Purpose: To study the corneal development in the human fetal eye with particular emphasis on the epithelial basement membrane and Bowman's layer. Thus, immunohistochemical markers supposed to stain this region were employed.
Material and methods: 19 formalin-fixed fetal eyes and a 16-day-old newborn's cornea without any obvious irregularities of the anterior segment were investigated. The age of the fetal eyes ranged from 11 to 38 week of gestation (WoG). The eyes (including the corneal thickness) were measured and, in addition to routine hematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) stains, immunohistochemical labeling with antibodies to collagen IV, V, IX, and XVII was performed.
Results: Analysis of the H&E stains revealed that measurements of corneal thickness correlated well with corneal development as a basic indicator for maturation. In a more detailed immunohistochemical analysis, collagen IV was expressed in the epithelial basement membrane (BM) of the cornea, conjunctiva, and Descemet's membrane in fetal eyes up to the age of 23 WoG. In fetal eyes older than 23 WoG, staining was confined to the limbal area only. With the antibody against collagen V, the corneal stroma and the BM were intensely stained. Bowman's layer (first detected at 17 WoG by light microscopy) was not labeled. Anti-collagen IX labeled predominantly the conjunctival and corneal epithelium. With anti-collagen XVII, the BM of the cornea and conjunctiva was stained in all fetal eyes, whereas intracellular expression in the epithelium increased with age.
Conclusion: Our results indicate maturation-associated variations of collagen expression in the human cornea. Measurements of the corneal thickness may serve as an additional parameter to narrow down the developmental age with possible implications for pediatric pathology and forensic issues.