Abstract
Purpose: :
Myopia development is characterised by an increased axial eye length. Therefore, identifying factors that influence eye size may provide new insights into the aetiology of myopia. In humans, eye size (axial length) is weakly related to height. The purpose of this study was to examine the relationship between eye size and body size in chickens from a genetic cross in which alleles with major effects on eye and body size were segregating.
Methods: :
Chickens from a cross between a layer line (small body size and eye size) and a broiler line (large body and eye size) were interbred for 10 generations so that alleles for eye and body size would have the chance to segregate independently. At 3-weeks of age, 509 chicks were assessed using in vivo high resolution A-scan ultrasonography. Equatorial eye diameter and eye weight were measured after enucleation. The variations in eye size parameters that could be explained by body length (BL), body weight (BW) and head width (HW) were examined using multiple stepwise linear regression.
Results: :
Together, BL, BW and HW explained 44% of the variation in axial length, 33% of the variation in vitreous chamber depth, 51% of the variation in eye diameter and 51% of the variation in eye weight. For axial length, BL, HW and BW were all significant independent explanatory variables (BL, P<0.001; HW, P<0.001; BW, P = 0.031). A one phenotypic standard deviation change in BL, HW and BW was associated with a 97µm, 44µm and 30µm change in axial length, respectively. There were no significant interaction effects. BL also had the strongest association with vitreous chamber depth and eye diameter, whilst BW had the strongest association with eye weight.
Keywords: genetics • myopia