The Influence of Instrument Length Calibration on Laparoscopic Depth Perception: A Randomised Controlled Trial

Mohammad K. Riaz (Lead / Corresponding author), Manhon Tang, Benjie Tang, Afshin Alijani

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Aim: Laparoscopic task performance relies on the interpretation of 2-D visual image with deteriorating depth perception. This study aims to investigate the impact of laparoscopic instrument length calibration on the depth perception through a randomised controlled trial.

Methods: Twenty medical students were randomised into two groups (scale and control). Studied instrument was calibrated with scale markings, 10 mm apart from instrument tip. Predesigned sheet (10 cm diameter) inside an endotrainer box was marked at 8 peripheral clockwise points. Total distance from the centre of sheet to any of these clockwise points was 10 cm. This distance was concealed from candidates. Instructions were provided to mark the sheet eight times at target distance (TD) from the centre of the sheet at 8 different clockwise directions. Instructions for TD and directions were randomised. There are four potentially opticalaxis to view angles (OATV) with a laparoscope and were set at standard for this trial. The task was repeated four times in 150, 450, 600, 900 OATV angles. Difference from TD to marked area was studied and recorded as + (mm) if mark overran and – (mm) if short of target. Data was analysed and statistical differences between both groups was calculated.

Results: Scale group was nearest to the target in all directions and OATV angles. At 150 OATV angle mean target distance was -8.4 ± 2.2 vs 1.9 ± 1 (mm ± sem) for control and scale group respectively (p <0.001). Similar variation was noted at 450: -12 ± 1.7 vs -5.8 ± 0.9 (p<0.01), 600: -11.7 ± 1.4 vs -4.4 ± 0.8 (p<0.001)and 900: 10.9 ± 1.8 vs -4.9 ± 0.8 (p<0.01).
Conclusion: Instrument calibration significantly improves laparoscopic task performance by enhancing depth perception in vitro settings.
Original languageEnglish
Pages (from-to)4-8
Number of pages5
JournalARC Journal of Surgery
Issue number4
Publication statusPublished - 2018


  • Depth perception
  • Instrument calibration
  • optical-axis-to-view angle


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