Ординатура / Офтальмология / Учебные материалы / Uveitis Text and Imaging Text and Imaging Text and Imaging 2009

of the WHO regions. The incidence of all forms of TB, the incidence of infectious (smear-positive) cases, and mortality are shown both as the total number of cases and as the rate per 100,000 population. The largest number of cases occurs in the South-East Asia Region, which accounts for 33% of incident cases globally. However, the estimated incidence per capita in subSaharan Africa is nearly twice that of the South-East Asia, at 350 cases per 100,000 population. It is estimated that 1.75 million deaths resulted from TB in 2003. As with cases of disease, the highest number of estimated deaths is in the South-East Asia Region, but the highest mortality per capita is in the Africa Region, where HIV has led to rapid increases in the incidence of TB and increases the likelihood of dying from TB.

Figures 4 and 5 show the TB notification rates in the world and in Europe.

The WHO has declared TB a global emergency, as it remains the most common cause of mortality from single infectious disease (Figure 6).

Table 2 shows the reported TB incidence rates (total cases and excluding HIV infection) in Italy from 1990 to 2003 (WHO global database). Data suggest that both are decreased to the half, from 14 cases/100,000 per year to 7/100,000 per year. The median age of nationals is between 55 and 64 yrs and of non-nationals between 25 and 34 yrs.

The most common clinical manifestation of TB is pulmonary disease, close to 80% of active cases.2 TB may affect many organs and systems, including lymph nods, larynx, middle ear, genitourinary tract, central nervous system, etc. Extra pulmonary TB including

Figures 4 and 5: TB notification rates in the world and in Europe, 2003 (WHO source)

ocular involvement occurs in less than 20% of the cases. There was an increase of extrapulmonary TB from 16% in 1992 to 21% in 2002 of all reported cases to the CDC.3 The ocular manifestations may follow the pulmonary TB or may occur without evidence of pulmonary or other systemic signs. Roughly 60% of

Figure 6: (WHO source)

Table 2: Incidence of TB in Italy

In 2004 the case notification rate was 7 per 100.000 as in 2003, confirming the decreasing trend of TB.

patients with extra pulmonary tuberculosis have no evidence of pulmonary involvement.4

Any ocular tissue may be affected, including the ocular adnexae, the cornea, the conjunctiva, the sclera, the uveal tract, the retina, and the optic nerve.5

Ocular manifestations associated with TB are caused by an active infection or an immunologic reaction in the absence of any infectious agent: it is related to delayed hypersensitivity and an aseptic reaction.6

Nowadays, in Europe the most frequent causes of infectious uveitis are toxoplasmosis and uveitis due to herpes-viruses,7 whereas the percentage of cases attributed to TB amounts to less than 2%. After a gradual decrease of the incidence of ocular TB since

the late 1950s, ocular morbidity due to this infectious agent, has re-emerged in the last decade.8 There are no reliable data to suggest the prevalence rates of ocular TB. However a 1997prospective study from Spain reported 300 culture-proven patients with TB; the authors examined 100 randomly selected patients with proven systemic TB to document ophthalmic involvement that was found in 18 patients with choroiditis, papillitis, retinitis, vasculitis, dacryoadenitis and scleritis.8

In a retrospective analysis of 200 referred patients with uveitis in Saudi Arabia, Islam and Tabbara9 reported tubercular etiology in 10.5%, next only to toxoplasmosis. Also in Japan there was an increase of tubercular infection (6.9%) in 189 referred patients with uveitis.10

CLINICAL SYMPTOMS AND SIGNS

Uveitis appears the most frequent ocular manifestation of TB. Patients with TB-associated uveitis present unilateral or bilateral redness, photophobia, myodesopsiae, and sometimes pain due to ocular hypertension. The most frequent clinical presentation is a chronic granulomatous uveitis that shows mutton-fat keratic precipitates (KPs), iris nodules, posterior synechiae and secondary glaucoma, retinal vasculitis and chorioretinal granuloma. Non-granulomatous panuveitis may also occur.11

In the acute phase of uveitis, the KPs (Figure 7) are white-yellowish and may appear moderate-large in

Figure 7: Granulomatous keratic precipitates (“mutton fat”) present in a patient with presumed TB uveitis. The KPs can be differentiated from sarcoidosis by being smaller and less confluent

Figure 8: Posterior synechiae in non granulomatous uveitis of presumed TB uveitis

size, with demarked edge, smaller and less confluent, in comparison with the same seen in sarcoidosis, localised in the lower half of the cornea. The anterior

chamber shows flare and cells and formation of the posterior synechiae (Figure 8), that in chronic phase can cause complications like cataract and/or ocular hypertension. Glaucoma may also be induced by anterior angle nodules (Figures 9A and B) and/or anterior synechiae.12,13

The iris nodules (Figures 10A and B) (Koeppe and Busacca) are also smaller compared with the same seen in sarcoidosis.

The vitreous involvement is variable from low grade of anterior vitritis to a more severe vitreous involvement with snowballs opacities visible inferiorly in the vitreous cavity (Figure 11).14

Neuroretinitis with optic disc oedema and macular star may be associated with tubercular retinal vasculitis (Figures 12 and 13).15

Multifocal choroidal involvement is the most important evidence that tuberculosis has haemato-

Figure 11: Optic nerve atrophy, occlusive vasculitis and mild vitritis in Ocular TB

Figure 12: Neuroretinitis with optic disc oedema and macular star (acute phase of ocular TB)

genous origin. For this reason choroid is the site with the most severe involvement, demonstrating multiple tubercles and sometime extending into the overlying retina. The introduction of indocyanine green angiography (ICGA) represents a useful tool to detect subclinical choroidal lesions: numerous lesions may be seen as hypofluorescent spots in the intermediate phases that become either isoor remain hypofluorescent in late phases. Other ICGA signs, indicating acute phase disease, are small hyperfluorescent pin-points, fuzziness of choroidal vessels, late choroidal hyperfluorescence. The ICGA changes are reversible and

may be used to monitor disease activity and to detect the response at the specific therapy.

On fundus examination, it is possible to see multiple, asymmetric, bilateral chorioretinal scars often pigmented that can be associated with choroidal lesions resembling like as yellow-grey deep discolourations, which are present in new cases (Figure 14). Choroiditis can be present alone or in association with retinal vasculitis and infiltration.

Retinal periphlebitis is also encountered in relation with Eales’ disease (Figure 15). This is a controversial topic referring to a syndrome occurring in young

Figure 14: TB related posterior granulomatous uveitis (well circumscribed choroidal lesions and occlusive peripapillary vasculitis)

healthy males with hypersensitivity to tubercular proteins including peripheral retinal periphlebitis, retinal capillary nonperfusion, and recurrent vitreous haemorrhages caused by neovascularisation.16 A recent study showed that reactive nitrogen species and reactive oxygen species were elevated in Eales’ patients, indicating that free radicals are involved in mediating tissue damage.17

The incidence and prevalence of TB-associated uveitis is still controversial.18

DIAGNOSIS

The diagnosis of proven tuberculous uveitis is difficult to make because ocular sampling for microbiologic

determination is not very effective. When performed, aqueous and vitreous paracentesis have generally failed to show positive bacterial culture.19

Therefore, in most cases the term of presumed ocular tuberculosis (POTB) should be used in the absence of hard microbiologic evidence: this term includes both the hypersensitivity uveitis and the unsubstantiated infectious cases where the diagnosis is rendered probable on the basis of a good clinical response following specific therapy.

Intradermal purified protein derivate (PPD) is the standard diagnostic and screening skin-test. The main use of the PPD test is to show supportive information when clinical signs and symptoms suggest tuberculosis.

The American Thoracic Society and CDC consider reaction of 5 mm or more to be positive in very high risk individuals (HIV-infected patients), 10 mm or more to be positive in high-risk patients (foreign-born individuals, HIV negative intravenous users and those with medical conditions that increase the risk of TB) and 15 mm or more to be positive in individuals with none of the previous risk factors.20

In some cases, the infectious agent seems to trigger an immune, hypersensitive response resulting in intraocular inflammation which is not the direct result of an ongoing infection.21,22

Ocular tuberculosis may occur without pulmonary findings (Figures 16 and 17).23

Early diagnosis and treatment are the most important goal to prevent ocular complication and to avoid the side effects of non specific therapies.

Figure 16: Right apical excavation in TB acute phase (Courtsey of Dr A Cavazza, Deptt of Anatomo-pathology, ASMN, Reggio Emilia, Italy)

Figure 17: Chest radiograph revealed intercleido-hilar infiltrate TB related in right lung (Courtsey of Dr A Cavazza, Deptt of Anatomo-pathology, ASMN, Reggio Emilia, Italy)

LABORATORY DIAGNOSTIC TESTS

The laboratory diagnosis of Mycobacterium tuberculosis is largely based on direct microscopy and culture for mycobacterium. Direct microscopic examination to detect acid-fast bacilli (Ziehl-Neelsen staining) has very low sensitivity. Furthermore the gold standard of isolation of mycobacterium is time consuming and has low sensitivity, especially in case of extra-pulmonary diseases. An alternative to these methods is the application of nucleic acid amplification (NAA) tests, that

represent very useful tools to detect Mycobacterium tuberculosis in clinical specimens, to identify mycobacterium species, to detect drug resistance and type for epidemiological investigation.24 The availability of a rapid, sensitive and specific test is crucial, especially in the management of extra-pulmonary tuberculosis. PCR has several advantages over culture, including confirmation of the presence of M. tuberculosis within 1 to 3 days as compared to 6 weeks with conventional culture techniques. DNA amplification can be used for tissue specimens which are already formalin-fixed and paraffin-embedded.

Among NAA tests the best-known and most widely used test is the Polymerase Chain Reaction (PCR), in particular nested PCR.25,26 Several groups use IS6110 primers to detect M. tuberculosis in specimen from patients with pulmonary and extra-pulmonary tuberculosis.22,26,27 But this method has shown low sensitivity and a group from Chennai, India has tried to improve the sensitivity of nested PCR using primers targeting the MPB64 gene.26-29 This technique represents a very useful tool for detection of M. tuberculosis in paucibacillary extra-pulmonary specimens.

In recent years the advent of real-time PCR has made possible serial quantitative monitoring of the microbial load during the therapy regimen, measuring the treatment efficacy and evaluating the prognosis of disease.

NAA tests are fundamental in paucibacillary diseases characterised by low mycobacterial load. In fact the presence of positive Ziehl-Neelsen smear with a positive NAA test is diagnostic of active tuberculosis, whereas positive Ziehl-Neelsen smear with a negative NAA test, in the absence of inhibitors, would indicate nontuberculous mycobacterial disease.

The sensitivity of NAA can be reduced by the presence of PCR inhibitors, especially in extra pulmonary specimens, leading to false-negative results. Extra extraction steps can overcome this problem even if additional process can invariably cause the loss of mycobacterial DNA.

Tuberculin skin test (TST) was the only test used for screening in latent TBC infection (LTBI).30-35 The TST measures delayed type hypersensitivity response to the purified protein derivative (PPD). A major limitation of PPD is the fact that it is a crude mixture of several antigens, many of which are shared among

M. tuberculosis, M. bovis BCG, and several non-tuber- culous mycobacteria (NTM). In fact, a positive TST result could potentially be due to true infection with M. tuberculosis, prior BCG vaccination, or due to exposure to NTM. TST has lower specificity in populations with high BCG coverage and NTM exposure. Also, its sensitivity may be low due to anergy in individuals with depressed immunity (e.g. HIV infection). Further, the administration and reading of TST poses several unique problems—under reading, within and between reader variability, digit preference, the need for trained personnel to read the test results, and the requirement for patients to return for the purpose test reading. On account of all these limitations, there has always been a need to develop alternative tests to detect latent TB infection. Recent advances in genomics, molecular biology, and immunology have led to a promising generation of alternative tests such as T cell based, in vitro, interferon-γ (IFN-γ) assays. The IFN-γ assay is based on the concept that T cells of individuals sensitised with M. tuberculosis release interferon-γ (IFN-γ), a Th-1 cytokine, when they reencounter mycobacterial antigens. A high level of IFN-γ response is likely to indicate previous sensitisation with M. tuberculosis, but does not necessarily imply active disease. The IFN-γ assay like TST cannot easily distinguish between latent infection and active disease. Early versions of IFN-γ assays employed PPD as the stimulating antigen while newer assays employ antigens that are highly specific to M. tuberculosis, including the early secretory antigenic target 6 (ESAT- 6) and culture filtrate protein (CFP-10) that are not shared with the BCG sub strains and most NTM species. Tests based on these TB specific antigens are called RD1 based IFN-γ assays. The QuantiFERON-TB ® assay (Cellestis Limited, Carnegie, Australia) was the first IFN-γ assay to become commercially available. This whole blood test was approved by the US Food and Drug Administration (FDA) in 2001 and is available in many countries.36 The first generation assay measures IFN-γ response to PPD and thus was susceptible to the same specificity problems as the TST. This PPD based assay has currently been replaced by an enhanced assay, the QuantiFERON-TB-Gold ® test (which uses ESAT-6 and CFP-10 in place of PPD), currently available in Europe, and approved by the US FDA in December 2004.

The enzyme linked immunospot (ELISPOT) is also employed to detect IFN-γ response.37 The T SPOT-TB ® (Oxford Immunotec, Oxon, UK) is an assay on peripheral blood mononuclear cells (PBMC), that employs ESAT-6 and CFP-10, and detects the number of IFN-γ producing T cells using a sensitive ELISPOT technology. This test, currently available in Europe, is awaiting US FDA approval.

The TST has variable sensitivity and specificity, depending on the population screened. Specificity of TST tends to vary more than sensitivity. TST has the ability to predict active TB among latently infected individual and is a simple test with low material costs that does not require a laboratory. Therefore, it has been extensively used in resource limited settings for both clinical testing (in children) and epidemiological field studies, like in India. IFN-γ assays outperform the TST showing a higher specificity, better correlation with indirect measures of exposure to M. tuberculosis, and relatively less cross reactivity due to BCG vaccination and NTM infection. In terms of sensitivity, RD1 based IFN-γ assays that use cocktails of specific antigens (a mixture of ESAT-6 and CFP-10) appear to be at least as sensitive as the PPD based TST. The other advantages include rapidity, a single patient visit, and the ability to perform repeat testing without boosting. A major limitation of IFN-γ assays is their higher material costs and the need for laboratory infrastructure (the laboratory has to have the capacity to run ELISA or ELISPOT. Because of the lack of a gold standard for latent infection, it is impossible to accurately determine the sensitivity and specificity of IFN-γ assays for the diagnosis of latent infection. Most studies reported modest to high agreement (60 to 80%) between the TST and IFN γ tests. TST and IFN-γ assays have advantages and limitations, and both tests appear to be useful. IFN-γ assays has increased the diagnostic tools available for LTBI. The decision to select one or the other will depend on the population, the goal of testing, and the resources available. Because of its higher specificity, IFN-γ assays will be helpful in low endemic populations where cross reactivity due to BCG and NTM pose problems in TST interpretation. It is also likely to reduce false positives and enhance targeted LTBI treatment, particularly in low incidence settings. Cross reactivity due to BCG appears to be an important issue in some populations where BCG

vaccination is not given at birth, but later on in life. Further, IFN-γ assays may be helpful in immunosuppressed individuals in which anergy cannot be discriminated from a true negative TST result.38 In high-burden and resource-limited settings such as India the TST might continue to serve a useful purpose. To fully evaluate the utility of IFN-γ assays in high burden countries such as India, long-term cohort studies are needed to determine the association between positive IFN-γ results and the subsequent risk of active TB.

OUR EXPERIENCE

Our collective patients included 37 HIV negative individuals (15 men and 22 women) affected by presumed ocular tuberculosis (POTB).

The diagnostic criteria for presumed ocular TB were: (1) Anterior uveitis, retinal vasculitis and/or chorioretinitis compatible with a tuberculous aetiology

(2) Mantoux tuberculin skin test (2 UI of PPD) > 15 mm diameter of induration or MultiMerieux tuberculin skin test (1 UI of PPD) > 9 mm diameter of induration (3) Exclusion of other possible causes of uveitis (4) Absence of recurrences after the induction period (at least three months) of specific therapy.

The median age of the group at diagnosis was 55.0 (range of age 20-77 years).

26 patients presented with a granulomatous panuveitis; 8 with a posterior uveitis; 2 a non-granulo- matous panuveitis and 1 with an anterior nongranulomatous uveitis with synechiae and iris infiltration.

Patients were divided into two groups: the first group included all patients for whom the diagnosis had been performed at the first presentation while the second group included all patients for whom the diagnosis was missed at the disease onset. In the latter group there were both chronically evolving referred patients and patients already being followed otherwise in the department and for whom a reappraisal was performed by the authors. Most of these patients were receiving with an ongoing systemic corticosteroid and/or immunosuppressive therapy.

For each patient the diagnostic delay was calculated from the onset of the disease to the time of diagnosis. Treatment in patients with the newly developing

disease included triple anti-tuberculous therapy (isoniazide 300 mg/day, rifampin 600 mg/day, ethambutol 15 mg/kg/day) associated in most cases with low-dose steroid anti-inflammatory treatment.

Patients diagnosed while already under inappropriate corticosteroid and/or immunosuppressive therapy underwent triple anti-tuberculosis therapy followed by progressive tapering of the ongoing corticosteroid and/or immunosuppressive therapy.

The average duration of the follow-up for the whole collective after initiation of anti-tuberculosis therapy was 30.4 ± 13.4 months.

For all patients the treatment included anti-tuber- culous triple therapy given for a minimum of 6 to a maximum of 24 months with a mean of 10.7 months. All patients received additional systemic corticosteroids at low dosage (2.5-5 mg/day) for a maximum of six months.

After the specific therapy the improvement of visual acuity was highly significant in both eyes (p < 0.001). Also the mean intraocular pressure (IOP) showed a highly significant decrease in both eyes (p < 0.001). Only 3 patients (10%) showed recurrences.

In the group of 30 patients with a delayed diagnosis the mean delay was 5.7+/- 4 years.

We used an angiographic score to quantify the ocular inflammation degree of retinal and choroidal inflammation. The angiographic evaluation was made in a masked fashion following a scoring system from 0 to 4 both for fluorescein and indocyanine green angiography as described previously.39

Using this scale the mean score of FA and ICGA decreased significantly (p< 0.001).

Extraocular involvement was found in 22 patients (59.4%): 18/22 in the pulmonary area, 2 in the urinary tract and prostate, 1 with sialoadenitis, 1 with abdominal lymphonodal calcification, 1 with annexitis (one patient having both an active urinary tract involvement and an old pulmonary involvement). In 6 of the 37 patients tuberculosis was considered active by the internist with a positive PCR in the blood for one of them.

Fluorescein angiography (FA) and Indocyanine green angiography (ICGA) were positive in all cases with pan or posterior uveitis.

The main fluorescein angiographic signs were:

(1) macular oedema; (2) Optic nerve hyperfluorescence

Figure 18: Acute phase FA showed papillitis, retinal vasculitis and macular oedema

with leakage; (3) Retinal vasculitis; (4) TB lesions with early hyperfluorescence with leakage around the margins (Figure 18).

The main indocyanine green angiographic signs were (1) hypofluorescent areas in the early phases of angiography; (2) diffuse small hyperfluorescent spots;

(3) choroidal fuzzy vessels; (4) Diffuse choroidal hyperfluorescence (Figure 19).

Our study shows that presumed tuberculous uveitis is recognized after a very long diagnostic delay

of more than five years. Many of these patients came to the referral centres after many years of corticosteroid and/or immunosuppressive therapy. Their therapeutic threshold of immunosuppressive therapy is characteristically high, with recurrences occurring during tapering of therapy when dosages are still elevated. It seems that these undiagnosed cases are the result of the low tuberculous prevalence that was experienced during the past decades with the consequence that the diagnosis was neglected.

Our data show that the ophthalmologist should be attentive and suspect of a presumed tuberculous aetiology when a patient is presenting with a granulomatous hypertensive uveitis of unknown origin that promptly recurs upon tapering corticosteroid and/or immunosuppressive therapy. The drawback with this entity is the difficulty to get a definite diagnosis as positive investigational tests can hardly be obtained. The indirect confirmation in patients presenting a compatible uveitis comes from the response to therapy,15 in particular the resolution of the inflammation and hypertension, the improvement of function and the quasi absence of recurrences despite decrease or discontinuation of immunosuppressive therapy that occur after the introduction of specific anti-tuberculous therapy. Very often systemic investigations are not contributory to the diagnosis of tuberculous involvement. In most of our patients, sputum, urine and blood cultures failed to isolate the suspected causative organisms. Similarly the chest X-ray very often did not

show any signs of pulmonary involvement. These elements speak for the fact that isolated ocular involvement or activity can occur as is the case for sarcoidosis. Given these diagnostic difficulties, the diagnosis relies only on the ophthalmologist’s experience and clinical sense and the objective improvement that is measured following the introduction of specific therapy. Even when the PPD skin test is performed and followed as an indicator for treatment we still can miss some cases as in 10 to 20% of patients with proven tuberculosis and no apparent immunosuppression the tuberculin skin test will be negative . One patient with biopsyproven choroidal tuberculosis has been described as having a negative tuberculin skin test reactions.41

Because choroidal lesions are frequently sub clinical and not detected by fundus examination or fluorescein angiography, indocyanine green is more useful in quantifying the choroidal involvement well related to the disease activity. For this reason ICG could be the best predictor in the diagnosis and follow-up to evaluate the efficacy of systemic therapy.

REFERENCES

1.Jasmer RM, Nahid P, Hopewell PC. Latent Tuberculosis Infection. N Engl J Med 2002;347(23):1860-6.

2.Tabbara KF. Ocular tuberculosis: anterior segment. Int Ophthalmol Clin 2005;Spring;45(2):57-69.

3.CDC. Reported tuberculosis in the United States, 2002. Atlanta, GA: US Department of Health and Human services, CDC; 2003.

4.Alvarez S, McCabe WR. Extra pulmonary tuberculosis revisited: a review of experience at Boston City and other hospitals. Medicine (Baltimore) 1984;63(1):25-55.

5.Helm CJ and Holland GN. Ocular Tuberculosis. Survey of Ophthalmology 1993;38(3):229-56.

6.Biswas J, Madhavan HN, Gopal L, et al. Intraocular tuberculosis. Clinic pathological study of five cases. Retina. 1995;15:461-8.

7.Tran VT, Auer C, Guex-Croiser Y, et al. Epidemiological characteristics of uveitis in Switzerland. Int Ophthalmol 1994-95;18(5):293-8.

8.Bouza E, Merino P,Munoz P, et al. Ocular tuberculosis. A prospective study in a general hospital. Medicine 1997; 76:53-61.

9.Islam SM, Tabbara KF. Causes of uveitis at The Eye Center in Saudi Arabia: a retrospective review. Ophthalmic Epidemiol 2002;9:239-49.

10.Wakabayashi T, Morimura Y, Miyamoto Y, Okada AA. Changing patterns of intraocular inflammatory disease in Japan. Ocul Immunol Inflamm 2003;11(4):277-86.

11.Abrams J, Schlaegel TF Jr. The role of the isoniazid therapeutic test in tuberculous uveitis. Am J Ophthalmol 1982;94(4):511-5.

12.Saricaoglu MS, Sengun A, Guven D, et al. Ocular tuberculosis with angle granuloma. Eye 2004;18:219-20.

13.Demirci H, Shields CL, Shield JA, et al. Ocular tuberculosis masquerading as ocular tumors. Surv Ophthalmol 2004; 49:78-89.

14.Gupta A, Gupta V, Arora S, et al. PCR-positive tubercular retinal vasculitis: Clinical characteristics and management. Retina 2001;21:435-44.

15.Wolfensberger TJ, Piguet B, Herbort CP. Indocyanine Green Angiographic features in Tuberculous Chorioretinitis. Am J Ophthalmology 1999;127:350-3.

16.Herbort CP, Cimino L, El Asrar AM. Ocular vasculitis: a multidisciplinary approach. Curr Opin Rheumatol 2005; 17(1):25-33.

17.Rajesh M, Sulochana KN, Punitham R, et al. Involvement of oxidative and nitrosactive stress in promoting retinal vasculitis in patients with Eale’s disease. Clin Biochem. 2003;36:377-85.

18.Helm CJ, Holland G. Ocular Tuberculosis. Survey of Ophthalmology 1993;38:229-56.

19.Woods AC. Endogenous Uveitis. Baltimore, Md: Williams and Wilkins; 1956.

20.American Thoracic Society and Center for Disease Control. Diagnostic standards and classification of tuberculosis. Am Rev Respir Dis 1990;142:725-35.

21.Bodaghi B, LeHoang P. Ocular tuberculosis. Curr Opin Ophthalm 2000;11:443-8.

22.Gupta V, Gupta A, Arora S, et al. Presumed tubercular Serpiginouslike Choroiditis: clinical presentations and management. Ophthalmology 2003; 110:1744-9.

23.Sarvananthan N, Wiselka M, Bibby K. Intraocular tuberculosis without detectable systemic infection. Arch Ophthalmol 1998;116(10):1386-8.

24.Cheng VC, Yew WW, Yuen KY. Molecular diagnostics in tuberculosis. Eur J Clin Microbiol Infect Dis. 2005;24:71120.

25.Yam WC, Cheng VC, Hui WT, Wang LN, Seto WH, Yuen KY. Direct detection of Mycobacterium tuberculosis in clinical specimens using single-tube biotinylated nested polymerase chain reaction-enzyme linked immunoassay (PCR-ELISA). Diagn Microbiol Infect Dis 2004;48:271-5.

26.Therese KL, Jayanthi U, Madhavan HN. Application of nested polymerase chain reaction (nPCR) using MPB 64 gene primers to detect Mycobacterium tuberculosis DNA in clinical specimens from extrapulmonary tuberculosis patients. Indian J Med Res 2005;122:165-70.

27.Ortega-Larrocea G, Bobadilla-del-Valle M, Ponce-de-Leon A, Sifuentes-Osornio J. Nested polymerase chain reaction for Mycobacterium tuberculosis DNA detection in aqueous and vitreous of patients with uveitis. Arch Med Res 2003;34(2):116-9.

28.Almeda J, Garcia A, Gonzalez J, Quinto L, Ventura PJ, Vidal R, et al. Clinical evaluation of an in-house IS6110 polymerase chain reaction for diagnosis of tuberculosis. Eur J Clin Microbiol Infect Dis 2000;19(11):859-67.

29.Madhavan HN, Therese KL, Gunisha P, Jayanthi U, Biswas J. Polymerase chain reaction for detection of Mycobacterium tuberculosis in epiretinal membrane in Eales’ disease. Invest Ophthalmol Vis Sci 2000;41(3):822-5.

30.Pai M. Alternatives to the tuberculin skin test: interferongamma assays in the diagnosis of Mycobacterium tuberculosis infection. Indian J Med Microbiol 2005;23(3):151-8.