Reconciling print-size and display-size constraints on reading

Research output: Contribution to journalArticlepeer-review


Two fundamental constraints limit the number of characters in text that can be displayed at one time—print size and display size. These dual constraints conflict in two important situations—when people with normal vision read text on small digital displays, and when people with low vision read magnified text. Here, we describe a unified framework for evaluating the joint impact of these constraints on reading performance. We measured reading speed as a function of print size for three digital formats (laptop, tablet, and cellphone) for 30 normally sighted and 10 low-vision participants. Our results showed that a minimum number of characters per line is required to achieve a criterion of 80% of maximum reading speed: 13 characters for normally sighted and eight characters for low-vision readers. This critical number of characters is nearly constant across font and display format. Possible reasons for this required number of characters are discussed. Combining these character count constraints with the requirements for adequate print size reveals that an individual’s use of a small digital display or the need for magnified print can shrink or entirely eliminate the range of print size necessary for achieving maximum reading speed.

Original languageEnglish (US)
Pages (from-to)30276-30284
Number of pages9
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number48
StatePublished - Dec 1 2020

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS. We thank the editor and two anonymous reviewers for their helpful suggestions and Paige Miller and Hunter Throndsen for their help with the data collection. This work was supported by NIH Grant EY002934 to G.E.L. Y.-Z.X. was supported by a fellowship from the Envision Research Institute during the preparation of the paper.

Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.


  • Reading | low vision | visual perception | visual displays

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