title: Pre-treatment choroidal thickness is not predictive of susceptibility to form-deprivation myopia in chickens.
abstract: OBJECTIVE
  Chicks developing experimentally-induced myopia show profound thinning of the choroid. We observed a wide range of choroidal thicknesses in a sample of normal chicks prior to their use in a pedigree-based study of form-deprivation myopia. Hence, we tested whether pre-treatment choroidal thickness predicted susceptibility to myopia.
  
  
  METHODS
  Retinal, choroidal and scleral thickness were measured using A-scan ultrasonography in normal White Leghorn chicks (n= 891) aged 4 days old, and again (n=498) after 4 days of monocular form-deprivation at age 8 days of age. Refractive error was assessed by retinoscopy. Relationships between pre-treatment choroidal thickness and other variables were investigated using general linear models and variance components analysis.
  
  
  RESULTS
  Untreated 4 day-old male chicks had choroids approximately 10% thinner than females (p<0.001), but sex explained <2% of the overall variability in choroidal thickness. Axial eye length in these untreated chicks was not significantly associated with choroidal thickness (p=0.25). Moreover, pre-treatment choroidal thickness was not predictive of susceptibility to form-deprivation myopia (p=0.89). Heritability analysis suggested that at least 50% of the variation in pre-treatment choroidal thickness was determined by additive genetic effects (p<0.001).
  
  
  CONCLUSIONS
  Parental choroidal thickness is the major determinant of choroidal thickness in untreated 4-day old chicks. Despite choroidal thickness potentially being indicative of ongoing emmetropisation to innate refractive errors, in this study it was not predictive of subsequent susceptibility to form-deprivation myopia.
authors: School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK. Guggenheim@cardiff.ac.uk
authors: Jeremy A
authors: JA
authors: Guggenheim
authors: Yen-Po
authors: YP
authors: Chen
authors: Elaine
authors: E
authors: Yip
authors: Hélène
authors: H
authors: Hayet
authors: Vladimir
authors: V
authors: Druel
authors: Ling
authors: L
authors: Wang
authors: Jonathan T
authors: JT
authors: Erichsen
authors: Alexandre R
authors: AR
authors: Tumlinson
authors: Boris
authors: B
authors: Povazay
authors: Wolfgang
authors: W
authors: Drexler
authors: Paul M
authors: PM
authors: Hocking
mesh_terms: D000818:Animals; D002645:Chickens; D002829:Choroid / Q000254:growth & development / Q000473:pathology*; D004198:Disease Susceptibility; D009216:Myopia / Q000235:genetics / Q000473:pathology*; D011237:Predictive Value of Tests