Uveitis is a complex intraocular inflammatory disease that results from several causes:
infections – endogenous and exogenous, systemic diseases, organ-specific autoimmune
processes (primarily to T-cell-mediated Th2 and or Th17 processes), trauma, and masquerade
syndromes presenting with clinical features of uveitis. About 3%–10% of blindness
in developed countries and 25% of blindness in India and other developing countries
are attributed to uveitis and its complications such as secondary cataract, glaucoma,
cystoid macular edema, or retinal photoreceptor or optic nerve damage. Infections
are a leading cause of uveitis in India and other developing countries, whereas idiopathic
uveitis, believed to be an organ-specific immune inflammatory process, is a leading
cause in developed countries and account for only 30% of patients.[1] Compared to
previous decades, now one is able to arrive at a specific etiology in about 55.4%–60.6%
of patients in India.[2
3] This is due to awareness of changing demographic features, recognition of specific
uveitis entities, and prompt and better reporting of newer etiologic agents – West
Nile Virus (WNV), chikungunya, and Rickettsia-induced uveitis. Now, we have well-defined
diagnostic criteria for entities – ocular tuberculosis (TB), Vogt–Koyanagi–Harada
(VKH), and ocular sarcoidosis. In the past two decades, other factors that have led
to a fall in incidence of idiopathic uveitis and an increase in specific diagnosis
are wide-field imaging, optical coherence tomography, autofluorescence, increased
availability of nucleic acid amplification techniques, such as polymerase chain reaction
(PCR) for infectious uveitides, such as TB, toxoplasmosis, viral uveitis (herpes simplex
virus [HSV], varicella zoster virus [VZV], and cytomegalovirus [CMV]), and bacterial/fungal
infections, high-resolution computerized tomography, positron-emission tomography
scan, and magnetic resonance imaging.[1
3]
Anterior uveitis is the most common uveitis presentation in most published studies
and regional change in patterns of anterior uveitis have been reported from tertiary
eye care centers in India. From Northeast India, Das et al. have recognized an increase
in the diagnosis of HLA-B27-associated acute anterior uveitis in 2012 and a sharp
decrease in the number of idiopathic anterior uveitis compared to 2005.[4] They have
also shown that diagnosis of herpetic uveitis (HSV, VZV, and CMV) and Fuchs' uveitis
syndrome was on the rise when compared to their 2005 study.[5] A similar finding is
also reported by Dogra et al. and they attribute the increased incidence of the viral
disease may be attributed to high clinical suspicion, based on classic signs (iris
changes/high intraocular pressure) and the recent availability of PCR-based diagnosis.[3]
Regional differences exist – Rathinam and Namperumalsamy have a higher incidence of
trematode and leptospira-induced anterior uveitis compared to studies from Northern
India.[2
3] Other causes of anterior uveitis reported are TB, sarcoidosis, leprosy, juvenile
idiopathic arthritis (JIA), phacolytic uveitis, syphilis, and masquerade uveitis.[2]
Ocular manifestations of parasitic infections – gnathostomiasis and dirofilariasis
have been reported from Northeast India.[6]
Less common are incidences of intermediate, posterior, and panuveitis, not necessarily
in that order. Older studies showed TB as the most common cause of intermediate uveitis
in North India,[7] while sarcoidosis and leptospiral uveitis were more common causes
in South India.[2] Other less common entities seen in this anatomical site are uveitis
due to idiopathic, multiple sclerosis, and JIA.[2]
Toxoplasmosis, TB, leptospirosis, sarcoidosis, and viral uveitis (acute retinal necrosis
and CMV) account for majority of the posterior uveitis. TB is the most common cause
of choroiditis and vasculitis, while viral and toxoplasmosis are common causes of
retinitis in North India. White dot syndromes such as acute posterior multifocal placoid
pigment epitheliopathy, multiple evanescent white dot syndrome are less commonly seen
in this part of the world. Rare causes reported were Behçets disease, neuroretinitis,
masquerade syndromes, metastasis, and cysticercosis.[3]
Diffuse or panuveitis can be caused by TB, sarcoidosis, VKH, sympathetic ophthalmitis,
Behcet's disease, viral (VZV, CMV), and endophthalmitis – both exogenous and endogenous
and sympathetic ophthalmitis.
Syphilis as an etiologic agent (0.2%–1.6%) ranks low in the list of infectious cause
of uveitis in many studies across India. Endophthalmitis accounted for 10% and idiopathic
panuveitis for 32.7% of panuveitis in South India, while in the North, it was 14.5%
and 23.5%, respectively.[2
3]
Since the mid-2000's, newer uveitic entities of infectious etiology have been reported
from South India – WNV-associated uveitis,[8] chikungunya-associated uveitis,[9] and
Rickettsiosis-associated retinitis.[10] One often encounters these patients in clusters,
most of them following a presumed outbreak of the disease in the community.
We treated 254 eyes of 248 patients with acquired ocular toxoplasmosis between October
2004 and May 2005 caused by a presumed outbreak of Toxoplasmosis from a contaminated
water source in South India.[11] We also recently treated a cluster of 12 patients
(23 eyes) with retinitis due to Rickettsia conorii infection proved serologically
(unpublished data).
In conclusion, causes of uveitis differ in developed and developing countries and
such etiologic differences could play a significant role in the high levels of blindness
that occur in developing countries. Periodic epidemiological studies can show changing
patterns in uveitis. Awareness of such regional variations of disease patterns is
imperative to arrive at a differential diagnosis and do tailored laboratory investigations.[12]
Ocular TB remains the most common infective etiology of uveitis, the emergence of
new infectious causes of uveitis which can also occur in clusters – WNV, chikungunya,
and Rickettsiosis needs to be kept in mind. There is a notable decreasing trend toward
the diagnosis of idiopathic uveitis. Local drug delivery and use of biological agents
are providing novel approaches to the management of recalcitrant noninfectious uveitis.