key: cord-0718737-tgjg5ntc
authors: Liu, John; Wang, Annie Y.; Ing, Edsel B.
title: Efficacy of slit lamp breath shields
date: 2020-05-11
journal: Am J Ophthalmol
DOI: 10.1016/j.ajo.2020.05.005
sha: 6fc5451ad208c577bedaa833f62cb11956254c12
doc_id: 718737
cord_uid: tgjg5ntc

PURPOSE: To evaluate the efficacy of slit lamp breath shields to prevent droplet spray from a simulated sneeze. DESIGN: Experimental study to test 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. We tested the designs of six commercially available breath shields, and one breath shield repurposed from a plastic container lid. Each breath shield was sprayed in a standardized fashion three times and the amount of overspray compared with no shield was quantified. The surface area that was sprayed was calculated using Adobe Photoshop’s 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 116-1254 cm(2) 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 a better barrier than those hung by the oculars of comparable size. A repurposed plastic lid breath shield was 513cm(2), was slightly curved toward the examiner’s face, and allowed only 2% overspray. The largest breath shield (1254 cm(2)) hung near the oculars and prevented essentially all the overspray. CONCLUSION: The performance of different designs of breath shields is 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 cloth mask during all slit lamp exams.

that approximated a patient sneezing on a dimensionally accurate cardboard slit lamp model.

We tested the designs of six commercially available breath shields, and one breath shield repurposed from a plastic container lid. Each breath shield was sprayed in a standardized fashion three times and the amount of overspray compared with no shield was quantified. The surface area that was sprayed was calculated using Adobe Photoshop's color range function.

The average percentage of overspray of each breath shield was computed in comparison to the control.

The breath shields ranged in surface area from 116-1254 cm 2 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 a better barrier than those hung by the oculars of comparable size. A repurposed plastic lid breath shield was 513cm 2 , was slightly curved toward the examiner's face, and allowed only 2% overspray. The largest breath shield (1254 cm 2 ) hung near the oculars and prevented essentially all the overspray.

The performance of different designs of breath shields is 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 cloth mask during all slit lamp exams.

The novel coronavirus pandemic is the most significant medical crisis of the 21st century thus far. COVID-19 is spread by droplets from talking, sneezing, or coughing and hand contact. Physicians from almost all specialties, including ophthalmologists, have died from COVID-19 during their patient care duties. 1 Slit lamp breath shields are recommended to decrease the risk of possible infection to the examiner, 2 and numerous commercial and homefabricated slit lamp breath shields are available. 34 Despite their pervasive use, we did not find a formal study on the efficacy of slit lamp breath shields. In this study, we test and compare the performance of six commercially available breath shield designs and one breath shield repurposed from a plastic container lid in protecting examiners against respiratory droplets using a spray gun sneeze simulation.

We conducted an experimental study to test the effectiveness of personal protective equipment. On April 15 th , 2020 the search terms "slit lamp breath shield", "breath shield", and "ophthalmology" were used to survey the English language literature on Google Scholar, PubMed and MEDLINE (Ovid). Articles from all years were searched. The Michael Garron Hospital Research Ethics Board (REB) deemed the study REB exempt. We complied with all ethical research principles compatible with the Declaration of Helsinki, although no human experimentation was involved. Five different commercially available polyethylene terephthalate slit lamp breath shields were purchased online from ChinRestPaperSource, Hillsboro, OR: Reichert and Keeler (AMBC2P, Panfundus, Inc., Hillsboro, OR), Haag-Streit Regular (AMBC4P, Panfundus, Inc., Hillsboro, OR), Haag-Streit Improved (AMBC5P, Panfundus, Inc., Hillsboro, OR), Universal Small (AMBUS1P, Panfundus, Inc., Hillsboro, OR), and Universal Large (AMBUL1P Panfundus, Inc., Hillsboro, OR). The breath shields were chosen based on popularity using the website reviews. The largest commercially available breath shield we found, the "Zombie Shield," (AMBUZ, Panfundus, Inc., Hillsboro, OR), was also the most expensive, and has been advertised for use during the COVID-19 pandemic. 5 Prior to the pandemic, conventional breath shields were much smaller than this size. Due to budget constraints, we simulated the dimensions of the sixth shield from cardboard. A seventh shield design was a repurposed disposable plastic salad container lid and had edges that curved towards the examiner at roughly 35 o .

Using four different slit lamps (Haag-Streit BM900, Switzerland; Shin Nippon SL-102, Japan; Ibex 2-Step, U.S.A.; and Ray Vision SLR5, China), the horizontal distance between the chin rest to the center illuminating arm and to the arm of the objective lens was measured, using direct illumination while focused on a prosthetic eye in the corneal plane. The aforementioned slit lamp dimensions were averaged to make a dimensionally accurate cardboard slit lamp simulation. Our spray would be directed at the cardboard phantom at the height of the average menton-subnasale length (vertical height from the chin to nares) that was determined from the literature. 6 The angular dispersion of droplet spray from a sneeze on the breath shield was estimated using two methods: i) published slow-motion videos 7 and ii) measuring the angle of vapor condensation on a window 26 cm from the authors' lips on a cold day. A spray gun ("Nicely Neat," Mr. Mister, Seattle, WA) was used to simulate a patient sneeze. The nozzle of the spray bottle was adjusted to our derived dispersion angle, and the air pump was preloaded with 20 actuations to ensure a consistent force of spray at each breath shield. The speed of the spray was calculated from observing slow-motion video footage of the spray shot at 60 frames per second. The spray bottle was filled with water mixed with green food coloring dye.

The performance of each breath shield at blocking the spray was measured. The cardboard slit lamp model was placed at the appropriate distance and height from the spray gun, and white poster paper was positioned directly behind the oculars of the cardboard slit lamp model to catch any overspray. The cardboard phantom was sprayed without a breath shield to establish our baseline control area of spray. The measurement was repeated three times, each time using a new piece of poster paper. Then each breath shield was placed at its intended position, either on the objective lens arm or hanging off the oculars and tested three times. Figure 1 shows the cardboard slit lamp and spray bottle setup. The area of spray was photographed immediately after the spray ( Figure 2 ). Adobe Photoshop (Adobe Inc., Mountain View, California) was used to determine the surface area of the green colorant. The color range function and Euclidean distances were used to calculate differences within the color space. 8 Any gravitational leakage of the colorant after the initial spray impression was accounted for. The average surface area from all three sets was calculated for each breath shield (see Table) .

No studies could be found from the literature evaluating the efficacy of slit lamp breath shields, with few studies mentioning slit lamp breath shields at all.

The average slit lamp horizontal distance measurements were as follows: from the chin rest to the center illuminating arm was 8.5cm; from the center illuminating arm to the objective lens arm was 8.0cm; from the objective lens arm to the oculars was 10cm. We estimated a 16.5cm distance from the patient's mouth to breath shields that are attached to the objective lens arm, and 26.5cm for breath shields that are hung by the oculars, as shown in Figure 1 . The vertical separation from the top of breath shields attached to the objective lens arm and the top of the breath shields hung by oculars was 9cm. The dimensionally accurate cardboard slit lamp phantom was constructed using the following averaged slit lamp measurements: i) the illuminating arm was 7.5cm x 3cm x 3cm at the base, with three 1.5cm rods extending vertically from the base, ii) the objective lens apparatus incorporated a 2cm x 2cm rod, supporting a 6cm

x 7cm x 8cm objective lens, connected to oculars measuring 9cm x 6cm x 6cm (approximated as a box), with 5cm long cylinders at the end. The average menton-subnasale length at the chinrest was 5.2cm 6 and confirmed by measuring the authors' faces. The average of the two methods for determining the angular dispersion of droplet spray from a sneeze was 47°, and the speed of the spray gun was calculated at 2m/s. The table shows each shield and their percentage of potential overspray. The range of the unblocked overspray varied from 0.3%-54% versus the control surface area measurement. On ANOVA, there was a statistically significant difference between the performance of the seven shields (F (6,14) = 10.63, p<0.05). The best performing breath shields were the largest shields (#6 and #7) measuring 1254cm 2 and 513cm 2 respectively. These two shields performed significantly better than the best conventional commercial shield (#3) on paired t-test (p=0.028, p=0.026). Between the two Haag-Streit shields -the regular model (#2) with surface area 115.5cm 2 and the "improved" model with surface area 179.6cm 2 (#3) -the improved model blocked more spray, although this was not statistically significant (p=0.21). The poorest performing breath shield measured at 184.2cm 2 and was hung by the oculars (#4).

Amongst conventional commercially available shields, the shields that were attached on the objective lens arm generally performed better, but still allowed 3%, 8%, and 34% of overspray. In contrast, the breath shields hung by the oculars did not protect against 36% and 54% of spray. Paired t-test showed that the best performing conventional commercial breath shield mounted on the objective lens arm (#3) performed significantly better than both conventional commercial breath shields hung by the oculars (#4 and #5) (p=0.041, p=0.017). There was no statistically significant difference within any of the commercially available breath shields that were attached to the objective lens arm, nor was there any statistically significant difference within the two commercially available breath shields hung by the oculars.

Ophthalmologists may be the initial caregiver of patients with COVID-19 who can be asymptomatic or present with conjunctivitis. 9101112 To date at least seven ophthalmologists have succumbed to COVID-19. 1 The late Dr. Li Wenliang, the "whistleblower" ophthalmologist from China, believed he was infected by an asymptomatic glaucoma patient. 13 Subsequently, two more of his ophthalmology colleagues at the same hospital died.

Appropriate protection is critical for ophthalmologists as we work in close proximity to the airway and tears of patients, especially during slit lamp examinations. COVID-19 viral loads can be high in both symptomatic and asymptomatic patients, 14 suggesting universal precautions should be taken at the slit lamp regardless of whether or not patients are symptomatic, although the risk of ocular transmission of infection from tears of patients without conjunctivitis is purported to be low. 15 Patients are advised to no longer talk during slit lamp exams. Examiners may be especially vulnerable when patients hyperventilate, cough, or sneeze at the slit lamp. Due to the photic sneeze reflex (or ACHOO Syndrome), estimated to occur in 18-35% of the population, 16 ophthalmologists may be at risk when exposing patients to bright lights. Sneezing may also occur with periocular injections due to the sternutatory reflex. 17 This is the first study to our knowledge that compares the designs of various slit lamp breath shields in the setting of a simulated ophthalmic exam. We demonstrate that commercially available slit lamp breath shields may not block up to 54% of a 47 o angle simulated oronasal spray. In this study, the more anteriorly fixed breath shields at the plane of the objective lens arm were more effective than the posteriorly positioned ocular shields of comparable size, consistent with "ray tracing" geometric principles (Figure 3) . In our simulation, there was a 10cm horizontal distance between breath shields attached to the objective lens arm versus breath shields hung by the oculars.

Size and shape are other factors that determine the performance of the breath shields. Of the three breath shields mounted on the objective arm, shield #3 of area 179.6cm 2 was wider superiorly and allowed 5% less overspray than the similarly shaped shield #2 measuring 115.5cm 2 , and 31% less overspray than the superiorly tapered shield #1 of area 140cm 2 .

Our repurposed plastic lid breath shield (courtesy Dr. Brent Weiser and Sharon Weiser) was an economical plastic lid from a salad container, purchased at a local grocery store, and yet was superior to five of the six commercially available breath shield designs that were tested, and can be easily replaced. Although larger shields may offer better protection, they may also impede access to slit lamp controls. A curved design such as in the repurposed plastic salad lid may protect the examiner from eccentric sneezes. There are a myriad of other breath shield designs available 3 and we did not have the resources to manufacture or test each one.

We acknowledge the limitations of our study. Ideally the patient and physician should both have face masks during the slit lamp exam, but when there is a shortage of PPE, the breath shields become even more important. As each slit lamp may be unique, the study results from the average dimensions of our cardboard phantom may not apply to other bio microscopes. We only simulated a straight-ahead spray; in reality, patients may sneeze at angles not blocked by the shield or slit lamp. Additionally, our spray velocity was 2m/s, but sneezes can achieve a velocity of 35 m/s (126 km/h) 7 . There was some variation in the spray measurements which we tried to minimize with three serial tests. We also could not quantify the volume of the overspray, which might correspond with the viral load -only the area. This is a limitation of the usage of imagery to capture the amount of overspray, as Adobe Photoshop cannot quantify the volume of water on the poster paper. Finally, we cannot account for the effects of microdroplets and aerosolization, which have been suggested as possible routes of transmission of COVID-19. Microdroplets are spread during a regular conversation and can rise high in the air and circulate well beyond the breath shield to reach the examiner. 18 The COVID-19 virus has been shown to stay viable in aerosols for at least 3 hours under experimental conditions in a Goldberg drum. 19 Slit lamp breath shields should be combined with infection control measures and PPE. 20 Patients should be pre-screened for symptoms of COVID-19 before arriving at the office, sit two meters away from other patients, wear a face covering, and minimize any talking during the slit lamp exam. Ophthalmologists should use appropriate PPE including gloves, eye protection, surgical mask, or N95 respirator when necessary. Additionally, there should be proper ventilation in clinics and waiting areas, frequent handwashing, and proper disinfection of surfaces frequently touched by healthcare workers and patients -in addition to the breath shield. 21 We demonstrated that commercially available slit lamp breath shields may allow up to 54% of overspray contamination. Breath shields that are attached to the objective lens arm can be made larger to offer more protection but can impede access to slit lamp controls. We did not combine breath shields at the objective arm and plane of the oculars together, but this can be done. A breath shield that curves towards the examiner such as our repurposed plastic lid design might better protect the examiner's face from eccentric sneezes. Breath shields should still be used in conjunction with other infection control measures to prevent the spread of COVID-19. Further research into protective devices against COVID-19 microdroplets is encouraged. 

• Conventional slit lamp breath shields were unable to block 3-54% of the overspray from a simulated sneeze

• Slit lamp breath shields that are more anterior and attached to the objective lens arm were more effective than posteriorly positioned ocular shields of comparable size

• Breath shields should be combined with masks, gloves and handwashing to decrease the possible risk of transmission of infection

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