Decontamination of human sclera: an in vitro study

The human sclera is frequently used in ophthalmic surgeries and must be preserved in disinfectants that prevent its contamination. In this study the efficiency of glycerin, absolute alcohol (ethanol), and benzalkonium chloride (1:5,000) as human sclera disinfectants were compared.

Fresh human scleras were trephined, the scleral disks divided into three groups and contaminated with Staphylococcus aureus (ATCC 29213), Pseudomonas aeruginosa (ATCC 27853), or Bacillus cereus (ATCC 11778) for 24 h. Thereafter they were transferred to preservation vials each containing glycerin, absolute alcohol, benzalkonium chloride diluted in 70% alcohol (1:5,000) or Trypticase Soy Broth (control), respectively, and stored at room temperature. From each vial, two scleral disks were removed after 1, 2, 3, 4, 7, 10, and 14 days of immersion. Both were plated on blood agar, one being macerated, and both incubated at 37 degrees C for 48 h.

Pseudomonas aeruginosa, S. aureus, and B. cereus were recovered from the glycerin-immersed scleral disks until the second, fourth, and fourteenth days, respectively. Bacillus cereus was recovered from those immersed in absolute alcohol until the fourteenth day, whereas disks infected with the other microorganisms and immersed in absolute alcohol presented no growth since the very first day of immersion. Bacillus cereus was recovered from scleral disks immersed in benzalkonium chloride diluted in 70% alcohol (1:5,000) only on the first day.

Resistant microorganisms can survive in scleral tissue preserved in glycerin and absolute alcohol. We conclude that benzalkonium chloride diluted in 70% alcohol (1:5,000) in vitro is the best disinfectant for human sclera after 24 h.