Corneal donor tissue can be safely stored for 11 days without negatively impacting the success of a transplant, a clinical trial has shown.Currently, donor corneas -- the eye's clear outer covering -- are generally not used for surgery if they have been preserved for longer than seven days.Expanding the window in which donor tissues can be considered suitable "by even just a few days" should help safeguard quality donor tissue and access to vision-saving transplantation procedures, the researchers said. "The current practice of surgeons to use corneas preserved for no longer than seven days is not evidence-based."Rather that practice is based on opinion, which hopefully will change with this new evidence," said lead investigator Jonathan Lass, from the Case Western Reserve University. For the study, appearing in the journal JAMA Ophthalmology, the team looked at three-year graft success rates among a total of 1,090 individuals (1,330 eyes) who underwent cornea transplant via Descemet's stripping automated endothelial keratoplasty by 70 surgeons at 40 surgical sites. Overall, the three-year success rates were the same for corneas preserved for eight-to-14 days compared with up to seven days (92.1 per cent versus 95.3 per cent). In a separate analysis, the team analysed the extent of endothelial cell loss (ECL) -- the loss of cells in the corneal endothelium that continued to occur as a normal part of ageing in the grafted donor cornea three years after it had been transplanted. They non-invasively measured ECL in the 945 eyes with successful grafts and found that corneas preserved up to seven days had a 37 per cent loss of cells versus a 40 per cent loss in corneas preserved for eight-to-14 days.Taken together, the separate analyses looked at graft success rates and ECL support that used corneas stored up to 11 days, the researchers said.