Determines glaucoma. The threshold of vision means the lowest size or intensity of a spot of light that the eye can see. A threshold visual field test is used to detect glaucoma: multiple small spots of light are placed in different areas in a specialized testing device and the patient presses a buzzer if he/she sees them. Glaucoma decreases peripheral vision and threshold testing would show fewer spots seen by you.
Measure of vision. The field of vision threshold is typically the minimum light intensity visible. Glaucoma patients are tested with visual fields to check if they see the expected minimum threshold for their age. More field loss than expected can be a sign of glaucoma.