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PubMed This is a summary of 11 peer-reviewed journal articles Updated
Ophthalmology · Primary Closed-Angle Glaucoma

Understanding Your Tests: Deciphering the Eye Exam

At a Glance

To diagnose Primary Closed-Angle Glaucoma (PACG), eye doctors use a gonioscopy exam to see if the eye's drainage angle is physically blocked by the iris. Specialized imaging scans like AS-OCT or UBM may also be used to measure the eye's internal structures and determine the exact cause.

Navigating the diagnosis of Primary Closed-Angle Glaucoma (PACG) often involves a series of specialized tests that look at the eye’s internal architecture. Unlike a standard eye exam for glasses, these tests are designed to find out exactly why your eye’s plumbing is failing and how much damage has occurred to your sight [1].

The Gold Standard: Gonioscopy

If you have been diagnosed with or suspected of having PACG, the most important test you can have is gonioscopy. During this exam, your doctor uses a special mirrored lens to look directly at the iridocorneal angle—the space where the iris meets the cornea [1][2].

This test is essential because it is the only way a doctor can distinguish between a “narrow” angle and one that is truly “closed.” It also allows them to see if the iris is just resting against the drain or if it has become permanently stuck [3]. If this test hasn’t been part of your evaluation, it is a vital step to request, as research shows it is sometimes overlooked in initial glaucoma evaluations [4].

High-Tech Imaging: AS-OCT and UBM

While gonioscopy is the “gold standard,” your doctor may use two other imaging tools to get a more detailed “blueprint” of your eye.

  • AS-OCT (Anterior Segment OCT): This is a non-contact laser scan that takes high-resolution, cross-sectional images of the front of your eye [5]. It is fast and painless, providing precise measurements of how crowded your eye’s drainage angle is [6].
  • UBM (Ultrasound Biomicroscopy): This uses high-frequency sound waves to “see” behind the iris—areas a laser cannot reach [6]. It is particularly useful for identifying the cause of the blockage, such as whether the ciliary body (the structure holding the lens) is pushing the iris forward [7].

Deciphering Your Exam Report

Medical reports can be filled with confusing acronyms. Here are the most critical terms you should look for and discuss with your doctor:

Term What it Means Why it Matters
ITC (Iridotrabecular Contact) The iris is touching the drainage system [8]. This is often the first sign of risk for angle closure.
PAS (Peripheral Anterior Synechiae) Permanent scarring where the iris is “stuck” to the drain [9]. More PAS usually means higher eye pressure and a higher risk of nerve damage.
C/D Ratio (Cup-to-Disc Ratio) A measurement (from 0.0 to 1.0) of the “hollow” area in the center of your optic nerve [10]. A higher number (e.g., 0.7 or 0.8) indicates that more nerve fibers have been lost to glaucoma.
Lens Vault How much your natural lens sticks out into the front of the eye [6]. A high lens vault is a major anatomical risk factor for closing the angle.

PACG vs. Open-Angle Glaucoma

The primary goal of these tests is to distinguish PACG from Primary Open-Angle Glaucoma (POAG). In POAG, the drainage angle looks perfectly open and normal during a gonioscopy, but the fluid cannot pass through the drain due to microscopic resistance [11]. In PACG, the angle is visibly blocked by the iris. This distinction is critical because the treatments for the two conditions are very different [1].

Return to Navigating Your Diagnosis.

Common questions in this guide

What is a gonioscopy and why is it important for glaucoma?
Gonioscopy is an eye exam where a doctor uses a special mirrored lens to look directly at the eye's drainage angle. It is the gold standard for determining if your drainage angle is narrow or completely closed.
What does PAS mean on a glaucoma exam report?
PAS stands for Peripheral Anterior Synechiae, which means there is permanent scarring where the iris has become stuck to the eye's drain. More PAS generally indicates higher eye pressure and a greater risk of optic nerve damage.
What is a cup-to-disc (C/D) ratio?
The cup-to-disc ratio measures the hollow area in the center of your optic nerve. A higher number, such as 0.7 or 0.8, indicates that more nerve fibers have been lost to glaucoma damage.
How do doctors tell the difference between closed-angle and open-angle glaucoma?
Doctors use a gonioscopy exam to look at the eye's drainage angle. In open-angle glaucoma, the drain looks open but fluid cannot pass through, while in closed-angle glaucoma, the angle is visibly blocked by the iris.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Was a gonioscopy performed at my last visit, and if not, can we do one today to check my drainage angles?
  2. 2.Did my gonioscopy show any permanent scarring (PAS) or just temporary contact (ITC) between my iris and the drain?
  3. 3.What is my current cup-to-disc ratio, and has it changed since my previous exam?
  4. 4.Would an AS-OCT or UBM scan help determine if my lens vault or my ciliary body position is causing my angle to narrow?
  5. 5.Based on these tests, are you confident we can rule out other types of glaucoma like primary open-angle glaucoma?

Questions For You

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References

References (11)
  1. 1

    Anterior Segment Imaging for Angle Closure.

    Chansangpetch S, Rojanapongpun P, Lin SC

    American journal of ophthalmology 2018; (188()):xvi-xxix doi:10.1016/j.ajo.2018.01.006.

    PMID: 29352976
  2. 2

    Assessment of Circumferential Angle Closure with Swept-Source Optical Coherence Tomography: a Community Based Study.

    Porporato N, Baskaran M, Tun TA, et al.

    American journal of ophthalmology 2019; (199()):133-139 doi:10.1016/j.ajo.2018.11.015.

    PMID: 30502338
  3. 3

    Diagnostic analysis of angle-closure using the iris-trabecular contact (ITC) index of CASIA2 swept source anterior segment optical coherence tomography.

    Rodriguez-Una I, Espinoza G, Martínez-Alberquilla I, et al.

    International ophthalmology 2025; (45(1)):410 doi:10.1007/s10792-025-03752-7.

    PMID: 41081976
  4. 4

    Low Sensitivity of the Van Herick Method for Detecting Gonioscopic Angle Closure Independent of Observer Expertise.

    Johnson TV, Ramulu PY, Quigley HA, Singman EL

    American journal of ophthalmology 2018; (195()):63-71 doi:10.1016/j.ajo.2018.07.026.

    PMID: 30071210
  5. 5

    Evaluation of phacoemulsification (ultrasound) cataract surgery on the dynamics of the anterior segment of primary angle closure by AS-OCT.

    Zhong L, Zuo J, Jin Q, et al.

    American journal of translational research 2021; (13(4)):3156-3164.

    PMID: 34017484
  6. 6

    Management of Primary Angle Closure Disease.

    Paulose S, Vinod K

    International ophthalmology clinics 2023; (63(4)):153-166 doi:10.1097/IIO.0000000000000478.

    PMID: 37755449
  7. 7

    Ultrasound biomicroscopy in glaucoma assessment.

    Potop V, Coviltir V, Schmitzer S, et al.

    Romanian journal of ophthalmology 2021; (65(2)):114-119 doi:10.22336/rjo.2021.24.

    PMID: 34179574
  8. 8

    Evaluation of the efficacy of laser peripheral iridoplasty in reversing the darkroom provocative test result in Chinese patients with primary angle closure status post laser iridotomy.

    Huang P, Wu LL

    International journal of ophthalmology 2015; (8(3)):580-4 doi:10.3980/j.issn.2222-3959.2015.03.26.

    PMID: 26086012
  9. 9

    Association of peripheral anterior synechia, intraocular pressure, and glaucomatous optic neuropathy in primary angle-closure diseases.

    Zhang M, Mao GY, Ye C, et al.

    International journal of ophthalmology 2021; (14(10)):1533-1538 doi:10.18240/ijo.2021.10.09.

    PMID: 34667729
  10. 10

    Retinitis pigmentosa with concomitant essential iris atrophy and glaucoma - case report.

    Meirelles SH, Barreto AS, Buscacio ES, et al.

    Clinical ophthalmology (Auckland, N.Z.) 2015; (9()):2139-45 doi:10.2147/OPTH.S75384.

    PMID: 26648683
  11. 11

    Proportion of Angle Closure Glaucoma in Tamale, Ghana.

    Liu CK, Ali O, Murdoch I, Simon J

    Journal of glaucoma 2024; (33(9)):709-714 doi:10.1097/IJG.0000000000002383.

    PMID: 38551403

This page explains diagnostic tests for primary closed-angle glaucoma for educational purposes. Always consult your ophthalmologist or eye care specialist for an accurate diagnosis and to interpret your specific exam results.

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