Classification of scleral inflammation

Scleral disease has been described sporadically in the older literature,
usually in association with rheumatic disease, syphilis or
tuberculosis. Galileo was possibly the most famous sufferer of
scleral disease.1 He certainly suffered from severe bouts of arthritis
that were aggravated by the cold and wet weather from the age
of 35 years. He had intermittent eye trouble throughout his life
and became totally blind at the age of 74 years from what was
probably a destructive scleritis complicated by keratitis and secondary
glaucoma. So much is now known about the disease and
how to treat it that history should not be allowed to repeat itself
but, even now, similar problems are seen from time to time.
Although scleral inflammation is only seen in 1 in every 6000 new
patients, the consequence of an incorrect diagnosis or inappropriate
treatment can be blindness. It is therefore important that all ophthalmologists
are aware of what constitutes serious disease needing
urgenttreatment,andwhatcansafelybeleftalonepossibly without any
treatment at all. This is relatively easy when the inflammation affects
the anterior sclera, but is much more difficult when the posterior
segment is involved. Many of those with posterior scleritis have no
associated anterior scleritis and indeed some have no physical signs,
and yet these are the patients who can go blind extremely rapidly.2
It may seem a daunting prospect to distinguish between the various
forms of scleral disease; however, the symptoms are usually
suggestive and almost always all the physical signs can be elicited
by a properly performed, careful ocular examination.

CLASSIFICATION
Inflammation of the sclera is classified by its location and severity
using the system devised by Watson.4 This classification is detailed in Box 2.1. Both episcleritis and scleritis are recurrent disorders.
Recurrences are often triggered by simple factors such as
a viral infection or even stress. However, long-term studies have
revealed that it is exceptional for one type of scleritis or episcleritis
to recur in a different form.5 As it is vital not to undertreat
serious disease or overtreat benign disease, it is important to identify
the exact condition when the patient first presents. The most
important differentiation is between episcleritis and scleritis,
because episcleritis rarely requires treatment (although it is usually
given) and scleral disease almost always requires systemic therapy.

DIFFUSE AND NODULAR EPISCLERITIS
Episcleritis can be diffuse or nodular and may affect both the
anterior and posterior segment of the eye. As the name implies
only episcleral tissue is involved in the inflammatory process,
although the conjunctival vessels and the vessels lying directly on
the scleral surface become dilated as a result of the inflammatory
process (Fig. 2.1). It is known from fluorescein angiographic
studies that the inflamed appearance results from leakage and
extravasation of fluid from blood vessels in the inflamed area.6 The
reason for this dramatic and sometimes severe inflammation is
unclear, nor is it known why the inflammatory process remains
localized in some individuals resulting in nodular episcleritis,
whereas in others all the episcleral vessels of one or both eyes are
dilated and involved by the inflammatory process resulting in
diffuse episcleritis.
Careful slit lamp examination is required to make the diagnosis
of anterior episcleritis. The crucial observation is whether or not
there is any underlying scleral swelling, as episcleral oedema can
be seen in patients with either episcleritis or scleritis.3 Scleral
oedema can usually be detected through eye observation using the
very fine beam at high magnification and the red-free (green) light
of the slit lamp. If the sclera underlying the inflamed episclera
cannot be easily visualized then phenylephrine (or other vasoconstrictor)
will blanche the superficial vessels. The area of the
episcleral oedema in the inflamed area will appear yellow in redfree
light – an appearance rarely seen in scleritis.
Posterior episcleritis probably exists but is difficult to detect
even with good modern ultrasonography. This is not necessarily
because the ultrasound technique is poor but, as the episcleral tissue
is extremely thin over the posterior pole, the inflammation
produces very little oedema. The “T” sign, seen with β scan
ultrasonography detects movement of the episclera away from the
scleral surface. This sign can be observed whenever there is posterior
episcleral inflammation, and is seen mostly in patients with
posterior scleritis as there is always overlying posterior episcleral
inflammation in patients with posterior scleritis.

DIFFUSE AND NODULAR ANTERIOR SCLERITIS
In diffuse and nodular scleritis the degree of inflammation of
both sclera and its overlying episclera and conjunctiva is verymuch more severe than that seen in episcleritis. As the scleral
tissue becomes stretched, the nerves are stimulated and, as a consequence,
severe pain accompanies the inflammation. This pain is
referred to the face and temple, unlike the discomfort of episcleritis,
which is confined to the eye alone.
Whereas there is little to choose in the degree of severity
between the diffuse and nodular episcleritis, this is not true of scleral
disease. Diffuse scleritis presents with severe pain, referred
largely to brow and jaw, and marked oedema of both the episcleral
and scleral tissue (Fig. 2.2). Provided that it is treated quickly
and intensively, the condition can be brought under control within
48 hours. Nodular disease, whether single or multiple, follows a
much more prolonged course (Fig. 2.3). The nodule may persist
even when the disease has been fully controlled and there is noactive inflammation. This makes the decision of how much and
how long to continue treatment much more difficult. Systemic
disease is much more commonly associated with nodular disease
than diffuse anterior scleritis.

NECROTIZING SCLERITIS WITH INFLAMMATION
This is the most destructive form of scleral disease and is a serious
threat to vision and the integrity of the globe (Fig. 2.4).7 It is
therefore essential to identify this pattern of scleral inflammation
by careful slit lamp examination of the sclera.
Although the onset of necrotizing scleritis is almost always rapid
and the pain intense, there are a few patients who present with an
inflamed eye without much pain. Such patients are often taking
low-dose systemic corticosteroid therapy for an associated disease
such as rheumatoid arthritis. Destruction of the sclera in patients
with necrotizing scleritis takes place within the deeper layers of the
sclera, and so the necrotizing nature of the condition can easily be
missed. This makes close inspection of the vasculature with or
without fluorescein angiography essential to distinguishing between
the more benign forms of scleritis and the necrotizing
disease. The blood within the vascular networks overlying the
necrotic area becomes static, even though the vessel contains
blood and is dilated.3 As a consequence there is no perfusion of
blood through the episclera in this region. If this stasis is notnoticed and the causative inflammation is not suppressed, necrosis
occurs, and this may rapidly lead to loss of tissue not only in
the sclera but also in the overlying conjunctiva and episclera.
These changes occur whether there is a nodule present or not.
However, if a nodule is necrotic the destruction is usually well
within the substance of the tissue and not at its surface. Nodules
become filled with fluid and heal as fibrous scar tissue. Tissue that
has been destroyed and has ulcerated is replaced by fibrous tissue
in due course. This may result in the sclera becoming variably thin
or translucent. However, the eye will remain intact unless the
intraocular pressure rises rapidly so that it is rarely necessary to
support the underlying choroid.

NECROTIZING SCLERITIS WITHOUT
INFLAMMATION (SCLEROMALACIA PERFORANS)
This unusual condition occurs virtually exclusively in elderly,
usually female, patients with longstanding destructive and inactive
rheumatoid arthritis. It is extremely rare. The eye is not painful.
Either the patient or their attendant notices that the white eye has
changed colour from porcelain white to yellow. The yellow spots
are necrotic areas of sclera and represent a sequestrum of scleral
tissue. Progression can be inhibited if the disorder is treated early,
but those regions that already contain necrotic sclera cannot be
influenced by treatment. Over time the necrotic area will be
resorbed, leaving the bare choroid exposed, covered only by a thin
film of fibrous tissue. These areas of exposed choroid are readily
visible on examination and appear blue/black in colour. Unless the
intraocular pressure rises this will not be harmful and no treatment
is necessary.

POSTERIOR SCLERITIS
Posterior scleritis is a very much underdiagnosed condition.
The use of β scan ultrasonography confirms that posterior scleritis
is far commoner than previously thought and, because of the
lack of visible physical signs and the proximity of the inflammation
to the macula, retina and optic nerve, it is potentially devastating.2
Undiagnosed and untreated posterior scleritis of whatever type
can rapidly lead to blindness.

DIFFUSE AND NODULAR POSTERIOR SCLERITIS
The exact diagnosis depends almost entirely on the ultrasonographic
appearances (Fig. 2.5). Physical signs such as choroidal
folds, disc oedema, choroid effusions, and retinal detachments are
not a guide to the type of posterior scleritis, and, commonly there
are no physical signs other than decreased vision. Attention is
drawn to the possibility of this disease by deterioration of vision
and by pain, which is not always a prominent feature. Fortunately
the ultrasonographic signs in these patients are characteristic and
allow the diagnosis of posterior scleritis to be made.2 Diffuse posterior
scleritis, if detected adjacent to the disc or macula, must be
treated extremely vigorously and at once, if the vision is not to be
affected permanently. Scleral nodules on the other hand can often
be enormous without apparently affecting vision at all.

POSTERIOR NECROTIZING SCLERITIS
Necrotizing scleritis involving the posterior sclera is seen occasionally
by vitroretinal surgeons when a scleral plomb becomes
infected following surgery.8 The necrotizing nature of the scleritis
is readily apparent at surgery; however, thus far it has not been
possible to make this diagnosis by ultrasonography.


REFERENCES

1. Germani GM. Rheumatoid arthritis and the blindness of Galileo Galilei.Ospedule Maggiore 1964;59:193–6.
2. McCluskey PJ, Watson PG, Lightman S, Haybittle J, Restori M, Branley M.Posterior scleritis: clinical features, systemic associations, and outcome in alarge series of patients. Ophthalmology 1999;106:2380–6.
3. Watson PG. The nature and treatment of scleral inflammation. Trans OphthalmolSoc UK 1982;102:257–64.
4. PG, Hayreh SS. Scleritis and episcleritis. Br J Ophthalmol 1976;60:163–8.
5. Tuft SJ, Watson PG. Progression of scleral disease. Ophthalmology 1991;98:467–1.
6. Watson PG, Bovey E. Anterior segment fluorescein angiography in the diagnosisof scleral inflammation. Ophthalmology 1985;92:1–11.
7. McCluskey PJ, Wakefield D. Scleritis and episcleritis. In: Pepose J, HollandGN, Wilhelmus K, eds. Ocular infection and immunity. St Louis: Mosby 1996;pp, 642–62.
8. O’Donoghue E, Lightman S, Tuft S, Watson PG. Surgically-induced necrotisingsclero-keratitis (SINS); precipitating factors and response to treatment. BrJ Ophthalmol 1992;76:17–21.