Scleritis

# Scleral Anatomy
The word "sclera" is derived from Greek word, "skleros" meaning hard. It consists of the posterior five-sixths part of the fibrous outer tunic of the eye. The outer scleral surface is in contact with Tenons capsule and the bulbar conjunctiva. The sclera is covered by a thin layer of loose tissue called episclera. It is separated from the choroid by the suprachoroidal space. The extraocular muscles are also inserted in the sclera. The thickness of the sclera varies from place to place. The thickest part is at the posterior pole and the thinnest underneath the insertion of rectus muscles.
At the point of entrance for the optic nerve in the orbit, the sclera is consists of a sieve-like membrane, the lamina cribrosa, which allows the passage of fasciculi of the nerve. The sclera receives the circulation of two long and ten to twelve short posterior ciliary arteries around the optic nerve. Slightly posterior to the equator, four vortex veins (venae vorticosae) drain the sclera. The anterior ciliary arteries and veins penetrate the sclera nearly 3 to 4 mm away from the limbus.
The histology of the sclera consists of three layers - episcleral tissue, sclera proper and lamina fusca. The episcleral tissue comprises fine loose elastic tissue fibers and contains a large number of small vessels. The sclera proper is formed by dense bands of parallel and interlacing collagen fibers. The collagen fiber bundles are arranged in concentric circles at the limbus and around the entrance of the optic nerve, elsewhere the arrangement is quite complicated. The lamina fusca has a brown color owing to the presence of a large number of branched chromatophores. The sclera is almost avascular and its histological structure resembles that of the cornea. However, sclera is opaque due to the hydration and irregular arrangement of its lamellae. The nerve supply of sclera comes through the ciliary nerves.

# Scleritis
Scleritis is a serious inflammatory disease that affects the sclera. The disease is often contracted through association with other diseases of the body, such as Wegener's granulomatosis or rheumatoid arthritis; it can also be attained through disorders of menstruation. For this reason, scleritis occurs frequently among young women. There are three types of scleritis: diffuse scleritis (the most common), nodular scleritis, and necrotizing scleritis (the most severe). Scleritis may be the first symptom of onset connective tissue disease.
The term "Episcleritis" refers to inflammation of the episclera.

# Classification
Inflammation of the sclera is classified by its location and severity using the system devised by Watson.

# Pathophysiology
AUTOIMMUNE DISEASE
Systemic autoimmune disease is a common finding in patients
with scleritis,2 and scleral and episcleral tissues appear to be particularly
at risk in a wide range of autoimmune disorders. Why
this should be the case is not clear. It is possible that everyday
exposure to irritants and pathogens provokes minor episodes of
inflammation that in some way prime the autoimmune-mediated
inflammation. The following description includes details of histology
-f some cases where precise information concerning aetiology
was not provided, but it has been assumed that the cases were of
autoimmune aetiology.
The detailed pathogenesis of this heterogeneous group of conditions
remains uncertain although it is agreed that autoimmunity
plays an important role. Immune complex deposition may be a
feature13 and, interestingly, one case of scleritis following treatment
with a mouse monoclonal antibody has been reported.4
Immune complex formation has also been described in at least
-ne pathological report.5 In conditions such as relapsing polychondritis,
autoantibodies, in this instance to type II collagen, may
have a role to play. It has been proposed that the presence of
higher levels of complement C1 in the anterior sclera may explain
the increased incidence of immune complex disease-associated
scleritis at the front of the eye.6
Necrotizing and non-necrotizing vasculitis (especially arteritis)
have been seen in some cases.2,7 The early involvement of sclera
adjacent to anterior and posterior ciliary vessels has been used to
support the notion that vasculitis is an important component in
the pathogenesis of scleritis,8 but non-vasculitic inflammatory
diseases, such as multiple sclerosis, are also characterized by
perivascular pathology. In addition, in many cases vasculitis is not
found and, although this may to a degree reflect problems with
sampling, it seems probable that vasculitis is not a universal
finding. Interestingly, other vascular changes, in the absence of
inflammation, vasculitic or otherwise, have been reported. These
include vascular closure,9 which might be anticipated to lead to
ischaemic necrosis in the absence of vasculitis.
There has been relatively little analysis of the detailed phenotype
-f the inflammatory cell infiltrate. In one study of two cases
there was a predominance of CD4 positive T cells with clusters of
B cells in a perivascular location.10 In this study no evidence of vasculitis
was seen. Relatively few of the T cells appeared activated as

# Signs and symptoms
Symptoms of the disease include:
- Redness of the sclera and conjunctiva, sometimes changing to a purple hue
- Severe ocular pain (not present in episcleritis) which may radiate to the temple or jaw
- Increased light sensitivity and tearing
- Decrease in visual acuity, possibly leading to blindness

# Diagnosis
Scleritis is best detected by examining the sclera in daylight; retracting the lids helps determine the extent of involvement.  Other aspects of the eye exam (i.e. visual acuity testing, slit lamp examination, etc) can be normal.  Ancillary tests CT scans, MRIs, and ultrasonographies can be helpful, but do not replace the physical examination.

# Treatment
In very severe cases of necrotizing scleritis, eye surgery must be performed to repair damaged corneal tissue in the eye and preserve the patient's vision. For less severe cases, nonsteroidal anti-inflammatory drugs, such as ibuprofen, are prescribed for pain relief. Scleritis itself is treated with an oral medication containing corticosteroids and an eye solution. In some cases, antibiotics are prescribed. Simply using eye drops will not treat scleritis. If not treated, scleritis can cause blindness.