular, virtual, stereoscopic indirect ophthalmoscopy examination could be successfully tested on three schematic model eyes using this prototype in conjunction with a +20 diopter indirect ophthalmoscopy lens.

Binocular video stereo ophthalmoscopic media could be obtained in all patients (n = 15). Anatomical correction of the examination view was achieved in all patients (n = 15) (Figure 2 a Additional video). The educational collateral view could be simultaneously streamed in all patients either to another set of virtual reality glasses (10 patients out of 10) and to the monitor screen (5 patients out of 5).

Figure 2 Viewing an indirect photo of the retina (AND) optical disc, (B) macular and (C) peripheral retinal pathology.

Discussion

The aim of this work was to investigate the feasibility of indirect binocular ophthalmoscopy using a newly designed fully digital binocular indirect ophthalmoscope, which replaces the conventional BIO optical system with two side-by-side mini-cameras. This achieves the goal of reducing the examiner’s IPD and enabling virtual binocular indirect simultaneous visualization through the subject’s pupil and the projection of two fundus view images onto the corresponding virtual reality set screen. This allows the examiner to see the fundus virtually and binocularly in real time.

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Conventional BIOs are unable to record examinations on images or videos. Video-enabled BIOs are available at significantly higher cost, are bulkier, provide 2D recordings, and can be limited by decentering the camera view relative to the examiner’s view, requiring frequent adjustments.4 In our proposal, the video fundus examination observed by the examiner is simultaneously recorded in side-by-side stereoscopic 3D format.

The fundus image seen by the examiner is inverted and laterally reversed relative to the actual anatomical orientation in conventional BIO examination.1 Using the design described by us, anatomical correction of the examination view can be achieved in real-time examination by digital horizontal inversion and vertical inversion of each of two juxtaposed fundus examination images. Although the skill of anatomical BIO image interpretation is usually mastered during years of residency training,3 providing the possibility of an anatomically corrected view can make this part of the BIO examination more pleasant.

Ophthalmology students can observe the results of an ophthalmoscopic examination through an additional teaching mirror attached to the front of conventional BIO instruments. These teaching mirrors provide a 2D image of the examiners’ point of view9 which the trainee can see in the narrow window between the examiner and the patient, which may be uncomfortable for the patient. In BIO with video support, trainees can watch the results of the examination in 2D in real time or after the examination on a connected monitor.5 Kong et al, described the use of two complementary cameras with conventional BIO to provide a 3D view to students.10 Thanks to this, the BIO is bulkier, harder to put on and does not prevent the decentralization of the participants’ view from the examiner’s point of view. Our design provides ophthalmology students with a real-time stereoscopic 3D view of ophthalmoscopy identical to the examiner’s view. Examinations can also be captured in 2D or 3D for documentation and clinical teaching. Limitations of our current provisional prototype include the use of commercially available affordable mini-cameras and virtual reality headsets, as our goal at this point was only to prove the concept. We think the view can be better than this and the device can be more compact if the mini cameras can be upgraded and custom designed.

Conclusion

We describe a new design of a BIO device with video recording capability that replaces the complex optical system of conventional BIO with two closely spaced side-by-side mini-cameras. Benefits of this new design include optional real-time anatomical correction of the examiner’s view of the fundus and optional BIO-identical recording of the examiner’s view in both stereoscopic 3D and 2D, which can improve clinical documentation and education.

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Data Sharing Statement

The data used in this study are available from the corresponding author upon reasonable request.

Ethical approval and consent to participate

This report was approved by the Ethics Committee of the Research Institute of Ophthalmological Research and followed the principles of the Declaration of Helsinki. Written informed consent was obtained from all participating patients.

Thanks

The design described in this article is related to a pending international patent for Dr. Omar Solyman (PCT # PCT/US2021/071604).

Financing

There are no funds to report.

Disclosure

Dr. Omar Solyman initiated the launch of Ophthalmology related hardware and software solutions for Wadjet: The Eye Gadget. The prototype design described in this article is related to the pending international patent for Dr. Omar Solyman (PCT # PCT/US2021/071604). The authors report no other conflicts of interest in this work.

Reference

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4. Instructions for use of Vantage Plus Digital. Available from: https://support.keeler-global.com/_manuals/Indirect%20Ophthlmoscopes/Vantage%20Plus%20Digital%20(EP59-09863-art-F)/EP59-09863-art-F.pdf. Made available November 202021 2022.

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9. Saunders RA, Bluestein EC, Berland JE, Donahue ML, Wilson ME, Rust PF. Can neo-ophthalmologists screen for retinopathy of prematurity? J Pediatr Ophthalmol Strabismus. 1995;32(5):302–304; discussion 305. doi:10.3928/0191-3913-19950901-08

10. Kong HJ, Cha JP, Seo JM, Hwang JM, Chung H, Kim HC. Development of a cold-light indirect ophthalmoscopic video system for sharing stereopsis. Annu Int Conf IEEE Eng Med Biol Soc IEEE Eng Med Biol Soc Annu Int Conf. 2007;2007:2219–2222. doi:10.1109/IEMBS.2007.4352765

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