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A little thought about how a micro-assistant could help surgeons access the posterior segment, writes Leigh Spielberg

If only there were a micro-assistant for the really 
tricky bits

Leigh Spielberg

Posted: Saturday, October 1, 2016

october-et-image

Scuba equipment?Very small scuba equipment. Illustration Eoin Coveney

Without a pretty significant zonular defect, it would be tricky to get our little micro-assistant into the posterior segment,” said Elke Kreps, the fourth-year resident helping me in the operating room that day.
“I know,” I replied. “Not ideal. But hey, I can live with an intentional, iatrogenic zonular defect if it serves the greater good.”
“Me too,” she agreed.
“Good,” I concluded.
“But how would she lower herself down into the retina?” she asked. “Attach a fine suture to some intact zonulae and rappel herself down?”
“Well, now that we’ve destroyed some zonulae, I don’t think we can really risk damaging more. I think we’d have to run a nylon 10.0 through the primary incision at the limbus and anchor it to the conjunctiva,” I said.
“Nylon?! Wouldn’t that be way too slippery for her to rappel down? She wouldn’t have any grip at all,” she said.
“Well, that depends. Would the posterior segment be filled with air?” I asked. I had been imagining a slow, aqueous descent from just under the iris to the posterior pole, but Elke had something else in mind.
“Of course. How would she breathe if it were filled with BSS?” asked Elke.
“Hmm… Scuba equipment? Yeah, very small scuba equipment,” I replied.
It was time to go back to the OR. We had started this absurd, yet instructive, thought experiment during the previous procedure, a vitrectomy for vitreous hemorrhage in an eye with proliferative diabetic retinopathy.
It had been my most difficult PDRP case since I had completed my advanced VR fellowship in Ghent. I had cleared the haemorrhage and had safely dissected all vitreoretinal and membranous adhesions. However, there remained a rather large fibrovascular tuft adherent to the optic disc, and it wasn’t immediately clear how I should best deal with it.
Use the cutter to shave it as closely as possible to the disc? Or the forceps to remove it? How vascular was it? Was the neovascularisation active? Fluorescein angiography had been impossible, so I had to rely on my instinct and experience. On the one hand, I wanted to remove it entirely. On the other hand, I wasn’t enthusiastic about the possibility of a massive haemorrhage covering the posterior pole or a sectorial avulsion of a quarter million retinal nerve fibres.
“I wish I had a tiny little assistant who could go check it out for us,” I said aloud while contemplating my options. “She could go stand next to the optic disc and look under the tuft to let me know what’s underneath. Is there a massive vessel attached to the disc? Or is it harmless?”
Elke didn’t miss a beat. “Yeah, that would be useful,” she said. “But if it did happen to bleed, you’d have to get her out quickly before you raised the intraocular pressure to 60mmHg. She might have trouble breathing under those conditions.”
“Yeah, and she’d get the bends when she came back out,” I added.
I decided to remove the tuft with forceps and, as expected, it bled a bit. But the optic disc was undamaged. I increased the intraocular pressure and waited patiently for the bleeding to stop.
As I was performing panretinal endolaser, Elke continued with our intraocular assistant musings. “How would we get her into the posterior segment in the first place?” she asked.
“Um, maybe inject her like an Ozurdex?” I blurted out, without thinking it through.
“That would be efficient but intense,” said Elke. “What if she ended up stuck inside a choroidal detachment? Or a choroidal haemorrhage? Doesn’t that occasionally happen with intravitreal steroid implants?”
Ha! Elke had clearly been doing her homework for her VR surgery rotation. “Not in my hands,” I countered, with a vitreoretinal surgeon’s typical braggadocio.
But she was right. Injecting our micro-assistant through the sclera wouldn’t work. That would require a custom-made injection capsule for her to fit into. And as long as we were operating, there would be enough entry ports: like the limbal incision of the cataract surgery, or the vitrectomy ports.
Our thought experiment had borne its fruits. We had, in an amusing fashion, thought intelligently, if somewhat irreverently, about the challenges facing VR surgeons: visualisation of, and access to, the posterior chamber, including anatomical considerations and the risks of complications.
I started thinking of other useful things a micro-assistant could do, like gently dislodge vitreomacular traction or make sure that there’s no posterior hyaloid left on the retinal surface after I had induced a posterior vitreous detachment. But it was time to operate, and we had to concentrate. The micro-assistant would have to wait until a later date.
Dr Leigh Spielberg is a vitreoretinal and cataract surgeon 
at Ghent University Hospital in Belgium   leigh.spielberg@gmail.com