Endoscopic vitrectomy may be indicated to bypass media opacities in the anterior segment or to allow for closer visualization of anterior structures including the ciliary body, posterior iris, pars plana, and anterior vitreous base. Specific situations include:
Each system is equipped with a light source, a camera and an endolaser (in a single instrument). Currently models are available in 19, 20, and 23-gauge systems. Gauge size determines the imaging resolution and field of view (Figure 21.1). The 23-gauge unit can be used with standard trocars but has less resolution and illumination. The other units need dedicated sclerotomies. The units come independently or combined with a diode laser probe.
Common models are the E2 or E4 fiber-optic systems (Endo Optiks, Little Silver, NJ, USA), the PolyDiagnost system (Germany), and the Fiber Tech system (Tokyo, Japan).
There may be a learning curve and it is recommended to practice using endoscopy during a case with clear media as a backup to a conventional wide-angle viewing system. The view from an endoscope can also be integrated into the display for a “heads-up” system. Magnification is inversely related to the distance from the tissue. Illumination is adjusted with a foot pedal or on the main unit.
When using the endoscope as an adjunct with a conventional pars plana vitrectomy through a wide-angle viewing system, the following steps may be taken:
Core and peripheral vitrectomy are performed under wide-angle viewing. Special attention needs be paid to the location where the endoscope will enter, to avoid inadvertent vitreous traction as the instrument enters and leaves the eye (Figure 21.2).
If a 19-gauge probe is being used, the sclerostomy where the probe will enter needs to be made with an MVR blade. It is often easier to perform Microincision Vitrectomy Surgery (MIVS) first, creating a fourth sclerostomy (19-gauge) once this has been completed. A localised conjunctival peritomy is made with Westcott scissors and a 20- gauge MVR blade inserted 4.0mm posterior to the limbus. The 20-gauge MVR blade should be used to extend the wound slightly to 19-gauge as it exits the eye. Keeping the sclerostomy posterior as possible allows better access to the ciliary process. Positioning the sclerostomy just to the right (for a right-hand dominant surgeon) of one of the small- gauge sclerostomies allows for passage of the endoscope through the 19-gauge incision, and a separate laser probe (if performing endocyclophotocoagulation with a non-combined endoscope) through the small-gauge sclerostomy. Sometimes more than one 19-gauge sclerostomy is required to allow access to the full circumference of the ciliary processes, pars plana and peripheral retina.
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