Vitrectomy Surgical Principles & Instrumentation

Overview: What PPV Is and Why It Works

Pars plana vitrectomy (PPV) removes the vitreous through the pars plana, a relatively avascular zone of the ciliary body. Instruments can cross it without damaging the lens anteriorly or the retina posteriorly. Taking out the vitreous removes it as a scaffold for traction and opens direct access to the retinal surface, the subretinal space, and the posterior segment for everything from membrane peeling to placing a tamponade (see intraocular tamponade agents).

The single most common indication is non-clearing vitreous hemorrhage from proliferative diabetic retinopathy: PPV clears the blood obscuring the view and treats the underlying neovascular disease and any tractional detachment at the same time. The same logic applies whenever a detachment, hemorrhage, or membrane is beyond what an external technique (scleral buckle) or an in-office procedure (pneumatic retinopexy) can manage alone.

Surgical Access: Sclerotomy Placement

Standard three-port PPV places sclerotomies a set distance posterior to the limbus, chosen to land reliably within the pars plana. In a phakic adult that distance is typically 3.5 mm posterior to the limbus, far enough to clear the lens anteriorly and close enough to stay off the retina posteriorly. A pseudophakic eye has no lens to protect, so the anterior constraint relaxes and sclerotomies can sit slightly more anteriorly, around 3.0–3.5 mm.

The Vitreous Cutter: Cut Rate and Duty Cycle

The vitreous cutter removes tissue through a guillotine-style port that opens and closes rapidly. Cut rate is the number of cutting cycles per minute. Raise it and each cycle takes a smaller vitreous bite, which lowers the traction transmitted to the retina and improves safety near mobile or detached retina. Duty cycle is the fraction of each cycle the port spends open to tissue flow. The two together let a surgeon trade flow rate against the holding force a cycle exerts on tissue before cutting it: push duty cycle up and flow increases, but so does the amount of tissue pulled toward the port first.

Maintaining the Eye: Infusion and Illumination

An infusion cannula delivers balanced salt solution, and later air or gas, into the eye throughout the case to hold intraocular pressure and keep the globe stable through instrument exchanges. Without continuous infusion the eye would simply collapse once the vitreous is removed; infusion is a distinct job from illumination or cutting.

Chandelier illumination is a fixed light pipe placed through its own sclerotomy. It frees both of the surgeon's hands for bimanual work: membrane peeling, or scleral depression done simultaneously with internal maneuvers, tasks a hand-held light pipe would otherwise block by occupying one hand.

Wide-Angle Viewing Systems

Wide-angle contact or non-contact viewing systems extend the visible field to the vitreous base and far peripheral retina. This matters for retinal detachment repair and vitreous base shaving, where the pathology sits well outside what a standard viewing setup would show.

Sutureless Microincision Vitrectomy

Modern small-gauge vitrectomy uses sutureless sclerotomies designed to self-seal. A beveled, two-step (angled) incision cuts a scleral tunnel whose tissue layers can shift and close on their own once the trocar is removed, so suture closure is rarely needed. Valved cannula systems back this up intraoperatively: the valve closes automatically the moment an instrument is withdrawn, so fluid doesn't escape and cause hypotony and globe instability with every exchange.

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