Instruments, Tools, and Their Use

Fig. 13.1 Comparison between the image seen through a high-resolution macula lens and the contact lens. (a) A large field and decent resolution with the BIOM high-resolution macula lens is achieved in this patient who had ICG-staining before removing the ILM for a macular hole. The EMP causes a “negative staining,” mostly in the vicinity of the hole. (b) At the same magnification of the microscope in the same patient, the field is noticeably smaller, but more details are visible when viewed through the plano-concave macular contact lens

Anterior chamber

a

b

c

Fig. 13.2 Schematic representation of the use of a fulcrum-type scissors. The distance of the fulcrum’s position (dark circle) from the wound (patterned lines) (the distance of the object to be cut from the wound is also important) determines the length of the incision needed to operate the instrument. The wound is the smallest when the fulcrum itself is at the incision (b). When the fulcrum remains outside the eye (a), the incision must be longer, while the longest incision is required with the fulcrum being in the AC itself (c). This is the most common clinical scenario (because most objects are further away from the point of entry than the length of the blade), demonstrating the advantage of VR microinstruments, where the wound length is the same regardless of how far away the tool (i.e., the object to be cut) is inside the eye (see Fig. 13.3 for the single exception to this rule). The black lines on the right of the image show the required wound length

Vitrectomy hand instruments can be classified into the following categories.

•Squeezable tools. It is the squeezing of a handle that initiates the action. Forceps and scissors6 belong to this category.

•Non-squeezable tools. The surgeon’s hand manipulates these stationary tools in toto, without the need for the fingers to separately activate parts of them. Blades, needles, spatulas, and pics belong to this category.

•Hybrid tools. Either minor finger activation (flute needle) or a one-time manipulation (pushing out retractable tools such as a magnet, laser probe, or scraper) is needed.

This distinction is more important for safety than whether the instrument is sharp or blunt (see below): squeezable tools require more dexterity since their operation demands much more complex maneuvers. The use of such instruments underlines the need for firm wrist support (see Sect. 16.2.1) to avoid inadvertent movements of the instrument’s tip, which would risk injuring the retina.7

There is a paradox regarding the use of sharp vs blunt instruments.8

Q&A

QHow can a blunt instrument (such as a spatula) be less safe in manipulating epiretinal membranes than a sharp tool (such as scissors)?

AThe answer lies in what was described under Sect. 3.2: control by the surgeon. Separation between two tissues is determined by the strength of two forces: adhesion (attachment of one tissue to another) and cohesion (tensile strength of a single tissue – how easily it tears). If the adhesion is stronger and a blunt tool is used for separation, the tissue tears in the area where its cohesion is the weakest. The surgeon’s control over what happens is rather limited. With the use of a sharp instrument, it is the surgeon who decides where to separate (cut the connection between) the two tissues, perhaps more difficult technically, but certainly more controlled (see Sect. 39.3).

6Certain vitrectomy machines allow the blades to be operated by the footpedal, without the need for the surgeon to squeeze the handle.

7Remember the obvious: you are manipulating the instrument extraocularly to achieve an effect intraocularly. You have visual feedback of the latter but only tactile feedback of the former. The less you need to manipulate the extraocular part, the better.

8A careful chef will have a smaller chance of cutting his fingers when slicing meat with a sharp than with a blunt knife: the blunt blade requires more force to be effective, thereby reducing the chef’s control over the process.

13.2.1 Squeezable Instruments9

13.2.1.1 General Concepts of Working with Squeezable Instruments

How the instrument reacts to the surgeon’s squeezing action differs according to the design of the tool, and the surgeon must understand this so that he can use the instrument in the most optimal way. There are two main design types, depending on what happens upon squeezing the handle.10

•The outer shaft forces two metal rods together; the movement of the two (occasionally three) endpieces is identical11 (forceps, most scissors; see Fig. 13.3a).

•Only one of the endpieces is mobile; the other one is stationary (vertical scissors; see Fig. 13.3b).

13.2.1.2 The Handle

•Choose a handle with a short travel route: on Fig. 13.4 “X” should not be more than 2 mm. Increasing the distance results in decreasing stability.

a

b

Fig. 13.3 Schematic representation of the workings of squeezable instruments. (a) The outside shaft slides forward (double arrow), forcing the jaws to close (single arrows). In the “fully open” position, the distance between the rods (or blades, depending on the design) exceeds the diameter of the outer shaft. This may cause difficulty when an object is too close to the small wound so that the instrument cannot be fully opened (this is the exception referred to in Fig. 13.2). A classic clinical example is a transcorneal iris suture (McCannel type), where the thread needs to be “fished out” from the AC through a paracentesis: the surgeon is often forced to either use a hook instead of a VR forceps or enlarge the paracentesis. (b) The outside tube slides forward (double arrow), but only the proximal blade moves (singular arrow). With this design, any maneuver is doable, irrespective of wound length or the distance of the target from it (in real life, unlike on the image, the tip of the blade does not reach beyond the imaginary extension of the shaft – otherwise, the tool cannot be inserted through the same size of cannula)

9The design of the handle (“squeezability”) makes a huge difference in how user-friendly they are.

10The default position of the tool is “open”: it is the surgeon’s action that forces the tool to “close.” There are also tools that work with “reverse” action: the default option is the “closed” position.

11They move simultaneously, along mirrored paths and equal distances – even if one blade is longer than the other.

–The longer the physical distance the surgeon’s fingers must cover to move the forceps jaws from “fully open” to “fully closed,” the more the risk of the jaws making inadvertent movement. This can cause grabbing a membrane too deep (retinal damage) or too superficial (no purchase).12

•The resistance to squeezing (i.e., the force needed to operate the instrument; see Sect. 4.1) is also important. Ideally, there is minimal resistance13 – and it must also be a smooth, even one.

•A handle that can be operated in a circular fashion (see Fig. 13.5) means that the surgeon is able to rotate the tool and easily maneuver the jaws/blades into the most optimal position.14

Fig. 13.5 Different handle designs on a permanent and a disposable ILM forceps. The permanent one (above) has two semicircles to squeeze; these have minimal resistance and a short travel distance. The only disadvantage is that occasionally the position of the semicircles and the grasping plane of the jaws are not aligned as demanded by the task, forcing the surgeon into holding the forceps in a somewhat awkward position. The disposable forceps (below) eliminates this problem because its circular handle can be squeezed with the same ease, regardless of the position of the jaws. However, the handle has a bit longer travel distance and, more importantly, requires a greater force of squeezing. The undesirable consequence of this is obvious if the forceps needs to be used over extended periods (an ILM that easily tears and needs to be regrasped frequently): the surgeon who had no tremor initially may develop fine shaking toward the end of the peeling

12To compensate for this, the surgeon should squeeze the handle before engaging the membrane. The aperture (distance between the blades/jaws) must be slightly larger than the tissue to be attacked. This is, however, still not an ideal solution since the fingers must now simultaneously fulfill two functions: squeezing the handle plus positioning the jaws on the target tissue. If the ILM forceps has a default opening of 1 mm, squeeze it by ~80% before any grabbing attempt.

13Think about a driver and the resistance of the gas pedal in the car. On a long trip, it is great to have a pedal with high resistance because the driver can simply rest his foot on it. When doing a fine maneuver such as starting to move a stopped car, however, and this is what describes the forceps analogy, the driver wants minimal resistance so that the car transitions from “stop to go” smoothly and the engine neither dies nor revs.

14The alternative is a reusable handle that allows the rotation of the jaws/blades into the ideal position before the handle is actuated (see Sect. 44.2.2).