Brainwaves replacing eye chart: Objective vision testing concept

Can Brain Signals Replace the Eye Chart? Objective Vision Tests Are Here

Beau Callahan in Health & Wellness August 2025 • 5 min read.

"New research shows how brainwave analysis using event-related potentials (ERPs) offers reliable, objective assessments of visual acuity, potentially revolutionizing vision testing for complex cases."

Visual acuity testing is a cornerstone of eye care, essential for diagnosing vision problems and monitoring treatment effectiveness. However, traditional methods rely on patient participation, which can be challenging in certain situations. Imagine trying to assess vision in someone who can't communicate effectively, like a young child or a patient with cognitive impairments. Or consider the possibility of a patient exaggerating their vision loss for secondary gain. In these scenarios, objective measures become invaluable.

Traditionally, clinicians have relied on subjective methods where patients actively participate by identifying shapes, letters, or orientations. While these tests are standard, they introduce variability due to patient cooperation and cognitive factors. This is where the promise of objective measures comes into play.

Researchers have been exploring ways to tap directly into the brain's response to visual stimuli, bypassing the need for conscious reporting. One promising technique involves analyzing event-related potentials (ERPs), which are tiny electrical signals produced by the brain in response to specific events or stimuli. The P300 ERP component, in particular, is associated with higher-level cognitive processing and has shown potential for objective acuity estimation.

Objective Acuity Testing: How Brainwaves Are Changing Vision Assessment

Brainwaves replacing eye chart: Objective vision testing concept

A recent study published in Investigative Ophthalmology & Visual Science sheds light on how event-related potentials (ERPs) can be used to objectively assess visual acuity using optotypes – the standard symbols like Landolt C rings used in eye charts. Unlike traditional visual evoked potential (VEP) tests that rely on grating or checkerboard patterns, this method uses the P300 ERP component, which is sensitive to small stimulus differences and can provide reliable acuity estimates, even with optotypes.

The research team, led by Sven P. Heinrich, Isabel Lüth, and Michael Bach at the University of Freiburg, Germany, demonstrated the feasibility of using Landolt C optotypes in a P300 acuity paradigm. Here's how the study worked:

Participants: The study involved a group of participants with normal vision, whose vision was artificially degraded using dioptric blur (lenses that simulate nearsightedness or farsightedness).
Stimuli: Participants were presented with two types of visual stimuli: Landolt C optotypes (with varying gap sizes) and grating patterns (with varying coarseness).
Procedure: An oddball paradigm was used, where infrequent target stimuli (Landolt Cs or gratings) were interspersed with frequent, non-target stimuli (closed rings or homogenous gray fields). Participants were instructed to silently count the infrequent target stimuli.
ERP Recording: The P300 ERP component was recorded from the participants' brains using electroencephalography (EEG).
Acuity Estimation: Thresholds were estimated by fitting a sigmoid curve to the P300 amplitudes as a function of Landolt C size or grating coarseness. Psychophysical thresholds were also obtained for both stimulus types for comparison.

The study found that reliable P300 acuity estimates could be obtained for both optotype and grating stimuli. Interestingly, there was a discrepancy between psychophysical acuity estimates for Landolt C and grating stimuli, likely due to "spurious resolution" with gratings – a phenomenon where individuals can sometimes perceive gratings even when they can't resolve the details of optotypes. However, the P300-based estimates reflected this discrepancy, suggesting that they capture the underlying visual processing differences between the two stimulus types.

The Future of Vision Testing: Objective, Accurate, and Personalized

These findings have significant implications for the future of vision testing. By using ERPs and optotypes, clinicians may be able to obtain more objective and accurate measures of visual acuity, especially in cases where subjective testing is unreliable. This could lead to earlier and more accurate diagnoses of vision problems, as well as more personalized treatment plans. The ability to objectively assess visual function also opens doors for evaluating the effectiveness of interventions in populations where traditional testing is challenging.

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Everything You Need To Know

What are Event-Related Potentials (ERPs), and how are they used in vision testing?

Event-Related Potentials (ERPs) are tiny electrical signals produced by the brain in response to specific events or stimuli. In vision testing, researchers analyze these signals to objectively assess visual acuity. The P300 ERP component, associated with higher-level cognitive processing, is particularly useful because it can provide reliable acuity estimates. This method bypasses the need for patient participation, making it valuable when traditional methods are unreliable, such as with young children or patients with cognitive impairments.

How does the P300 ERP component help in estimating visual acuity using optotypes like Landolt C rings?

The P300 ERP component is used to estimate visual acuity by analyzing the brain's response to different sizes of optotypes. In studies, participants view Landolt C rings (with varying gap sizes) and the P300 ERP component is recorded using electroencephalography (EEG). Participants are instructed to focus on the infrequent target stimuli. The amplitude of the P300, in response to different Landolt C sizes, is measured and used to create a curve. This curve helps determine the smallest optotype size a person can accurately perceive, thus estimating their visual acuity. This is a more objective method compared to traditional tests that depend on the patient's active participation.

What is the difference between traditional visual acuity testing and the method using Event-Related Potentials (ERPs)?

Traditional visual acuity testing relies on subjective methods where patients identify shapes, letters, or orientations on an eye chart. This approach requires the patient to actively participate and can be affected by factors like patient cooperation and cognitive abilities. In contrast, the method using Event-Related Potentials (ERPs) is an objective measure. It taps directly into the brain's response to visual stimuli, specifically measuring the P300 ERP component. This method does not depend on the patient's conscious reporting, providing reliable results even when subjective testing is challenging or unreliable.

What are the advantages of using Event-Related Potentials (ERPs) for vision testing, and in which scenarios is this method most beneficial?

The primary advantage of using Event-Related Potentials (ERPs) for vision testing is its objectivity. It allows for accurate and reliable measurement of visual acuity without relying on patient cooperation. This method is particularly beneficial in situations where traditional, subjective testing methods are unreliable. Examples include assessing vision in young children, individuals with cognitive impairments, or patients who might exaggerate vision loss. It also offers potential for evaluating treatment effectiveness and early and more accurate diagnoses of vision problems. This can ultimately lead to more personalized treatment plans.

How did the study by Heinrich, Lüth, and Bach contribute to understanding the use of ERPs in vision testing, and what were the key findings?

The study by Sven P. Heinrich, Isabel Lüth, and Michael Bach at the University of Freiburg, Germany, demonstrated the feasibility of using Landolt C optotypes in a P300 acuity paradigm. Their study found that reliable P300 acuity estimates could be obtained using both Landolt C optotypes and grating stimuli. They also observed a discrepancy between psychophysical acuity estimates for Landolt C and grating stimuli, which was accurately reflected in the P300-based estimates. This suggests that ERPs can capture the underlying visual processing differences between these different types of stimuli, offering a comprehensive and objective way to measure and assess visual acuity, and making way for more objective diagnostic assessment.