Expression of extracellular matrix protein in advanced keratoconus and the normal human cornea

The pre-Descemet layer (Dua's layer) (PDL/DL) and the Descemet membrane (DM) have the highest expression of elastin in normal corneas. Reduced expression of elastin occurs in the corneal stroma of patients with keratoconus (KC). This study aimed to examine the expression of elastin and that of other extracellular matrix (ECM) components, and proteoglycan proteins in the PDL/DL and DM in advanced KC.

Corneal tissue obtained from four subjects with KC who underwent penetrating keratoplasty was compared with tissue from four normal corneas. The tissues were sectioned and analyzed with specific markers for extracellular matrix proteins and proteoglycans-namely, elastin, collagens I, IV, and VI, fibulin-2, and decorin-using immunohistochemical analysis. Fluorescence intensity was measured using ImageJ software and compared to controls.

The expression of elastin was significantly reduced in the PDL/DL and DM in KC cases compared to controls. Concurrently, an increased expression of elastin was noted anteriorly in the subepithelial region. Expression of collagen IV, collagen VI, and decorin was reduced in the PDL/DL and DM, whereas expression of collagen I and fibulin-2 was unaltered in KC cases compared to controls.

The significant reduction of elastin in the PDL/DL and DM in cases of advanced keratoconus with acute corneal hydrops (ACH) may play a crucial role in the pathology of KC and the subsequent onset of ACH. Furthermore, elastin is considered to be pivotal in the disease progression, as keratoconus typically starts with a posterior elevation affecting these two layers.