Study findings support use of non-letter optotypes in VA testing to improve patient accessibility

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A recent study, published in Investigative Ophthalmology & Visual Science, found that non-letter optotypes provide visual acuity (VA) measurements that are comparable to Latin-letter ETDRS chart results at the population level. Due to wide variability in the study’s results, individual-level agreement remains limited.

The study was led by first author Michael Kalloniatis, BSc(Optom), MSc(Optom), PhD, FAAO, of the University of Houston College of Optometry, in collaboration with researchers from various Australian institutions. “Non-letter optotypes, such as Tumbling E and Landolt C, can expand access to visual acuity testing for patients who are illiterate or unfamiliar with the Latin alphabet. Although there is individual testing variability, at the population level the various optotypes are comparable, helping make eye care and clinical research more inclusive without sacrificing clinical utility,” Kolloniatis said in a statement to Optometry Times.

Background

The most commonly used clinical VA assessment in office and clinical trials are Bailey-Lovie logMAR principle-based eye charts.^2-5 These charts are often letter-based, which can provide a disadvantage for certain patients. Landolt C and Tumbling E optotypes have been proposed as alternative because they “reduce dependence on letter knowledge, instead requiring observers to report the orientation of a gap or optotype,” as stated by the study authors. However, both Landolt C and Tumbling E can provide challenges in optotype size progression, spacing, and scoring. These challenges remain even when the logMar or ETDRS format is adhered.

While previous research provides evidence that different optotypes have mean VA measurement agreement, their findings indicate “substantial variability,” according to study authors.^1,6,7 The current study aimed to address 3 crucial gaps on EDTRS typography accessibility. The first was the impact of pinhole (PH) VA measurements, which are useful for evaluating refractive error. The second was finding the association between Latin letter acuity, Landolt C, and Tumbling E optotypes. Lastly, they aimed to compare their results amongst a range of vision functionalities. Through their findings, the researchers hope to increase accessibility for EDRS vision screening.

Methods

Researchers recruited 78 patients (mean age 59.8 ± 14.6 years; mean refractive error −0.89 ± 3.4 diopters) from the Centre for Eye Health, a referral-only diagnostic clinic in Sydney, Australia. VA was measured using a Medmont AT20P chart in ETDRS format across the optotype conditions, with letter or optotype orientation randomized after each presentation. For each chart, VA was measured uncorrected, with pinhole, and with habitual refractive correction. Using the patient’s collected habitual refractive correction, researchers evaluated the relationship between corrected VA and the 3 optotypes.

Ordinary least squares regression was used to model the relationship between optotypes, with slopes tested against 1.0 and intercepts tested against 0. Bland-Altman analysis was used to assess agreement, reporting mean bias and 95% limits of agreement (LoA). To extend the comparable range, researchers extracted Landolt C and letter VA data from a previously published study and combined it with their own Landolt C dataset.⁷

Results

Pinhole VA improved over uncorrected VA similarly across all 3 optotypes, with no significant differences in slope (F(2,225) = 1.722, P = 0.18) or intercept (F(2,227) = 2.303, P = 0.10) between charts. The average slope was 0.584, and limits of agreement (LoA) ranged from 7.4 to 8 lines. This wide range limits interchangeability at the individual level.¹

For uncorrected VA, letter acuity was closely predicted by both Tumbling E (slope = 1.036; R² = 0.947) and Landolt C (slope = 0.975; R² = 0.942), with minimal bias. For corrected VA, however, slopes were significantly below 1.0: 0.708 for Tumbling E (P < .00001) and 0.576 for Landolt C (P < 0.0001), with R² values of 0.729 and 0.701, respectively, indicating that corrected letter acuity worsens more slowly than corrected Tumbling E or Landolt C acuity as vision declines.¹

When data from this study was combined with previous research, the overall relationship extended across a 20/20 to 20/2000 range for Landolt C and letter VA (slope(uncorrected) = 0.98, slope(corrected) = 1.01, R² > 0.94) “with no systematic bias”, according to study authors.¹

Findings and limitations

The authors concluded that for uncorrected VA, letter, Tumbling E, and Landolt C optotypes produce comparable results at the population level, supporting their use in epidemiological studies and clinical trials that aim to include patients unfamiliar with Latin script. For corrected VA, however, the authors noted that conversion factors are needed to estimate equivalent letter acuity.

Habitual pupil size was not measured, though pupil size is known to affect VA. Few participants had corrected VA worse than 0.3 logMAR, so the reported correction factors should be considered preliminary outside that range. Additionally, the extended comparison data relied on extracted rather than raw data, and used different methodologies and patient populations.

The authors cautioned that despite population-level comparability, the wide limits of agreement observed across comparisons indicate the optotypes should not be substituted for one another when evaluating individual patients. The LoA range collected from each optotype “reinforces that VA should be interpreted in the context of the specific optotype, correction status, and testing conditions used,” the study authors noted.¹

References

1. Kalloniatis M, Wang H, Meier K, Patel NB, Phu J. Visual acuity: Comparison of ETDRS charts using Latin letters, Tumbling E, or Landolt C optotypes. Invest Ophthalmol Vis Sci. 2026; 67(11). doi:10.1167/iovs.67.11.4

2. Early Treatment Diabetic Retinopathy Study Research Group. Early photocoagulation for diabetic retinopathy: ETDRS Report Number 9. Ophthalmology. 1991;9(5 Supplement):766–785.

3. Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for neovascular age-related macular degeneration. N Engl J Med. 2006;355(14):1419–1431. doi:10.1056/NEJMoa054481.

4. Bailey IL, Lovie JE. New design principles for VA letter charts. Am J Optom Physiol Opt. 1976;53:740– 745. doi:https://doi.org/10.1097/00006324-197611000-00006

5. Ferris FL, III, Kassoff A, Bresnick GH, Bailey IL. New VA charts for clinical research. Am J Ophthalmol. 1982;94:91– 96.

6. Van der Zee C, Muijzer MB, Claessens JLJ, Wisse RPL. Determining the variability associated with visual acuity and refractive error measurements: A systematic review. Ophthalmology. 2025;132:1020–1032. doi:10.1101/2025.01.17.25320329

7. Schulze-Bonsel K, Feltgen N, Burau H, Hansen L, Bach M. Visual acuities “hand motion” and “counting fingers” can be quantified with the Freiburg VA test. Invest Ophthalmol Vis Sci. 2006;47:1236–1240. doi:10.1167/iovs.05-0981