Abstract
Purpose: The optimal method for scoring visual acuity measures is unknown. Our goal was to determine, in a clinical setting, the method of scoring visual acuity with the lowest test-retest variability.
Methods: We investigated the effect of three different scoring methods using the Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity chart comparing 32 patients with macular disease and 38 age-matched normal subjects. All subjects completed six repetitions of ETDRS charts. Three scoring methods were then used (line assignment, ETDRS or letter-by-letter and probit), the results were converted to log MAR values and the test-retest variabilities analysed.
Results: We found significant differences in variability among the three scoring methods (p<0.0001). The variability was greatest with the line assignment method and less with the ETDRS and probit methods. The ETDRS and probit methods had similar variabilities. The difference in variability between normals and patients was not statistically significant. There were no differences in the calculated visual acuities among the three methods, only the variabilities. Using the ETDRS or probit methods, the within-test standard deviation was about 0.04 log MAR units (two letters).
Conclusion: Test-retest variability of visual acuity measurements is lower using the ETDRS or probit methods than the traditional line assignment method.
Similar content being viewed by others
Article PDF
References
Snellen H . Probebuchstaben zur Bestimmung der Sehscharfe. Utrecht: PW van de Weijer, 1862.
Arditi A, Cagenello R . On the statistical reliability of letter-chart visual acuity measurements. Invest Ophthalmol Vis Sci 1993;34:120–9.
Bailey IL, Bullimore MA, Raasch TW, Taylor HR . Clinical grading and the effect of scaling. Invest Ophthalmol Vis Sci 1991;32:422–32.
Bailey IL, Lovie JE . New design principles for visual acuity letter charts. Am J Optom Physiol Opt 1976;53:740–5.
Ferris FL, III, Kassoff A, Bresnick GH, Bailey I . New visual acuity charts for clinical research. Am J Ophthalmol 1982:94:91–6.
Frisen L, Frisen M . How good is normal visual acuity? A study of letter acuity thresholds as a function of age. Graefes Arch Klin Exp Ophthalmol 1981;215:149–57.
Hedin A, Olsson K . Letter legibility and the construction of a new visual acuity chart. Ophthalmologica 1984;189:147–56.
Klein R, Klein BE, Moss SE, DeMets D . Inter-observer variation in refraction and visual acuity measurement using a standardized protocol. Ophthalmology 1983;90:1357–9.
Lovie-Kitchin JE . Validity and reliability of visual acuity measurements. Ophthalmic Physiol Opt 1988;8:363–70.
Anonymous. Recommended standard procedures for the clinical measurement and specification of visual acuity. Report of working group 39. Committee on vision. Assembly of Behavioral and Social Sciences, National Research Council, National Academy of Sciences, Washington, DC. Adv Ophthalmol 1980;41:103–48.
Parr JC . Clinical assessment of visual acuity. Trans Ophthalmol Soc NZ 1981;33:157–67.
Sakuma JT, da Silva JA, Velasco e Cruz A . Measurement of visual acuity with logarithmic charts: comparison between methods of threshold estimation. Optom Vis Sci 1991;68:666–9.
Sloan LL, Rowland WM, Altman A . Comparison of three types of test target for the measurement of visual acuity. Q Rev Ophthalmol 1952;8:4–15.
Sloan LL . Measurement of visual acuity: a critical review. Arch Ophthalmol 1951;45:704–25.
Sloan LL . New test charts for the measurement of visual acuity at far and near distances. Am J Ophthalmol 1959;48:807–13.
Strong G, Woo GC . A distance visual acuity chart incorporating some new design features. Arch Ophthalmol 1985:103:44–6.
Tinning S, Bentzon MW . A new method for exact measurements of visual acuity. Determination of threshold curves for the resolving power of the eye by computerized curve fitting. Acta Ophthalmol (Copenh) 1986;64:180–6.
Wong D, Kaye SB . Chart for visual acuity screening. Br J Ophthalmol 1989;73:457–60.
Gibson RA, Sanderson HF . Observer variation in ophthalmology. Br J Ophthalmol 1980;64:457–60.
Elliott DB, Sheridan M . The use of accurate visual acuity measurements in clinical anti-cataract formulation trials. Ophthalmic Physiol Opt 1988;8:397–401.
Early Treatment Diabetic Retinopathy Study. Manual of operations. Chapter 12, 1985.
Heijl A, Lindgren A, Lindgren G . Test-retest variability in glaucomatous visual fields. Am J Ophthalmol 1989;108:130–5.
Werner EB, Petrig B, Krupin T, Bishop KI . Variability of automated visual fields in clinically stable glaucoma patients. Invest Ophthalmol Vis Sci 1989;30:1083–9.
Chauhan BC, House PH . Intratest variability in conventional and high-pass resolution perimetry. Ophthalmology 1991;98:79–83.
Wall M, Lefante J, Conway M . Variability of high-pass resolution perimetry in normals and patients with idiopathic intracranial hypertension. Invest Ophthalmol Vis Sci 1991;32:3091–5.
Reeves BC, Hill AR, Aspinall PA . The clinical significance of change. Ophthalmic Physiol Opt 1987;7:441–6.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Vanden Bosch, M., Wall, M. Visual acuity scored by the letter-by-letter or probit methods has lower retest variability than the line assignment method. Eye 11, 411–417 (1997). https://doi.org/10.1038/eye.1997.87
Issue Date:
DOI: https://doi.org/10.1038/eye.1997.87
Keywords
This article is cited by
-
Simultaneous real-time analysis of tear film optical quality dynamics and functional visual acuity in dry eye disease
Eye and Vision (2023)
-
Predictors of problems reported on the EQ-5D-3L dimensions among people with impaired vision in northern Portugal
Health and Quality of Life Outcomes (2022)
-
Crowding can impact both low and high contrast visual acuity measurements
Scientific Reports (2022)
-
AI-based structure-function correlation in age-related macular degeneration
Eye (2021)
-
Digital Tools for the Self-Assessment of Visual Acuity: A Systematic Review
Ophthalmology and Therapy (2021)