Acute corneal hydrops (hydrops corneae) is an incompletely understood complication of keratoconus and other corneal ectatic disorders, including keratoglobus and pellucid marginal corneal degeneration. Keratoconus is a relatively common condition; its prevalence is estimated to lie between 6.8 and 86 per 100,000 with considerable variation among international studies. With an estimated prevalence of 2.8 per cent among patients with keratoconus, corneal hydrops is considerably less common than keratoconus per se. There appears to be a gender predisposition toward males with typical age of onset around 25 years. Earlier age, poorer visual acuity and steeper keratometry at diagnosis of keratoconus, as well as severe allergic eye disease and eye rubbing, have been identified as risk factors for developing corneal hydrops. Interestingly, a history of atopy and contact lens wear do not demonstrate an increased likelihood of developing hydrops, while having a family history of keratoconus appears to have a negative correlation. Acute corneal hydrops is characterised by the development of significant corneal oedema, typically due to a spontaneous break in Desçemet’s membrane and the overlying corneal endothelium, which allows aqueous humour to migrate into the corneal stroma and epithelium. It is hypothesised that the resolution of acute corneal hydrops requires two steps. The first involves re-attachment of the detached Desçemet’s membrane to the posterior stroma, while the second involves the migration of endothelial cells to cover the gap between the edges of the two borders of the break in Desçemet’s membrane. The time taken for the first step to occur is dependent on the depth of detachment of Desçemet’s membrane and can be hastened by anterior chamber paracentesis and intra-cameral injection of non-expansile gas such as sulphur hexafluoride (SF6) speeding up the time to resolution. The second step is dependent on the size of the break in Desçemet’s membrane and the time taken for this step to occur cannot currently be shortened. The corneal oedema associated with acute corneal hydrops is self-limiting, usually resolving within six to 14 weeks in the majority of cases; however, it often leaves a visually debilitating scar in its wake. Scarring of the cornea may necessitate corneal transplantation by penetrating keratoplasty (PKP) or deep anterior lamellar keratoplasty (DALK); however, in practice, the extent of scarring dictates which procedure should be carried out. In cases where there is extensive corneal scarring, PKP is the procedure of choice due to the increased likelihood of perforation when attempting DALK.