Pars Plana Vitrectomy
Pars plana vitrectomy is typically used for removing vitreous opacities (vitreous hemorrhage), relieving vitreoretinal traction, restoring the normal anatomical relationship of the retina and retinal pigment epithelium (RPE), and accessing the subretinal space. This vitreoretinal surgical technique involves a closed-system approach in which 3 ports are placed 3–4 mm posterior to the surgical limbus. One port is typically dedicated to infusion of balanced salt solution into the vitreous cavity, by which intraocular pressure (IOP) can be maintained at a desired level. Epinephrine can be added to the infusion solution for mydriasis and to induce vasoconstriction to reduce intraoperative bleeding, but it may promote ischemia and increase inflammation. Dextrose is often added to infusions to reduce cataractogenesis for phakic diabetic patients. The remaining ports are used to access the vitreous cavity with tools such as a fiber-optic endoilluminator to visualize the posterior segment and other instruments to manipulate, dissect, or remove intraocular tissues, fluids, and objects.
Vitrectomy is performed using an operating microscope in conjunction with a contact lens or noncontact viewing system. Direct and indirect visualization are possible; the latter requires the use of an inverting system to orient the image. The advantages of indirect visualization include a wider viewing angle, which enables visualization through media opacities and miotic pupils, as well as when the eye is filled with gas. Although direct viewing systems offer greater magnification and enhanced stereopsis, their field of view is smaller. Many vitreoretinal surgeons use both types of viewing systems, selecting the type according to the pathology.
Various instruments, visualization aids, and vitreous substitutes are used during vitreoretinal surgery. Advanced instrumentation includes the high-speed vitreous cutter, intraocular forceps, endolaser probe, micro-pic, intraocular scissors, extrusion cannula, and fragmatome, among others. Examples of visualization aids include indocyanine green (ICG) or brilliant blue G (BBG) (not FDA-approved) dyes and triamcinolone suspension. These substances aid in the visualization of the internal limiting membrane (ILM) and, in the case of triamcinolone, also help identify the vitreous. Perfluorocarbon (PFC) liquids, which are heavier than water, can be used to temporarily stabilize the retina during dissection and facilitate anterior drainage of subretinal fluid during retinal detachment repair. Tamponade of the retina can be achieved using air, gas, or silicone oil as a vitreous substitute. Commonly used gases include sulfur hexafluoride (SF6) and perfluoropropane (C3F8), which last approximately 2 and 8 weeks, respectively, at nonexpansile, isovolumic concentrations.
The development of smaller-gauge vitrectomy instrumentation has facilitated transconjunctival, sutureless vitrectomy techniques. With these systems, surgeons place 23-gauge, 25-gauge, or 27-gauge trocar cannulas to align conjunctival and scleral openings and to allow instrument insertions. These cannulas obviate the need for opening the conjunctiva, including cautery, and the wounds generally do not usually require suture closure when constructed with self-sealing architecture. Before small-gauge vitrectomy instrumentation, 20-gauge was the norm. The diameter of 20-gauge sclerotomies is 1 mm, compared to 0.7 mm, 0.5 mm, and 0.4 mm for 23-gauge, 25-gauge, and 27-gauge instrumentation, respectively. Potential advantages of small-gauge vitrectomy include fewer intraoperative iatrogenic retinal tears, shortened operative time, increased postoperative patient comfort, faster visual recovery, and reduced conjunctival scarring.
Fujii GY, de Juan E Jr, Humayun MS, et al. Initial experience using the transconjunctival sutureless vitrectomy system for vitreoretinal surgery. Ophthalmology. 2002;109(10):1814–1820.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.