THYROID EYE DISEASE
Autoimmune disorder
characterised by infiltrative
orbitopathy
Graves' disease
Graves' disease is the most common thyroid
abnormality associated with thyroid
orbitopathy, but other disorders of the thyroid
can have similar ocular manifestations. These
include Hashimoto's thyroiditis, thyroid
carcinoma, primary hyperthyroidism, and
neck irradiation.
Approximately 40% of patients with Graves'
disease have or will develop thyroid
orbitopathy.
THYROID EYE DISEASE
Associated with normal to abnormal
thyroid function which may coexist,
precede or follow the orbitopathy.
Related to but not the same as Graves
Ophthalmopathy (GO) The natural
history was described by Rundle and
Wilson in 1945
Thyroid status-
Of those patients with thyroid orbitopathy,
approximately 80% are clinically hyperthyroid
and 20% are clinically euthyroid.4 Most
patients with euthyroid Graves' orbitopathy,
however, have some detectable laboratory
evidence of subclinical hyperthyroidism.
Both hyperthyroid and euthyroid patients can
develop clinical signs and symptoms of
thyroid orbitopathy. In general, patients with
euthyroid Graves' disease tend to have less
severe orbitopathy
THYROID EYE DISEASE
The goal is to identify and treat patients who are at
particular risk of sight threatening complications. The
disease has a finite period of activity until it becomes
burnt out.The yellow region shows the early phase
where there is the best response to treatment.
Type 1 younger age group, whiter eyes with
proptosis. Inflammation is mostly in orbital fat not
muscles.
Type 11 older patient with red eyes, severe sight
threatening disease, tobacco addiction is frequent.
General Considerations
Severe exophthalmos and compressive optic
neuropathy are slightly more common in older
men.
There appears to be an increased prevalence
of thyroid disease in smokers, for whom the
relative risk of developing Graves' orbitopathy
is twice as high as it is for nonsmokers.
The reason for this difference is not known,
but one possibility is that the decreased
immunosuppression in smokers may allow
greater expression of autoimmune processes.
PATHOGENESIS
Type II reaction:- autoimmune antibodies target somatic tissues
such as extraocular muscles causing an antigen-antibody
reaction. A large number of lymphokines are implicated in the
inflammatory process.
Inflammation results in production of mucopolysaccharides by
fibroblasts leading to swelling followed by collagen production
resulting in restriction.
There is a high concentration of macrophages in the inferior
rectus muscle as well as CD4+ memory T cells and CD8 T cells.
This may account for the clinical observation of maximal disease
activity in this muscle.
ETIOLOGY
In 1956, Adams and Purves isolated a factor in the serum of
patients with Graves' hyperthyroidism that caused stimulation of
the animal thyroid gland. This factor was very similar to TSH but
had a longer half-life. It was therefore called long-acting thyroid
stimulator (LATS).
In 1964, Kriss and colleagues showed that LATS had the
structure of an IgG immunoglobulin and its action could be
neutralized by thyroid tissue, indicating that it was an antibody.
Further experiments showed that the antibody was directed
against the receptor for TSH on the follicular cell of the thyroid
gland.
Thyrotropin receptor
antibodies (TRAb).
antibodies were originally classified into
those with stimulatory properties called
thyroid-stimulating immunoglobulin or
antibody (TSI, TSAb) and those with
inhibitory properties called TSH-binding
inhibiting immunoglobulin or antibody
(TBII, TBIA). Both of these groups are
now referred to as thyrotropin receptor
antibodies (TRAb).
PHYSIOLOGY
Hypothalamus TRH pituitary TSH
thyroid T3 and T4
85% of T4 converted to T3 in tissues.
T3 has 5 times the activity of T4.
Pathology
The predominant orbital pathology is
inflammation of the orbital soft tissues and
extraocular muscles. This immune-mediated
inflammation consists mostly of lymphocytes
and plasma cells, with a scattering of mast
cells. These inflammatory changes differ from
the more exuberant lymphocytic infiltration of
the orbital fat and muscles, including their
tendinous insertions seen in orbital
pseudotumor
Pathology
The earliest change in extraocular muscles
appears to be inflammation of the endomysial
connective tissues, which stimulates
endomysial fibroblasts to produce first
hyaluronic acid and then collagen. In the
acute stage there is inflammation, edema,
and deposition of glycosaminoglycans.
Eventually there is tethering of orbital tissues
due to fibroblast proliferation.
CLINICAL
(orbitopathy in general is worst in the older age groups.)
LID RETRACTION1. sympathetic overactivity2. infiltration of levator / SR complex3.
hypotropia (retraction disappears on downgaze)
SIGNS:- Dalrymples (lid retraction), von Graefe (lid lag), Kocher´s (staring appearance)
INFILTRATION
1. soft tissue involvement :- chemosis, conjunctival injection over the recti insertions, puffy
lids
Superior limbic keratoconjunctivitis (SLK) due to redundant conjunctiva
2. muscle involvement :- diplopia due to restriction.
Order of involvement IR, MR, SR (LR)
Braley´s sign = increased IOP on upgaze (>4mmHg)
3. proptosis :- TED is the commonest cause of unilateral or bilateral proptosis
Sight Threatening
Complications
optic nerve compression :- 25mg/ day. Best effect
in acute disease.Do not irradiate patients with
diabetes mellitus as they are more
susceptible to radiation retinopathy.2000rads/
10days, effect starts at 4 weeks, maximal 4
months.
Compressive Optic Neuropathy
Compressive optic neuropathy can cause
permanent visual loss. The treatment
possibilities include high doses of
corticosteroids, irradiation, and orbital
decompression. Some patients require only
one of these modalities, while other patients
need combined therapies.
Compressive Optic Neuropathy
As in the treatment of acute congestive thyroid
orbitopathy, radiation therapy is becoming
increasingly popular. A retrospective series of 84
patients with compressive optic neuropathy treated
with either corticosteroids or radiation therapy
supports mounting evidence that radiation therapy
may be safer and more effective than corticosteroids.
Radiation therapy, however, must be administered in
fractionated doses, which delays its beneficial effect.
For this reason, if visual dysfunction progresses while
the patient is on corticosteroids, surgical
decompression is usually recommended if the patient
is a surgical candidate.
Orbital decompression
Orbital decompression is indicated for compressive
optic neuropathy when there has been failure of or
contraindication for corticosteroids or radiation
therapy or if corticosteroid dependence has
developed with intolerable side effects. Other
indications include excessive proptosis with exposure
keratitis and corneal ulceration, pain relief, and
cosmesis for disfiguring exophthalmos. Orbital
decompression may also be indicated as a
preliminary procedure to extraocular muscle surgery
on a patient with sufficient proptosis to suggest that
decompression might ultimately be required.
Orbital decompression
A variety of approaches may be used, each
with its own advantages and associated
complications.
The transorbital (via fornix or eyelid)
approach to inferior and medial wall
decompression is the most common
approach used by ophthalmologists. The
addition of a lateral wall advancement has the
advantage of both further increasing the
orbital volume and simultaneously improving
upper eyelid retraction; this is the technique
we prefer.
ORBITAL DECOMPRESSION
Subciliary approach.Inferior & medial wall
(6mm proptosis).Remove bone to posterior
wall maxillary sinus (5mm more posterior on
medial wall), Avoid IO neurovascular bundle,
and the anterior and posterior ethmoidal
arteries.Incise periosteum in A-P direction
posteriorly and circumferentially anteriorly.
Complications:
visual loss,
A pattern ET
Motility Disorders
A major source of morbidity in thyroid orbitopathy, and the most
frequent problem associated with orbital decompression
surgery, has been strabismus. In patients with relatively minimal
degrees of ocular misalignment, diplopia can be avoided with a
compensatory head posture, Fresnel plastic press-on prisms, or
temporary occlusion. Unfortunately there is significant image
degradation as larger prisms are used, limiting their efficacy. If
there is marked asymmetry in ocular deviation in different fields
of gaze, prisms are also less effective. In some cases during the
inflammatory period, use of intramuscular botulinum toxin has
shown some efficacy.
Extraocular muscle surgery should be postponed until the
muscles are no longer inflamed and the deviation has remained
stable for at least 6 months.
Surgery
STRABISMUS SURGERY:-Aim for maximal area of fusion without
abnormal head posture.IR recession on adjustable +/- contra SR
recession
iii) EYELID SURGERY:-
Upper Lid retraction - Muller´s tenotomy (<2mm), levator Z myotomy or
recession on hangback sutures, levator tenotomy +/- horns.
Lower Lid retraction - Usually needs a spacer from donor sclera (lid
retraction X 2 = amount of sclera required)
iv) BLEPHAROPLASTY for excess skin and fat
Ideally treatment combines a multidisciplinary coherent approach such
as
Combined radiotherapy and immunosuppression trial
Eyelid Abnormalities
As with other thyroid eye problems, eyelid retraction will often
improve with time, and only an estimated 50% of patients with
eyelid retraction have a significant eyelid abnormality 5 years
later.
Eyelid retraction can result from excessive autonomic discharge,
levator fibrosis, or contraction of the inferior rectus muscle.
Surgical correction of eyelid abnormalities should be performed
only after orbital or extraocular muscle surgery because these
operations may change eyelid position. For example, inferior
rectus muscle restriction may cause upper eyelid retraction
because of the superior rectus/levator palpebrae superioris
overaction against the restriction. Specific techniques for repair
of eyelid retraction are discussed in other chapters.