Illustration of a visual field grid partially obscured by darkness, symbolizing glaucoma-related vision loss.

Glaucoma Detection: How the Visual Field Index Can Help

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Reese Marlowe in Health & Wellness December 2025 • 5 min read.

"Advanced glaucoma and visual field testing: Understanding the Visual Field Index (VFI) and its role in monitoring vision loss."


Glaucoma quietly steals sight, often without noticeable symptoms until significant damage has occurred. This makes early detection and consistent monitoring essential. One of the key tools in managing glaucoma is the Humphrey Visual Field (HVF) test, which measures a person's peripheral vision. The results of this test are summarized by the Visual Field Index (VFI), a single percentage that indicates the overall health of your visual field.

The Visual Field Index (VFI) is a powerful metric used by eye doctors to track the progression of glaucoma. It works by assessing the percentage of visual function remaining, with 100% representing a normal visual field and 0% indicating complete loss of sight. By monitoring changes in the VFI over time, doctors can assess the effectiveness of treatment and make necessary adjustments to prevent further vision loss.

But what happens when glaucoma advances? A study published in Investigative Ophthalmology & Visual Science sheds light on how the VFI behaves in advanced stages of the disease, particularly when the Mean Deviation (MD) crosses the -20 decibel (dB) threshold. This is a critical point, as the algorithm used to calculate the VFI changes at this stage. Understanding these nuances can help patients and caregivers better interpret test results and work with their doctors to make informed decisions.

What is the Visual Field Index (VFI) and Why Does It Matter?

Illustration of a visual field grid partially obscured by darkness, symbolizing glaucoma-related vision loss.

The Visual Field Index (VFI) is essentially a summary of your entire visual field, translated into a single, easy-to-understand percentage. It's calculated using data from the Humphrey Visual Field (HVF) test, which maps out your sensitivity to light at various points in your field of vision. This test helps identify areas where you may be experiencing vision loss, even if you haven't noticed it yourself.

The VFI is calculated differently depending on the severity of glaucoma. When the mean deviation (MD) – another measure of visual field loss – is better than -20 dB, the VFI is based on the pattern deviation probability plot (PDPP). This plot highlights localized areas of visual field loss, taking into account a person's age-related decline in vision. However, when the MD crosses -20 dB, the VFI calculation switches to the total deviation probability plot (TDPP). This plot considers the overall reduction in visual sensitivity compared to a healthy, age-matched individual.

  • Early Detection: Helps identify early signs of vision loss, even before you notice symptoms.
  • Progression Monitoring: Tracks the rate of visual field loss over time, allowing for timely adjustments to treatment.
  • Treatment Effectiveness: Assesses whether current treatments are effectively slowing or halting the progression of glaucoma.
  • Informed Decisions: Provides valuable information for patients and doctors to make collaborative decisions about glaucoma management.
This shift in calculation method can sometimes lead to a noticeable change in the VFI, even if there hasn't been a significant change in your actual vision. The Investigative Ophthalmology & Visual Science study aimed to quantify this change and identify the factors that influence it.

What Does This Mean for Glaucoma Patients?

The Investigative Ophthalmology & Visual Science study highlights the importance of understanding how the VFI behaves, especially in advanced glaucoma. A sudden drop in VFI when the MD crosses -20 dB doesn't necessarily indicate a rapid worsening of the condition. Instead, it may be due to the change in the calculation algorithm. By being aware of this, patients can avoid unnecessary anxiety and work with their doctors to get an accurate assessment of their glaucoma progression. Using the correction formula from this study can be a tool to calculate change in VFI. Consistent monitoring and open communication with your eye care provider remain the best strategies for managing glaucoma and preserving your vision.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

1

What is the Visual Field Index (VFI), and how does it help in glaucoma management?

The Visual Field Index (VFI) is a single percentage derived from the Humphrey Visual Field (HVF) test that summarizes the overall health of your visual field. It ranges from 100% (normal vision) to 0% (complete vision loss). Eye doctors use the VFI to track the progression of glaucoma, assess treatment effectiveness, and make informed decisions about patient care. Monitoring changes in the VFI over time allows for timely adjustments to treatment plans, aiming to prevent further vision loss.

2

How is the Visual Field Index (VFI) calculated, and why does the calculation method change?

The VFI calculation uses data from the Humphrey Visual Field (HVF) test. When the Mean Deviation (MD) is better than -20 decibels (dB), the VFI is based on the pattern deviation probability plot (PDPP). This plot highlights localized areas of visual field loss. However, when the MD crosses -20 dB, the calculation switches to the total deviation probability plot (TDPP). This change considers the overall reduction in visual sensitivity. This shift in calculation method can influence the VFI, especially in advanced stages of glaucoma.

3

What is the significance of the Mean Deviation (MD) threshold of -20 dB in relation to the Visual Field Index (VFI)?

The -20 dB threshold of the Mean Deviation (MD) is a critical point in glaucoma management because it triggers a change in how the Visual Field Index (VFI) is calculated. When the MD is worse than -20 dB, the calculation method switches from the pattern deviation probability plot (PDPP) to the total deviation probability plot (TDPP). This shift can lead to a noticeable change in the VFI, even if the patient's vision hasn't significantly worsened. This change is important for patients and caregivers to understand to avoid misinterpreting test results.

4

How can understanding the Visual Field Index (VFI) calculation change help glaucoma patients?

Understanding how the Visual Field Index (VFI) is calculated, particularly when the Mean Deviation (MD) crosses the -20 dB threshold, is crucial for glaucoma patients. A sudden drop in VFI may not always mean a rapid worsening of the condition; it could be due to the change in the calculation method. This awareness helps patients avoid unnecessary anxiety and facilitates accurate assessments of glaucoma progression. Patients can then work with their doctors for informed decisions and consistent monitoring.

5

What are the key benefits of using the Visual Field Index (VFI) in managing glaucoma?

The Visual Field Index (VFI) offers several key benefits in glaucoma management. Firstly, it aids in early detection of vision loss, even before noticeable symptoms occur. Secondly, it helps in monitoring the progression of visual field loss over time, allowing for timely adjustments to treatment plans. Thirdly, it assesses the effectiveness of current treatments. Finally, the VFI provides valuable information for patients and doctors to make collaborative decisions about managing glaucoma, helping preserve vision and improving quality of life.

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