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Addressing phaco aerosolization concerns due to COVID-19: A human cadaveric eye with trypan blue


by Amrit Rai, MD, Robert Mele, Amandeep Rai, MD, Rosa Braga-Mele, MD

With COVID-19 still a major concern in the U.S. and around the world, EyeWorld Cataract Editor Rosa Braga-Mele, MD, shared results from a study where a series of experiments were conducted to evaluate whether the phaco probe could generate aerosols, as the virus has been shown to be transmitted via aerosols (among other ways). In this article, Dr. Braga-Mele provides details of the study, the methods, and some of the results.

COVID-19 is a severe respiratory illness caused by the novel coronavirus SARS-CoV-2. The virus has been shown to be transmitted via fomites, droplets, and aerosols.1–2 The SARS-CoV-2 virus has been isolated from conjunctival swabs of infected individuals.3–4 There are concerns among ophthalmologists regarding whether the rapid oscillations of the phacoemulsification probe could generate aerosols. To evaluate this concern, we set up a series of experiments. For each experiment, we used a human cadaveric eye, a 2.2-mm clear corneal incision, and a 2.2-mm phacoemulsification sleeve, utilizing a Centurion phacoemulsification machine (Alcon) and evaluating both longitudinal and torsional phacoemulsification modalities. At the beginning of each experiment, we filled the anterior chamber with trypan blue dye to simulate “viral” aqueous and allow for easy visualization.

What we studied

1. For Experiment 1, after creating our corneal wounds and injecting trypan blue into the anterior chamber of a human cadaveric eye, we performed irrigation and aspiration of the anterior chamber fluid with a sleeved I/A tip. Theoretically, doing this for 6–10 seconds should be adequate to remove the volume of aqueous in the anterior chamber. Recorded video (youtu.be/epcDtNN-PkI) shows successful removal of the “viral” fluid without the creation of aerosols. Next, we injected OVD into the eye and proceeded with longitudinal and torsional phacoemulsification independently. Again, no visible aerosols were produced, either with microscope or side filming views. The surgeon’s hands remained dry the entire time, as did the microscope. Therefore, performing irrigation and aspiration at the start of the case is shown to effectively evacuate the anterior chamber volume. Furthermore, following formation of the anterior chamber with OVD, no trypan blue was seen to be aerosolized during phacoemulsification.

2. For Experiment 2, we also injected trypan blue into the anterior chamber after creating corneal incisions to mimic “viral” aqueous. We then displaced the “viral” aqueous humor with OVD prior to introducing our phacoemulsification probe. In this experiment, we did not perform irrigation and aspiration to start the case. The viscoelastic successfully displaced the “viral” aqueous out of the eye without creating any aerosols. When the phacoemulsification probe was introduced into the eye, we did not see any aerosols created by the longitudinal and torsional phacoemulsification, as listed above and seen in the video.

3. Experiment 3 was used as a control to demonstrate that applying phacoemulsification to an open sky model does create a visible plume. Furthermore, trypan blue was visible on the surgeon’s gloves in this case, while this did not occur in either Experiment 1 or Experiment 2.

Discussion

In our series of experiments, we demonstrate two methods of performing phacoemulsification in a human cadaveric eye without the production of aerosols. Although no studies to date have analyzed whether SARS-CoV-2 is present in the aqueous humor, it has been isolated on the conjunctival surface and other viruses have been isolated from the aqueous humor.2–4 Povidone-iodine solutions are routinely used to disinfect the surface of the eye prior to cataract surgery. Povidone-iodine solutions have been shown to have highly effective viricidal activity against a broad range of viruses, including coronaviruses such as SARS-CoV-1 and MERS-CoV.5–6 This viricidal activity likely extends to the novel coronavirus, SARS-CoV-2. The rate of aqueous humor production is 2.4±0.6 µL/min.7 By comparison, conventional aspiration rates (20–40 mL/min) during cataract surgery are 3–4 orders of magnitude greater. Therefore, once the initial aqueous humor from the anterior chamber has been evacuated (either through initial irrigation and aspiration or by displacement with OVD), the rate of viral accumulation in the anterior chamber would be exceedingly low during the surgery. Darcy et al. demonstrated that phacoemulsification tip size can affect the production of aerosols.8 They found that while aerosols were created by a 2.75-mm phacoemulsification tip, there were no visible aerosols created when using a 2.2-mm tip. They also found that coating the surface of the cornea with a viscoelastic can block aerosols, however, this effect was short-lived. Furthermore, we also found that significant visible aerosols were not produced with either longitudinal or torsional phacoemulsification through a 2.2-mm incision.

Conclusions/recommendations

Removal of aqueous humor with irrigation and aspiration or by displacement with viscoelastic at the beginning of the case are both sufficient to remove potential viral particles from the anterior chamber without the production of aerosols. Longitudinal and torsional phacoemulsification with a 2.2-mm tip does not generate significant aerosolization. We also recommend the continued use of povidone-iodine to sterilize the conjunctiva and ocular surface as per regular protocol.

About the authors

Department of Ophthalmology and Vision Sciences
University of Toronto
Toronto, Canada

Contact

Braga-Mele: rbragamele@rogers.com

References

1. van Doremalen N, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564–1567.
2. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11:940.
3. Xia J, et al. Evaluation of coronavirus in tears and conjunctival secretions of patients with SARS-CoV-2 infection. J Med Virol. 2020;92:589–594.
4. Wu P, et al. Characteristics of ocular findings of patients with coronavirus disease 2019 (Covid-19) in Hubei Province, China. JAMA Ophthalmol. 2020;138:575–578.
5. Parhar HS, et al. Topical preparations to reduce SARS-CoV-2 aerosolization in head and neck mucosal surgery. Head Neck. 2020;42:1268–1272.
6. Eggers M, et al. In vitro bactericidal and virucidal efficacy of povidone-iodine gargle/mouthwash against respiratory and oral tract pathogens. Infect Dis Ther. 2018;7:249–259.
7. Goel M, et al. Aqueous humor dynamics: A review. Open Ophthalmol J. 2010;4:52–59.
8. Darcy K, et al. Reducing visible aerosol generation during phacoemulsification in the era of Covid-19. MedRxiv. 2020. Epub ahead of print.

Addressing phaco aerosolization concerns due to COVID-19: A human cadaveric eye with trypan blue Addressing phaco aerosolization concerns due to COVID-19: A human cadaveric eye with trypan blue
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