The Science behind the Tip

False depressions due to a misaligned trial lens or a lens holder which was placed too far from the patient's eye are sometimes mistaken for glaucomatous field defects. They can appear in any quadrant and are located in the extreme periphery of an automated perimetry test. This is very unlike glaucomatous field defects which typically are arcuate depressions located in the nasal mid-periphery of the test.

The only time a trial lens artifact could cause some doubt is when it is confined to the nasal periphery. Unlike glaucomatous field defects however, this artifact nearly always crosses the horizontal meridian. The pattern deviation map nicely demonstrates that this small depression is located in both hemifields.

Trial lens artifacts can get quite impressive when the patient gradually withdraws his head from the forehead rest and there was lack of supervision by the technician during the test.

Contributor: Ann Hoste, Antwerp

Tip Reviewer: Roger Hitchings
Tip Editors: Ann Hoste, John Salmon and John Thygesen