Exophthalmos (also known as proptosis) is the protrusion of one eye or both anteriorly out of the orbit. It derives from Greek, meaning 'bulging eyes.' It occurs due to an increase in orbital contents in the regular anatomy of the bony orbit. Depending on the underlying cause, exophthalmos may be accompanied by systemic symptoms. Vision may be disturbed if the optic nerve is compressed in conjunction with the underlying etiology of exophthalmos.
In adults, the most common cause of unilateral and bilateral exophthalmos is thyroid-associated eye disease, such as Graves-related ophthalmopathy.
In children, orbital cellulitis is the most common cause, whereas bilateral exophthalmos is most likely due to neuroblastoma and leukemia.
Typically, exophthalmos originates from four likely etiologies:
The incidence of exophthalmos may vary depending upon the underlying cause. In unilateral exophthalmos, under one-third of patients will have thyrotoxic activity. Ninety percent of bilateral exophthalmos was historically a result of endocrine abnormalities. The mean position of the globe, as measured using an exophthalmometer, is 16 mm. There is variation between the sexes and between races.
Exophthalmos typically arises from an increase in orbital contents within the bony orbit, leading to forward displacement of the globe. The origin of the increased orbital content depends on the underlying cause. In Graves ophthalmopathy, enlargement of the extraocular muscles and expansion of the orbital adipose tissues occurs due to abnormal hyaluronic acid accumulation and edema collection into the retro-orbital space. The mechanism of trauma and pathogenesis of neoplastic disease are also important factors to consider in exophthalmos.
The presentation may be variable, depending on the underlying cause. Symptoms can include:
A thorough history will help establish the underlying cause. Symptoms such as heat intolerance, weight loss, change in bowel habits, and palpitations may support a diagnosis of thyrotoxicosis. There may be a history of trauma or constitutional symptoms such as weight loss that may suggest cystic or tumoral growth. The rate of onset may provide insight into its etiology. Rapid onset may suggest inflammatory disease, malignant tumors, and carotid-cavernous fistula, while gradual onset implies somewhat benign pathology. The presence of pain may commonly indicate infection (e.g., orbital cellulitis). Temporary exophthalmos triggered by the Valsalva maneuver may be consistent with orbital varices.
The examination should include a general examination of the patient to identify any systemic disease such as Graves' Disease, leukemia, visceral neoplasm, or constitutional signs that may give rise to suspicion of malignancy. Clinicians must undertake a full eye examination, assessing a patient's extraocular movements, visual acuity, field assessment, pupil accommodation, and reflexes. Intraocular pressures, anterior segment, and fundoscopy should be performed.
Exophthalmos may be seen on examination and quantified using an exophthalmometer, whereby the extent is measured by the distance from the corneal apex to the midpoint of the anterior rim of the orbit. It may be accompanied by other extraocular and systemic signs relevant to systemic causes. The physician should remain at the same level as the patient. The white of the sclera is commonly exposed inferiorly to the iris in exophthalmos.
A full diagnostic workup must include a full screen of blood tests, including complete blood count (FBC), thyroid function and auto-antibody tests, renal function, and C-reactive protein. Nasal swabs and blood cultures may be warranted if a severe infection is suspected e.g., orbital cellulitis.
Radiological imaging is essential for diagnostic and management purposes. Computed tomography (CT) and magnetic resonance imaging (MRI) is the gold standard modalities in evaluating the orbit or cranium for causes of severe infection, mass growth, and foreign bodies related to exophthalmos. Positron emission tomography (PET) allows the assessment of metastatic disease, including leukemia, lymphoma, and metastases from secondary cancers.
As many cases may present with overlapping clinical features and may provide difficulty in confirming the diagnosis, a tissue biopsy may be necessary to ascertain a definitive answer.
Proptosis or exophthalmos may be associated with other deviations of the globe, namely, hyperglobus, hypoglobus, esoglobus, or exoglobus.
Treatment of the underlying cause is necessary for the management of exophthalmos to maintain ocular function. In the case of thyroid-associated orbitopathy and other secondary causes, effective management requires a multidisciplinary approach between eye specialists, primary care, and general medicine e.g., endocrinology.
Smoking cessation is paramount in the prevention and progression of thyroid eye disease.
Supportive therapies will provide appropriate symptomatic relief for patients while treatment of the underlying cause commences. Topical preservative-free ocular lubricants and taping eyelids should be administered to patients with dry eye. Around 66% of mild cases resolve within six months, hence supportive therapy may suffice. Sunglasses and protective eyewear can be encouraged to help protect against photosensitivity and glare. Diplopia is manageable with Fresnel prism or monocular occlusion. Finally, upper eyelid retraction may be corrected with botulinum toxin injection directly into the levator palpebrae superioris.
Moderate-to-severe thyroid orbitopathy is treated with oral and intravenous corticosteroids. Inflammatory and autoimmune causes will benefit from reducing edema and orbital congestion. Chemotherapy agents may be options to reduce tumor bulk and burden.
Surgery is indicated to remove the offending tissue, tumor, or malignant disease where appropriate.
Orbital decompression and extraocular muscle repair have served to protect vision in severe cases of exophthalmos for decades, particularly when patients fail to respond to medical therapy. The visual function has reportedly improved by up to 82% of cases.
Autoimmune, inflammatory conditions, trauma, and neoplastic disease are the most common differentials that must merit consideration in the differential diagnosis. These include thyroid-associated orbitopathy linked with Graves disease; infectious conditions such as orbital and preseptal cellulitis; vascular malformations including carotid-cavernous fistula; benign and malignant tumors including malignancy including capillary haemangioma, neuroblastoma, leukemia, lymphoma, mucocele, pseudotumors and secondary metastatic tumors that may give rise to metastatic deposits in the orbit. Other rare differentials may include Crouzon syndrome and Apert syndrome. Periorbital fractures due to trauma may result in periorbital hemorrhage that can potentially protrude the globe.
Early detection of the underlying cause of exophthalmos is vital for resolution. Any associated swelling, pain, or erythema will be typically self-limiting after 2 to 3 months, although this may vary from patient to patient. Thyroid-related exophthalmos may take much longer, or may not return to normal, with up to 5% of cases retaining permanent diplopia, worsening or sustaining permanent visual impairment.
These typically related to the underlying disease. Prolonged exposure of the cornea may result in secondary exposure keratopathy if the cornea becomes very dry, particularly at night, if there is incomplete eyelid closure. This condition may lead to chemosis and conjunctivitis. Corneal ulceration and keratitis may follow as further complications. Permanent visual disturbance such as diplopia is rare if the underlying etiology receives treatment early and swiftly. Other rare complications have also included superior limbic keratoconjunctivitis and optic atrophy.
Patients should be aware that regular monitoring and supportive strategies for their exophthalmos will provide symptomatic relief, in addition to the medical or surgical management of the underlying cause. As such, regular lubrication of the eyes, monitoring, and engagement with the treatment plan set by your ophthalmologist, family care physician, hospital care physician will ensure that your eyes are appropriately treated and looked after.
An interprofessional approach between eye specialists, primary care, and general medicine, e.g., endocrinology, if thyroid-related, is essential in coordinating best outcomes for patients with exophthalmos. Regular monitoring of visual function is necessary for prognosis. Shared decision-making in the management planning of a patient's care provides maximum benefit in line with the patient's ideas, concerns, and expectations. Synergistic collaboration with the patient on their health will lead to more favorable outcomes.
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