What is a Visual Field Test?

The Visual Field Test is a computerized test that maps your side (peripheral) vision and helps your eye doctor monitor your glaucoma. During the test, you look straight ahead at a target while small lights flash in different locations. You press a button each time you see a light. The test typically takes 4-10 minutes per eye.

Understanding Your Test Results

Your visual field report contains several important measurements that help you and your doctor track your glaucoma:

Mean Deviation (MD)

This number shows how your overall vision compares to people your age with healthy eyes. It's measured in decibels (dB).

• A number close to 0 dB means your vision is similar to normal
• Negative numbers (like -3 dB or -10 dB) mean some vision loss
• More negative numbers indicate more vision loss[2]

Your doctor uses MD to classify your glaucoma as early (better than -6 dB), moderate (-6 to -12 dB), or advanced (worse than -12 dB).[2]

Pattern Deviation

This shows where specific areas of vision loss are located in your visual field. The report displays a pattern of symbols or numbers that highlight unusual areas. Your doctor looks for patterns that match typical glaucoma damage.[2][3]

Visual Field Index (VFI)

This percentage (0-100%) represents how much of your visual field remains healthy. A VFI of 100% means normal vision, while lower numbers indicate more vision loss. This number is particularly useful for tracking changes over time.[4]

Test Duration

The test usually takes 4-10 minutes per eye. Longer test times may occur if you're having difficulty seeing the lights or maintaining focus, which can affect the reliability of results.[5]

Reliability Measures

These three measurements help your doctor determine if the test results are trustworthy:

Fixation Losses

This measures how well you kept your eye focused on the central target during the test. The result appears as a percentage. Tests with fixation losses under 20% are generally considered reliable. Higher percentages may mean you had difficulty maintaining steady focus, which can happen with more advanced glaucoma or fatigue.[3][5]

False Positives

This tracks how often you pressed the button when no light was actually shown. A false positive rate under 15% is considered reliable. High false positive rates (pressing the button too often) can make your vision appear better than it actually is and the resulting test report will therefore be misleading[3][6]

False Negatives

This measures whether you missed seeing lights in areas where you previously saw them. While high false negative rates were once thought to indicate poor attention, research shows they're more closely related to the severity of your glaucoma damage rather than how well you performed the test. Your doctor takes this into account when reviewing your results.[3]

What Makes a Reliable Test?

A reliable test typically has:

• Fixation losses less than 20%
• False positives less than 15%
• False negatives less than 33%[2][3]

However, even if one of these numbers is higher, your test may still provide useful information. Your doctor will consider all factors, including the severity of your glaucoma, when interpreting your results.[5]

Tips for Better Test Results

• Rest well before your appointment
• Take breaks if your eye gets tired during the test
• Let the technician know if you need to pause
• Try to stay naturally focused on the central target but do not stare
• Blink naturally
• Remember to breathe
• Don't worry about "passing" the test—just respond when you see lights

Questions to Ask Your Doctor

• How does my current test compare to my previous ones?
• Is my glaucoma stable, improving, or getting worse?
• Do I need to repeat the test?
• Should we adjust my treatment based on these results?

Remember, visual field testing is just one tool your doctor uses to manage your glaucoma. Your doctor will also examine your optic nerve and may use other tests to get a complete picture of your eye health.

References

1. Humphrey Visual Field Made Easy for Residents. Mansoori T. Indian Journal of Ophthalmology. 2024;72(10):1535. doi:10.4103/IJO.IJO_2519_23.
2. Estimated Utility of the Short-term Assessment of Glaucoma Progression Model in Clinical Practice. Proudfoot JA, Zangwill LM, Moghimi S, et al. JAMA Ophthalmology. 2021;139(8):839-846. doi:10.1001/jamaophthalmol.2021.1812.
3. Role of Visual Field Reliability Indices in Ruling Out Glaucoma. Rao HL, Yadav RK, Begum VU, et al. JAMA Ophthalmology. 2015;133(1):40-4. doi:10.1001/jamaophthalmol.2014.3609.
4. Comparison of Humphrey Field Analyzer and Imo Visual Field Test Results in Patients With Glaucoma and Pseudo-Fixation Loss. Goukon H, Hirasawa K, Kasahara M, Matsumura K, Shoji N. PloS One. 2019;14(11):e0224711. doi:10.1371/journal.pone.0224711.
5. Analysis of Reliability Indices From Humphrey Visual Field Tests in an Urban Glaucoma Population. Birt CM, Shin DH, Samudrala V, et al. Ophthalmology. 1997;104(7):1126-30. doi:10.1016/s0161-6420(97)30173-0.
6. The Usefulness of Gaze Tracking as an Index of Visual Field Reliability in Glaucoma Patients. Ishiyama Y, Murata H, Asaoka R. Investigative Ophthalmology & Visual Science. 2015;56(11):6233-6. doi:10.1167/iovs.15-17661.