Diagnostic Vitrectomy

■Diagnostic vitrectomy should be considered only if the information sought will result in therapeutic and diagnostic consequences for the patient.

■Diagnosis of endophthalmitis, necrotizing viral retinitis and intraocular lymphoma are the most common indications for diagnostic vitrectomy.

■For diagnosis of primary intraocular lymphoma (PIOL), systemic steroids should be discontinued for at least 2 weeks before the vitrectomy.

■Air infusion allows maximal collection of undiluted vitreous.

■Direct communication between the ophthalmic surgeon and the laboratory staff is essential to ensure suitable investigations and to avoid delays in processing the vitreous specimens.

Contents

24.2Indications  . . . . . . . . . . . . .   237

24.2.1Endophthalmitis  . . . . . . . . . .   238

24.2.1.1Classification and Epidemiology  . . . .   238

24.2.1.2Clinical Features  . . . . . . . . . .   239

24.2.1.3Diagnosis  . . . . . . . . . . . . .   240

24.2.2.1Classification and Epidemiology  . . . .   241

24.2.2.2Clinical Features  . . . . . . . . . .   242

24.2.2.3Diagnosis  . . . . . . . . . . . . .   243

This chapter contains the following video clips on DVD: Video 40 shows Vitrectomy for Endophthalmitis and Video 41 shows Vitreous biopsy with indentation (Surgeon: Marc de Smet).

24.1 Introduction

Intraocular inflammation comprises a spectrum of entities. Although diagnosis is usually based on medical history, clinical findings and noninvasive testing, it may be necessary in some cases to collect intraocular fluid or tissue samples to confirm a diagnosis and to enable specific therapy. This diagnostic approach has benefitted both from advances in vitreoretinal surgery and from

24.2.2.4 Treatment  . . . . . . . . . . . . .   243

24.2.3Primary Intraocular Lymphoma  . . . .   244

24.2.3.1Classification and Epidemiology  . . . .   244

24.2.3.2Clinical Features  . . . . . . . . . .   244

24.2.3.3Diagnosis  . . . . . . . . . . . . .   244

24.2.3.4 Treatment  . . . . . . . . . . . . .   244

24.2.3.5Special Considerations  . . . . . . . .   245

modern laboratory techniques. Microbiological culture and detection of antibodies are traditional techniques to analyze intraocular fluid; polymerase chain reaction (PCR), cytological analyses and measurement of cytokine levels are now also routinely performed [4].

In this chapter we provide an overview on the indications and technique of diagnostic vitrectomy as well as management of vitreous specimens from patients with intraocular inflammatory disorders.

24.2 Indications

Pars plana vitrectomy is a major ocular surgical procedure, and diagnostic vitrectomy should be considered

only if the information gained from it may result in therapeutic or diagnostic consequences for the patient [10]. It is assumed that routinely performed ophthalmological examinations, such as biomicroscopy and fundoscopy, other noninvasive diagnostic methods (X-ray, ultrasound, MRI) and conventional laboratory testing from peripheral blood have failed to classify an intraocular inflammation. Diagnostic vitrectomy is usually considered in patients in whom an acute, chronic or progressive course of the disease is threatening vision and in whom empirical medical treatment has failed to control intraocular inflammation [26]. Common indications for diagnostic vitrectomy include severe, persistent infiltration of the vitreous which is not responding to established anti-inflammatory drug regimens with systemic corticosteroids or immunosuppressants in adequate dose and duration, intraocular inflammatory conditions suspicious for bacterial or mycotic endophthalmitis, and necrotizing viral retinopathies. Moreover, diagnostic vitrectomy represents the most important tool in the diagnosis of intraocular lymphoma, which belongs to the so-called masquerade syndromes mimicking uveitis. In the following, some of these entities will be described in more detail with the main focus on intraocular lymphoma as the most diagnostically challenging disease.

24.2.1 Endophthalmitis

24.2.1.1Classification and Epidemiology

Infective endophthalmitis is an urgent situation in ophthalmology, since it may result in substantial loss of vision or even in loss of the eye despite medical and surgical treatment. Endophthalmitis is classified as exogenous or endogenous depending on the route of infection.

Acute postoperative endophthalmitis after cataract surgery is the most common type of exogenous endophthalmitis with an estimated incidence of 0.2–0.3%. Whereas acute endophthalmitis following cataract surgery decreased continuously until the early 1990s, an increase in the incidence has been observed during the last decade, perhaps due to sutureless clear corneal incisions in modern cataract surgery [34]. Acute endophthalmi-

24 tis, which occurs between days 2 and 7 after cataract surgery, is most commonly caused by gram-positive bacteria, especially coagulase-negative staphylococci such as

Staphylococcus epidermidis, and Staphylococcus aureus. Gram-negative organisms like Pseudomonas aeruginosa can also cause endophthalmitis after cataract surgery. Postoperative delayed-onset endophthalmitis typically occurs 6 weeks or later after surgery when topical ster­

Fig. 24.1  Posttraumatic endophthalmitis [21]

oid therapy is discontinued and the balance between the immune response of the patient and the mostly low-vir- ulence bacteria becomes disturbed. Posttrabeculectomy endophthalmitis can be delayed for months or years after initial surgery but in other respects behaves as an acute endophthalmitis since it occurs from a new infection through the filtering bleb [21]. Propionibacterium acnes, an anaerobic gram-positive organism, is a well-known cause of chronic persistent endophthalmitis, which may occur months to years after extracapsular cataract surgery with implantation of an intraocular lens [6].

Whereas the course of posttraumatic endophthalmitis is similar to that of an acute postoperative endophthalmitis, its visual prognosis is even worse. Eyes with an intraocular foreign body of rural origin are at high risk to develop endophthalmitis (Fig. 24.1). Especially if the foreign body is contaminated with Bacillus cereus, a fulminant course with poor prognosis may occur [21].

Endogenous endophthalmitis, which comprises approximately 5–7% of all cases of endophthalmitis, is a result of the hematogenous spread of bacteria or fungi from a remote focus of infection to the eye. Although cases in healthy immunocompetent individuals have been reported, endogenous endophthalmitis usually occurs in patients with predisposing systemic risk factors, such as chronic immune-compromising conditions (e.g., diabetes mellitus), immunosuppressive diseases or therapies (e.g., malignancies, HIV, chemotherapy) or also long-term intravenous catheters. Persons with abuse of intravenous drugs or anabolic steroids are also at a higher risk to develop endogenous endophthalmitis [31, 42]. Streptococcus and Staphylococcus represent the most common bacterial, and Candida the most common fungal, organisms causing endogenous endophthalmitis [21].

24.2.1.3Diagnosis

Identification of the causative organism is the best way to ensure effective antimicrobial therapy in endophthalmitis. Pars plana vitrectomy and vitreous tap are common techniques to collect vitreous samples for microbiologic analysis. Pars plana vitrectomy allows simultaneous removal of the reservoir of pathogens and inflammatory mediators from the eye. Regarding visual outcome after postoperative bacterial endophthalmitis, the Endophthalmitis Vitrectomy Study (EVS) indicated a benefit of early vitrectomy over vitreous tap only in those patients with initial vision worse than hand motions [13]. On the other hand, the results of the EVS could be interpreted as demonstrating that pars plana vitrectomy has not shown results inferior to vitreous tap, even in eyes with initial vision better than light perception included [19]. Thus in some cases, pars plana vitrectomy can be recommended before visual acuity drops to light perception. Moreover, subsequent publications of the EVS data have shown that a larger proportion of patients with diabetes achieved 20/40 visual acuity after pars plana vitrectomy than after vitreous tap, although this difference was not statistically significant [11].

Bacterial or fungal culture of vitreous samples is a proven and routinely performed diagnostic technique. A positive result can be expected as soon as after 1 day, whereas the confirmation of a negative result may need 4–7 days. However, in various studies, less than 50% of bacterial or fungal cultures of intraocular fluids from eyes suspicious for endophthalmitis yielded a positive result. Several reasons, such as small sample sizes or prior use of antibiotics, have been postulated [25, 35]. The detection of DNA of sparse or fastidious organisms is one advantage of polymerase chain reaction (PCR), a molecular biologic technique of increasing importance. PCR has been demonstrated to be rapid, with results within 1–2 days, and to have higher sensitivity than bacterial or fungal culture. This high sensitivity makes PCR susceptible to false-positive results due to exogenous contaminations of the samples. Moreover, compared to culture, PCR does not confirm viability of the organism or allow assessment of antibiotic susceptibility [18]. Thus, in routine practice, both techniques are used in parallel. In a first step, universal PCR is performed to detect bacterial DNA in the sample. In a second step, se-

24 quencing of DNA could theoretically be used to identify the organism, or more specific primers could be used to identify selected organisms. At the same time, culture media are inoculated. Microbiologic culture still represents the “gold standard” in detecting bacteria or fungi.

To obtain optimal results within a short period of time, undiluted vitreous specimens should be forwarded immediately to an experienced microbiologist. When

vitrectomy is performed as an emergency procedure after hours, it may be necessary to inoculate the vitreous samples directly in the operating room on appropriate media, incubate them and pass them to the microbiologist later. The successful use even by less experienced residents of a special “endophthalmitis set” containing all necessary equipment to culture vitreous samples in the operation room has been reported by Ness et al. [24]. Although it is easy to perform, inoculation of blood culture bottles holds the risk that a rapidly growing microorganism may overwhelm others that are growing more slowly in the rare case of polymicrobial infection [24].

In cases of endogenous endophthalmitis with hematogenous spread of organisms, blood culture may additionally be helpful to establish the diagnosis, but it cannot replace culture and PCR testing of intraocular fluids [18].

24.2.1.4Treatment

Aims of endophthalmitis therapy are the eradication of the infective agent as well as the reduction of immune response. Primary vitrectomy may be beneficial not only to collect enough material for microbiological tests but also because it offers theoretical advantages, including removal of the infectious organisms and their toxins, removal of vitreous membranes potentially leading to retinal detachment, clearing of vitreous opacities and possibly a better distribution of intravitreal antibiotics [13]. To avoid further damage to the eye, medical treatment should start immediately. As the causative organism is usually not identified at this time, broad spectrum antibiotics are used.

For the treatment of exogenous bacterial endophthalmitis, we prefer systemic administration of either imipenem or vancomycin combined with ceftazidime. Ceftazidime is commonly recommended as effective for both gram-positive and gram-negative bacteria. Because the blood–eye barrier reduces penetration of systemic antibiotics into the vitreous, intravitreal antibiotics are the drugs of choice. Nevertheless, we commonly use intravenous application as well as periocular and topical application of antibiotics [21, 22]. Whereas the European Society of Cataract and Refractive Surgeons recommends vancomycin for intravenous use [3], we prefer imipenem because clinical studies suggest that therapeutic drug levels in the vitreous are achieved after intravenous application of imipenem but not after vancomycin [1, 14]. Combining the antibiotic regimen with systemic corticosteroids treats the concomitant intraocular inflammatory response [21].

In chronic persistent postoperative endophthalmitis due to Propionibacterium acnes, pars plana vitrectomy

with total capsular bag removal, exchange or removal of the intraocular lens and the application of intravitreal antibiotics may be necessary to stop recurrent intraocular inflammation [6]. Table 24.1 provides therapy regimens for various forms of exogenous bacterial endophthalmitis.

Treatment of endogenous endophthalmitis has to be coordinated with other involved specialties depending on the extraocular focus of the infection. Systemic antibiotics are more important in endogenous than exogenous bacterial endophthalmitis, but intravitreal antibiotics are still critically important in most cases.

Systemically administered antimycotic drugs are the mainstay in the therapy of endogenous fungal endophthalmitis. Whereas fluconazole is most commonly used in Candida endophthalmitis, amphotericin B remains the first choice for Aspergillus endophthalmitis. In the case of intolerance or contraindications for systemic antimycotic treatment or to improve efficacy, amphotericin B may also be injected intravitreally in doses of 5 µg in 0.1 ml. Table 24.2 provides an overview of treatment for fungal endophthalmitis. Intravenous or

intravitreal voriconazole is a newer option for the treatment of fungal endophthalmitis and provides broadspectrum antifungal coverage. The usual intravitreal dose of voriconazole is 50 µg in 0.1 ml.

24.2.2 Necrotizing Viral Retinopathies

24.2.2.1Classification and Epidemiology

Necrotizing viral retinopathies present acutely and are potentially blinding diseases. Three classic forms caused by viruses of the herpes family are acute retinal necrosis syndrome (ARN), progressive outer retinal necrosis (PORN) and cytomegalovirus (CMV) retinitis.

ARN is characterized by the triad of retinal and choroidal vasculitis, retinal necrosis and vitritis [12, 38]. Varicella zoster virus (VZV) and herpes simplex virus (HSV) types 1 and 2 are major pathogens in both healthy and immunocompromised individuals. However, cytomegalovirus (CMV) has been identified as a

Amphotericin B

or

in case of intolerance of systemic application, maximal every second day 0.005–0.01 mg intravitreally. Treatment duration depends on clinical course.

initially: 1x 0.1 mg/kg BW per day i.v. within 7 days: increase to 1x 1–1.5 mg/kg

causative agent of ARN in single cases in immunocompetent patients [12, 33, 37]. Although ARN may affect patients of any age, most of them are between 20 and 60 years of age with two peaks at about 20 and 50 years of age. There might be a slight predilection of the male gender [12].

PORN has been described as a disease with an extremely poor prognosis which is caused by VZV and HSV predominantly in patients with a compromised immune status either due to an underlying disease (e.g., HIV) or immunosuppressive treatment [39].

In the 1980s, CMV retinitis was the most common cause of blindness in patients with AIDS. CMV retinitis 24 usually develops at a late stage of AIDS and is strongly associated with the immune status of the patients which can be assessed by the number of CD4+ cells in peripheral blood. Patients in whom the CD4+ cell number drops below 50–100/mm³ are at high risk to develop CMV retinitis. With the introduction of highly active antiretroviral therapy (HAART) in AIDS patients, the incidence of CMV retinitis has decreased dramatically. Nevertheless, cases of CMV retinitis still may occur in

patients who do not respond to anti-HIV therapy or in non-HIV patients who are under systemic immunosuppressive treatment for other diseases [15].

24.2.2.2Clinical Features

ARN affects both eyes in approximately one third of patients with a delay of several weeks being not uncommon. Patients may complain of mild to moderate ocular or orbital pain, foreign body sensation, a red eye and decreased vision with floaters [12]. The main clinical characteristics of ARN defined by the American Uveitis Society include focal, well-demarcated areas of retinal necrosis located in the peripheral retina, rapid circumferential progression of necrosis, evidence of occlusive vasculopathy and a prominent inflammatory reaction in the vitreous and anterior chamber. Optic atrophy, scleritis and pain are supportive but not required for the diagnosis [16]. At a later stage of the disease, retinitis typically spreads to the posterior pole. Retinal holes that in combination with vitreous traction lead to rheg-

Diagnostic Vitrectomy

matogenous retinal detachment are frequently seen as a complication of ARN [38].

PORN is characterized by multifocal lesions of deep retinal opacification without granular borders. Lesions are located in the peripheral retina with or without macular involvement and tend to progress to confluence rapidly. In contrast to ARN, there is no or only mild intraocular inflammation and no vasculitis is present [39].

CMV retinitis can occur with two distinct clinical pictures. Fluffy, dense, white confluent opacifications of the retina with no central atrophic zone and multiple retinal hemorrhages with perivasculitis characterize the first type. Lesions are commonly located closer to the posterior pole and follow the nerve fiber layer in an arcuate distribution (Fig. 24.5). The second form presents with more granular, less opaque-appearing lesions with a central atrophic zone as well as fewer hemorrhages and perivasculitis. In both forms the retinal lesions are not sharply edged and only a mild vitritis and anterior chamber reaction occur. Although the retinal infiltrations usually proceed slowly, without treatment, destruction and necrosis of the entire retina will develop within 3–6 months [15].

24.2.2.3Diagnosis

Necrotizing viral retinopathies often present with an atypical clinical picture or with dense vitreous infiltration which can make clinical diagnosis difficult. Meas­ urement of serologic antibody levels may be of limited diagnostic value due to the normally high seroprevalence of antibodies against herpes viruses in the normal population, and because an infection located in the eye may not induce a detectable increase of antibodies in peripheral blood. Thus, sampling of intraocular fluid may be necessary to identify the causative virus and to enable specific antiviral therapy. Harvested aqueous or vitreous can be analyzed for local antibody production against herpes virus antigens. However, the presence of intraocular specific antibodies is not necessarily the result of a local antibody production, as a breakdown of the blood–eye barrier due to inflammation may lead to a passive antibody passage into the eye. Confirmation of local antibody synthesis is determined by calculating the Goldmann-Witmer coefficient, which compares antibody titers in serum and vitreous while adjusting for total immunoglobulin levels:

A value of 3 or higher is usually assumed as positive [36].

Fig. 24.5  CMV retinitis

Currently, polymerase chain reaction (PCR), a highly sensitive method to detect infectious DNA in small fluid samples, has been established as a means to identify the causative virus in necrotizing retinopathies. Because PCR may become negative due to prior antiviral treatment, concomitant determination of the GoldmannWitmer coefficient may be useful [5].

24.2.2.4Treatment

Intravenous acyclovir, which is effective for HSV and VZV, represents the mainstay of therapy in ARN. In resistant cases, a switch to more aggressive antiviral treatment with ganciclovir or foscarnet, or combination antiviral therapy, can be considered. After intravenous administration for 7–10 days, antiviral therapy should be continued orally for a period of 3 months or longer. In addition, intravitreal instillation of ganciclovir or foscarnet can be performed. Laser photocoagulation of retinal holes may be necessary to prevent retinal detachment [5]. There is a trend toward the use of oral rather than intravenous antivirals initially in the treatment of ARN, especially when combined with intravitreal injections.

Ganciclovir intravenously followed by oral administration as well as supplementary intravitreal application is the classic approach to treat CMV retinitis. Valganciclovir, foscarnet and cidofovir represent alternative anti-CMV drugs for systemic use. Additionally, etoposide, a topoisomerase II inhibitor, has been experimentally used for severe and refractory CMV infections [17,

20]. A major goal of treatment in patients with AIDS is the prevention of opportunistic infections such as CMV retinitis by recovery of immune status through the use of highly active antiretroviral therapy (HAART) [5].

24.2.3 Primary Intraocular Lymphoma

24.2.3.1Classification and Epidemiology

Primary intraocular lymphoma (PIOL) is the most common of the neoplastic masquerade syndromes. These are defined as disease entities that mimic uveitis [29]. PIOL generally signifies a primary central nervous system lymphoma (PCNSL) (a highly malignant non-Hodg- kin lymphoma) that presents with involvement of ret- ina–choroid, the vitreous and rarely the optic nerve. If both eyes and the CNS are affected, the disease is called “oculocerebral lymphoma”. Only half of the patients with ocular presentation are found to have CNS lesions on neuroradiologic examination at the time of diagnosis of intraocular lymphoma. Most PIOL are diffuse large cell B-cell lymphomas, typically affecting elderly patients in their fifth to seventh life decade with a clear preference for females. The prognosis is poor: PIOL is the ocular disorder with the highest five-year mortality [8, 41, 43]. Although there are no exact data available, PIOL shows an increasing incidence in both immunocompetent and immunocompromised populations. This may be due to the incidence of PCNSL, which has increased slowly since 1960, and which has tripled over the past 15 years [27, 28].

24.2.3.2Clinical Features

Whereas PIOL may be unilateral or bilateral at onset, both eyes will ultimately be involved in the majority of patients.

Blurred vision and floaters are the most common symptoms of patients with PIOL; pain and redness of the eye rarely occur [40]. About 20% of patients may be asymptomatic [27].

The clinical picture of PIOL is diverse. Slit lamp examination may reveal an anterior uveitis with granulo- 24 matous keratic precipitates. However, more typical presentations of PIOL are cellular infiltration of the vitreous often mimicking intermediate uveitis, as well as characteristic creamy orange-yellow chorioretinal infiltrations.

Glaucoma, neovascularization and optic neuropathy are rare findings in PIOL [8, 43].

24.2.3.3Diagnosis

The variability in the clinical picture and, often, an initial, moderate response to systemic corticosteroids frequently leads to a delay in the diagnosis of PIOL. However, an early diagnosis of PIOL is crucial both to prevent blindness and to allow early treatment. If there is clinical suspicion of PIOL, the diagnostic program usually includes ultrasound, fluorescein angiography and MRI of the brain. To confirm PCNSL, cytological analysis of the cerebrospinal fluid and occasionally brain biopsy may be indicated; however, vitreous biopsy is the mainstay of diagnosis of intraocular lymphoma.

Vitreous specimens are usually sent as rapidly as possible in nonfixed (fresh) state to a pathology laboratory. A delay during transportation may diminish the quality of the fragile samples. Recently, HOPE fixative (HEPES-glutamic acid buffer mediated organic solvent protection effect) has been demonstrated as a promising conservation medium for vitreous specimens, enabling preservation of cytomorphology and immunoreactivity. Fixation facilitates sending vitreous samples to external reference laboratories in good quality [9].

A wide range of laboratory investigations are in use to analyze vitreous specimens for lymphoma cells.

For cytomorphological evaluation, the unfixed or fixed vitreous specimens are best prepared by the Cytospin preparation technique, at 500 rpm for 5 minutes to concentrate the cells onto glass slides. Subsequently, the slides are air-dried and stained conventionally (May- Gruenwald-Giemsa, hematoxylin-eosin; Fig. 24.6a) and immunocytologically. Cytological analysis of PIOL samples usually reveals a mixture of mature inflammatory cells, large neoplastic lymphocytes and necrotic debris. As nearly all PIOL are B-cell lymphomas, immunocytology looks for the expression of B-cell surface antigens, such as CD20, CD79a or PAX5, and light immunoglobulinchains(Fig.24.6b).Flowcytometryisusedforimmuno­ phenotyping and quantitating monoclonal populations of cells in the vitreous specimens. Gene rearrangements detected by polymerase chain reaction (PCR) are indicative of monoclonality [8, 43]. Cytokine analysis uses the fact that B-lymphocytes produce interleukin (IL)-10 whereas T-lymphocytes produce IL-6. Therefore, elevated levels of IL-10 and an IL-10/IL-6 ratio larger than 1 in the vitreous have been reported to be supportive but not conclusive for the diagnosis of PIOL [2, 23].

24.2.3.4Treatment

So far, no uniform recommendations for the treatment of PIOL with or without CNS involvement exist. Treatment strategies include radiation therapy of the CNS and the

Fig. 24.6  Microphotographs of a vitreous specimen of PIOL. a Hematoxylin-eosin stain, showing atypical cells with large pleomorphic nuclei, as well as deteriorated cells in the background (×1,000, oil immersion). b CD20 stain demonstrating that the large majority of the vital cells are B-lymphocytes.

eyes alone or in combination with systemic chemotherapy with or without intrathecal chemotherapy. Recent promising data suggest that monotherapy with six cycles of high-dose methotrexate intravenously, which has been shown to induce complete remission in 40–89% of patients with PCNSL, may also lead to a dramatic reduction of 5-year mortality in patients with PIOL [32, 43].

24.2.3.5Special Considerations

Diagnosis of PIOL is challenging. To obtain reliable results from diagnostic vitrectomy, vitreous specimens have to contain an adequate number of evaluable cells, which necessitates a suitable surgical technique. Moreover, the preoperative preparation of the patients is highly important. Because prior steroid therapy will increase the fragility of tumor cells, diagnostic vitrectomy to confirm PIOL should be performed only at a time when patients are on the lowest dose of corticosteroids as possible; a completely corticosteroid-free interval of at least 2 weeks prior to diagnostic vitrectomy is preferred [27, 28]. Even with these precautions, false-nega- tive results of diagnostic vitrectomy are not uncommon. If the suspicion of PIOL persists, diagnostic vitrectomy can be repeated, on the contralateral eye if necessary. If repeated vitrectomies remain negative and a subretinal infiltration is present, a choroidal biopsy can be considered. In rare cases, when vision has been lost or a definitive diagnosis cannot be reached, enucleation may be a further diagnostic option [7, 30].

There are some negative-staining cells, which are probably either reactive T-cells or macrophages (×400). (Courtesy of Dr. S. Coupland, Dept. of Cellular and Molecular Pathology, University of Liverpool)

24.3 Surgical Procedure

Vitreous biopsy can be obtained by vitreous tap (according to the guidelines of the EVS Study [13]) or during complete vitrectomy with a 20-G, 23-G or 25-G pars plana approach. The main disadvantage of vitreous tap is the small amount of harvested volume for microbiological, virological, pathological and immunological laboratory investigations. This disadvantage can be overcome by an approach via pars plana. However, using the standard procedure, diluting the removed vitreous volume with balanced salt solutions would interfere with testing for which undiluted specimens are preferred, such as PCR, antibodies, and cytokine determinations. For that reason, the “air vitrectomy” has been introduced in the armamentarium of vitrectomy techniques. Only two steps of the standard approach need to be modified:

1.Aspiration of the vitrectomized fluid must be performed manually using a 10-ml syringe connected to the aspiration line of the vitreous cutter by an adaptor.

2.To exchange the aspirated volume by air, the automatic air pump of the vitrectomy machine is used. The pressure should be adjusted to 30–40 mmHg to avoid globe collapse by manual aspiration.

performing a posterior vitreous separation and complete anterior vitrectomy to harvest cell-rich material for cytological investigation, which can then be performed after centrifugation of the whole volume.

Two remarks must be made:

1.In eyes following severe ocular trauma with ruptured choroid, air vitrectomy is contraindicated because of the risk of fatal air embolus via the vortex veins.

2.No attempt should be made to create a posterior vitreous separation by manual aspiration under air, because of the high risk of globe collapse and retinal injury.

24

24.4 Processing of Vitreous Specimens

Vitreous specimens should be marked as “urgent” and have to be sent off immediately after surgery to the diag-

laboratories of the involved specialties.

In Table 24.3, we provide a recommendation on how to portion the intraoperatively harvested vitreous for subsequent laboratory investigations. However, specimen sizes which are needed for investigation as well as the containers for transport (e.g., syringes or tubes) may differ between various laboratories and have to be arranged on site.

Take Home Pearls

■Diagnostic vitrectomy is a helpful tool if conventional diagnostic methods fail to classify a uveitis or if intraocular inflammation does not respond to empirical medical treatment.

■Modern molecular biologic techniques assist analysis of vitreous specimens for infection or masquerade syndromes.

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