Visual Field Testing
Authored By Kristin Bretz, MD
Humphrey visual field (HVF) testing is an important tool to measure the degrees of functional vision for a patient. It helps to diagnose and follow glaucoma progression, find patterns of visual field loss to pinpoint anatomic lesions with masses or strokes, assess for optic nerve compression with thyroid eye disease, assess the impact of ptosis on function and diagnosis, identify drug toxicities, and follow many other conditions. While the normal visual field includes 60 degrees nasal, 100-110 degrees temporal, 70-75 degrees inferior and 60 degrees superior, the HVF tests 30, 24 and 10 degrees in the 30-2, 24-2 and 10-2 testing.
The HVF has algorithms to compare sensitivity, size, and location of lights to map out a person’s visual field. The size of the dots is determined by the test taker, with size III being the most common. In patients with poor vision less than 20/100 and certainly less than 20/200, increasing the spot size to V may help to obtain a better test result. In patients with vision worse than 20/600, the HVF may not be an appropriate measure—just as your doctor if it is appropriate to proceed. In patients with restricted fields, a 10-2 test may be better to focus on the central portion of vision.
During the test, the patient will be instructed to fixate on the central light. It is important to remind the patient that they may blink as the duration of the light exceeds blink time. They may also “miss” lights that are on,but in their blind spot. Encourage patients not to worry and do the best that they can. Patient comfort is important to help them tolerate the exam and maintain focus. If patients have difficulty sitting at the machine, it may be best to take extra time setting up to make sure they are comfortable before starting the exam. Artifacts can occur if the patient has the left eye tested under right eye documentation, the wrong patient is tested, the wrong prescription is put in, the rim interferes with the testing, the patient is inattentive or trigger happy, or it’s just a bad testing day.
If you ever have any questions about setting up a test, have difficulties with the test, or would like to review results of the test, please just ask! I’m happy to review the particulars on cases to help us all give our patients their best shot at this beloved test!