Is your Visual Acuity chart well calibrated?

An email with the results of your visual acuity (VA) chart’s calibration and any error calculation has been sent to you.

It is important to remember that international organizations such as the International Council of Ophthalmology (ICO)1 and the World Health Organization (WHO)2 strongly recommend the use of VA optotypes designed based on the principles of the Bailey-Lovie logarithmic charts,3 along with the modifications introduced in the Early Treatment of Diabetic Retinopathy Study (ETDRS).4,5

These authorities advocate for the widespread use of logarithmic VA charts to achieve standardization and to address the poor reliability often associated with traditional VA charts.6,7,8

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Optonet Vision Unit VA

1. International Council of Ophthalmology (ICO). Visual acuity measurement standard. Kos, Greece: ICO; 1984. Available at: Accessed March 20, 2011.
2. World Health Organization. Consultation on development of standards for characterization of vision loss and visual functioning. Geneva, Switzerland: WHO. Available at: (2003).
3. Bailey, I. L. & Lovie, J. E. New design principles for visual acuity letter charts. Am. J. Optom. Physiol. Opt. 53, 740–5 (1976).
4. Ferris, F. L., 3rd, Kassoff, A., Bresnick, G. H. & Bailey, I. New visual acuity charts for clinical research. Am. J. Ophthalmol. 94, 91–96 (1982).
5. Ferris, F. L., Freidlin, V., Kassoff, A., Green, S. B. & Milton, R. C. Relative letter and position difficulty on visual acuity charts from the Early Treatment Diabetic Retinopathy Study. Am. J. Ophthalmol. 116, 735–740 (1993).
6. Gibson, R. A. & Sanderson, H. F. Observer variation in ophthalmology. Br. J. Ophthalmol. 64, 457–60 (1980).
7. Lovie-Kitchin, J. E. Validity and reliability of visual acuity measurements. Ophthalmic Physiol. Opt. J. Br. Coll. Ophthalmic Opt. Optom. 8, 363–370 (1988).
8. McGraw, P. V., Winn, B., Gray, L. S. & Elliott, D. B. Improving the reliability of visual acuity measures in young children. Ophthalmic Physiol. Opt. J. Br. Coll. Ophthalmic Opt. Optom. 20, 173–84 (2000).