Cytology and Pathology
Anterior chamber paracentesis for cytologic studies may be diagnostic in cases involving the anterior or sometimes the posterior segment. Anterior chamber paracentesis in suspected leukemia or lymphoma is sent for cytologic analysis. When there is concern for primary vitreoretinal lymphoma, undiluted vitreous biopsy fluid is sent for cytology and flow cytometry analysis with gene rearrangement studies and cytokine analysis.
Chorioretinal biopsy for pathology is technically challenging and calls for an experienced vitreoretinal surgeon. It may be useful in rapidly progressive posterior uveitic entities for which the etiology is unknown and the therapeutic regimen undetermined. Suspected intraocular lymphoma confined to the subretinal space is also an indication for a chorioretinal biopsy. It is usually performed only if diagnosis cannot be confirmed after all other less-invasive testing. Directed conjunctival biopsy of visible lesions can be useful in lymphoma, cicatricial pemphigoid, and sarcoidosis. Rarely, scleral biopsy can be useful when considering infectious etiologies for scleritis (see Chapter 7). Vitreous biopsy can also be done to identify the etiology of certain uveitides, particularly in suspected cases of infectious chorioretinitis.
Anterior chamber paracentesis technique
Paracentesis involves using sterile technique at the slit lamp or with the patient supine on a treatment gurney or chair. Topical anesthetic drops are instilled; the eye is prepared with topical povidone-iodine solution; and a lid speculum can be placed. A tuberculin (1-mL) syringe is attached to a sterile 30-gauge needle. The syringe is then advanced under direct or slit-lamp visualization into the anterior chamber through the temporal limbus or clear cornea parallel to the iris plane. As much aqueous is aspirated as is safely possible (usually 0.1–0.2 mL), avoiding contact with the iris and lens. Possible complications include anterior chamber bleeding, infection, and damage to the iris or lens.
Vitreous biopsy technique
Vitreous specimens can be obtained either by needle tap or by using a vitrectomy instrument. If a small sample is desired, a needle tap of the vitreous is typically performed with the patient partially reclining in an examination room chair. Topical and subconjunctival anesthesia are administered; the eye is prepared with topical povidone-iodine solution, and a lid speculum is placed. Typically, a 25-gauge, 1-inch needle on a 3mL syringe (to provide greater vacuum) is introduced through the pars plana, directed toward the midvitreous cavity, and used to aspirate the vitreous sample. A diagnostic vitrectomy is performed via a standard 3-port pars plana vitrectomy (see BCSC Section 12, Retina and Vitreous). The most common indications for vitreous biopsy include suspected infection, primary intraocular lymphoma or other intraocular malignancy, and infectious etiologies of posterior uveitis or panuveitis. (Endophthalmitis is discussed in detail in Chapter 12, and intraocular lymphoma in Chapter 13.) In addition, chronic uveitis that has an atypical presentation or an inadequate response to conventional therapy may warrant diagnostic vitrectomy.
In all these scenarios, testing typically requires undiluted vitreous specimens. It is possible to obtain 0.5–1.0 mL of undiluted vitreous for evaluation using standard vitrectomy techniques. Complications of diagnostic vitrectomy in uveitic eyes can include retinal tears or detachment, suprachoroidal or vitreous hemorrhage, worsening of cataract or inflammation, and, rarely, sympathetic ophthalmia. Although vitreous surgery can be therapeutic and diagnostic in cases of uveitis, the pharmacokinetics of delivered intravitreal drugs are markedly altered in eyes that have undergone pars plana vitrectomy; the half-life of intravitreal corticosteroids, for example, is significantly reduced in vitrectomized eyes.
Chorioretinal biopsy technique
Video 5-1 demonstrates chorioretinal biopsy.
Courtesy of P. Kumar Rao, MD.
Access the video at www.aao.org/bcscvideo_section09.
Excerpted from BCSC 2020-2021 series: Section 9 - Uveitis and Ocular Inflammation. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.