Abstract
Abstract: :
Purpose:. Chicks raised in constant light (CL) have smaller, thicker corneas with higher stromal cell densities than normal(12/12), also larger corneal radii, shallower anterior chambers, and hyperopia (Wahl et al., 2001, Vis. Res.42 (4), S298; Li et al.,1995, Vis. Res. 35(9):1203-1209). We wished to study some histological and biochemical aspects of recovery from CL treatment. Methods: After three weeks exposure to CL, chicks were returned to 12/12 conditions for one week. Tissues of the anterior segment were evaluated using standard paraffin histology. Glycosaminoglycan (GAG) content of the corneal stromal matrix was assayed using the 1,9-dimethylmethylene blue (DMMB) assay. Refraction was measured using IR photoretinoscopy. Results: After one week in 12/12, "recovery" chicks (R) had totally lost their CL hyperopia. This rapid optical return towards emmetropia included equally rapid changes in the tissues of the anterior chamber of the eye. In the central region of the cornea, normal 4 week chicks have 733 cells/0.1mm2 (S.E. +/- 18), CL chicks at 4 weeks of age have 1,020 cells/0.1 mm2 (S.E. +/- 20), and R chicks have 1,265 cells/0.1 mm2 (S.E. +/- 45). There was no significant difference in GAG content/gram of cornea between 12/12, CL, and R corneas at 4 weeks. However, the lumenal cross-sectional surface area of the scleral venous sinuses in the three experimental groups differed dramatically. The CL scleral sinus at 4 weeks is 69% larger than the 12/12 sinus (p<.0001). The R scleral sinus is only 30% larger than 12/12 (p < .03), indicating that sinus volume shrinks by nearly 40% in just one week of 12/12 conditions following 3 weeks of CL exposure. Conclusion: The tissues of the eye of the chick are still remarkably plastic at 3 and 4 weeks of age, allowing rapid correction of the flattening of the cornea that occurs in CL. This occurs in part via increased cell numbers, and-presumably-in part via altered aqueous drainage.
Keywords: 318 anterior segment • 374 cornea: stroma and keratocytes • 397 emmetropization