When infectious endophthalmitis is suspected, a vitreous tap and intravitreal injection of antibiotics are often employed to obtain a specimen for diagnosis and administer treatment. This in-office procedure normally consists of introducing a short 25- or 27-gauge needle on a 5-mL or 10-mL syringe 3 mm to 4 mm posterior to the limbus of an anesthetized eye using standard sterile technique.1 Gentle suction is manually applied to withdraw a vitreous sample to be sent to the laboratory for microbiologic analysis. Next, multiple intravitreal injections of antibiotics and/or steroid are administered.
Multiple ocular piercings can be quite painful on an inflamed eye of an anxious and uncomfortable patient. Each injection bears its own risk of complication. We previously reported on a technique using a 25-gauge trocar and cannula to obtain a vitreous sample and administer intravitreal antibiotic and steroids.2 The advantages of this method were eliminating multiple piercings through an inflamed sclera, enhancing comfort, decreasing pain, and decreasing trauma to the conjunctiva from multiple injections. Furthermore, an assistant is not required.
One potential complication can occur with using a standard scleral cannula for vitreous tap and intravitreal injections in a previously vitrectomized eye. Upon inserting the device, it is possible for a fair amount of vitreous volume to exit the eye due to a lack of resistance in the bore of the cannula. Furthermore, the antibiotics and steroid injected into the eye has the potential to immediately reflux back through the cannula.
Several companies have introduced scleral cannulas with built in anti-reflux valves. Using a valved 25-gauge cannula eliminates the possibility of fluid loss on inserting the trocar and also prevents reflux of intravitreally administered medications during the procedure (Video). We found that using a valved cannula is straightforward for surgeons familiar with microincision vitrectomy surgery.
The following items are required: one 25-gauge trocar with a valved cannula (Ref # 8065751448; Alcon, Fort Worth, TX), several short 25-gauge needles, and 1-mL syringes (#309626; Becton Dickson and Company, Franklin Lakes, NJ) depending on how many antibiotics and/or steroid injections are planned. The cost is approximately $25 to $35 for the single cannula/trocar kit.
Usually, topical or subconjuctival anesthesia is sufficient, but in some cases, a patient may require a peribulbar block. In the inferotemporal quadrant, the conjunctiva is displaced with a cotton applicator or forceps and the 25-gauge valved entry system is inserted posterior to the limbus in the standard biplanar fashion (3 mm for aphakic/pseudophakic eye or 3.5 mm for phakic eye). Initially, the blade is inserted obliquely at a 30° angle and then the entry is made perpendicular to the sclera.3 During removal of the trocar, the valved cannula is held in place with 0.12 forceps to prevent dislodgement.
The cannula can then be left in place to allow for withdrawal of a vitreous sample and intravitreal injections of medications. When there is no needle inserted into the cannula, fluid will not flow out of a vitrectomized eye because of the valve. Currently, vancomycin (1 mg/0.1 mL) is given to cover gram-positive microorganisms and ceftazidime (2.2 mg/0.1 mL) or amikacin (400 mg/0.1 mL) is given to cover gram-negatives, depending on local sensitivities. Dexamethasone (400 mg/0.1 mL) may also be injected.
When the vitreous procedures are complete, the cannula is grasped with forceps and removed in the direction of the scleral tunnel. A cotton-tipped applicator is immediately applied onto the conjunctiva, rotating the conjunctiva back over the sclerotomy and holding pressure onto the sclerotomy for approximately 30 seconds for hemostasis and wound closure.
A patient with an inflamed and painful eye is unlikely to prefer multiple sticks into their eye. This technique reduces the necessary trauma to one puncture — potentially reducing patient discomfort. An additional advantage is that the valve prevents hypotony in previously vitrectomized eyes. In our experience, the technique is safe, well-tolerated, and easily performed in the office or at the bedside.
- Hersh PS, Zagelbaum BM, Cremers SL. Ophthalmic Surgical Procedures. New York, NY: Thieme Publishers;2009:329.
- Chan A, Leng T, Moshfeghi DM. Cannula-based 25-gauge vitreous tap and injection: A new surgical technique. Retina. 2012;32(5):1021–1022. doi:10.1097/IAE.0b013e318248e6ba [CrossRef]
- Singh R, Bando HD, Brasil OFM, Williams DR, Kaiser P. Evaluation of wound closure using different incision techniques with 23-gauge and 25-gauge microincision vitrectomy systems. Retina. 2008;28(2):242–248. doi:10.1097/IAE.0b013e318156dea3 [CrossRef]