Jonathan Lass of Case Western Reserve University School of Medicine has found that corneal donor tissue can be safely stored for 11 days before transplantation surgery to correct eye problems in people with diseases of the cornea. This is four days longer than the current conventional maximum of seven days in the United States. The findings were published in the  JAMA Ophthalmology .

Patients who need corneal transplants are typically age 50 and older. According to projections by the US Census Bureau, that population will grow from about 109 million currently to about 133 million by 2030 in this country. The cornea, the eye's clear outer covering, helps focus light so people can see clearly. When it is damaged, incoming light can become distorted, harming quality of vision and often resulting in blindness .

When the blurred vision and / or pain are serious enough, transplantation of a new cornea may be necessary. Transplanted corneas come from people who chose to donate them when they died. The study includes 18 other authors, 70 eye surgeons at 40 surgical sites nationwide performed a corneal transplant called a Descemet stripping automated endothelial keratoplasty ( DSAEK ) on 1,090 people (1,330 eyes).

The majority of the patients underwent transplantation for Fuchs' dystrophy, which causes a gradual decline in vision due to corneal swelling and clouding. Patients were randomly assigned to one of two treatment groups: those who received corneas preserved for up to seven days and those who received corneas preserved for eight-14 days.

Lass and the surgeons found that three-year graft success rates were 92.1% for corneas preserved for eight to 14 days and 95.3 percent for corneas preserved up to seven days. Probing further, they discovered that there were not statistically significant difference between patients who received corneas preserved up to seven days and those who received ones preserved eight to 11 days. Rather, much of the difference between the groups was attributed to those who received corneas preserved 12 to 14 days.

Although results of the study directly apply to the use of donor corneas used for these specific conditions, the researchers hope that results could be extended to the donor corneas used for other types of transplants and other eye diseases. Separately, the investigators assessed the degree of corneal endothelial cell loss , which typically occurs after transplantation. The endothelium is a single layer of cells lining the inner surface of the cornea; among its functions, it helps keep the cornea clear and from not swelling.

The surgeons found that in corneas preserved up to seven days, there was a 37% loss of cells versus a 40% loss in corneas preserved eight-14 days. Again probing further, they discovered a comparable rate of loss in corneas preserved four-13 days. "This finding also supports the use of  corneas  stored up to and including 11 days," said Lass.