BLOG: How scleral buckles work
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Why doesn’t our superior retina detach? Why does it stay pressed against the retinal pigment epithelium? It would stand to reason that — especially once we’ve had a vitreous detachment — gravity would just let it slip off every now and then.
For example, I’m currently at sea level in a major city in the Northern hemisphere very close to the Summer Solstice with the full 9.8 m/s2 bearing down on me while I’m double-bouncing my nephew on a trampoline, and not once has it crossed my mind that the sum of the forces bearing down on my eye might overcome their adversaries and push my superior retina clean off my retinal pigment epithelium (RPE), leaving me with a (nephew-sized) inferiorly-positioned scotoma just as I try to look down for a safe landing spot on said (kid-sized) trampoline.
Should I be worried? Should my nephew? And what of these gravitational adversaries? What is preventing or protecting my superior retina from detaching? Why did I leave the trampoline today (and every day of my life thus far, knock on wood) with a superior retinal attachment?
The answer has a lot to do with why scleral buckles work to attach the retina. If you think about it from a 21st century point of view, scleral buckles are not a very efficient way to reattach a detached retina. Inserting a gas bubble into the vitreous chamber and pushing the retina back onto the RPE seems to make more intuitive sense than squeezing the RPE closer to the detached retina. But buckles do work and work comparatively efficiently in regard to their competitors, pneumatic retinopexy and vitrectomy.
Recall that, “rhegmatogenous retinal detachment occurs when factors maintaining attachment are overwhelmed by the volume of intravitreal fluid entering the potential subretinal space through retinal breaks,” (Brinton DA et al.). Put simply, scleral buckles reapproximate the RPE to the posterior retinal surface so those factors can resume the job they’ve done our whole lives (provided the retinal breaks are now sealed). The force that keeps the superior retina from detaching due to gravitational (trampoline-related), momentum, centripetal or centrifugal forces is mainly the maintenance of negative pressure in the subretinal space. This negative pressure acts as an always-on vacuum, sucking the retina close to the RPE.
The metabolic pumps of the RPE and the relatively higher oncotic pressure in the choroid create this negative pressure, which allows not only the superior retina to stay attached, but also the sensory retina to stay relatively detergesced, and the outer segments of the photoreceptors to be phagocytosed. No wonder that the choroid (which perfuses the RPE) has one of the highest blood flow rates of any tissue in the body. And yes, there is a secondary force of friction from the interdigitation of the photoreceptor outer segments and the RPE microvilli that also helps keep the retina attached, but this is much less of a factor than the RPE pumps.
My research for this question led to a lot of reading about scleral buckles, and I learned that Charles L. Schepens, MD, is credited with pioneering the first scleral buckle technique as well as developing the binocular indirect ophthalmoscope, microscissors for vitreous surgery and the scanning laser ophthalmoscope (amongst other inventions). I recalled walking by the Schepens Eye Research Institute in Boston’s West End and I googled “Charles Schepens” to learn more about the legendary doctor.
I urge you all to do the same, because pioneering ophthalmic techniques is not even the most impressive thing on his resume. An ophthalmologist practicing in Belgium when it was invaded by the Nazis, he began working with the Belgium and French Resistance movements (Marquard). He uprooted his family several times, was arrested twice, developed an alias, hid his children indoors (to prevent the Gestapo from discovering their French accents) and began to smuggle people over the Pyrenees. He helped save over 100 people this way and was given the Medal of the French Légion d'Honneur. He then went on to enjoy an inspiring career, considered by the American Academy of Ophthalmology as one of “The Ten Most Influential Ophthalmologists of the Twentieth Century.” Two years before he passed away in 2006 he told the Boston Globe, “'It was a wonderful life, you know.” I can only hope that any of us uses our careers to advance the public a good a fraction of the distance that Dr. Schepens did.
References:
- Brinton DA, et al. Retinal Detachment. 3rd ed. Oxford University Press, 2009.
- Harvard Medical School Department of Ophthalmology. Charles L. Schepens, MD. Available at: https://eye.hms.harvard.edu/charlesschepens. Posted 2006. Accessed July 6, 2020.
- Marquard B. Charles Schepens, 94, leader in Nazi resistance, pioneer in retina surgery. The Boston Globe. Available at: http://archive.boston.com/news/globe/obituaries/articles/2006/04/05/charles_schepens_94_leader_in_nazi_resistance_pioneer_in_retina_surgery. Posted April 5, 2006. Accessed July 6, 2020.
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