Murat V. Kalayoglu, M.D., Ph.D.
Contributing Editor
Binocular indirect ophthalmoscopy has become an indispensable tool to diagnose and manage a variety of vitreoretinal disorders. The instrument has a rich history, evolving through many generations to yield the current diagnostic marvel. Sophisticated additions to the basic technology include high–magnification lenses built in to the ophthalmoscope, video adapters that facilitate patient and student education as well as open up an array of telemedical possibilities, and laser photocoagulation systems mounted onto the indirect ophthalmoscope to treat peripheral tears through a 20 diopter lens.
The ophthalmoscope was invented by Hermann von Helmholtz in the 19th century. Helmholtz made this discovery through attempts to understand why the pupil was black under certain conditions, yet emitted a bright red light under other conditions. In attempting to answer this problem, Helmholtz discovered that a specific arrangement of lenses could produce an image of the fundus. He reasoned that since light emitted from the pupil follows the same course as that entering the pupil, then the emitted light is also the reflected light back to its source. He understood how the emitted and reflected rays could form optical images, and therefore was able to create an instrument to see an optical image of the fundus. Helmholtz was able to do this by gluing a lens, microscope cover glasses, and cardboard to create the first ophthalmoscope in 1850. This reflecting ophthalmoscope was to be developed and perfected for the next 150 years; however, despite being a breakthrough technology of its time, its acceptance and adoption by the Ophthalmology community was to come very gradually. Since Helmholtz first described the ophthalmoscope, hundreds of variants have been described and produced, and many of them have been commercially available.
Perhaps the most useful, successful variant of the ophthalmoscope is the binocular indirect headband ophthalmoscope, first described by Charles Schepens in 1945. Dr. Schepens designed the instrument to help examine patients following retinal detachment. His invention was a stereoscopic viewing system and light source held on a headband; Dr. Schepens examined his patients by peering through the stereoscopic mirrors, holding a condensing lens inches from the eye. This allowed him to see a virtual inverted image of the fundus, similar to the images produced by today’s modern binocular indirect ophthalmoscopes.
Modern binocular indirect ophthalmoscopes are used widely throughout the world by most ophthalmologists. They have become an indispensable tool for all ophthalmologists diagnosing and managing vitreoretinal disorders including lattice degeneration, retinal holes or tears, retinal detachments, retinopathy of prematurity, retinoschisis, sickle cell retinopathy, and an array of other diseases. Binocular indirect ophthalmoscopy is one of the most important tools for a vitreoretinal surgeon, who relies on the instrument pre-, intra- and post–operatively to diagnose and manage retinal disorders.
Today’s indirect ophthalmoscopes come with a myriad of features, which may include adjustable interpupillary distance, portable power packs, adjustable mirrors, dust sealed optics, and red-free and cobalt blue filters. Most ophthalmologists prefer using a 20 diopter aspheric lens with the indirect ophthalmoscope, although pediatric ophthalmologists examining newborns for retinopathy of prematurity may prefer a 28 diopter lens. Video capture capabilities built in to some indirect ophthalmoscopes allow the patient to see his or her fundus on video and, in some instances, in real time. Students, residents and fellows of Ophthalmology also greatly benefit from this feature since the teaching ophthalmologist is often able to obtain excellent images during her examination, which then can be recorded or shared with students real time.
Magnification lenses built into ophthalmoscopes allow enlarged, but more restricted, views of the retina through the 20 diopter lens; since these lenses can usually be flipped into and out of the indirect’s axis of focus, they allow the ophthalmologist to first visualize the diseased area of the fundus in low magnification, then zoom in to the area at high magnification. This feature can be especially useful when determining if a small peripheral lesion is a small hole or tear, versus a scar. Finally, photocoagulation laser systems that can be mounted onto the indirect ophthalmoscope allow the surgeon to treat peripheral tears without relying on the patient to tolerate a contact lens at the slit lamp. With the help of the 20 diopter lens, the ophthalmologist is able to easily focus the coherent laser beam projecting from the indirect ophthalmoscope onto the retina.