Fig. 9.1
Color montage photograph of the right eye showing active periphlebitis in all four quadrants and healed chorioretinitis lesions (arrows) overlying blood vessels
Fig. 9.2
Color photograph of the right eye showing active retinal periphlebitis in inferotemporal quadrant but no focal lesions overlying blood vessels
Retinal periphlebitis in association with other forms of ocular TB: These include coexisting multifocal serpigenoid choroiditis (Fig. 9.3) [16], neuroretinitis, or intermediate uveitis and help in establishing a TB etiology for the disease process.
Fig. 9.3
Color montage photograph of the right eye showing active periphlebitis in infero-nasal quadrant and multifocal serpigenoid choroiditis at macula
Isolated retinitis lesions without periphlebitis: These occur typically as neuroretinitis (Fig. 9.4), but rarely focal retinitis lesions can be seen in the peripheral fundus that must be distinguished from other infectious and noninfectious etiologies, through detailed clinical and laboratory evaluation.
Fig. 9.4
Color montage photograph of the left eye showing full-thickness retinitis along the inferotemporal arcade, associated with a partial macular star
The Eales’ disease conundrum: Henry Eales described idiopathic retinal vasculitis with recurrent vitreous hemorrhage in 1880, in young men from poor socioeconomic backgrounds [17]. Since then, the term has established itself in ophthalmological lexicon, even though advances in modern medicine should lead us to overcoming our deficiencies in etiological diagnosis. Indeed Eales’ disease has been associated with several causative factors, most prominently M. tuberculosis [18]. But regardless of its association with TB, the term Eales’ disease is best avoided since it puts an unwarranted diagnostic label on a patient, preventing us from exploring potentially serious etiological conditions such as TB, anterior retinal necrosis (ARN), sarcoidosis or, Behçet’s disease.
Imaging
Imaging has a crucial role in determining etiological diagnosis in retinal TB, as also in identification of its complications and sequelae.
- I.
Fluorescein angiography (FA) is probably the most vital investigation for etiological diagnosis, since it reveals capillary non-perfusion (CNP) in the quadrants affected by retinal periphlebitis (Fig. 9.5). While it is also seen in certain other conditions such as Behçet’s disease, the presence of CNP areas in association with retinal periphlebitis and corroborative evidence of TB helps in distinguishing TB from several other conditions such as sarcoidosis. Apart from CNP areas, FA also helps in identification of retinal and disc neovascularization and cystoid macular edema (CME).
Fig. 9.5
Color photograph of the right eye showing active periphlebitis and retinal hemorrhages along supero-temporal quadrant with corresponding mid-phase fluorescein angiogram showing extensive capillary non-perfusion
- II.
Optical coherence tomography (OCT) helps in noninvasive identification of CME and other macular complications, such as epiretinal membrane and full-thickness macular hole. In addition, high-resolution OCT can also help distinguish a primarily retinal lesion from a choroidal one.
- III.
OCT angiography is a recently introduced noninvasive tool for mapping retinal and choroidal vasculatures. It can also help in etiological diagnosis by identifying CNP areas without the need for fluorescein dye (Fig. 9.6). However, it cannot reveal active processes such as dye leakage.
Fig. 9.6
Color photograph of infero-nasal quadrant of the right eye showing active periphlebitis and corresponding OCT angiogram showing flow void areas in the deep retinal capillary plexus
Diagnosis
The diagnosis of retinal TB is largely based on clinical and imaging characteristics, outlined above. In TB-endemic regions, these include retinal periphlebitis associated with focal chorioretinal lesions overlying blood vessels and presence of CNP areas on FA/OCT angiography. It is crucial to recognize past exposure to open pulmonary TB patients. The role of ancillary tests such as tuberculin skin test, interferon-gamma release assay, and chest radiography is overemphasized in diagnosis of ocular TB in general. While they provide useful supportive evidence, neither their presence confirms the diagnosis nor their absence excludes ocular TB. A detailed clinical evaluation to rule out other etiology is more valuable in establishing the association with TB. In recent years, PCR has been used to provide definitive evidence of M. tuberculosis in aqueous or vitreous samples from eyes with retinal TB. Although it provides a more direct evidence as compared to the ancillary tests, it is still fraught with the possibility of both false-positive and false-negative results [9]. Quantitative real-time PCR can be useful in overcoming these weaknesses and providing more accurate results.
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