Method
This study utilised a Zeiss OPMI Vario S88 microscope, used in operating theatres throughout our institution (Carl Zeiss AG, Jena, Germany). The microscope was set up in the normal position for ear surgery and focused on a scaled target used in competitive world archery (Figure 1). This target has 10, equally spaced concentric circles, with 5 coloured zones. The microscope was set with a focal length of 300mm and the position of the microscope and zoom were adjusted to ensure that the target filled the entirety of the view afforded by the microscope (with the outer edge of the target matching the perimeter of the surgical view).
ENT surgeons were asked to position themselves for using the microscope, with a comfortable posture that would allow them to operate for an extended period (Figure 1). Each surgeon adjusted the inter-pupillary distance, height of the chair and microscope angle to ensure an optimal and comfortable view. The surgeons were asked to state how much of the target they could see in their peripheral vision, whilst staring at the centre point with their head in the usual neutral position. A score of 1 (outer white ring) represented a full view of the target, with progressively higher scores indicating a more restricted view that allowed for visualisation of a central portion of the target only. The percentage of target visible was calculated from these scores (diameter and area). The distance between the most anterior aspect of the surgeon’s cornea and the edge of the microscope eyepiece was measured to the nearest millimetre, with care taken to avoid parallax error. This was done with the aid of a ruler secured to the side of the microscope (Figure 1). This process was then repeated with the surgeon wearing an FFP-3 mask and various forms of eye/face protection. Scores for view (outer-most complete ring visible) and eye-microscope distance were recorded for each PPE condition. The PPE trialled is outlined in Table 1 and Figure 2. For the purposes of this study, combinations of PPE were categorised from A to E, with A representing no PPE and E representing a full face visor. Surgeons who wear prescription glasses for surgery continued to wear their normal glasses, with additional PPE.