Pars Plana Vitrectomy - EyeWiki (2024)

Overview

Pars plana vitrectomy (PPV) is a commonly employed technique in vitreoretinal surgery that enables access to the posterior segment for treating conditions such as retinal detachments, vitreous hemorrhage, endophthalmitis, and macular holes in a controlled, closed system. The procedure derives its name from the fact that vitreous is removed (i.e. vitreous + ectomy = removal of vitreous) and the instruments are introduced into the eye through the pars plana.

History

David Kasner first described vitrectomy, or removal of the vitreous body, using an open-sky technique in 1969.^[1] Two years later, Robert Machemer created the first closed system vitrectomy setup – which enabled intraocular pressure control – using 17-gauge instruments with a pars plana approach, the beginning of what became known as pars plana vitrectomy.^[2][3] In 1974, Conor O’Malley and Ralph Heintz developed the modern-day three-port vitrectomy system – with dedicated ports for vitreous removal using the vitrectomy cutter, infusion of fluid to maintain IOP, and illumination of the posterior segment – using 20-gauge instruments.^[4] Subsequent innovations include the development of a trocar-cannula system for insertion of instruments by Robert Machemer and Dyson Hickingbotham, 23-gauge instrumentation by Gholam Peyman and Claus Eckardt, 25-gauge instrumentation by Gildo Fujii and Eugene de Juan, and 27-gauge instrumentation by Yusuke Oshima and colleagues more recently in 2010.^{[5][6][7][8][9][10][11][12][13]}

Indications

Indications for pars plana vitrectomy include removal of vitreous opacities, relieving vitreoretinal traction, restoring the normal anatomical relationship of the retina and retinal pigment epithelium (RPE), and accessing the subretinal space.

Specific conditions include:

• Macular hole
• Epiretinal membrane
• Vitreomacular traction
• Vitreous hemorrhage
• Tractional retinal detachment
• Rhegmatogenous retinal detachment
• Refractory macular edema
• Vitreous biopsy
• Endophthalmitis
• Dislocated intraocular lens
• Retained lens material
• Intraocular foreign bodies

Basic Setup

The basic components of a vitrectomy setup include the following elements:

• Vitrectomy machine (e.g., Alcon Constellation, DORC EVA, Bausch + Lomb Stellaris PC)
• Surgical microscope and wide-angle viewing system (e.g., Zeiss RESIGHT, Oculus BIOM, AVI)
• Infusion cannula: to maintain intraocular pressure set by the vitrectomy machine
• Endoillumination light source: for visualization of the posterior segment including vitreous and retina
• Vitrectomy cutter (or vitrector): for vitreous removal, aspiration, and peeling and cutting membranes among other functions

Gauges

The gauge refers to the size of the instruments with higher numbers corresponding to smaller instruments (20-gauge = 0.9mm diameter, 23-gauge = 0.6mm diameter, 25-gauge = 0.5mm diameter, 27-gauge = 0.4mm diameter). When vitrectomy was first introduced, 20-gauge instrumentation was the most commonly used.^[4] Sclerotomies created with 20-gauge instruments would need to be sutured. While seldomly used nowadays, there are still indications for which 20-gauge is necessary including removal of retained lens material using the fragmatome and removal of intraocular foreign bodies (IOFB) using IOFB forceps. In addition, patients with 20-gauge, sutured wounds may have a decreased rate of endophthalmitis compared to patients undergoing smaller-gauge vitrectomy surgery, a finding possibly related to hypotony and wound leakage more commonly seen in sutureless surgery. Previous studies have found endophthalmitis rates twelve to twenty-eight times higher with 25-gauge vitrectomy compared to 20-gauge vitrectomy although endophthalmitis rates were low in both groups.^[14][15] However, subsequent studies have found similar rates of endophthalmitis with 20-gauge and 25-gauge vitrectomy.^[16][17]

On the other hand, there are numerous advantages of small-gauge vitrectomy, including:

• Ability to use trocar-cannula entry systems which reduce retinal and vitreous incarceration, neovascularization at sclerotomy sites, and iatrogenic breaks and dialyses at the vitreous base^[18]
• Increased patient comfort^[19][20]
• Decreased corneal astigmatism^[21][22]
• Decreased operative times^[19][20]
• Decreased conjunctival scaring^[23]

Moreover, the previously held concern that small-gauge vitrectomy systems were only suitable for cases not requiring extensive vitrectomy or membrane dissection – such as epiretinal membrane or macular hole cases – due to lack of instrumentation is no longer true given advances in technology.^[18]

Viewing Systems

Visualization of the posterior segment is critical to performing pars plana vitrectomy. The advent of wide-angle viewing systems in the 1980s has revolutionized vitreoretinal surgery by enabling a panoramic view of the posterior segment, thereby enabling safer and more efficient surgery.^[24][25][26]

There are two main categories of surgical viewing systems: non-contact systems and contact lens systems. Both require the use of an operating microscope. An example of a contact lens system is the Advanced Visual Instruments or AVI system which offers two different handheld lenses: one with a 68-degree view to the equator and one with a 130-degree view to the ora serrata.^[27] The AVI system requires coupling of the lens to the cornea with viscoelastic and an assistant to hold the lens in place while the eye is maintained in primary position. It is usually used with Leica scopes.

Two popular non-contact viewing systems are the Zeiss RESIGHT and Oculus BIOM wide-angle viewing systems.^[28] The Zeiss lens requires use of a Zeiss microscope whereas the Oculus lens is typically used with Leica scopes but can be adapted to fit Zeiss microscopes as well. Both lens systems do not require coupling to the corneal surface but viscoelastic is placed on the corneal surface to help maintain a clear view. In addition, no assistant is needed to hold the lens in place as the lenses attach directly to the operating microscope, and they allow for up to 130 degrees of visualization.

For macular surgery, special contact lenses such as the DORC flat vitrectomy lens enable higher resolution and magnification viewing of the posterior pole for more delicate maneuvers such as epiretinal membrane (ERM) and internal limiting membrane (ILM) peeling.^[28] However, non-contact macular lenses also exist such as with the Zeiss RESIGHT system.

Instruments

Below is a list of commonly used instruments in pars plana vitrectomy:^[29]

• Trocar-cannula system: for placing ports
  • Available in 20-, 23-, 25-, and 27-gauge
• Endoilluminators: available in focal and wide-angle illumination
  • Uses varying light sources including Xenon and LED
• Chandelier lighting systems: placed using trocar-cannula systems that enable bimanual surgery without having to devote one hand to holding a traditional endoilluminator
• Vitreous cutter: now available with cut speeds up to and exceeding 10,000 cuts per minute
• Forceps: for grasping membranes including epiretinal membrane, internal limiting membrane, and proliferative membranes from PVR and diabetes
  • e.g., ILM forceps, Grieshaber Maxgrip serrated forceps
• Scissors: for cutting retinal bands and tractional membranes
  • Available in horizontal, vertical, and angled designs
• Membrane scrapers: for lifting an edge of a membrane
  • e.g., Finesse Flex Loop, Tano scraper, pick
• Extrusion cannulas: used to drain subretinal fluid, perform fluid-air exchange, and disperse fluids resting on the retinal surface
  • E.g., soft-tip cannula, backflush cannula
• Diathermy: for providing hemostasis, marking the border of retinal tears, and creating drainage retinotomies
• Endolaser: to perform laser photocoagulation intra-operatively
  • Available in straight and curved designs
• Fragmatome: for pars plana lensectomy

Dyes

Adequate visualization of tissues and tissue planes is a prerequisite for safe and efficient surgery. Chromovitrectomy – the use of vital dyes during vitreoretinal surgery – aid with such visualization. An ideal dye should be safe to use intraocularly, easy to apply and remove, and provide adequate staining of the desired tissue.^[30] The following four dyes are the most commonly used in vitreoretinal surgery:

1. Triamcinolone acetonide: available in non-preservative-free formulation called Kenalog and preservative-free formulation called Triescence, the latter of which is FDA approved for intraocular use. Triamcinolone is particularly useful for staining the vitreous gel.^[31][32]
2. Trypan blue: a hydrophilic dye also used for staining the anterior capsule during phacoemulsification surgery. It is used in vitreoretinal surgery to stain the ERM and ILM and is FDA approved for use in ERM removal cases.^[33]
3. Brilliant blue: commonly used worldwide and recently approved by the FDA in 2019, it is used primarily for staining the ILM with minimal toxicity.^[34]
4. Indocyanine green: traditionally used for angiography, indocyanine green also effectively stains the ILM. However, at higher concentrations, it is toxic to the retina and RPE.^[35][36]

Surgical Principles

The following section provides an overview of three common surgeries that utilize pars plana vitrectomy: 1) retinal detachment repair, 2) membrane peeling, and 3) crystalline lens removal.

Retinal Detachment

The principles of retinal detachment repair via pars plana vitrectomy are to remove the vitreous gel and any vitreoretinal traction, locate and laser any retinal tears, and insert an intraocular tamponade.^[28]

The basic steps are as follows:

1. Insert trocars in the pars plana (3.0-4.0mm from the limbus depending on the lens status) typically using a beveled incision technique.
2. Perform a core vitrectomy to remove the central vitreous gel. Use of triamcinolone can aid with vitreous removal.
3. Induce a posterior vitreous detachment if a natural one has not already occurred. This is often done using the vitrectomy cutter on the aspiration only setting (i.e., the cutter function is turned off).
4. Perform a peripheral vitrectomy and release traction over the detached retina, at the retinal tears, and any areas of lattice degeneration. Again, triamcinolone can be helpful during this step.
5. Flatten the retina by draining subretinal fluid from a pre-existing break or a newly created drainage retinotomy while performing a fluid-air exchange, typically using a soft tip cannula. Alternatively, heavy liquids such as perfluorocarbons can be injected posteriorly to push subretinal fluid anteriorly out through a pre-existing break.
6. Once the retina is flattened, endolaser is then performed around the retinal breaks.
7. Insert an intraocular tamponade. SF6 (lasting 2-3 weeks) and C3F8 (lasting 6-8 weeks) gas are most commonly used although there are indications for silicone oil (lasting permanently until it is taken out) if longer tamponade is needed or in patients who are monocular, must fly, or cannot position.

Membrane Peel

To treat conditions such as epiretinal membranes, macular holes, vitreomacular traction, tractional retinal detachments, and proliferative vitreoretinopathy, membrane peeling may be necessary. As with retinal detachment surgery, the initial steps of inserting trocars, performing a core vitrectomy, and inducing a posterior vitreous detachment if not already present are similar. The degree of peripheral vitrectomy performed may depend on the clinical scenario.

Next, attention is turned to the membrane itself that requires peeling. A different set of techniques is used here compared to retinal detachment surgery. First, a higher magnification and resolution lens is used, which may be the 68-degree AVI lens, the green macular lens with the Zeiss RESIGHT, or the DORC flat vitrectomy lens.^[27][28] Next, a vital dye can be instilled in the posterior segment to improve tissue visualization. With any membrane peel, an initial flap must be created if not naturally present, followed by peeling of the membrane off the retinal surface. The initial flap can be created with Maxgrip or ILM forceps, an MVR blade, a Tano scraper, a Finesse Flex loop, or a pick.^[28]

Lens Removal

Removal of the crystalline lens during pars plana vitrectomy may be needed in several situations. If visualization of the posterior segment is poor due to media opacity from a cataract, either phacoemulsification or pars plana lensectomy can be performed. If there is retained nucleus or retained cortical fragments causing significant inflammation and intraocular pressure rise, pars plana lensectomy must be performed.^[37] There may also be a benefit to removing both the crystalline lens and lens capsule in proliferative vitreoretinopathy cases to remove a scaffold for future membrane growth.^[38]

For pars plana lensectomy, soft lenses can be removed using the vitrectomy cutter, but denser lenses may require use of the fragmatome. The fragmatome operates similarly to a phacoemulsification probe although use of the conventional fragmatome requires enlarging sclerotomies, often using an MVR blade. If the lens is sitting in the vitreous cavity, a thorough vitrectomy should be performed first to remove vitreous attachments to any lens fragments. If indicated, lens capsule can subsequently be removed using different types of intraocular forceps.

Complications

The following are a list of complications that may be seen intra-operatively or post-operatively with pars plana vitrectomy:^[39][40][41]

• Cataract
• Glaucoma
• Endophthalmitis
• Retinal tear
• Retinal detachment
• Hypotony
• Suprachoroidal effusion
• Suprachoroidal hemorrhage
• Vitreous hemorrhage
• Cystoid macular edema
• Optic neuropathy
• Phototoxicity

References

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