Expert perspectives on the evolution of retina practice, procedures, technologies and instrumentation.
Steve Charles, MD, FASRS
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In addition to conventional transscleral cryopexy, which required extraocular muscle traction sutures and a periotomy, the late Robert Machemer, MD—who brought us vitrectomy—initially utilized both monopolar endodiathermy diathermy and endocryopexy, both of which had significant hazards. My motivation when I developed endophotocoagulation was to provide a safer, more effective, and more practical solution for retinopexy, hemostasis, and panretinal photocoagulation.
Monopolar diathermy can damage the optic nerve because the nerve becomes the radiofrequency energy return path to the ground plane. Diathermy also causes retinal necrosis extending beyond the bleeding vessel. Endodiathermy primarily causes retinal necrosis, not retinal pigment epithelium (RPE) thermal damage, which results in low-tensile-strength retinopexy.
Endocryopexy is very unwieldy because of the length and weight of the probe, large diameter handle and tip, and very rigid hose. During cryo application, the probe adheres to retina and choroid. Surgeon hand movement or patient movement is, therefore, highly likely to tear the retina and/or choroid and cause severe bleeding. Endocryopexy likely increases proliferative vitreoretinopathy risk due to dispersion of living RPE cells and reactive Müller cells.
I developed endophotocoagulation in 1974 while I was a clinical associate at the National Eye Institute. Endophotocoagulation was initially intended for single-port vitrectomy and later adapted for 3-port vitrectomy.
Endophotocoagulation eliminated the need for a conjunctival incision to apply trans-scleral cryopexy. My first system used the very large Zeiss xenon source and an adapter I built with Charles McCarthy, PhD, an engineer at the National Institutes of Health. The aluminum adapter had cooling fins and a vacuum line to create airflow to cool the input termination of the multifiber, 18-inch, 20-gauge endo-delivery device. I was able to use this device on diabetic and proliferative vitreoretinopathy patients within 2 months of initiating the project.
My first commercial system used Patrick O’Malley’s Clinitex Log III photocoagulator xenon source based on the Varian integral parabolic reflector for the xenon arc. Many of these adaptors were sold by Clinitex. It was very effective and reliable, although the short multifiber fiber optic bundle was challenging ergonomically. I had no economic interest in this product.
Several years later. Drs. Maurice Landers, Jay Fleischman, and I simultaneously and independently developed endophotocoagulation systems using an argon laser source. Later, Yasuo Tano, MD, developed the near-infrared diode laser source, and finally several companies developed 532-nm, flash-tube-pumped, frequency-upconverted laser sources. The laser source for the Alcon Accurus was a separate box that fit on top of the Accurus console.
Unlike the HGM and Coherent, laser diode sources did not require water cooling. The Alcon Constellation was the first to use a thin disk laser that eliminated thermal lensing, which in turn greatly increased beam stability. In addition, this Alcon PurePoint laser had no kinematic lens mounts. All optic components were rigidly soldered in place, which increased reliability. The Alcon PurePoint laser was incorporated into the Constellation console.
Laser endophotocoagulation is preferred over diathermy for hemostasis because the green laser energy is absorbed in the red blood column but not the near-transparent retina.[1] When diathermy is used for hemostasis of vascular attachment points after delamination of diabetic epiretinal membranes, so-called atrophic holes develop months to years later, and are often incorrectly attributed to ischemia.
My initial publication on endophotocoagulation in Retina also included the first description of endocyclophotocoagulation.[2] This technique was used in conjunction with vitrectomy, typically for neovascular glaucoma, before the advent of anti-VEGF agents. Scleral depression of the ciliary body was easy because of intraocular pressure control, and eliminated the need for endoscopy. The non-pigmented ciliary epithelium was directly visualized with the operating microscope.
References
(Milestone essay published 2024)
Additional Resources
Hear from Steve Charles, MD, FASRS, on his inspiring career in a Leaders & Legends interview at https://retinahistory.asrs.org/video-interviews/steve-charles.