Efficacy of Slit Lamp Breath Shields

Abstract

Purpose: To evaluate the efficacy of slit lamp breath shields to prevent droplet spray from a simulated sneeze.

Design: Experimental study to test the effectiveness of personal protective equipment.

Methods: The nozzle of a spray gun was adjusted to angularly disperse a mist of colored dye that approximated a patient sneezing on a dimensionally accurate cardboard slit lamp model. The designs of 6 commercially available breath shields and 1 breath shield repurposed from a plastic container lid were tested. Each breath shield was sprayed in a standardized fashion 3 times, and the amount of overspray was compared to spray with no shield and quantified. The surface area that was sprayed was calculated using a commercially available software with color range function. The average percentage of overspray of each breath shield was computed in comparison to the control.

Results: The breath shields ranged in surface area from 116 to 924 cm², and the amount of overspray varied from 54% to virtually none. Larger breath shields offered better protection than smaller ones. Breath shields attached to the objective lens arm were better barriers than those of comparable size hung by the oculars. A repurposed plastic lid breath shield, 513 cm², was slightly curved toward the examiner's face and allowed only 2% overspray. The largest breath shield (924 cm²) hung near the oculars and prevented essentially all overspray.

Conclusions: The performance of different designs of breath shields was variable. Even high-functioning shields should be used in conjunction with personal protective equipment including masks, goggles, and gloves and handwashing. Ideally patients should also wear a face mask during all slit lamp examinations.

Figure 1

Spray gun and cardboard slit lamp simulation with setup measurements. Arrows indicate the positions of the breath shield. (Top) The breath shield is attached to the objective lens arm. (Bottom) The breath shield is hung by the oculars.

Figure 2

Sample overspray patterns from control (top), a breath shield attached to the objective lens arm (1, Reichert and Keeler style, middle row), and a breath shield hung by the oculars (5, Universal Large, bottom row).

Figure 3

Dimensionally accurate ray diagram of the spray angle from a simulated sneeze. The slit lamp model is shown with breath shields placed in their appropriate relative positions.

John Liu recently graduated from medical school at the University of British Columbia (class of 2020) where he served as president of their Medical Undergraduate Society. He has interests in health advocacy, teaching, and innovation within ophthalmology and aims to integrate these passions into a future career. He is currently an ophthalmology research fellow at the University of Toronto under Dr. Ike Ahmed, and hopes to begin an ophthalmology residency program the following year!

Edsel Ing is a professor of ophthalmology at the University of Toronto. He completed his residency in Toronto, his fellowships at Wills Eye, the Mayo Clinic, and Allegheny General Hospital, his MPH at Harvard, and will soon finish his PhD at Kingston University.