Changes in corneal ultrastructure resulting from early lens removal in the developing chick embryo.

Lenses were removed from chick embryos at 4 days of incubation and the corneas were studied at various time intervals postoperatively through 17 days of incubation. Approximately 2 to 4 hours postoperatively a wave of mesenchymal tissue, presumably perilimbic in origin, moved in to cover the posterior surface of the cornea. This retrocorneal sheet of tissue grew in thickness and differentiated along lines similar to that of the sclera. At 17 days of incubation, the collagen fibrils within this band of tissue had cross-sectional diameters that were 1.8 to 3.0 times greater than those of fibrils within normal corneal stromas. These changes were found only within the lentectomy group. The corneal stroma, Descemet's membrane, and the mesothelium (endothelium) failed to develop in the lentectomized eyes. Failure of vitreous body enlargement, a concomitant feature of lens removal at 4 days of incubation (Coulombre and Coulombre, 1966), was explored as a causal mechanism. Eyes of chick embryos were intubated at 4 days of incubation, allowing vitreous to escape, and the corneas were studied at various time intervals postoperatively through 17 days of incubation. At 17 days of incubation, the collagen fibrils within the stromas of the intubated group had cross-sectional diameters that did not differ significantly from those in normal stromas. In the corneas of the intubated eyes, Descemet's membrane and the mesothelium were present, having a normal cytoarchitecture, thereby negating lack of vitreous body enlargement as a causal factor. Other possible mechanisms to explain the aberration in corneal development following early lens removal are discussed.