Research Article: Do picture-based charts overestimate visual acuity? Comparison of Kay Pictures, Lea Symbols, HOTV and Keeler logMAR charts with Sloan letters in adults and children

Date Published: February 2, 2017

Publisher: Public Library of Science

Author(s): Nicola S. Anstice, Robert J. Jacobs, Samantha K. Simkin, Melissa Thomson, Benjamin Thompson, Andrew V. Collins, Marko Nardini.


Children may be tested with a variety of visual acuity (VA) charts during their ophthalmic care and differences between charts can complicate the interpretation of VA measurements. This study compared VA measurements across four pediatric charts with Sloan letters and identified chart design features that contributed to inter-chart differences in VA.

VA was determined for right eyes of 25 adults and 17 children (4–9 years of age) using Crowded Kay Pictures, Crowded linear Lea Symbols, Crowded Keeler logMAR, Crowded HOTV and Early Treatment of Diabetic Retinopathy Study (ETDRS) charts in focused and defocused (+1.00 DS optical blur) conditions. In a separate group of 25 adults, we compared the VA from individual Kay Picture optotypes with uncrowded Landolt C VA measurements.

Crowded Kay Pictures generated significantly better VA measurements than all other charts in both adults and children (p < 0.001; 0.15 to 0.30 logMAR). No significant differences were found between other charts in adult participants; children achieved significantly poorer VA measurements on the ETDRS chart compared with pediatric acuity tests. All Kay Pictures optotypes produced better VA (p < 0.001), varying from -0.38 ± 0.13 logMAR (apple) to -0.57 ± 0.10 logMAR (duck), than the reference Landolt C task (mean VA -0.19 ± 0.08 logMAR). Kay Pictures over-estimated VA in all participants. Variability between Kay Pictures optotypes suggests that shape cues aid in optotype determination. Other pediatric charts offer more comparable VA measures and should be used for children likely to progress to letter charts.

Partial Text

In pediatric eye care the measurement of visual acuity (VA) is central to the diagnosis of refractive error,[1] amblyopia[2] and pathology.[3] Nevertheless, factors such as the inability of many preschool children to name letters and individual differences in cognitive development complicate acuity measures.[4] Although a gold standard pediatric visual acuity system exists (the Electronic Visual Acuity (EVA) tester)[5] it is primarily used for clinical trials rather than mainstream clinical practice. It is unclear why the EVA tester has not been adopted more widely in general ophthalmic practice. However, its reduced utility for other clinical techniques, such as subjective refraction, coupled with increased cost, may diminish the appeal of the EVA system for many eye care providers.

In summary, we found the Crowded Kay Pictures chart over-estimated VA which may be due to the overall shape cues available within each picture as has been reported in other studies[20]. The other pediatric charts investigated produced consistent measures of VA and, based on the four pediatric charts examined, Lea Symbols are more appropriate for children who are likely to progress to letter-based charts. Redesign of the Kay Pictures so the pictures are more equally discriminable may be possible. However, in its current format, VA results from the Crowded Kay Pictures chart should be interpreted with caution when compared to other tests.




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