Full-field Anterior Chamber Angle Measurement Based on Optical Reflection Tomography
Objective Angle-closure glaucoma(ACG)is one of the major eye-blinding diseases.To diagnose ACG,it is crucial to examine the anterior chamber angle.Current diagnostic tools include slit lamp gonioscopy,water gonioscopy,ultrasound biomicroscopy(UBM),and anterior segment optical coherence tomography(AS-OCT).Slit lamp and water gonioscopy allow convenient observation of the anterior chamber angle,but pose risks of invasive operation and eye infections.UBM can accurately measure the structure of the anterior chamber angle.However,it is complex to operate and unsuitable for patients,who have undergone trauma or ocular surgery.Although AS-OCT provides detailed images,it is costly.The aim of this study is to explore a non-invasive,non-destructive optical reflection tomography(ORT)technique.This technique can achieve low-cost three-dimensional imaging and full-field anterior chamber angle measurement of the porcine eye.Methods The experiment involved assembling an optical reflection tomography system,which included a complementary metal oxide semiconductor(CMOS)camera,a telecentric system,a stepper motor,and a white light source,achieving a spatial resolution of approximately 8.5 μm.The process required positioning the porcine eye at the center of the field of the imaging system and rotating it around its central axis using a stepper motor.Reflection projection images were captured at each angle with an exposure time of 1.0 ms and an interval of 2°.The collected reflection-projection data were processed using a filtered reflection tomography algorithm,generating a series of two-dimensional slice data.These slices essentially represented cross-sectional views of the three-dimensional structural image,and were reconstructed into a complete three-dimensional structural image.Based on the reconstructed three-dimensional structural image of the porcine eye,the anterior chamber angles at different positions were measured,and a distribution map of these angles was drawn.Simultaneously,the ORT measurements were compared with the standard results obtained from optical coherence tomography(OCT)to assess the accuracy of ORT measurements.Results In this study,we successfully obtained the reflection projection data of a porcine eye using ORT technology,reconstructed its three-dimensional structural image,and measured the anterior chamber angle,generating the corresponding distribution map.To better distinguish the different structural parts of porcine eye,the three-dimensional structural image was marked with blue,green,and yellow dashed lines from the outer to the inner layers.The area between the blue and green dashed lines corresponded to the sclera.The area between the green and yellow dashed lines corresponded to the iris.The area inside the yellow dashed line corresponded to the pupil.The three-dimensional structural image clearly revealed the key anatomical features of the porcine eye.It was able to measure the anterior chamber angle at different positions.Additionally,the anterior chamber angle measurements of the porcine eye using ORT were compared with the measurements obtained using a TEL320C1 type OCT system,showing an average deviation of 0.51° and a mean square error MSE of 0.317.Conclusion ORT is a non-invasive,non-destructive,low-cost,and high-resolution imaging technique capable of achieving three-dimensional structural imaging and full-field anterior chamber angle measurement of a porcine eye.This technology offers a new perspective for the diagnosis of angle-closure glaucoma and is significant for the screening,diagnosis,and monitoring of eye diseases,potentially benefiting clinics and small hospitals in remote areas in the future.
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