Research Of Computer-aided Design And Fabrication Of Ocular Prostheses

Part ? Research of computer-aided semi-automatic design and fabrication of ocular prosthesesPurposeIt is important to correct the ocular disfigurement by wearing prostheses as soon as possible after healing from the eye enucleation surgery.Traditional methods to make custom ocular prostheses(COPs)take a long time to complete due to series of complex steps,and taking conjunctival sac impression is a critical process,which strongly depend on the experience of the oculist.However,there still exists unsatisfactory match between COPs and the patients' conjunctival sac in clinical practice.Computer-aided design/Computer-aided manufacture(CAD/CAM)involve computer image analysis,reverse engineering(RE),three-dimensional(3D)printing and other technologies,which may provide new ideas for designing and fabricating COPs.This part of experiment was aiming to develop a new semi-automatic approach to fabricate COPs with higher accuracy and efficiency,which based on the conjunctival sac impression,combined with reverse engineering and 3D printing.MethodsFive cases were included in this part of experiment,and we took conjunctival sac impression for the patients.We performed 3D scanning for the conjunctival sac impression,and reconstructed digital model of the conjunctival sac in software.The key measurements of the model included height(mm),thickness(mm),and basal area(mm2).The contour lines were obtained in the software.Based on the above data,preliminary models of the COPs were designed by reverse engineering technologies.3D printing technology was applied to realize semi-automatic production of COPs.The quality of COPs was evaluated by measuring the palpebral fissure width and the mobility.ResultsThe bilateral palpebral fissure width was measured and independent sample t test was performed on the data.The results showed that the palpebral fissure height of the COPs group was 0.8000 + 0.09529 cm,N=5;the palpebral fissure height of the companion eye group was 0.7660 ± 0.1147 cm,N=5.There was no statistical difference between the two groups,p>0.05.The 3D printed prostheses effectively restored the upper eyelid deformity,and the questionnaire results showed that both of the patients and doctors were satisfied with the upper eyelid reconstruction.Accurate measurement of the mobility was carried out:COPs' horizontal mobility was(0.24?0.87)cm,which accounted for 15.3%?49.2%of the companion eyes;the COPs'vertical mobility was(0.57?1.06)cm,which accounted for 45.2%?72.8%of the companion eyes.The extent of COPs' pupil movements was(0.0418?0.1295)cm2,accounting for 6.7%?22.5%of the companion eyes.ConclusionsIn this study,the production of semi-automatic COPs was realized by RE,3D printing and other computer aided design technologies.The semi-automatic COPs accurately restored the patients' eyelid deformity and had an extent of mobility.CAD technologies digitized the conjunctival sac impression,which can remove deformation of the impression material.RE and 3D printing technologies can effectively make the COPs suitable for patients' conjunctival sac.This semi-automatic workflow improved the accuracy of the COPs,and also reduced patients' waiting time.Part ? Research of computer-aided automatic design and fabrication of ocular prosthesesPurposeThis part of experiment was aiming to develop a new automatic approach to fabricate COPs based on computed tomography(CT)image,combined with image segmentation,self-reference computation and 3D printing.MethodsThe second part was automatic design and fabrication of COPs,which based on the patients' CT data.We had developed a new CT-based three-dimensional volume difference reconstruction(VDR)method for building a model of soft tissue differences using facial self-referenced prototyping computation,and a CAD workflow for fabricating COPs.In facial self-referenced prototyping computation,an ocular prosthesis is constructed from a combination of a top surface,shape contour and bottom surface,with key measurements being made with respect to the patient's healthy eye.The top surface is derived from the outer region of the healthy eyeball,using Hough transformation.In the meantime,the shape contour and bottom surface are computed from facial edges fitted to Fourier curves.Once these self-referenced parameters had been obtained,finite element analysis was used to generate a primitive prosthesis model.Before being converted into a format suitable for 3D printing techniques,the model was refined using surface equations.Oculists chose the final optimized model for printing.ResultsThe semi-automatic workflow of design and fabrication of COPs:COPs made by RE and 3D printing technology can effectively make the COPs suitable for patients'conjunctival sac.This workflow improved the accuracy of the COPs,and also reduced patients' waiting time.The automatic workflow of design and fabrication of COPs:Geometric errors,compared to a manually-fabricated prosthesis which had gone through multiple rounds of time-consuming manual adjustment,was as low as 0.46%,and the fabrication time and human error had been greatly reduced.The fill density of the COP was 60%,the wall thickness was 1.6 mm and the weight was 1.59 g.The reconstructed contours and symmetry of the COP were satisfactory with doctors'evaluation and the patient was able to have a normal appearance.ConclusionsThe application of RE and 3D printing technologies in the COPs workflow can improve the efficiency and quality of the COPs,which is worthy to be popularized and applied.The CT-based VDR method we first proposed here can accurately build a model of the soft tissue difference.The full CAD workflow has improved prosthesis design and manufacturing efficiency.This flow can also be applied to other soft issue reconstruction.