An increase in intraocular pressure is often associated with changes and blockages in the eye's internal drainage pathways. In a healthy eye, the fluid that nourishes the internal organs is continuously produced and drained through small channels located at the junction of the iris and the cornea - the angle. We examine the angle using a special lens to evaluate its structure and characteristics, aiming to identify risk factors or complications that could lead to drainage blockage and a subsequent rise in intraocular pressure.

What does the test measure and why is it critical?

The test allows me to classify the eye's condition into two main categories:

  • Open-Angle Glaucoma: The angle appears structurally open and normal, but the drainage system itself is not functioning efficiently (similar to a drainpipe clogged from the inside).
  • Narrow or Closed-Angle Glaucoma: The iris is too close to the cornea, physically blocking access to the drainage angle. This is a condition that can lead to a sharp, sudden pressure spike or slow chronic damage.
Distinguishing between these two categories can significantly influence how the disease is treated and managed, tailoring it to the specific case.

Does it hurt? How is the test performed?

The examination is performed at the slit lamp after instilling local anesthetic drops into the eye. The doctor gently places a special lens on the surface of the eye for about a minute. Thanks to the anesthesia, the test is not painful, though it may cause a slight feeling of discomfort or very mild pressure.

Advanced Technologies for Drainage Angle Imaging

While manual gonioscopy allows me to evaluate the angle directly, there are cases where imaging is required to properly document the eye's various structures as well as evaluate structures lying behind the iris. In these cases, we use the following tools:

1. Anterior Segment OCT
This technology uses light rays to create a microscopic optical "cross-section" of the drainage angle.
Benefit to the patient: The test is entirely non-contact (similar to a standard photograph).
Clinical value: It enables quantitative, precise measurement of angle width and provides objective documentation that can be compared over time. This is an excellent tool for diagnosing a "narrow angle" and monitoring changes following laser treatment or surgery.

2. UBM (Ultrasound Biomicroscopy)
A UBM test is essentially high-frequency ultrasound designed for the front part of the eye.
Unique advantage: Unlike OCT or gonioscopy which are based on light, UBM sound waves can penetrate the iris ("the colored part of the eye") and detect structural changes that cannot be demonstrated by other methods.
When is it used? It is essential for diagnosing complex cases like "Plateau Iris", cysts or tumors behind the iris, and examining the position of implanted lenses or shunts. It allows us to understand the exact mechanism causing the angle closure, even when it is hidden from the eye.