**4. Surgical principles and techniques**

Prior to the procedures described henceforth, an informed consent should be obtained from the patient after discussing the potential for complications. Since modern diagnostic techni‐ ques may require special preparation (e.g. special stains or cultures) the laboratory or pathol‐ ogist should be notified of the procedure and upcoming samples, and any requirements regarding the handling of the sample prior to delivery should be noted.

#### **4.1. Anterior chamber tap**

**2. History**

164 Advances in Eye Surgery

here.

**3. Indications**

diagnose and commence treatment.[3]

The earliest attempts at elective pars plana vitreous surgery were directed toward cutting opaque vitreous. While still not used for the diagnosis of the etiology, papers as early as the 19th century report on the procedure in the context of ocular inflammation. Bull reported in 1890 on 17 cases in which a pars plana approach (first introduced by Von Graefe in 1863) involving a discission needle introduced through the pars plana was used to cut vitreous

The 1970s were a period of major advancement in the field of pars plana vitrectomy (PPV), with the introduction of advanced instrumentation, such as the vitreous-infusion-suctioncutter (VISC). Indications for diagnostic procedures and the diagnostic methods themselves were limited at that time. In a review paper from 1974, Michels et al. [1] described vitreous biopsy as a procedure that is rarely needed, with the most frequent indications being mycotic endophthalmitis and reticulum cell sarcoma. The diagnostic methods that were mentioned included only cytology and culture. Vitrectomy for endophthalmitis was also mentioned in

One of the first papers to describe diagnostic vitrectomy was published by Engel et al in 1981. [2] Findings resulting from early procedures in that era included ocular tumors such as reticulum cell sarcoma and leukemic infiltration, as well as infectious entities such as fungal endophthalmitis and acute retinal necrosis (ARN). The methods described there included cytology, histopathology, and ultrastructural studies, with "new" methods such as using a

Since these early days, the field of diagnostic procedures has advanced rapidly. Methods including polymerase chain reaction (PCR), flow cytometry, and other advanced methods introduced in the general field of medicine have been adopted by ophthalmologists for use in ocular diagnostic procedures. With the introduction of these methods, the list of etiologies that can be recognized by invasive diagnostic techniques has also expanded, as will be described

Accurate diagnosis of the etiology behind intraocular inflammation is essential in order to provide the proper treatment and management and for prognostic reasons. While the general approach to uveitis patients includes history taking, review of systems, examination, and ancillary tests, at times none of these result in a conclusive diagnosis. In these atypical cases a diagnostic vitrectomy may lead to the correct diagnosis. An example for such an indication is primary intraocular lymphoma (PIOL), which requires a definitive tissue diagnosis to

this paper, and showed that performing the procedure for this entity was a novelty.

membranes resulting from inflammation or hemorrhage. [1]

millipore filter and celloidin-bag cell-block techniques.

Unlike diagnostic vitrectomy, an anterior chamber tap may be done in an office setting and is less invasive. It is important to note that this procedure yields a smaller amount of fluid for analysis in comparison with diagnostic vitrectomy, and as such may be considered in cases in which a small sample may suffice for diagnosis.

The procedure is done under an aseptic technique. The area around the eye is cleaned with povidone-iodine and a local anesthetic is instilled into the eye. It may be done at the slit lamp or with the patient in a supine position by using binocular loupes. The eye is opened and fixated with a speculum. The conjunctival surface is washed with povidone-iodine solution. A 27-30 gauge needle on a tuberculin syringe is inserted to the anterior chamber using a limbal approach, and 200 to 250 µL of fluid can be obtained. At the end of the procedure, an antibiotic drop and povidone-iodine solution is instilled into the eye and a broad spectrum antibiotic drop is prescribed for several days. [6, 7]

Anterior chamber tap is a relatively safe procedure. Possible complications include trauma to the cornea, lens, and iris; hyphema; corneal abscess; and endophthalmitis. However these complications are rare. [7]

#### **4.2. Vitreous aspiration needle tap**

A vitreous specimen for analysis can be obtained by straight needle vitreous aspiration, or vitreous tap. This procedure has the advantages of being easier to perform, being less traumatic to the eye than diagnostic vitrectomy, and offering the ability to perform it in an office setting. Disadvantages of vitreous aspiration include: (1) the risk for retinal detachment from vitreor‐ etinal traction during aspiration [8]; (2) a smaller amount of specimen in comparison to diagnostic vitrectomy as the procedure only yields about 300 µL of ocular fluid [9], which allows for fewer diagnostic tests and possibly a lower yield; (3) it is also not therapeutic, as a diagnostic vitrectomy could be, since it does not clear a large amount of vitreous (and thus does not allow for better diffusion of intraocular medications, [10] removal of pathogens or improved media clarity [11, 12]).

The procedure is done under an aseptic technique. The area around the eye is cleaned with povidone-iodine and a local anesthetic is instilled into the eye. The eye is opened and fixated with a speculum and the conjunctival surface is washed with povidone-iodine solution. A large-caliber needle is usually needed, such as a 21-gauge hollow needle, mounted on a 1 ml syringe as an aspirating device, which permits better control during the procedure. The needle is directed posteriorly in the direction of the optic nerve head and vitreous humor is obtained. At the end of the procedure an antibiotic drop and povidone-iodine solution is instilled into the eye, and a broad spectrum antibiotic drop is prescribed for several days. [9]

#### **4.3. Diagnostic vitrectomy**

The aim of vitrectomy is to try to obtain the maximum possible amount of tissue from which a diagnosis can be made. A small sample volume may reduce the diagnostic yield. A variety of techniques involving the use of 20, 23, and 25 G PPV have been described in the literature. [13-19] An undiluted vitreous sample is obtained using a 3 or 5 mL syringe attached to the vitreous cutter. When the vitrector is cutting the vitreous, the assistant manually aspirates it until the eye softens, and the infusion is turned on. This provides between 1-2 mL of undiluted vitreous. Some authors propose using continuous infusion of air or perfluorocarbon liquid to substitute the vitreous removed from the eyeball which allows obtaining a larger amount of vitreous. [20, 21]

Following collection of undiluted specimen, fluid infusion is initiated and a second syringe is placed on the vitreous cutter to collect 3-10 mL of a diluted vitreous sample. [11, 15, 18] The surgeon may then proceed with core vitrectomy, induction of a posterior vitreous detachment, and peripheral vitrectomy using a standard approach if necessary. [16, 19, 21] Meticulous peripheral vitrectomy in the presence of significant media opacity, as may occur in many uveitis patients, is accompanied by potential complications and should generally be avoided. [21]

#### *Complications*

Diagnostic vitrectomy carries the possibility of complications encountered in vitrectomy for other indications, with some added due to the nature of the underlying etiology.

Cataract formation is a common complication after vitrectomy procedures reported to range from 12.5%-80% in 20-gauge PPV and 22.7%-79.3% in small gauge PPV. [22] The rate of cataract progression is higher in individuals older than 50 years. [23]

Retinal detachment is a possible complication of any PPV. In the setting of diagnostic vitrec‐ tomy, this complication may be related to the underlying etiology. For example, in cases of viral or fungal endophthalmitis it may already appear at the time of surgery, complicating the diagnostic procedure. [24]

Retinal detachment may also occur as a result of surgery. Iatrogenic retinal tears at the time of surgery may lead to retinal detachment. [25] This complication is especially true in ARN, where necrosis of the retina leads to its atrophy and subsequent retinal break formation. [26] It also may occur due to the development of new retinal breaks postoperatively.

Other, rarer complications of PPV include open-angle glaucoma, [27] retinal and vitreous incarceration, endophthalmitis, and vitreous hemorrhage. [28]

#### **4.4. Chorioretinal biopsy**

diagnostic vitrectomy could be, since it does not clear a large amount of vitreous (and thus does not allow for better diffusion of intraocular medications, [10] removal of pathogens or

The procedure is done under an aseptic technique. The area around the eye is cleaned with povidone-iodine and a local anesthetic is instilled into the eye. The eye is opened and fixated with a speculum and the conjunctival surface is washed with povidone-iodine solution. A large-caliber needle is usually needed, such as a 21-gauge hollow needle, mounted on a 1 ml syringe as an aspirating device, which permits better control during the procedure. The needle is directed posteriorly in the direction of the optic nerve head and vitreous humor is obtained. At the end of the procedure an antibiotic drop and povidone-iodine solution is instilled into

The aim of vitrectomy is to try to obtain the maximum possible amount of tissue from which a diagnosis can be made. A small sample volume may reduce the diagnostic yield. A variety of techniques involving the use of 20, 23, and 25 G PPV have been described in the literature. [13-19] An undiluted vitreous sample is obtained using a 3 or 5 mL syringe attached to the vitreous cutter. When the vitrector is cutting the vitreous, the assistant manually aspirates it until the eye softens, and the infusion is turned on. This provides between 1-2 mL of undiluted vitreous. Some authors propose using continuous infusion of air or perfluorocarbon liquid to substitute the vitreous removed from the eyeball which allows obtaining a larger amount of

Following collection of undiluted specimen, fluid infusion is initiated and a second syringe is placed on the vitreous cutter to collect 3-10 mL of a diluted vitreous sample. [11, 15, 18] The surgeon may then proceed with core vitrectomy, induction of a posterior vitreous detachment, and peripheral vitrectomy using a standard approach if necessary. [16, 19, 21] Meticulous peripheral vitrectomy in the presence of significant media opacity, as may occur in many uveitis patients, is accompanied by potential complications and should generally

Diagnostic vitrectomy carries the possibility of complications encountered in vitrectomy for

Cataract formation is a common complication after vitrectomy procedures reported to range from 12.5%-80% in 20-gauge PPV and 22.7%-79.3% in small gauge PPV. [22] The rate of cataract

Retinal detachment is a possible complication of any PPV. In the setting of diagnostic vitrec‐ tomy, this complication may be related to the underlying etiology. For example, in cases of viral or fungal endophthalmitis it may already appear at the time of surgery, complicating the

other indications, with some added due to the nature of the underlying etiology.

progression is higher in individuals older than 50 years. [23]

the eye, and a broad spectrum antibiotic drop is prescribed for several days. [9]

improved media clarity [11, 12]).

166 Advances in Eye Surgery

**4.3. Diagnostic vitrectomy**

vitreous. [20, 21]

be avoided. [21]

diagnostic procedure. [24]

*Complications*

Chorioretinal biopsy should only be considered when the inflammatory process is localized primarily in the sensory retina, retinal pigment epithelium, or choroid and when in a previous workup neither aqueous nor vitreous samples provided the diagnostic answer. The main indication is diagnosis of a suspected intraocular lymphoma.

It is important to remember that this procedure involves a greater risk, including subretinal hemorrhage, vitreous hemorrhage, and retinal detachment, [29, 30] and should therefore only be used as a last resort.

The procedure may be done using 20 or 23 G 3-port PPV. Prior to the biopsy, undiluted and diluted vitreous samples are collected as described previously. The vitreous is separated over the biopsy site and intraocular diathermy is used to delineate the biopsy site and the border between the lesion and normal retina. A sample size of 1 x 1 mm or 2 x 2 mm is excised using vertical scissors or a diamond blade, while elevating the intraocular pressure temporarily to 70-90 mm Hg to prevent bleeding. The tissue is then grasped using intraocular forceps and removed through the sclerotomy site. Endolaser is applied around the biopsy site and the procedure is ended with long-acting gas or silicone tamponade. [21]
