Ophthalmology

Decoding Your Diagnostic Tests: Faucets, Drains, and Maps

At a Glance

Suspected hypersecretion glaucoma is evaluated with several tests rather than one result. Pressure measurement, drainage-angle examination, optic-nerve scans, visual fields, and corneal-thickness testing help assess the cause of high eye pressure, detect damage, and identify secondary problems.

Diagnosing the cause of high eye pressure requires a series of tests that look at the eye’s structure, function, and fluid pathways. If you have been told you have “hypersecretion” or high pressure with “open angles,” your doctor is determining if the problem is at the “faucet” (fluid production) or the “drain” (fluid outflow), while ruling out secondary causes ^[1]^[2].

The Standard Glaucoma Toolkit

Most patients will undergo several core tests. Importantly, doctors do not rely on just one test; they interpret structural imaging (OCT) alongside functional vision (visual fields) and direct clinical examination over time.

Slit-Lamp and Dilated Exam: The doctor uses a microscope to look at the front of your eye and a bright light to examine the optic nerve and retina at the back. This is essential for spotting inflammation, unusual blood vessels, or characteristic nerve damage.
Tonometry (The Pressure Check): This measures your intraocular pressure (IOP). The gold standard uses a blue light and a small plastic prism to gently touch your numbed eye ^[3]^[4].
Gonioscopy (The Angle Exam): The doctor uses a special mirrored lens to look directly at the eye’s “drain” (the trabecular meshwork). This confirms if the angles are accessible and looks for hidden issues like pigment or inflammatory debris ^[5]^[3].
Optical Coherence Tomography (OCT): This is a non-invasive scan that measures the thickness of your Retinal Nerve Fiber Layer (RNFL). It can detect microscopic thinning of the optic nerve, though it can sometimes be thrown off by high myopia or unique nerve anatomy ^[5]^[6].
Visual Field Test (Perimetry): You sit at a machine and click a button when you see faint lights. This maps out any developing “blind spots,” but results can be affected by fatigue and require practice ^[5]^[6].
Pachymetry: Measures your Central Corneal Thickness (CCT).

Completeness Checklist

To ensure your diagnosis is accurate, your clinical record should ideally contain these specific data points.

Data Point	Why It Matters
Max Recorded IOP	Your “baseline” highest pressure helps set your treatment goals ^[7].
Central Corneal Thickness	Thickness affects some tonometry methods. While there is no simple mathematical formula you can use to “correct” your own pressure, a thin cornea is an independent risk factor for glaucoma ^[3].
Gonioscopy Grade	A formal note that your angles are open (e.g., “Grade 4” or “Open to Ciliary Body”) ^[5].
Steroid History	A record of any past or current use of steroid sprays, creams, or pills ^[7].
OCT RNFL Thickness	The baseline “map” of your optic nerve health to compare against in the future ^[1].
Visual Field Reliability	Notes on whether you had high “false positives,” “false negatives,” or “fixation losses,” which tell the doctor if the test was a true representation of your sight ^[5].

Rarely Needed Specialized Tests

If your case is highly unusual, your doctor might mention specialized tests. While these were more common in historical research trying to “prove” hypersecretion, they are now rare ^[8]^[9].

Tonography & Fluorophotometry: Older or highly specialized tests that attempt to estimate outflow facility and fluid production rates. They are not routine diagnostic tools ^[10]^[11].
Advanced Imaging (CTA/MRA/Catheter Angiography): If the doctor specifically suspects an abnormal vascular connection like a carotid-cavernous fistula based on symptoms (bruits, corkscrew vessels), they may refer you for advanced imaging of the blood vessels behind the eye ^[12]^[13]. Most glaucoma patients do not need brain imaging.

Common questions in this guide

Which tests help doctors evaluate high eye pressure with open angles?

Doctors usually combine a slit-lamp and dilated eye examination with tonometry, gonioscopy, OCT, visual-field testing, and pachymetry. Together, these tests measure pressure, inspect the drainage angle, assess the optic nerve, check vision, and account for corneal thickness. Results are interpreted over time rather than from a single test.

Does an open drainage angle mean high eye pressure is harmless?

No. An open angle means the drainage pathway is physically accessible, but pressure can still rise if fluid does not leave efficiently, if fluid production is excessive, or if a secondary cause is present. The optic nerve and visual field still need evaluation for damage.

What do OCT and visual field testing tell me?

OCT measures the thickness of the retinal nerve fiber layer and can show structural thinning around the optic nerve. A visual field test looks for functional blind spots. Doctors compare both tests with the examination and consider reliability because fatigue, distraction, or unusual anatomy can affect results.

Why is central corneal thickness measured during glaucoma testing?

Central corneal thickness can affect some eye-pressure measurements, and a thin cornea is an independent risk factor for glaucoma. There is no simple formula that lets patients correct their own pressure reading, so the ophthalmologist interprets the measurement with the rest of the examination.

When might I need blood-vessel imaging for high eye pressure?

Brain or blood-vessel imaging is not routine for most glaucoma patients. If the examination or symptoms suggest an abnormal connection such as a carotid-cavernous fistula—for example, a bruit or corkscrew vessels—an ophthalmologist may arrange CTA, MRA, or catheter angiography.

Are tonography and fluorophotometry standard tests for hypersecretion glaucoma?

These are older or highly specialized tests that estimate fluid outflow or production. They are rarely used in routine evaluation, so most patients do not need them.

Curated prompts to bring to your next appointment.

1.What is my 'gonioscopy grade,' and does the drainage angle look physically open or obstructed?
2.Did you see any blood in Schlemm's canal or abnormal 'corkscrew' vessels during the exam?
3.How does my central corneal thickness (pachymetry) factor into my overall risk profile?
4.Based on my OCT and visual field tests, is there any evidence of actual damage, or am I currently an 'ocular hypertensive'?
5.Are we considering any specialized tests or imaging for my blood vessels to rule out secondary causes?

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References (13)

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This page explains diagnostic testing for suspected hypersecretion glaucoma for informational purposes only and does not constitute medical advice. Your ophthalmologist should interpret your results and recommend next steps.

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