Slit-Lamp Breath Shields Provide Some Protection From COVID-19
American Journal of Ophthalmology, October 2020
Liu et al. assessed the capability of seven slit-lamp breath shields in preventing droplet overspray from a simulated sneeze. They found varying degrees of effectiveness among the tested shields, with the quantity of overspray ranging from 0.3% to 54% of the dispersion amount.
For their study, a dimensionally accurate slit-lamp model was constructed from cardboard, and the nozzle of a spray gun was adjusted to disperse a mist of colored dye that approximated a sneeze. Five popular commercial breath shields were purchased. Another was created from cardboard and simulated the size and shape of a sixth commercial shield. The seventh shield was a salad container lid with edges that curved toward the examiner. Surface area of the breath shields ranged from 116 to 1,254 cm2.
The cardboard slit-lamp model was sprayed without a breath shield in place to establish the control area of spray. Each shield was placed on the objective lens arm or was hung from the oculars. The shields were sprayed three times each, in a standardized fashion, using a fresh sheet of white poster paper placed directly behind the oculars. Areas of spray were photographed, quantified, and averaged. The amount of overspray was compared with the unshielded (control) quantity of spray.
Shields attached to the objective lens arm prevented more spray than those hung by the oculars. Moreover, with one exception, larger shields performed better than smaller ones. The best-performing conventional commercial shield was the cardboard-simulated “Zombie Shield,” which was hung near the oculars; it allowed only 0.3% of the spray to reach the poster paper.
A disadvantage of larger shields is their tendency to impede access to slit-lamp controls. Another factor affecting performance is the shape of the shield. The plastic lid, although not large in surface area (513.1 cm2), was more effective than five of the six commercial shields. The authors noted that even high-functioning shields should be used with other personal protective equipment. They emphasized that patients should wear a mask and avoid speaking during slit-lamp exams.
The original article can be found here.