Measurement of corneal curvature radius by pointolites

The cornea is an important dioptric media for the human eyes, and its diopter accounts for about two-thirds of the total diopter of the human eyes. It is important to study corneal curvature. The appearance of the keratometer provides a convenient and quick measurement method for accurately obtaining corneal curvature. The keratometer is used to measure the curvature of the anterior surface of the cornea. Currently, the corneal curvature measuring device is basically designed by optical reflection method. The measuring principle is to place a specific size object at a specific position in front of the cornea. The object reflects off the front surface of the cornea and produces a virtual image. The curvature of the anterior surface of the cornea can be calculated by measuring the size of the image. With the rapid development of optoelectronic technology, it is feasible to measure optical images quickly and accurately with mature image processing methods. Western countries have started research in this area earlier. In the 1980s, the idea of using computer-aided processing of corneal reflection images was proposed. In recent years, well-known ophthalmic equipment companies and scientific research teams at home and abroad have carried out a lot of research and improvement on automatic keratometer. Based on the previous studies, this paper proposes a simplified corneal curvature measurement system.

Simulate corneal reflex image

    The research team of Associate Professor Wang Cheng from the Institute of Biomedical Optics & Optometry, School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, has been working on the measurement equipment of eye biometric parameters for many years. Good research results have been made in the measurement of eye parameters such as corneal curvature, anterior chamber depth, and axial length. In the simplified corneal curvature measurement system proposed by the research team, using the principle of corneal reflection imaging, six point light sources arranged in a regular hexagon are collimated and projected into the central region of the cornea, reflected through the anterior surface of the cornea and then imaged on CMOS. Image processing is performed on the corneal reflection image, and the distance between the two point light sources on the long diagonal of the regular hexagon in the image is obtained, and the radius of curvature of the cornea is obtained. The measurement system designed in this paper has a corneal curvature radius ranging from 5.5 mm to 11 mm (corresponding to corneal diopter 30 m-1 to 60 m-1) with a measurement error of ±0.02 mm. 

About team
Institute of Biomedical Optics & Optometry, School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology uses the principles and techniques of modern optics to conduct research on biological tissue detection using light as information and diagnosis and treatment using light as an energy carrier. The research direction of the team is based on optics, combining biomedicine, modern medicine, computational science and other disciplines, mainly researching medical optical imaging, tissue spectroscopy, visual restoration theory and technology, medical optical instruments, etc., providing reliable optical theory and technology for the diagnosis and treatment of diseases.  The research work currently carried out mainly includes three aspects: firstly, the early diagnosis of carcinogenesis based on tissue eigenspectrum; secondly, food quality control research based on multi-spectral imaging; thirdly, research on eye biological parameter measuring equipment. The institute has one professor, two associate professors, one lecturer, more than 20 graduate students, 15 invention patents and more than 20 SCI papers have been published.

Chen Peng, Wang Cheng, Zheng Gang, et al. Optimization design and realization of a keratometer[J]. Opto-Electronic Engineering, 2019, 46(1): 180373.
DOI: 10.12086/oee.2019.180373