Rapid detection of gram-negative endotoxin contamination of contact lens saline solutions

The use of the limulus amoebocyte lysate for the early and rapid detection of gram-negative endotoxin contamination of contact lenses and their solutions could reduce the risk of a keratitis developing that is associated with these devices. Using multiple aliquots from 17 unopened brands of commercially available contact lens saline solutions (15 for soft, two for hard), plus multiple aliquots from these solutions mixed with bacterial endotoxin, we evaluated the ability of two limulus amoebocyte lysate (0.125 endotoxin units/mL) products to detect the presence or absence of gram-negative endotoxin contamination. Sensitivity ranged from 65% (11/17) to 82% (14/17) when the solutions were tested undiluted. When diluted 1:8, the sensitivity increased to 100%. Specificity was 100% for undiluted and diluted specimens. The solutions used for hard contact lenses had the highest false-negative results. The limulus amoebocyte lysate can be used to detect the presence of gram-negative endotoxin in contact lens solutions.