LAUSR

We read the article published this month with interest and raising awareness of this concern should be relevant to all specialists and not just those with an interest in corneal disease. The treatment for corneal endothelial pathology has altered over time from full thickness corneal transplantation (first performed in 1905 by Zirm) [1], posterior lamellar keratoplasty techniques (performed by Melles in 1998) [2] to recent advances where Descemet’s membrane (DM) and endothelium were stripped from the host cornea (descemetorrhexis) and replaced with a donor button consisting of posterior stroma, DM and endothelium—Descemet’s stripping endothelial keratoplasty—clinical results published first by Price in 2006 [3]. Transition has now occurred from microkeratome donor dissection—termed (ultrathin) Descemet stripping automated endothelial keratoplasty (DSAEK) [4], to Melles’ technique involving only donor DM and endothelium being transplanted—termed Descemet’s membrane endothelial keratoplasty in 2006 (DMEK) [5]. Penetrating keratoplasty to DS(A)EK to DMEK has allowed progressively better visual outcome, less corneal astigmatism and rapid visual recovery [6]. DMEK has been shown to provide better visual outcomes compared to DSAEK [7] with the advantage of a smaller incision (2.4 versus around 5 mm, respectively) [8]. The donor graft preparation for DMEK can be challenging and there is evidence to show that there is an increased risk of rebubbling compared to DS(A)EK [9]. Risks of endothelial keratoplasty (EK) include but are not limited to graft dislocation, failure, rejection, interface opacification, pupillary block, cystoid macular oedema, and epithelial ingrowth [6, 10]. Most common adverse events do not impact the long-term visual outcome [10], but there has been growing evidence of hydrophilic intraocular opacification (IOL) following DSAEK and more recently with DMEK surgery (Table 1). Intraocular gas injection has been routinely used in vitreoretinal surgery for around 4 decades, and similarly in the last 2 decades for EK. Due to the risk of rebubbling, some surgeons prefer to use sulfur hexafluoride (SF6) 16–20% to allow for a longer period of tamponade of the graft. There have been concerns about use of intraocular long acting gases such as SF6 or perfluoropropane (C2F6) causing an increase in intraocular pressure during nitrous oxide anaesthesia [11], or during changes in atmospheric pressure. Furthermore, it is important that the recipient base is smooth without any residual DM so again some surgeons do a larger area of descemetorrhexis and ensure the DM is stripped without any agitation of the overlying posterior stroma. Some surgeons may do this under air. With the higher risk of rebubbling, there is a higher risk of IOL opacification [12]. IOL opacification is thought to be from calcium phosphate deposits on the surface or just within the substance of the lens [13, 14]. Several mechanisms are thought to play a role in IOL opacification. Potential changes in the metabolic composition of the aqueous humour are thought to occur the presence of exogeneous gas and an exacerbated inflammatory reaction due to multiple surgeries [15]. Dehydration of the hydrophilic IOL may affect the surface that encourages the formation of crystallisation nuclei [14]. UV exposure has also been postulated to play a part with the typical findings of IOL calcification seen centrally with the periphery of the IOL protected by the iris [16]. Implementing a new technique within hospital services requires an analysis of the potential risks associated and one major factor is the use of hydrophilic intraocular lenses. The implications would be for patients needing EK who previously had cataract surgery and furthermore determining what type of IOL was used. Whether a hydrophilic lens was used, or the IOL type could not be found, the patient should * Ankur Barua [email protected]