Eye-Piece of Arthroscope

Eye-piece is the proximal end of the Arthroscope that offers the final image to the surgeon or camera, as the case may be. This end is called Eye-piece because the surgeon places his/her eye in front of it to view the image. Hence, such a scope with eye-piece is called as Direct-View Arthroscope. There are other types of scopes that can be connected directly to the camera head of video system. These scopes that come with video sub-assembly are termed as Video Arthroscopes. The eye-piece or the video sub-assembly contains an ocular lens inside it through which the image is actually viewed. The eye-piece also has a post on it that attaches to the light source system components. The light that is generated by the light source is passed through this Light Post which connects to fibre optic strands which run parallel to the long axis of scope. These strands transmit light and through it onto the object of desire. This light post also performs a secondary function of helping the surgeon find his orientation inside the joint. This is because of the fact that the light post is always opposite to/on the same side of the direction of view. The most commonly used scopes have light post on the opposite side of direction of view. Thus, a surgeon only has to look at the direction of light post and he/she can understand that he/she is looking on its opposite side. This helps in orienting himself/herself inside the joint. Note that this orientation is never an issue if 0deg scope is used. For this reason, 0deg scope is very popular among beginners. A 30deg/70deg scope offers much more view just by rotating whereas, with a 0deg scope the surgeon has to point his/her scope directly towards the anatomy of interest.

The Direct-View Arthroscope can be used even when performing Arthroscopy with the help of video system. This is possible because the eye-piece of the direct-view scope can be coupled to camera head using special couplers that make it possible. These couplers are made so as to fit around the eye-piece on one end and to the camera head on the other. These couplers are of two types depending upon which type of camera head they attach to. That means, the couplers have either C-mount screw thread or V-mount screw thread depending upon the type of camera head. Also, the couplers can be focussed so that the surgeons can make fine adjustments to best view the image. Technically, endoscopes have depth focus that ranges from zero to infinity but actually the focus changes as the scope is moved away or closer to the anatomy. While viewing directly, surgeon’s eye makes fine adjustments to maintain clarity in spite of changes in distance between the object and tip. When coupled through couplers, it is done by focussing ring provided on the coupler. In case of Video Arthroscopes, the video sub-assembly carries a focus ring on itself. Endocouplers are commonly available in fixed focal lengths of 25mm and 35mm.

Apart of all the features discussed above, arthroscopes are also available in different types based on the cleaning method they employ. It should be noted that the above-described scopes cannot be autoclaved because of the simple reason that at high temperatures, the adhesive binding the lenses and spacers with the shaft melts and this makes the alignment of the scope faulty. It should be obvious by now that perfect image transmission is a result of perfect alignment of lenses inside the shaft. Any disturbance in alignment causes the image to deteriorate for slightly bad to completely black. To enable autoclaving of scopes, special technique is used whereby the glass of lens and metal of scope are welded together. This welding can withstand high temperatures of autoclave. Also, the tips of autoclavable scopes are Sapphire tipped to make it more rugged.

As is evident, Arthroscopes can be classified in many different ways. They can be classified based on diameter of the shaft, direction of view, method of viewing, length of the shaft and even on the basis of the sterilisation method used for its cleaning. Thus, it becomes obvious that it is not possible to identify any Arthroscope based on only one particular dimension. Typically, an Arthroscope is referred as 4mm, 30deg, Direct-View, Non-Autoclavable Arthroscope. Note that first figure specifies the diameter of shaft while second figure specifies the direction of view. Normally, the length of shaft and FOV are not specified to identify the scope but are mentioned as technical specifications of the scope.