Research On The Optical-mechanical System Of Corneal Topographer Based On Placido Disk

The corneal topograph is one of the important instruments for measuring the shape of the cornea.It can accurately measure the curvature parameters of the corneal surface and present the measurement results in the form of digital topographic maps.The corneal contact lens inspection,corneal disease diagnosis and corneal postoperative recovery evaluation Has an important guiding role.Corneal topographs on the market are based on a variety of principles,such as crack scanning,three-dimensional triangulation,Scheimpflug uniform rotation measurement,etc.,while Placido disk-based corneal topographs have high measurement accuracy,accurate topographic map drawing,diverse measurement data,It has many advantages such as strong analytical ability and moderate price,and is widely welcomed in the medical market.At present,the standard error of the corneal topograph based on Placido disk is ± 0.03 D,and the measurement range is generally 5.5mm-10.9mm.In order to further improve the corneal detection accuracy,expand the corneal coverage,and increase market competitiveness,a high-precision,high-coverage corneal topograph opticalmechanical system is designed in this paper.The paper analyzes the corneal detection theory and optical-mechanical system based on Placido disk,constructs the overall system scheme,and derives the corneal curvature solution model.Based on this,Placido disk and its processing technology are designed: using injection molding,spraying,The CNC process processes the Placido disk,improving the sharpness of the edges of the black and white concentric rings on the inner surface of the Placido disk,improving the imaging quality and image processing accuracy;using a ringshaped high-brightness LED light source,and using a BaSO4 reflector on the inner surface to increase the light source illumination The uniformity of the cornea can be improved to improve the detection accuracy of the cornea.The Cook's three-separation structure imaging objective lens system has been designed to further improve the aberration correction effect through optimization.The total length of the optical system is shorter and conforms to the concept of miniaturization of modern instruments.The structure of the light source is designed.The contact surface of the pressure ring,the lens holder and the lens adopts a spherical interface design with the least pressure on the lens to improve the accuracy of installation.The standard prototype eye was used to calibrate the prototype.The standard deviation of the measured radius of curvature was less than 0.03 mm,which met the national standard A.The calibrated experimental prototype was used for the standard simulated eye with a radius of curvature of 8 mm and five groups of actual human eyes.Measurement experiments and error analysis were performed,and the results showed that the detection standard error was within ± 0.015 D,and the corneal measurement range was 5.5 mm-12 mm,which met the national ophthalmic instrument testing standards specified by the pharmaceutical industry.