(1)
St. Johns, FL, USA
(2)
Helen Keller Foundation for Research and Education, International Society of Ocular Trauma, Birmingham, AL, USA
(3)
Consultant and Vitreoretinal Surgeon, Milos Eye Hospital, Belgrade, Serbia
(4)
Consultant and Vitreoretinal Surgeon, Zagórskiego Eye Hospital, Cracow, Poland
In Chap. 6, I stated that the VR surgeon is only as good as his nurse. This is almost1 equally true regarding the armamentarium at the surgeon’s disposal.
An entire book could be written about the equipment used by today’s2 VR surgeon. Only a selected few items are discussed here and even those to only a certain extent.
12.1 The Vitrectomy Machine and Its Components3
The key factor determining the quality of the machine is how precisely the surgeon can control what happens inside the eye as a consequence of his maneuvers, i.e., how little traction the probe exerts on the retina during vitreous removal.
12.1.1 The Pump
12.1.1.1 Peristaltic Pump: Flow Control
This is the pump used in the original, early machines; it now lives its renaissance because it allows precisely controlled removal of material from the vitreous cavity, regardless of whether the probe’s port is submerged in fluid or gel (see below, under Venturi pump).
The amount to be removed has an upper limit, set by the surgeon.4 This amount cannot be exceeded unless the settings are changed on the console. This increases the control the surgeon has over his actions, reducing the risk of the probe inadvertently biting into the retina5 when working in its proximity.
12.1.1.2 Venturi Pump6: Vacuum Control
Due to the much lower resistance to flow of fluid (BSS or aqueous in syneresis lacunae; see Sect. 26.1.2) compared to gel vitreous, the machine’s settings must be calibrated to fluid removal.7 This not only slows down the speed of surgery but also makes vitreous removal in the vicinity of (especially detached) retina riskier.
12.1.1.3 Combination Pump (e.g., VacuFlow8)
Combining the advantages of both pumps, this design virtual eliminates flow pulsation, therefore minimizing the risk of retinal injury while allowing fast gel removal.
12.1.2 The Probe
A fair number of characteristics are important.
12.1.2.1 Size/Gauge9
In principle, the smaller the size, the better for the patient; however, this is different for the surgeon; it is true that “size matters.”
A significant downside of smaller-gauge instrumentation is the bending of the tools as the surgeon rotates the eyeball or maneuvers the instruments into certain intraocular positions. The smaller the diameter, the higher the tendency of the tool to bend, which may be frustrating and divert attention away from the task itself (see Sect. 3.7). With experience, the surgeon is able to overcome this shortcoming (or switch to a larger gauge as a last resort).
Despite claims to the contrary by some in the industry and the profession, smaller instrument size does mean slower surgery, and with today’s technology certain tasks can either not be completed at all or are more difficult (such as phacofragmentation, implantation/removal of 5,000 cst silicone oil).
12.1.2.2 Port Location
The more distal the port10, the better (see Fig. 12.1): this makes work in close proximity to the retina safer and more effective (e.g., shaving the vitreous over detached retina). With more distally placed ports, the surgeon relies less on scissors for cutting epiretinal membranes.
Fig. 12.1
Distal, large port on a 23 g vitrectomy probe. See the text for details
12.1.2.3 Port Configuration and Size
A probe with a slit-shaped opening, especially if with a double slit, is able to remove vitreous with increased speed and safety: there is higher fluid flow but decreased fluid/gel acceleration that could drag the retina into the port.
The port size is obviously limited by the diameter (gauge) of the probe, which in turn is one factor in the speed of vitrectomy.11
12.1.2.4 Cut Rate
The probe (vitrectomy machine) should provide for:
Q&A
Q
Is the probe’s cut rate truly so important in VR surgery?
A
Yes. In principle, the higher the cut rate, the less likely that the probe will inadvertently bite into the retina, whether detached or attached. (The duty cycle also plays an important role in the fluid “surge” at the aspiration port.) Conversely, higher cut rates also mean that, in the true sense of the word, less “vitrectomy” than “vitreous shaving” occurs: the tissue is released before the actual cut. Just think of performing lensectomy in the vitreous cavity: the cut rate must be low to avoid the fluid surge pushing the material away from the port (see Sect. 38.2.2).
12.1.2.5 Duty Cycle14
The higher, the better; this reduces the risk of drawing retina to the port. Probes with a port that is always open (continuous flow) are becoming available and greatly reduce the risk of iatrogenic retinal injury.
12.1.2.6 Probe Length
In highly myopic eyes, most probes are unable to reach the posterior retina. The surgeon usually compensates for this by indenting the eyewall, which unfortunately distorts the image. This is an especially important issue if a contact lens for high-resolution viewing is used.
12.1.3 The Light Source/Pipe
The light provided by the vitrectomy machine must be bright enough to allow safe execution of any surgical maneuver. It should be color-adjustable with no harmful UV/IR rays. At least two bulbs should be housed in the console, so if one burns out, the other can be instantly switched on.
Most surgeries are performed with the surgeon holding the light pipe in his nondominant hand. This tool must be:
Shielded (blocking light on one side so as to prevent blinding the surgeon with direct light).16
Wide angle (simultaneous illumination of most of the retina).
There are definite benefits for the surgeon if he can use two active hands (bimanual surgery; see Sect. 4.3), which requires a different concept of lighting, even if the “chandelier” type of illumination has its own disadvantages (see Table 12.1). Certain manufacturers provide a 20 g light pipe equipped with a pic, which allows performing surgery with “one-and-a-half” hands.
Table 12.1
Illumination options for the VR surgeon
Illumination option | Benefits | Disadvantages |
|---|---|---|
Traditional light pipe | The light can be shown from different directions The light pipe can be held in either hand The light pipe can be used as a blunt dissecting instrumenta | The surgeon does not have two working hands |
“Chandelier”b | The surgeon has two working hands | It is difficult, although not impossiblec, to adjust the angle of illumination More than one light may have to be used to provide adequate illumination or avoid shadowing |
Illuminated instruments | There is no need to have separate scleral entries for the light: it is either built into the infusion cannula and/or the working instruments | The issues of shadowing and the inadequacy of lighting are still not completely resolved |
More is found on endoillumination in Chap. 22.
12.1.4 The Infusion Supply
Gravity-fed systems17 are no longer acceptable. Automatic resupply (infusion compensation) is the optimal solution, in which the vitrectomy machine instantly reestablishes and continually maintains the preset IOP value, irrespective of how much material and how fast a material is removed from the eye.
Pearl
The bottle height is about as specific an indicator of the IOP as the tachometer is about the car’s speed. It is only a rough estimate.
12.1.5 The Trocar
It should require a low piercing force to avoid major IOP elevation during insertion.
Its shape should be slit-like to allow spontaneous closure of the scleral incision at the conclusion of surgery.
The one-step system is preferable to the two-step one.
Q&A
Q
What are the disadvantages of the two-step entry system?
A
Both the transconjunctival and the scleral openings may get lost during the switch from the blade to the trocar. This is frustrating, and if the scleral opening is not found by blindly poking under a conjunctiva that bled or is swollen due to the fluid leaking from the vitreous cavity, the conjunctiva may have to be incised.
12.1.6 The Cannula
The cannula should be valved to avoid fluid loss when no instrument is inserted in the cannula. Having a plug in the cannula is better than having neither, but the valve is the ideal option.
Even in the OR’s dark environment, it should be easy for the surgeon to find the entrance of the cannula (so that even a presbyopic surgeon does not need the nurse’s help; see Chap. 6).
The cannula should be color-coded, based on its size (gauge).
12.1.7 System to Inject/Extract Viscous Fluid
The drainage connection for silicone oil removal should be internal, not external: a blunt needle inserted through the cannula into the vitreous cavity, rather than a silicone sleeve that is held over the cannula’s head.
The latter can easily aspirate outside air, not silicone oil, if the fit is not watertight.
The needle should be long enough to reach any remnant silicone oil bubble, even if it is stuck at some distance from the cannula’s internal port. The needle companies provide with their machine is typically too short.
Ideally, the plunger head of the syringe used for oil extraction does not get stuck (making it impossible for the vitrectomy machine to create vacuum and start oil removal).
12.1.8 The Pedal
Its switches (buttons) should be programmable so that they can be set according to the individual surgeon’s preferences.
It should allow for linear, dual linear, and “3D” modes (see Sect. 16.3).
Having a wireless pedal avoids the accumulation of wires/cables under the surgeon’s feet.
One of the most crucial functions of the pedal is the “backflush” option, similar to that with the flute needle (see Sect. 13.2.2.1): if the retina is inadvertently caught in the probe’s port, the surgeon must be able, with a readily available button, to immediately reverse the flow and blow the retina away.
12.1.9 Integrated Laser20
It is very important for the laser probe to be curved. There is no location in the eye that cannot be reached with a curved probe; conversely, some areas are risky or impossible to reach with a straight one; a straight probe prevents doing proper endolaser cerclage21 in the phakic eye.
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