*2.7. Visual Field*

Glaucoma is known as the "sneak thief of sight" because of its tendency to affect the peripheral visual field first. As a result, many patients do not realize that they have glaucoma until the visual field loss encroaches centrally. In clinic, standard automated perimetry (SAP) is performed to detect visual field loss. The patient places his/her head on a chinrest in front of a white bowl. While fixating on a target, he/she is instructed to push a button whenever a spot of light is seen. The machine will display light stimuli at various locations and intensities. In the end, the machine will map out spots that the patient did significantly worse relative to his/her age group.

Because SAP is a large device only available in clinic, it cannot be used in a screening program outside or at home. Alternatives of SAP include online perimetry performed on a computer, tablet, or with virtual reality glasses.

#### 2.7.1. Peristat Online Perimetry

This is a visual field test accessed at keepyoursight.org and is performed on a computer with a 17-inch or larger monitor. In the beginning, the patient is asked to adjust his/her distance from the monitor until a flashing light temporal to the fixation point disappears (i.e., enters the blind spot). The patient is then asked to fixate at a central point. Stimuli are presented at various locations across a 24-degree horizontal by 20-degree vertical field with various intensities, and the patient is asked to push the spacebar whenever one is seen. The test takes less than 5 min per eye. Similarly to SAP, the Peristat test generates a report with reliability indices and a grayscale visual field image; the results are emailed to the doctor who ordered the test.

A prospective study [57] comparing Peristat Online Perimetry with Humphrey Visual Field 24-2 test reported Spearman rank correlations ranging from 0.55 to 0.77 for abnormal points in both tests. Peristat Online Perimetry demonstrated a high diagnostic ability, with the AUC ranging from 0.77 to 0.81 for mild glaucoma and 0.85 to 0.87 for moderate to severe glaucoma.
