Defining Optical Distortion in Rigid Endoscopes

作者：Abel Eric^*; Fotiadis Nikolaos; Miah Mohammed; White Paul

来源：Laryngoscope, 2015, 125(3): 561-566.

DOI：10.1002/lary.24971

• Rigid endoscopes
• definitions of distortion
• barrel distortion
• perspective distortion
• depth perception

Objectives/HypothesisTo describe lens and perspective distortion using new measures that have practical meaning to the surgeon, and to apply these measures to show the extent of optical distortion in rigid endoscopes used in endoscopic sinus surgery.
Study DesignLaboratory measurements on rigid endoscopes.
MethodsBarrel and perspective distortion were measured in 4-mm diameter 0 degrees, 30 degrees, 45 degrees, and 70 degrees rigid sinus endoscopes. Images of square grids were obtained with the endoscopes aligned in a specially constructed test rig. The terms relative size (RS) and relative distance (RD) were introduced to describe size and distance errors; and the term relative angle (RA) was used for assessing perspective errors.
ResultsAll the endoscopes exhibited similar barrel distortion. RS of the image at the periphery was 52%; RD was 80%. For RA values of 30 degrees, 45 degrees, and 70 degrees, RS values were 77%, 58%, and 32%, respectively. Objects at the edge of the surgical field appear significantly more distant than suggested by their screen position. Perspective distortion occurs, unless RA=0 degrees. Barrel distortion of the lens helped to offset the effects of perspective distortion.
ConclusionOptical distortion can be quantified and understood using straightforward definitions. High levels of distortion are common, particularly due to perspective distortion, which is dependent on RA but independent of barrel distortion and the viewing angle of the endoscope.

• 出版日期2015-3