High Pressure Tonometer Puff, Low Intraocular Pressure Produce More Aerosolization

Non-contact tonometry (NCT) produces significant aerosolization from the tear film, according to a study published in the American Journal of Ophthalmology. The amount of the aerosolization depends on the patient’s intraocular pressure (IOP), the air-puff pressure, and whether eye drops were used before the measurement. 

Researchers enrolled 20 participants (mean age 45.6 years, 17 men) in a study to assess aerosol conditions related to IOP measurement. They also created a model mannequin eye to simulate abnormally high and low IOP measurements. The team performed IOP measurements using 20 and 40 mm Hg air-puff pressures on both the model and study participants, and recorded the number of aerosol particles generated in 5 seconds with a visualization video. They also performed NCT measurements on participants with and without eye drop instillation.

The researchers determined that lower IOPs combined with higher air puff pressures generated the most aerosol particles. During the simulated study, an air puff pressure of 40 mm Hg generated more particles at 5 mm Hg IOP compared with 25 mm Hg IOP (390.2±64.9 vs 165.2±54.3 particles/field; P =.0079). They noted similar results with an air puff pressure of 20 mmHg (142.0±64.1 particles/field for 5 mm Hg IOP and 37.6±29.9 particles/ field for 25 mm Hg IOP; P =.0159).  The team also noted that aerosol generation was significantly higher in patients with eye drops compared with those without eye drops (P =.047).

Although the report states that it is difficult to prove that viruses such as SARS-CoV-2 can be transmitted during NCT, investigators highlight the fact that tear aerosolization does take place during NCT measurement. “While the risk of infection from IOP measurement by NCT may be slim, it may be clinically wise and safe to suggest disinfection of the chin and head rest, the device table and upper surface of the NCT instrument between the patients and refrain from eye drop instillations immediately before IOP measurements when possible,” according to the researchers. 

Study limitations include a small sample size, limited camera views of the traveling aerosols, and a failure to assess aerosolization under various humidity and ventilation conditions. 

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures. 

Reference

Kojima T, Dogru M, Yazu H, Kudo H, Tsubota K. Noninvasive visualization of the tear film microaerosol during noncontact tonometry measurements. Am J Ophthalmol. Published online April 22, 2022. doi:10.1016/j.ajo.2022.03.031.