Diagnostic Tests and Imaging: Mapping Your Eye's Drainage

Diagnosing elevated episcleral venous pressure (EVP) is a two-part detective process. First, your eye doctor must determine if the high pressure has actually damaged your eye. Second, they must look “downstream” from the eye to investigate why the drainage system is backed up ^[1].

Because your eye is a window into the body’s vascular system, your eye doctor may discuss tests that seem unrelated to your vision, such as brain or neck scans ^[1].

The Eye Exam: Looking for Clues

During your clinical exam, the doctor will use a slit lamp (a high-powered microscope) to look at the veins on the white of your eye. If they see dilated, “corkscrew” vessels, they will perform a test called gonioscopy ^[2][3].

• Blood in Schlemm’s Canal: Using a special mirror-lens, the doctor looks at your eye’s drainage angle. In a healthy eye, fluid flows out. When venous pressure is high, blood may “back up” or “reflux” into the drainage canal (Schlemm’s canal), appearing as a red line within the eye’s drain ^[4][5]. While this is a useful clue that pressure outside the eye is higher than inside, it must be interpreted with the complete examination. Reflux can be influenced by IOP, posture, and gonioscopy technique, so it is not diagnostic proof on its own ^[4].

Distinguishing Hypertension from Glaucoma

Not everyone with high venous pressure has glaucoma. Your doctor will use two primary tools to see if the pressure is actively damaging your optic nerve:

1. Optical Coherence Tomography (OCT): This is a painless light-reflection scan that measures the thickness of your retinal nerve fiber layer (RNFL) ^[6].
2. Visual Field Test: You will sit at a machine and click a button when you see flashes of light. This checks for “blind spots” in your peripheral vision ^[7].

Ocular hypertension and glaucoma are clinical categories that can evolve. Glaucoma is diagnosed from the overall examination, and characteristic structural damage or characteristic functional loss may be sufficient to make the diagnosis ^[7].

The “Downstream” Search: Why Brain Scans?

Because the veins from your eye drain into a large space behind the eye called the cavernous sinus, any blockage or “leak” there will cause a backup into the eye ^[8]. Based on your specific symptoms, your doctor may consider specialized imaging:

• MRI and MRA: An MRI looks at the soft tissues (like tumors or the optic nerve), while an MRA (Magnetic Resonance Angiography) looks specifically at the blood flow in your arteries. These are used to look for carotid-cavernous fistulas or swollen veins ^[1][6].
• CT and CTA: A CT scan is often better for seeing bone, and a CTA (CT Angiography) uses a contrast dye to map out your blood vessels in high detail ^[8][9].
• Digital Subtraction Angiography (DSA): If non-invasive scans are normal but your doctor still strongly suspects a low-flow vascular leak, they may refer you for a DSA. This is a catheter angiogram performed by a neurovascular specialist. It carries invasive risks (such as contrast, radiation, and neurologic risks) and its benefits must be carefully discussed ^[10][11].

Possible Tests Your Team May Consider

Your medical team selects tests based on your unique presentation; not every patient needs every study ^[8][1]:

• [ ] Goldmann Applanation Tonometry: To measure your intraocular pressure ^[1].
• [ ] Gonioscopy: To check the drainage angle ^[4].
• [ ] Dilated Fundus Exam: To inspect the health of your optic nerve ^[1].
• [ ] OCT Scan: To measure nerve fiber thickness ^[6].
• [ ] Visual Field Test: To check your peripheral vision ^[7].
• [ ] MRI/MRA, CT/CTA, or Venography: To assess for vascular anomalies or thyroid disease ^[8][1].

By completing appropriate tests, your doctor can move toward a firm diagnosis of either a secondary condition or Idiopathic Elevated EVP ^[12].