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Visual acuity testing is one of the most fundamental measurements in eye care. From routine exams to clinical trials, the accuracy and repeatability of results directly affect patient assessment, treatment decisions, and research outcomes. For decades, ETDRS LogMAR testing has been widely regarded as the gold standard for standardized visual acuity measurement. However, while chart design is highly standardized, one critical variable is often overlooked: luminance.
A recent independent clinical evaluation conducted by Payal Sangani, BS Optom, and Pinakin Davey, OD, PhD, compared two commercially available ETDRS systems, a fluorescent-based Precision Vision system and an LED-based Good-Lite ETDRS system. The study assessed whether the two systems produced repeatable and clinically equivalent visual acuity measurements when luminance was closely matched.
Why luminance consistency matters
Visual acuity results can be affected by multiple testing conditions, including distance, chart design, optotype spacing, refractive correction, and room environment. Among these, luminance is one of the most important and least visible variables. Variations in luminance across systems, or even within the same device over time, can directly influence measured visual acuity.
The evaluation highlights that luminance differences may occur due to device age, electrical input, or degradation of fluorescent components. This is not a minor technical detail. A visual acuity system is not just a chart, it is a complete measurement platform. If illumination changes, the result can change.
For clinicians, researchers, and clinical trial sponsors, measurement consistency is essential. Without stable luminance, repeatability becomes difficult to maintain, particularly in environments where accuracy is critical.
Study design and controlled comparison
The evaluation compared two retro-illuminated ETDRS systems:
Precision Vision ETDRS System
A fluorescent-based system using traditional illumination.
Good-Lite ETDRS System
An LED-based system designed for controlled luminance and long-term consistency.
Both systems used standardized ETDRS charts and were tested at a 4-meter distance following standard protocol. The Precision Vision system operated at 170 cd/m², while the Good-Lite system operated at 159 cd/m². A total of 30 adult participants were included, with 24 completing test-retest measurements. Testing order was randomized, performed monocularly, and masked from observers.
Repeatability confirmed with the Good-Lite system
The Good-Lite LED ETDRS system demonstrated strong test-retest repeatability.
Measured results showed:
- Attempt 1: -0.048 logMAR
- Attempt 2: -0.058 logMAR
- Difference: 0.0096 logMAR
- p-value: 0.30
This difference was not statistically significant, indicating stable performance with no meaningful learning effect between tests. In clinical terms, the system delivered consistent visual acuity measurements across repeated testing.
Clinically equivalent results across systems
The study also compared visual acuity measurements between the Good-Lite system and the fluorescent-based system.
The mean difference between systems was:
- Attempt 1: -0.006 logMAR
- Attempt 2: -0.0056 logMAR
These differences were not statistically significant, with reported p-values of 0.13 and 0.21. Clinically, this represents less than half a letter difference on a LogMAR chart, confirming that both systems produced equivalent visual acuity results under matched luminance conditions.
LED illumination as a modern platform
The key takeaway extends beyond equivalence. The Good-Lite ETDRS system achieved clinically equivalent results using LED illumination, a platform designed for greater consistency over time.
Fluorescent systems have historically been widely used, but they introduce practical challenges. Tubes degrade, output shifts, and luminance can vary depending on system condition and electrical factors. These variations can directly affect visual acuity measurements.
LED illumination addresses these issues by providing a more controlled and stable light source. For standardized ETDRS testing, this level of consistency becomes a meaningful advantage, particularly in environments where repeatability is critical.
ETDRS Consistency becomes the differentiator
When two systems produce statistically similar results, the decision shifts from accuracy alone to long-term performance. Which system delivers more consistent measurement over time?
In clinical trials, research environments, and high-volume practices, small variations in luminance can introduce variability in results. A system designed around stable illumination supports more reliable outcomes.
The Good-Lite LED ETDRS platform is built with this principle in mind, combining standardized testing with a modern illumination system aligned to current clinical expectations.
User experience remained comparable
Participants were also asked which system they preferred, with identities masked during testing.
- 14 participants reported no preference
- 7 preferred the Good-Lite system
- 9 preferred the fluorescent system
No clear preference emerged, suggesting that the Good-Lite system performs comparably not only in measured outcomes, but also in the user experience of testing.
What this means for clinical practice
The findings support several important conclusions. The Good-Lite system provides repeatable visual acuity measurements and produces results that are clinically equivalent to traditional fluorescent-based systems. The observed differences are minimal and not statistically significant.
More importantly, the evaluation reinforces that visual acuity testing should be considered as a complete system, including chart design, protocol, testing distance, and illumination stability.
For clinics and research teams using older fluorescent systems, the study provides a strong case for transitioning to LED-based ETDRS testing. Equivalent clinical results can be achieved while benefiting from a more consistent and controlled illumination platform.
Conclusion
In this independent, IRB-approved evaluation, the Good-Lite LED ETDRS system demonstrated repeatable performance and clinically equivalent visual acuity results compared with a fluorescent-based system under matched luminance conditions.
The study highlights a broader point for modern eye care. Illumination consistency is central to measurement accuracy. Because luminance variability can influence visual acuity results, systems designed around LED illumination offer a meaningful advantage.
By combining standardized ETDRS testing with a modern illumination platform, Good-Lite supports consistent, repeatable visual acuity measurement across clinical and research environments.
