Crowding in Central Vision in Normally Sighted and Visually Impared Children Aged 4 to 8 Years: The Influence of Age and Test Design

Abstract

Background/aims: To investigate crowding ratios in children with a visual impairment due to ocular disease (n = 58) and normally sighted children (n = 75) aged 4 to 8 years using several variants of two clinically available tests with different optotype spacing (fixed or proportional to the optotype size).

Methods: Crowding ratios, calculated by dividing the single acuity by the linear acuity, were measured binocularly with the C-test and the LH line chart. Ratios >1.00 indicate crowding.

Results: The charts with fixed spacing revealed significantly higher crowding ratios for visually impaired children than normally sighted children (both for measurements at 40 cm and 5 m). The age-related reduction of the crowding ratios seen in normally sighted children when tested with near-vision charts with fixed spacing was not present in the visually impaired group. Visually impaired children with nystagmus showed higher crowding ratios than visually impaired children without nystagmus. The chart with proportional intersymbol spacing (ISS) did not reveal differences between the normally sighted and visually impaired children; nor did it show group, age, or nystagmus effects.

Conclusion: Visually impaired children showed higher crowding ratios than normally sighted children when measured with charts with fixed ISS. This study illustrates that test design and target/flanker interference as a manifestation of crowding are critical issues to bear in mind when assessing crowding ratios in children.

KEYWORDS::

• Children
• crowding
• selective visual attention
• visual impairment

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Erratum

ACKNOWLEDGMENTS

The authors wish to express their appreciation to Loukie de Vaere and Laura Dorland for their contribution to this research. We also thank the parents and children for their participation. This research was funded by the Dutch Organization for Health and Research Development (grant number 60-00635-98-066, ZonMW, program Insight).

Declaration of interest: The authors declare no conflicts of interest.