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.