Two of Four Disinfectants for Cleaning Eye Exam Equipment Are Ineffective

Newswise — Two of four disinfectants recommended for cleaning eye exam equipment are ineffective, a new study concludes.

Many people who have had eye exams are familiar with the applanation tonometer, a medical instrument pen that is used to check the pressure in your eyes.After the patient is given numbing eyedrops, an applanation tonometer is applied gently to the front surface of the eye and provides a pressure reading to check for glaucoma.

Health-care workers are required to disinfect the applanation tonometer after each use.

However, a new study conducted by the University of North Carolina Health Care System has found that two of four disinfectants recommended for this purpose by the U.S. Centers for Disease Control and Prevention (CDC) are ineffective at inactivating adenovirus type 8, which is a common cause of epidemic keratoconjunctivitis (pink eye) outbreaks in eye clinics.

Fortunately, two disinfectants recommended by the CDC and the Association for Professionals in Infection Control and Epidemiology - 70 percent ethyl alcohol and 5,000 parts per million chlorine -- were found to be effective in removing a test virus after 1 minute of contact.

"While adenovirus type 8 is relatively resistant to disinfectants, it is fortunate that these two disinfectants work well," said Dr. William A. Rutala, UNC Health Care's director of Hospital Epidemiology and a professor in the UNC School of Medicine. "The two disinfectants that did not inactivate adenovirus type 8 -- 3 percent hydrogen peroxide and 70 percent isopropyl alcohol -- should no longer be used for disinfecting applanation tonometers."

These results are published in the April issue of the journal Antimicrobial Agents and Chemotherapy. Large outbreaks of epidemic keratoconjunctivitis have been documented in eye clinics and hospitals. In such settings it is typically transmitted by the hands of medical caregivers or contaminated eye exam equipment, such as tonometers and slit lamps, or contaminated ophthalmic solutions. However, only one prior study examined the effectiveness of a single germicide in removing adenovirus type 8, which can survive on plastic and metal surfaces for more than 30 days.

Against this backdrop, Rutala and colleagues set out to determine the effectiveness of 21 germicides against adenovirus type 8 under various test conditions. They contaminated metal disks with the virus and tested each germicide under five separate conditions: with the germicide mixed with hard water and contact times of 1 minute and 5 minutes, with the germicide mixed with hard water plus 5 percent fetal calf serum and contact times of 1 minute and 5 minutes, and with the germicide mixed with sterile water for a contact time of 1 minute.

Based on their results, the researchers recommended that eye exam equipment be disinfected with 70 percent ethyl alcohol or 5,000 parts per million chlorine. In addition, health-care workers who handle the equipment should wash their hands with antimicrobial soap and water instead of alcohol-based hand rubs. Previous research conducted at UNC Health Care found that alcohol-based hand rubs are not as effective as soap and water against viruses such as adenovirus type 8. Rutala was lead author of the study. His co-authors were Jeffrey E. Peacock, a second-year medical student at Wake Forest University; Maria F. Gergen, a medical technologist at UNC Hospitals; Mark D. Sobsey, professor of environmental sciences and engineering in the UNC School of Public Health; and Dr. David J. Weber, medical director of Hospital Epidemiology for the UNC Health Care System. Weber is also a professor in the UNC Schools of Medicine and Public Health.