Corneal stromal collagen fibrils are heterotypic, co-assembled from quantitatively a major fibril forming collagen, e.g., collagen I and regulatory fibril-forming collagen, e.g., collagen V. Regulatory fibril-forming collagens have a partially processed N-terminal propeptide, retaining a non-collagenous domain that must be in/on the gap region/fibril surface. This is the major regulatory domain.