Spread of Respiratory Droplets in a Simulated Ophthalmic Surgery

Performing ophthalmic surgery safely during the coronavirus 2019 pandemic is important to ophthalmologists, anesthesiologists, nurses, patients, and health policy analysts. Although ophthalmic procedures themselves are not a major source of transmission,¹ the upper respiratory tract may harbor high concentrations of severe acute respiratory syndrome coronavirus 2.² Because concern exists that routine ophthalmic procedures may potentiate the spread of respiratory droplets onto operating room personnel, some centers mandate masks for all operative patients.³ Herein, a series of simulations of a coughing patient during ophthalmic surgery were conducted to identify the potential spread of respiratory droplets and to evaluate interventions aimed at mitigating droplet spread from patients to operating room personnel. No human subjects were included in this study. Individual patient-level consent was not required.

In a series of simulations, a manikin was placed on a surgical bed in an operating room. For each simulation, a standard cataract surgical drape with a transparent adhesive quadrangle (level 4 eye surgical drape, 70 × 65 inches; Association for the Advancement of Medical Instrumentation PB70, MEDLINE) was placed over the surgical site, the adhesive drape was cut, and a speculum was inserted. The surgeon donned a clean surgical gown and gloves and sat with his hands adjacent to the surgical field (Fig 1A; Video 1, available at www.aaojournal.org). Three simulations were conducted as follows: (1) no surgical mask for the patient and a complete seal of the drape around the surgical field, (2) an ear loop surgical mask (American Society for Testing Materials level 2; 3M, Ontario, Canada) for the patient and an incomplete seal of the surgical drape intentionally applied by leaving a gap near the medial canthus, and (3) an ear loop surgical mask for the patient and a complete surgical seal with the adhesive of the drape. In scenarios 2 and 3, the superior edge of the mask was taped so that it adhered to the face. Methods previously validated for visualization of cough droplets were used3, 4, 5 and are described in more detail elsewhere (Supplementary Appendix, available at www.aaojournal.org).

Figure 1.

A, Simulation setup under ultraviolet light conditions with the surgeon in surgical positioning. B, Series of simulations involving no surgical mask for the patient and a complete seal of the surgical drape. C, An ear loop surgical mask (secured with tape) and an incomplete seal of the surgical drape. D, Surgical mask (secured with tape) and a complete surgical seal of surgical drape.

In the first simulation (no mask, complete seal), no visible droplet contamination of the surgical field or the surgeon was seen (Fig 1B). However, diffuse droplets appeared on the underside of the drape and on the manikin’s body (Fig 2A, available at www.aaojournal.org). In the second simulation (mask, incomplete seal), droplets were seen on the surgical field (Fig 1C) and the surgeon’s gloves, with minimal contamination of the underside of the drape. In the third simulation (mask, complete seal), no droplets were seen on the surgical field or the surgeon (Fig 1D), and minimal contamination occurred on the underside of the drape. During drape removal, droplets spread from beneath the mask onto the manikin’s lower eyelid in all 3 simulations (Fig 2B, available at www.aaojournal.org).

These simulations demonstrate that a complete surgical seal and masked patient minimize droplet spread and that an incomplete seal may allow respiratory droplets to travel onto the surgical field. Incomplete seals are not uncommon, the reasons for which include a prominent nose, deep-set orbits, reflex blepharospasm, blepharitis, insufficient drying of the skin after prepping, progressive loss of the adhesion of the drape as the case progresses, or a combination thereof. In addition to drying the area adequately before application of the drape, a transparent adhesive film dressing can be used to reinforce adhesion of the draping further. An aerosol box⁵ and additional plastic drapes⁶ have been used in other medical disciplines to minimize risk of droplet spread during surgery, but these methods are not adapted as easily in ophthalmic surgery, where access to the eyes and adnexa in close proximity to the airways is required.

Consistent with the present findings, in vitro and clinical studies have shown that placing a surgical mask on patients significantly reduces the dispersion distance of virus-infected bioaerosol from patients.⁷ Because droplets still were spread under the drape by the masked patient, operating room personnel should wear appropriate personal protective equipment before reaching under the drape and should perform hand hygiene afterward. Personal protective equipment is essential in protecting healthcare workers from transmissible acute respiratory infections in clinical settings.^{3 , 7} Humans produce respiratory droplets measuring 0.1 to 1000 μm.⁷ Studies of cough aerosols and exhaled breath have detected particles smaller than 5 μm from patients with various respiratory infections.⁷ Because the smaller particles of coronavirus have the potential to spread over long distances,⁷ many surgical centers have implemented nasal cannula instead of external broad flow to deliver oxygen directly into the patient’s nasal cavity and to reduce airflow directed toward the surgeon. Given our evolving understanding of severe acute respiratory syndrome coronavirus 2 transmissibility risk factors, reference to the latest local hospital and public health guidelines regarding appropriate personal protective equipment for protection against droplet spread in an operating room setting is recommended.

In each simulation, fluorescent dye was projected onto the surgical field while removing the adhesive drape. Because administration of postoperative drops often requires manual opening of the eyelids, we recommend having an assistant instill postoperative drops before the surgeon removes the speculum and drape. Although coughing likely produces fewer droplets than resuscitation procedures,⁶ spread of droplets was visualized under the drape, and hence rapid removal of the drape may be a source of droplet spread.

A limitation of these simulations is that they do not identify the spread of aerosols and very small droplets. Second, alternate rates or methods of oxygen supplementation when applied to a real patient may have variable results. Third, the differences in style and technique of applying the surgical drape may affect the generalizability of these findings. Future studies examining quantification of droplets and aerosol contaminants in other ophthalmic procedures are warranted.

In summary, these simulations demonstrate that the spread of respiratory droplets may be minimized with a patient mask that is taped to the face and a tight seal of the surgical drape. Personnel should be mindful when removing the surgical drape because of the potential for spread of droplets underneath the drape. Furthermore, administration of postoperative drops should be carried out before complete removal of the drape or with clean gloves to avoid direct contact with the patient’s face.

Supplementary Data

Video 1

VidClip of respiratory droplet spread during a simulated patient cough undergoing ophthalmic surgery.