Illustration of an eye representing glaucoma and VFI

Beyond the Numbers: Understanding How Glaucoma Affects Your Vision

Lena Voss in Health & Wellness August 2025 • 4 min read.

"Unpacking the Visual Field Index and What It Means for Your Eye Health"

Glaucoma, a sneaky thief of sight, often progresses silently, making early detection and monitoring crucial. One key tool in managing this condition is the Visual Field Index (VFI), a metric used to assess the extent of vision loss over time. But what exactly is the VFI, and how does it help doctors and patients navigate the complexities of glaucoma?

This article unpacks the concept of VFI, explaining how it is calculated and how it changes as glaucoma progresses. We'll explore the impact of the shift in the calculation method as the disease advances, offering valuable insights for anyone affected by or interested in understanding this sight-stealing disease.

Whether you're a patient seeking clarity, a caregiver wanting to be informed, or just curious about eye health, this guide provides a clear, comprehensive look at the VFI and its significance in managing glaucoma.

Decoding the Visual Field Index (VFI): A Closer Look

Illustration of an eye representing glaucoma and VFI

The VFI is essentially a percentage that represents the overall function of your visual field. Think of it as a score, where 100% indicates a perfectly healthy visual field, and 0% means complete blindness. The VFI helps eye care professionals track how much of your vision remains and how it changes over time due to glaucoma.

VFI calculation involves assessing your visual field at various points, where visual thresholds are measured, i.e. how well you can see at each point. The VFI is derived from different plots, specifically, the pattern deviation probability plot (PDPP) is used for eyes with mild to moderate glaucoma and the total deviation probability plot (TDPP) for those with more advanced disease. These plots translate your visual performance into a single, easy-to-understand number, aiding in monitoring progression of glaucoma.

Pattern Deviation Probability Plot (PDPP): Used in earlier stages; it focuses on how your vision deviates from what's considered normal for your age and general population.
Total Deviation Probability Plot (TDPP): Applied in later stages; it considers the overall visual field, which can be useful when significant damage is present.

The shift from PDPP to TDPP calculation method becomes especially important as the disease progresses, particularly when the mean deviation (MD) of your visual field crosses a certain threshold, like -20 decibels (dB). This shift is essential for accuracy in later stages, but it can also introduce variability in the VFI results, something we will discuss further.

Empowering Your Vision Health

Understanding the VFI and how it is used is a crucial step in managing glaucoma. By partnering with your eye care professional and staying informed, you can proactively safeguard your vision. Remember, early detection and consistent monitoring are key, making tools like the VFI essential allies in the fight against glaucoma.

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.

This article is based on research published under:

DOI-LINK: 10.1167/iovs.12-10836, Alternate LINK

Title: Behavior Of Visual Field Index In Advanced Glaucoma

Subject: General Medicine

Journal: Investigative Opthalmology & Visual Science

Publisher: Association for Research in Vision and Ophthalmology (ARVO)

Authors: Harsha L. Rao, Sirisha Senthil, Nikhil S. Choudhari, Anil K. Mandal, Chandra S. Garudadri

Published: 2013-01-14

Everything You Need To Know

What is the Visual Field Index (VFI), and why is it important in managing glaucoma?

The Visual Field Index (VFI) is a percentage that represents the overall function of your visual field, where 100% indicates a perfectly healthy visual field and 0% means complete blindness. It's a crucial metric used by eye care professionals to track the extent of vision loss over time due to glaucoma. Monitoring changes in the VFI helps in assessing the progression of the disease and making informed decisions about treatment and management strategies. Without the VFI, quantifying and tracking visual field loss would be significantly more challenging.

How is the Visual Field Index (VFI) calculated, and what do the different plots signify in this calculation?

The Visual Field Index (VFI) is calculated by assessing your visual field at various points and measuring visual thresholds (how well you can see at each point). The calculation uses different plots depending on the stage of glaucoma. In earlier stages, the pattern deviation probability plot (PDPP) is used, which focuses on deviations from the normal visual field for your age. As glaucoma progresses, especially when the mean deviation (MD) crosses a threshold like -20 decibels (dB), the total deviation probability plot (TDPP) is used, which considers the overall visual field. These plots translate visual performance into a single percentage that is used to track the progression of Glaucoma.

What are Pattern Deviation Probability Plot (PDPP) and Total Deviation Probability Plot (TDPP), and when is each used in assessing glaucoma?

The Pattern Deviation Probability Plot (PDPP) and the Total Deviation Probability Plot (TDPP) are visual field analysis tools used to assess the extent and nature of visual field loss. The PDPP is used in earlier stages of glaucoma to assess areas of localized loss in the visual field, while accounting for generalized depression from cataracts or other factors. The TDPP is applied in later stages when there is significant damage of the visual field. The TDPP gives a broader view of overall visual field, by looking at the overall visual field instead of just a few key spots as in the PDPP.

Why is there a shift from using the Pattern Deviation Probability Plot (PDPP) to the Total Deviation Probability Plot (TDPP) in glaucoma management, and what implications does this shift have?

The shift from the Pattern Deviation Probability Plot (PDPP) to the Total Deviation Probability Plot (TDPP) occurs as glaucoma progresses, particularly when the mean deviation (MD) reaches a certain threshold. This shift is essential for accuracy in later stages when generalized visual field loss becomes more prominent. Using the TDPP in advanced glaucoma provides a more comprehensive assessment of the remaining visual field. This shift can introduce variability in VFI results. Consistent and correct interpretation of the VFI, considering which plot is used, is essential for accurate monitoring and management of glaucoma.

Beyond the Visual Field Index (VFI), what other factors are important for proactively managing glaucoma and safeguarding vision?

While the Visual Field Index (VFI) is crucial for monitoring glaucoma progression, proactive management involves several other factors. Early detection through regular eye exams is critical, as glaucoma often progresses silently. Partnering with your eye care professional to understand your specific condition and treatment options is essential. Consistent monitoring and adherence to prescribed treatments, such as eye drops or surgery, are vital for slowing the progression of the disease. Although not specifically covered, Intraocular Pressure (IOP) and Optical Coherence Tomography (OCT) measurements of the optic nerve are important factors. IOP measurements provide information on the pressure inside the eye, while OCT scans help assess the structural health of the optic nerve, both of which are critical in glaucoma management.