Morphometrics of corneal growth in chicks raised in constant light

Abstract

In this study we wish to augment our understanding of the effect of environment on corneal growth and morphology. To understand how corneal development of chicks raised in constant light differs from that of 'normal' eyes exposed to cyclic periods of light and dark, white Leghorn chicks were raised under either constant light (approximately 700 lux at cage top) or in 12 h light/12 h dark conditions for up to 12 weeks after hatching. To determine whether corneal expansion is uniform, some birds from each group received corneal tattoos for periodic photographic assessment. By 16 days of age, constant light corneas weighed less than light/dark regimen corneas [7.39 ± 0.35 mg (SE) vs. 8.47 mg ± 0.26 mg SE wet weight, P ≤ 0.05], and corresponding differences were seen in corneal dry weights. Spatial expansion of the corneal surface was uniform in both groups, but the rate of expansion was slower in constant light chicks [0.0327 ± 0.009 (SE) vs. 0.144 ± 0.018 (SE) mm 2 day -1 for normal chicks, P ≤ 0.001]. At 1 day of age, there were 422 ± 12.5 (SE) stromal cells 0.01 mm -2 in the central cornea and 393 ± 21.5(SE) stromal cells 0.01 mm -2 peripherally. Although this difference is not statistically significant, the cell densities in the central cornea were always larger than those of the peripheral cornea in all eight measurements over a 10.5-week period, and this difference is significant ( P ≤ 0.008, binomial test). Light/dark regimen birds show no such consistent difference in cell densities between central and peripheral corneas. Thus, the density distribution of corneal stromal cells of chicks grown in constant light differs from that of normal chicks. Taken together, all these observations suggest that diurnal cycles of light and darkness are necessary for normal corneal growth.

The effects of light regimes and hormones on corneal growth in vivo and in organ culture

“…Internal regulation of the eye's growth and proper shaping is adversely affected by continuous light, as first demonstrated in growing chickens (Harrison & McGinnis, 1967). Constant light (CL) causes increased ocular size and weight, decreased corneal diameter, and decreased corneal mass (Wahl et al 2009). Chicks raised in CL exhibit significant hyperopia after as few as 10 days as a result of corneal flattening, and this is independent of visual experience (Li et al 1995).…”

The chick eye in vision research: An excellent model for the study of ocular disease

“…This enlargement is related to flattening and thickening of the cornea (Boote et al, 2009), similar to corneal growth changes seen in chicks undergoing constant light exposure (Wahl et al, 2009). Both radial globe diameter and corneal radius of curvature were significantly increased in rge chicks as early as one month post-hatch (Montiani-Ferreira et al, 2003).…”

Morphometry Applied to the Study of Morphological Plasticity During Vertebrate Development

“…We found differences in the pattern of corneal growth between chicks raised in CL vs. normal light conditions (N, raised in 12 hours light/12 hours darkness) using morphometric techniques, including: a) a comparison of eye weights and wet and dry corneal weights, b) measurement of corneal thicknesses and corneal diameters, c) spatial dynamics of corneal expansion, d) measurement of corneal curvatures, and e) stromal cell densities (Wahl, 2009). We learned that the eye's ability to model its shape towards emmetropia is diminished in the absence of periods of light and dark.…”