Evidence of pre-descemetocele and stromal remodelling in post-DSAEK corneal melt

Corneal melt is an uncommon but sight-threatening corneal emergency.It can be caused by various pathologies, including infection, inflammation, neurotrophic keratopathy, and chemical/ thermal injury, amongst others [1].Progressive corneal melt can lead to baring of Descemet membrane (DM), known as "descemetocele", and subsequent corneal perforation [1].Herein, we present a case of threatened corneal perforation in an eye with previous Descemet's stripping automated endothelial keratoplasty (DSAEK) where the host DM was already removed, providing supportive evidence on the role of pre-Descemet's layer/Dua's layer (PDL) in corneal melt/perforation.An 84-year-old lady, with a previously failed DSAEK, presented with a two-month gradual painless loss of left eye vision.At presentation, the left eye corrected-distance-visual-acuity (CDVA) was hand movement, and corneal sensation was completely absent.Slit-lamp examination/photography revealed a significant central corneal melt and a translucent bulging corneal structure resembling "'descemetocele" (Fig. 1A).Anterior segment optical coherence tomography (AS-OCT) similarly demonstrated a thin hyper-reflective, anteriorly herniated corneal structure resembling "descemetocele" (Fig. 1B).Seidel's test was negative.The patient was treated for severe corneal melt secondary to active PCRproven herpes simplex keratitis, neurotrophic keratopathy, and exposure keratopathy.Following 3 weeks of intensive medical management, significant stromal tissue migration/remodelling beneath the "predescemetocele" was noted, likely originating from the stromal tissue of DSAEK (Fig. 2A,B).Amniotic membrane grafting and tarsorrhaphy were subsequently performed to enable complete corneal healing (Fig. 2C)."Descemetocele" is a rare clinical entity characterised by anterior herniation of intact DM through an area of stromal thinning due to progressive corneal melt [1].If left untreated, it may progress to corneal perforation with significant loss of vision.However, the discovery/characterisation of PDL has raised the question whether descemetocele is always truly DM-baring.Emerging evidence suggests that the posterior corneal biomechanical strength is conferred by PDL instead of DM, which usually ruptures with relatively low pressure as observed in DALK surgery (when a type-2 big-bubble is created) [2][3][4].PDL has been described to contain predominantly collagen type I, collagen type