title: Crowding in central vision in normally sighted and visually impaired [corrected] children aged 4 to 8 years: the influence of age and test design.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Behavioural Science Institute, Radboud University Nijmegen, The Netherlands. b.huurneman@psych.ru.nl
authors.forename: Bianca
authors.initials: B
authors.lastname: Huurneman
authors.forename: F Nienke
authors.initials: FN
authors.lastname: Boonstra
authors.forename: Antonius H N
authors.initials: AH
authors.lastname: Cillessen
authors.forename: Ger
authors.initials: G
authors.lastname: van Rens
authors.forename: Ralf F A
authors.initials: RF
authors.lastname: Cox
mesh_terms: D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D012107:Research Design; D014787:Vision Tests; D015354:Vision, Low / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D019987:Persons with Visual Disabilities