VA‑CAL (Visual Acuity – Contrast – Ambient Luminance) is an innovative research project developed at the Institute for Ophthalmic Research, University of Tübingen. Its goal is to measure visual acuity under true everyday lighting conditions rather than the artificial constraints of standard clinical testing.

Traditional clinical visual acuity tests evaluate vision at one fixed luminance and maximum contrast, which does not reflect the wide range of environments people experience in daily life. In contrast, VA‑CAL quantifies a person’s visual acuity space across up to 46 combinations of ambient luminance (0–10,000 cd/m²) and contrast (18–95%), covering everything from indoor dim light to bright daylight and glare conditions. This results in a comprehensive 3‑dimensional characterization of functional vision in the real world.

How VA‑CAL Works

VA‑CAL uses automated presentation of Landolt optotypes combined with an adaptive psychophysical staircase method. It precisely measures acuity while systematically varying:

• Ambient luminance (from darkness to intense daylight)
• Object contrast (low to high visibility)

The system produces individual visual performance maps, revealing visual strengths and limitations that standard best‑corrected visual acuity (BCVA) tests often overlook.

Applications in Vision Research & Clinical Care

VA‑CAL has proven especially valuable for:

• Glare‑sensitive retinal diseases, such as achromatopsia, where visual acuity deteriorates dramatically at high luminance.
• Evaluation of assistive devices, e.g., short‑wavelength cutoff filter glasses, which VA‑CAL objectively showed to improve achromats’ visual acuity by ~0.2 logMAR under everyday lighting.
• Investigating the impact of different glare types, demonstrating that both uniform and point‑light glare influence vision but in distinct ways relevant for daytime vs. night‑driving assessments.

Why It Matters

VA‑CAL reveals aspects of visual performance that remain invisible in conventional clinical testing. It enables:

• More realistic assessment of daily visual functioning
• Better understanding of glare‑related impairment
• Quantitative endpoints for therapeutic trials
• Personalized evaluation of visual aids

Ultimately, VA‑CAL helps bridge the gap between clinical vision measurement and real‑life visual experience, advancing both scientific understanding and patient care.

Ongoing Development: Reliability Studies and Normative Data

The VA‑CAL project is currently being advanced through a research grant from Johnson & Johnson. As part of this collaboration, a dedicated study has been conducted to rigorously evaluate the test–retest reliability of the VA‑CAL method, ensuring robust measurement stability across repeated assessments. In addition, the project is establishing a comprehensive set of normative reference values for healthy individuals across different age groups, alongside baseline profiles for various patient populations. These datasets will provide essential comparative frameworks for interpreting individual visual performance and will further strengthen the clinical and scientific utility of VA‑CAL in both diagnostics and treatment evaluation.

1. Hilmers J, Straßer T, Bach M, Stingl K & Zrenner E (2022) Quantification of the Dynamic Visual Acuity Space at Real-World Luminances and Contrasts: The VA-CAL Test. Transl Vis Sci Technol 11: 12
2. Hilmers J, Bach M, Stingl K, Zrenner E & Straßer T (2023) The VA-CAL Test Quantifies Improvement of Visual Acuity in Achromatopsia by Means of Short-Wave Cutoff Filter Glasses in Daily Living Conditions. Transl Vis Sci Technol 12: 20
3. Onyszkiewicz M, Hilmers J, Rejdak R, Zrenner E & Straßer T (2024) Effects of Miosis on the Visual Acuity Space under Varying Conditions of Contrast and Ambient Luminance in Presbyopia. J Clin Med 13: 1209
4. Hilmers J, Koschka M, Zrenner E & Straßer T (2025) The Impact of Glare Type and Intensity on Objective and Subjective Visual Performance. medRxiv: 2025.04.18.25326064 doi:10.1101/2025.04.18.25326064 [PREPRINT]