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Anterior chamber (AC) paracentesis is a valuable procedure in the management of uveitis, particularly in diagnosing infective causes.1,2 It may also be used therapeutically to lower intraocular pressure,3 and it provides samples for clinical research. Nevertheless, there have been isolated reports of AC paracentesis related serious complications, including endophthalmitis and corneal abscess.4,5 As the risk of trauma to the iris and lens are also major concerns, AC paracentesis is often used with reluctance. Although there are many studies on the analysis of aqueous humour obtained from AC paracentesis, our literature search showed only one publication on the safety of AC paracentesis.6
The purpose of this study was to describe a method of AC paracentesis that can be easily performed as an outpatient procedure with the patient sitting at the slit lamp.
Methods and results
A total of 70 patients (41 male, 29 female) aged 18–83 years (median 39 years) with various types of active uveitis attending the Birmingham and Midland Eye Centre underwent AC paracentesis. Fourteen paracenteses were performed for diagnostic purposes while the remainder for experimental analysis as part of another study. Patients with dilated and undilated pupils were included. Local research ethics committee approval and informed consent was obtained.
Benoxinate 0.4% eye drops (minims) were instilled three times over a 3 minute period, followed by instillation of betadine 5% antiseptic solution that had been drawn up into the empty benoxinate minim container. The patient was positioned at the slit lamp, the upper lid and eyelashes held out of the way by an assistant. No lid speculum was required.
Of the 70 paracenteses, 48 were performed using a 27 gauge needle attached to an insulin syringe, while the remaining 22 were performed using an aqueous pipette. Where a 27 gauge needle was used, this was inserted at the paralimbal clear cornea in a plane above and parallel to the iris with the bevel of the needle facing forward until the whole bevel penetrated the cornea (fig 1). Under direct vision, the sampler pulled the plunger of the syringe to aspirate the aqueous. The aqueous pipette (Visitec, Sarasota, FL, USA designed by O’Rourke) consists of a short 30 gauge needle mounted inside plastic tubing, which in turn is connected to a soft polyethylene suction-infusion bulb. The bulb was squeezed to create a vacuum and the needle inserted at the limbus as described above (fig 2). When pressure on the bulb was released, aqueous spontaneously filled the pipette. Using either method, the eye can be fixed with a pair of forceps at the opposite limbus, if necessary. After sampling an antibiotic drop was prescribed for three days. The whole procedure takes less than five minutes. All patients were re-examined 20 minutes after the procedure and 1–2 weeks later.
Two patients had an air bubble inadvertently injected into the AC. The visual acuity returned to normal at review in both cases. One patient developed an acute allergic conjunctivitis to betadine, which settled after treatment with prednisolone 0.5% eye drops. None of the 70 patients developed detectable corneal damage, lens changes, or endophthalmitis.
Various methods for performing AC paracentesis have been described.6–9 However, our literature search only identified one systematic report investigating the safety of AC paracentesis.6 This technique required the patient to lie supine under the microscope, needed insertion of a lid speculum and preincision of the cornea with a 15° micro sharp blade, and the aqueous was aspirated using a 27 gauge needle on a tuberculin syringe. No serious complications were reported in 361 uveitis patients. A small hyphaema occurred in 5/72 (6.9%) patients examined 30 minutes after the paracentesis. The method described by O’Rouke using the aqueous pipette7 is relatively new and no systematic analysis of its safety profile has been published. Other methods for AC paracentesis include not using a syringe8 or a syringe with the plunger removed,9 thus avoiding any potential complications associated with aspirating with a plunger, but collecting the aqueous specimen may be technically difficult.
The cases of inadvertent injection of an air bubble into the AC both occurred using the aqueous pipette and was most likely caused by air trapped inside the bulb prior to inserting the pipette into the AC. We recommend ensuring the bulb is thoroughly depressed to evacuate all air before inserting the needle into the eye. Pressure on the bulb must also be maintained while the needle is being inserted, to avoid air entry.
Our study showed that performing AC paracentesis with the patient sitting at the slit lamp is safe using either the 27 gauge needle or the aqueous pipette. Preincision with a sharp blade and the use of a lid speculum is unnecessary.
We are grateful to Robert Harvey and Salman Mirza for their help in this study.