The vitreous body presents a high acoustic permeability in terms of acoustic property, and appears as anechoic status on US image of normal human eyes [24]. Once there are some lesions, such as VO, VH and retinal detachment (RD) in the vitreous cavity, the echoes with different intensity and shape will be shown on US images. However, limited by the principle of ultrasonic imaging, the ophthalmic US images can also produce speckles and noises like those of other tissues and organs in human body, leading to a linear decline in ultrasonic image quality, which is a key factor for lesion analysis [25, 26]. At the same time, training a qualified and skilled ophthalmic sonographer also requires a certain amount of time and efforts. In addition, due to the subjectivity of ultrasound operation and image analysis, the results vary from person to person [27]. Therefore, objective and accurate acquisition and interpretation of ophthalmic ultrasonic images is increasingly becoming the demand of ophthalmic clinicians and ophthalmic imaging.
In recent years, the application of AI technology based on DL in ophthalmic diseases has been favored by more and more ophthalmic clinicians, and has become a hotspot of ophthalmic imaging research around the world. Many research findings revealed that DL assisted ophthalmic imaging examination improves the objectivity and accuracy of eye disease diagnosis [28, 29]. Therefore, the present study introduced two DL convolutional neural networks (CNN), residual network (Resnet) and GoogLeNet, to train the computer to automatically identify the US images of vitreous opacities with different properties and compare their differences. The results showed that GoogLeNet inceptionV1 had the highest classification and recognition accuracy while using the fewest parameters among the seven DL models. GoogLeNet is a kind of CNN proposed by Szegedy et al. [30], which is used for machine learning classification tasks through Inception network structure. Its core idea is to increase the depth and width of the network without increasing the computational cost [31, 32]. ResNet proposed by He et al. after GoogLeNet also achieved very good results in image recognition and detection tasks, speeding up CNN training speed, but its disadvantage is that the training precision is not high [33]. In addition, if too many parameters are used in network training, it is prone to overfitting [34] and affecting the efficiency of the model. GoogLeNet inceptionV1 is the most suitable DL model in this study to assist the automatic classification and recognition of vitreous opacity US images, and its classification accuracy is as high as 96%. Especially for VH, its precision, recall and F1score can reach 97%, which is more conducive to the formulation and implementation of clinical diagnosis and treatment strategies.
More and more ophthalmology clinicians and scholars are concerning DL assisted automatic recognition of ophthalmic US images. Di Chen et al [35] used the deep convolutional neural network 1 (DNN1), DNN2 and other neural networks to automatically classify and segment ophthalmic B-type ultrasound images of normal, RD, VD, VH and other lesions with an accuracy rate of over 90%. Some research use DL models such as Densenet and CNN to assist ultrasound biomicroscopy (UBM) to automatically determinate phakic status in pediatric and adult [36], classify the anterior angle chamber [37], automatically localize the scleral process [38], and intelligently measure the anterior segment parameters [39], which provide a more accurate and objective imaging verification and measurement means for the evaluation of anterior segment diseases such as lens disease and glaucoma. Our results are consistent with the above research results, which further confirm the application value of DL technology in ophthalmic gray-scale ultrasound image analysis. However, the US images used in their studies are all fan-shaped scanning images with the small probes, which suffer from inconsistent field width [40]. Different from their studies, the US images in this study are scanned by linear array probe of color Doppler flow imaging (CDFI), which is characterized by the same field width in both the far field and the near field [41]. Compared with B-ultrasound for ophthalmology, the display images are clearer and more conducive to the recognition of lesion features by DL.
Our study also has limitations. Although the DL model has achieved ideal classification and recognition results in this study, our study is limited to the automatic recognition of vitreous opacity. For more complex intraocular diseases, such as RD and choroidal detachment, because the data set is still small, the generalization ability of the model and the accuracy of classification and recognition need to be improved. Moreover, considering that CDFI can fully display the blood flow features of eye diseases, we will further study the CDFI images of intraocular lesions. In conclusion, results in this study indicate that an automated classification and recognition DL model can achieve a high accuracy in identifying the vitreous opacity based on CDFI gray scale images and may be a good tool in future clinical practice. The combination of DL technology and ophthalmic ultrasound images not only helps to reduce the misdiagnosis of eye diseases, but also greatly improves the work efficiency of ophthalmic sonographers. At present, there are still many problems in the application of AI in the field of Ophthalmology, but it is believed that with the progress of computer technology and the in-depth research of researchers, AI technology represented by DL will play a more significant role in the field of Ophthalmology research and clinical diagnosis and treatment.