Starting with the invention of the first ophthalmoscope by Hermann von Helmholtz in 1851 (or Charles Babbage in 1847 by some accounts), ophthalmologists have been fascinated with methods of viewing the retina, the tissue that lets us see. It has undergone innumerable modifications and re-inventions by innovators.
The light source was initially a flickering candle, which was then replaced by an oil lamp, after that by a paraffin lamp and much later by a gas lamp. The gas lamp gave a more uniform and brighter light without the dark area caused by a burning wick. In 1879, Thomas Alva Edison invented the electric incandescent bulb which led to ophthalmologist William Dennett developing the first electric ophthalmoscope in 1885. Thomas Reed, Sir James McKenzie Davidson, and Henry Juler made similar designs.
Coming towards the present day, the light sources evolved from incandescent bulbs which had short lifespans to halogen bulbs which lasted longer, but still depended on a tungsten filament. They were then replaced by longer-lasting xenon bulbs which produce light from electrical discharge between two electrodes in a sealed quartz capsule containing the noble gas xenon. Finally, the latest are the Light Emitting Diode (LED) bulbs which use much lower power and last much longer without the problem of burning out. Even though LEDs were invented way back in 1907 and in production since 1962, it was the Nobel Prize winning invention of the blue LED which led to the production of white LEDs in 1993.
The conventional non-contact methods of viewing the fundus include the direct ophthalmoscope, indirect ophthalmoscope (with a 15D, 20D, 28D, 40D, or 2.2 Panretinal lens), and slitlamp biomicroscopy with a non-contact lens (60D, 66D, 78D, or 90D). Besides these, there are the contact fundus lenses and the gonioscopy lenses which allow a virtual, erect retinal view.
The advent of smartphone fundus photography has been a boon for quick and low-cost documentation of the retina. Previously, fundus photos could only be taken on large, expensive, table-mounted fundus cameras. Handheld fundus cameras were then developed but were expensive and had very poor software interfaces. Smartphone fundus photography allows dilated fundus photos of considerably good quality to be taken on “pocket computers” which have photo editing capability including montage creation.
Smartphones are the fuel of much of the Frugal “Indovation” in recent years. Smartphone fundus photography attachments include the small D-Eye and Peek Retina which can photograph a small area of the posterior pole, the 3D printed oDocs Fundus and Ahmed Ateya's fundus camera adapters, and the 20D lens attachments like DIYretcam, MIIretcam, JaizRetcam and HopeScope. Recently, Pujari et al. had shown that 90D lens can also be used for smartphone fundus photography by using an extra magnifying lens attachment.
Biju Raju and NSD Raju used only a smartphone and DIYretCam, to take smartphone fundus photos, edit them into a montage using a smartphone App (PicsArt Photo Studio) and sent it for publication and was selected as the cover picture of that issue of Kerala Journal of Ophthalmology.
Chrishan D. Gunasekera and Peter Thomas published in November 2018, an interesting but difficult technique to take smartphone fundus photographs using only an unmodified iPhone X and no additional attachments. This was made possible due to the near-coaxial placement of the flash illumination in this particular smartphone camera.
The authors of the accompanying article have innovatively used this new technique to take smartphone video of the fundus of a small child with retinoblastoma, which was then edited into a montage fundus photo. This allows us to cover a much larger field of view than what is optically available and shows us the bigger picture. A physical limitation of the field of view was gotten around by thinking out of the box. Software like i2k Retina (DualAlign LLC, Clifton Park, NY), AutoMontage (OIS, Sacramento, CA), IMAGEnet (Topco, Oakland, NJ), or Retina Montage Software (RSIP Vision) can be used to automatically make the fundus mosaic images.
It will not be long before this process of taking fundus photo and montage creation is automated and can be done from a distance. This patent from Tristan Swedish, Karin Roesch and Ramesh Raskar of MIT Media labs gives us a glimpse of the near future where a video camera automatically combines retroreflection images of the retina automatically into a montage.
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9. Swedish T, Roesch K, Raskar R. Methods and apparatus for retinal retroreflection imaging [Internet] 2019cited 2019 Apr 12 Available from: https://patents.google.com/patent/US10248194B2/en/