The viewing angle of an endoscope refers to the angle between the optical axis of the lens and the main axis of the lens body. Due to the complex structure of the human body and the various scenarios in which endoscopes are used, endoscopes can be designed with different viewing angles to meet diagnostic and therapeutic needs. Field of view reflects the size of objects observed within the visual field of the endoscope. There are vertex field of view, entrance pupil field of view, and exit pupil field of view. The size of the field of view determines the range of observation of the endoscope at the working distance. If the observation range is too large, interference, shadows, and ghosting may occur in the field of vision, making medical observation difficult; if the observation range is too small, it may not be possible to fully understand the lesion area and its surroundings, resulting in unsystematic and unscientific diagnostic results. Therefore, the choice of field of view and viewing angle is an important basis for clinical workers based on actual usage requirements and application environment when selecting a rigid endoscope.
The angular resolution of an endoscope is a key optical parameter. The size of the angular resolution is directly related to the resolution of details on the endoscope. If the angular resolution is too small, the tissue characteristics of the observation site and the details of the lesion area cannot be clearly resolved, and the operator cannot achieve the corresponding clinical effects of the endoscope. At the same time, a resolution that is too small causes the edge of the field of view to be blurred, thus reducing the observing range of the optical lens. Although there are no specific requirements for angular resolution in the standards, the manufacturer should stipulate the limitation value according to the requirements of the application environment, and the operator should choose an endoscope with suitable angular resolution according to clinical needs.
The complex structure of the internal organs in the human body requires endoscopes not only to be able to clearly observe objects at the specified optical working distance, but also to observe the lesion area clearly within a certain range of optical working distance, because some structural parts have large gradient variations. This range of work where the lesion can be observed clearly is called the effective depth of field of the endoscope. The effective depth of field is determined by the manufacturer based on the actual situation of the lenses and the application environment, and is specified in the technical documentation. The lack of an effective depth of field must also be declared in the technical documentation.
Although the field quality of view of a rigid endoscope is a more direct means of inspection, it is also a prerequisite for ensuring the clinical effects of endoscopy. Only when the endoscope field of view is complete, without interference such as ghosting, impurities, or bubbles, can the other optical parameters of the endoscope be meaningful.
Color resolution and restoration reflect the accuracy of the endoscope's color resolution and its ability to restore the true color of tissue structures. The colors of tissues in the human body are very similar, and the color gradient changes between adjacent sites are not obvious. If the color resolution of the endoscope is insufficient, it is easy to confuse diagnostic results, and increase diagnostic and surgical risks.
The endoscope is mainly composed of an optical illumination system and an imaging system. The illumination system is composed of optical fibers. The complete optical imaging system consists of three main systems: objective lens system, imaging system, and eyepiece system. The position, shape, and quality of any optical component in the entire optical system can affect the optical performance by changing the optical path. High temperature, high pressure, chemical reagents, and so on, used for sterilization or disinfection, may cause changes in the optical path of the endoscope, so it is necessary to perform sterilization or disinfection tests in accordance with the manufacturer's random file regulations on optical rigid endoscopes and examine the changes in their output light flux. The standard requires that the rate of change be below 20%.