COVID-19: Additional Precautions against Aerosols for the Slit Lamp User.

Abstract

To the Editor: We read with great interest the article by Lam et al,1 which describes the special precautions in ophthalmic practice required due to COVID-19. However, precautions related to aerosol transmission may need to be emphasized due to evolving understanding of transmission of the disease. Early in the COVID-19 pandemic, droplet and contact transmission were postulated to be the main modes of transmission. Droplets were defined as being “large” and measuring 20 to 100 μm. Upon expulsion, these droplets rapidly drop to land within 1 m of the infected individual. Transmission may also occur by direct contact with an infected individual or a surface that the person has touched. Recently, the World Health Organization (WHO) has relooked into the modes of transmission for COVID-19.2 Aerosols are generally defined as respiratory particles <10 μm. Generation of aerosols has been normally associated with coughing or sneezing but notably, may be produced even by normal breathing and speech. In fact, SARS-CoV-2 RNAs have been detected in air samples near infected patients despite them not coughing during sample taking.3 Pertinently, aerosols can remain suspended in the air and viral particles have been found in greater concentrations closer to the infected person.4 These aerosols may be carried by air currents to distances above 10 m, which may greatly increase its transmissibility. Furthermore, aerosols are thought to be able to penetrate the lower respiratory tract including the alveoli. Since SARS-CoV-2 in aerosols can be viable for up to 3 hours,5 these may pose an increased risk to those in proximity to infected individuals through breathing and normal speech. THREAT TO THE SLIT LAMP USER Ophthalmologists have been identified as an at-risk specialty for contracting respiratory disease due to the proximity at the slit lamp and higher likelihood of potential exposure to patients’ conjunctival and respiratory secretions.1 In view of the evolving knowledge of aerosol transmission in the chain of spread of COVID-19, we wish to bring attention to current personal protective equipment (PPE) recommendations which may not adequately protect the ophthalmologist. EXISTING PPE RECOMMENDATIONS AND PITFALLS Various ophthalmological societies have provided guidelines on the use of PPE. The Royal College of Ophthalmologists and the American Academy of Ophthalmology (AAO) recommend ophthalmologists to wear surgical masks and eye protection when examining patients. In addition, the AAO has also recommended the use of commercially available slit lamp breath shields to protect against droplets from coughs and sneezes. In view of the mounting evidence of aerosol transmission particularly in indoor environments, there is an increased risk of COVID-19 infection to the ophthalmologists due to inadequate PPE. This is considerably so as presymptomatic transmission may be as high as 50% to 60%.6 IMPLICATIONS TO THE SLIT LAMP USER Administrative procedures such as the setting up of triage stations at hospital entrances which include symptom-based questionnaires and temperature screening have been recommended as part of infection control measures.7 This should be complemented with universal masking for those who wish to seek ophthalmic care as COVID-19 patients may not exhibit any symptoms. Surgical masks have been shown to reduce coronavirus RNA in aerosols and droplets from exhaled air samples8 and could be used to reduce transmission risk. This has already been adopted in the current AAO guidelines. Universal patient mask-wearing at the slit lamp seems particularly prudent. To mitigate against aerosol transmission at the slit lamp, ophthalmologists must adhere to the wearing of a protective mask and eye protection. Despite some evidence of surgical masks and respirators providing similar levels of protection,9 respirators have been shown to have stronger association with reduced infection rates compared to surgical masks.10 Where local resources permit and prevailing rates of community transmission are high, the use of respirators should be preferred to surgical masks. CONCLUSIONS In the presence of evolving evidence of aerosol and presymptomatic transmission in COVID-19, it is timely to reevaluate existing PPE recommendations to ophthalmologists. Slit lamp shields may reduce contamination and exposure to large droplets but aerosols will circumvent these to reach the ophthalmologist. Universal masking within eye clinics should be considered to reduce presymptomatic transmission. PPE recommendations for ophthalmologists could also be reviewed to include the use of a respirator during routine slit lamp examination. In the context of frequent close contact with many patients over the course of a day and in communities with high prevalence of COVID-19 cases, this makes good sense. However, the ideal protective measures will depend on the availability of resources locally. An alternative is the use of surgical masks for both ophthalmologists and patients.