The three main indications for diagnostic vitrectomy in uveitis are (a) severe vitreitis that precludes visualization of the fundus and diagnosis is not clear, (b) suspicion of intraocular lymphoma, and (c) retinochoroiditis of unclear etiology that threatens vision in the short term and (d) cystoid macular edema (CME) unresponsive to medical management.

Whenever diagnostic vitrectomy is performed, great care should be taken with the vitreous sample, which, after all, is the main goal of the surgery. There are variations in the surgical technique that can provide adequate vitreous samples. The authors will present the techniques that they find preferable in their hands. Surgery begins by placing the inferotemporal 25-gauge cannula and attaching to it the infusion cannula in the off position (without infusion). Following the placement of the superior 25-gauge cannulas, removal of undiluted vitreous sample can begin. For this step, the aspiration line coming from the vitrectomy probe is disconnected from the Constellation vitrectomy system and attached to a syringe. With adequate visualization with the endoilluminator and plano irrigating contact lens, the surgeon engages the cutting action of the vitrectomy probe and immediately after orders the assistant to begin gentle aspiration with the syringe on the line. It is important to have the assistant wait for cutting to begin before aspirating on the syringe, thereby preventing peripheral retinal tears. The surgeon can then direct the sampling of the vitreous to the area that has the most apparent cellular infiltration. This increases the yield of the vitreous biopsy and increases safety since the retina is visualized at all times during the dry aspiration. As soon as the eye appears to become soft, the surgeon can direct the assistant to stop manual aspiration and then disengages the cutter action. Immediately the fluid infusion can be initiated and the intraocular pressure normalized. Appropriate order of steps is important to decrease the potential for iatrogenic retinal tears.

Some surgeons prefer to use air infusion during the undiluted vitreous biopsy, trying to decrease intraoperative hypotony. The authors’ main objection to this technique is that it compromises visualization during the vitrectomy and prevents adequate positioning of the cutter on the most pathological area of the eye. Once the undiluted vitreous sample has been obtained, standard vitrectomy can continue with normal pars plana infusion. The vitrectomy cassette can then be sent directly to the laboratory or a syringe can be used to aspirate from the cassette to be sent.

As in all vitrectomy cases, great care should be taken at the end of the surgery to visualize the retinal periphery and verify the absence of peripheral retinal tears. The creation of a posterior vitreous detachment (PVD) during surgery has potential pitfalls. If there are any areas of retinitis, the likelihood of retinal tears during PVD creation is high. On the other hand, patients with dense vitreitis who undergo core vitrectomy will have postoperative PVDs and can often bitterly complain of floaters. Surgical safety should override minor issues such as postoperative floaters. The authors do not recommend performing PVDs routinely during diagnostic vitrectomies, but do explain to patients the possibility of floaters. As long as the patient understands that the reason for the surgery is to prevent blindness, issues such as floaters can be placed in their appropriate perspective.

The authors cannot overemphasize the importance of personal communication with the pathologist prior and following diagnostic vitrectomies. Given the small volumes of the authors’ samples, protocol-based testing can potentially waste highly valuable samples on unimportant tests. Since clinical laboratory techniques are constantly changing and improving, the vitrectomy surgeon may be unaware of the availability of certain tests that can provide the needed diagnosis. The authors strongly advocate personally explaining to the pathologist the differential diagnosis and following the pathologist’s recommendations regarding handling of the material and prioritizing of studies.