Digital measurement of corneal curvature and eccentricity of guinea pigs using Python

To investigate an accurate and quantitative method to measure the eyeball morphological parameters of guinea pigs through a method that combines programmed digital techniques and mathematical geometric principles.

Twenty-two three-week-old clean-grade male tricolor guinea pigs were selected and sacrificed by anesthesia overdose.Eyeballs were enucleated.The horizontal and sagittal images of the eyeball were taken with the high-speed photographic model of 13 million pixels macro meter, and the pictures were imported into pycharm programming software.Using the pre-written analysis program of Python 3.9, the conversion coefficient between the photo pixel and the actual length was obtained by a scale, and then the corneal surface was fitted by arc fitting and conic curve fitting.The results of arc fitting were converted to calculate the corneal radius of curvature.The corneal eccentricity was calculated according to the general conic equation (Ax²+ Bxy+ Cy²+ Dx+ Ey+ F=0). The corneal asphericity was evaluated by curve fitting between the central 3-mm and the whole cornea.The use and care of the animals complied with Regulations for the Administration of Affairs Concerning Experimental Animals by State Science and Technology Commission.The study protocol was approved by the Ethics Committee of Shanghai Public Health Clinical Center (No.2022-A009-01).

The digital method of Python programming can show the corneal contour of guinea pigs completely and clearly.In the transverse plane, there was no significant difference in the corneal curvature measurements among the digital fitting in central 3-mm cornea, digital fitting in whole cornea and curvature meter (F=1.693, P=0.190). In the sagittal plane, there was a significant difference in the corneal curvature measurements among the three methods (F=3.500, P=0.030), and the corneal curvature measurements of the whole cornea measured by the curvature meter were significantly greater than those measured by the digital fitting (P<0.05). There was no statistical significance in the measurements of corneal curvature radius among the three methods in the transverse plane and the sagittal plane (F=1.817, P=0.170; F=2.050, P=0.133). The horizontal and sagittal corneal eccentricity measured by digital fitting in central 3-mm cornea were 0.55±0.15 and 0.53±0.17, which were lower than 0.66±0.10 and 0.64±0.14 measured by digital fitting in whole cornea, and the differences were statistically significant (t=-4.860, -5.210; both at P<0.01).

It is feasible to use Python programming digital method to measure the corneal curvature and eccentricity of guinea pigs.