You have the best chance of detecting an appositional angle closure using gonioscopy when examining your patient in a completely dark room, according to a study in Octobers Archives of Ophthalmology. Of 18 individuals with the gonioscopic finding of appositional angle closure, the examining clinicians used ultrasound biomicroscopy (UBM) to verify gonioscopic findings.
They found that 17 subjects (96%) had iridotrabecular opposition by UBM under dark room conditions. However, when the lights were turned on, only 10 patients (56%) had a closed angle by UBM.
If you suspect a patient has a narrow angle or a history of angle closure, its a good practice to observe the angle through gonioscopy in a dark room with minimal illumination from the biomicroscope, says Denise Goodwin, O.D., of Pacific University College of Optometry,
The amount of light in the eye changes the appearance of the angle substantially, Dr. Goodwin says. Dim illumination while performing gonioscopy not only causes the peripheral iris to thicken, but also allows the iris to assume a more convex appearance, increasing the likelihood of correctly diagnosing a patient who is at risk for angle closure.