Approach Considerations
Workup in cases of compressive optic neuropathy should begin with a history and physical examination, followed by laboratory studies and imaging studies.
Laboratory Studies
Blood tests can be helpful in the diagnosis of compressive optic neuropathy. However, the serologic workup should be guided by the history and clinical presentation. [16]
If thyroid ophthalmopathy is suspected, blood tests for thyroid function, including TSH, serum T4 and T3, thyroid-stimulating immunoglobulins, and anti-thyroid antibodies should be performed.
An elevated angiotensin-converting enzyme level may be seen in 52%-90% of patients with active sarcoidosis. [17]
Since prostate cancer can metastasize to the brain and orbit, an elevated prostate specific antigen (PSA) level may be helpful in male patients with suspected bony orbital metastases and optic nerve compression. [18]
Insulin-like growth factor 1 (IGF-1), prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin-releasing hormone (TRH) and alpha subunit, cortisol, and thyroxine (T4) can be obtained to assess a pituitary tumor.
Bony tumors or protrusions of the orbit can lead to CON. [19] Alkaline phosphatase levels would be elevated in Paget disease of bone; an elevated bone-specific alkaline phosphatase (BSAP) has 84% sensitivity. [20]
Imaging Studies
Whenever there is clinical suspicion of compressive optic neuropathy (CON), a neuroimaging study is indicated to determine the presence and location of the responsible lesion. Given the high sensitivity and specificity of modern neuroimaging, a negative scan finding essentially reduces the possibility of CON as the cause of vision loss.
In most cases of CON, magnetic resonance imaging (MRI) is the imaging modality of choice because of the excellent soft-tissue resolution of the anterior visual pathway and parasellar area. Typically an orbit and brain MRI with and without contrast is ordered to evaluate a patient for CON. Abnormalities within the peri-optical spaces are more consistent with meningiomas, whereas a global increase in the size of the optic nerve is in favor of a glioma. Example MRIs are shown below.
Axial MRI taken 3 weeks after the onset of distorted vision in the right eye; visual acuity is reduced to counting fingers at 1 ft. Evidence of optic nerve compression is not seen; disease in the sphenoid sinus is reported.
MRI of same patient as in the image above taken 4 months later. Patient responded well to IV Solu-Medrol, but symptoms returned when steroids were reduced. Large mass compressing the right optic nerve is seen. Biopsy revealed lymphoma.
Neuroimaging study (MRI of brain and orbits) revealed an extensive meningioma involving the left orbital apex (arrow).
Computed tomography (CT) scanning offers excellent visualization of the bony anatomy and is particularly useful to evaluate the intraconal space of the orbit. However, for imaging the orbital apex and optic canal, MRI is preferred over CT due to the absence of signal interference from adjacent bone seen on tomography.
Ultrasonography may be useful to document the presence of anterior orbital lesions but offers limited penetration into the deep orbit. However, in certain clinical situations, ultrasonography may be used to image patients quickly in the office in order to determine whether CT or MRI is warranted.
Histologic Findings
If a malignant orbital tumor is suspected, fine-needle aspiration can be used to determine the pathology of the tumor. [21]
Staging
If the source of CON is a tumor, staging is an important aspect of the evaluation. The tumor, nodes, and metastasis (TNM) system is most commonly used to stage tumors. Tumor (T) is the size of the mass. Nodes (N) is the measure of lymph node involvement. Metastases (M) is the measure of tumor extension to different parts of the body. Taken together, the TNM system is used to evaluate the stage of the tumor. [22] Secondary tumors in the orbit due to metastases suggest an advanced stage of the primary tumor.
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Axial MRI taken 3 weeks after the onset of distorted vision in the right eye; visual acuity is reduced to counting fingers at 1 ft. Evidence of optic nerve compression is not seen; disease in the sphenoid sinus is reported.
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MRI of same patient as in the image above taken 4 months later. Patient responded well to IV Solu-Medrol, but symptoms returned when steroids were reduced. Large mass compressing the right optic nerve is seen. Biopsy revealed lymphoma.
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A 72-year-old man with a moderate decrease in vision in the left eye (20/20 right, 20/25 left). Fundus examination revealed a normal right optic nerve.
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Same patient as in image above of a 72-year-old man with a moderate decrease in vision in the left eye (20/20 right, 20/25 left). Fundus examination revealed an atrophic left optic nerve.
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Neuroimaging study (MRI of brain and orbits) revealed an extensive meningioma involving the left orbital apex (arrow).
