Is your Visual Acuity chart well calibrated?
We have just sent you an email with the results of the calibration and the calculation of the error, if any.
Remember that international organizations such as the International Council of Ophthalmology (ICO)1 or the World Health Organization (WHO),2 strongly recommend the use of Visual Acuity optotypes designed with the principles of the Bailey-Lovie logarithmic tests,3 together with the modifications introduced in the Early Treatment of Diabetic Retinopathy Study (ETDRS).4,5
All of them advocate the widespread use of VA logarithmic charts to achieve standardization and overcome the poor reliability found with traditional VA charts .6,7,8
1. International Council of Ophthalmology (ICO). Visual acuity measurement standard. Kos, Greece: ICO; 1984. Available at: http://www.icoph.org/dynamic/attachments/resources/icovisualacuity1984.pdf. 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: http://whqlibdoc.who.int/hq/2003/WHO_PBL_03.91.pdf. (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).