Illumination |
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22.1The Light Pipe
Typically held in the surgeon’s nondominant hand, this light source is a very versatile one. The surgeon can influence the amount of light reaching the retina by changing the setting on the vitrectomy machine but also by changing the distance between the light pipe and the target area.1 The distance also influences the field of illumination. The surgeon can also change the angle of the light emission,2 enhancing the visibility of certain structures while “hiding” others. When using the BIOM, a wideangle light pipe should be used.
The light pipe can be employed in three basic ways.
•Direct illumination: the light is shone directly on the area where the surgeon is working.
•Indirect3 illumination: the light is shone behind or in front of the actual work area.
•Transillumination: the surgeon performs the scleral indentation with the light pipe itself.4
1The intensity of the illumination is proportional to the inverse square of the distance from the light source.
2A fine epiretinal membrane may be invisible under direct light but very visible with indirect light (see below); this can mimic the effect of the slit illumination.
3Also called retroillumination.
4This may be helpful in identifying a retinal break.
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During the operation the surgeon’s attention is focused on the actions executed by his dominant hand; moving and monitoring the position of the light pipe are rather automated.
•The less experienced the surgeon, the closer he tends to hold the light pipe to the retina, dramatically increasing the risk of phototoxicity.5
–It is not intuitive to keep the light pipe pulled back, close to the cannula. The light should be held as far away from the retina as consistent with stilladequate illumination. The surgeon must consciously monitor the light pipe’s position and hold it at a safe distance.
Q&A
QHow can the surgeon ensure that he is keeping the light pipe far from the retina?
ABy constantly reminding himself to do it – and by asking his nurse to do the same.
–The power of the light on the vitrectomy machine should also be kept at the minimum level necessary to allow proper illumination; do not set the machine so that it is always on full power.
Pearl
Especially with older video cameras, there may a conflict between the needs of the surgeon (who can usually get by with less light) and the camera (which needs more light for a decent recording). Whatever the compromise, the safety of the patient is the decisive factor.
•During much of vitreous removal the surgeon works under partial retroillumination: the light is directed slightly anterior or posterior to the actual plane of the probe’s tip. Some of the light he utilizes is reflected back from the eyewall (retina, choroid, even sclera), not the vitreous itself.
–When vitrectomy is done in the periphery on the side where the light pipe is inserted, directly illuminating the vitreous is great to visualize it – but completely hides the retina underneath it. Safety demands that the surgeon alternates between direct and indirect illumination in this scenario.
•Direct illumination is used for vitreous removal some of the time and for retinal work most of the time (addressing membranes, performing laser etc.).
–When the retina is directly illuminated, the working distance must be increased (see above).
5 At a brightness of 8 lm, increasing the distance the light pipe is held from the retina from 4 to 8 mm multiplies (3–4×) the time needed to cause phototoxicity.
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•During fine macular work the light should not be shone directly onto the macula itself. This is mostly because of the risk of phototoxicity, but also because the reflected light may be bothersome. I try to direct the light, holding it as far from the retina as possible, toward the perimacular area.
–Even if the surgeon must illuminate the macular area directly, he must avoid shining the light onto the same area for more than a few seconds at a time.
•Under air, visibility worsens (see Sect. 31.2), even if the BIOM front lens is adjusted (see Table 16.5).
–Fine details become impossible to discern; what was very obvious before is now invisible.
–There is significant light reflection from the interface between air bubble and BSS/retina. It takes some time for the surgeon to find the most acceptable angle and distance of illumination,6 and even that may be suboptimal.
•Although most of the time the light pipe is held in the surgeon’s nondominant hand, under certain circumstances it has be switched over to the dominant hand. This switch may be mandated by the task (e.g., laser cerclage, 360° vitrectomy
a |
b |
Fig. 22.1 Light reflected in the air-filled eye. (a) If the light is shone across the eye, the angle of the reflected light is such that it blinds the surgeon. (b) If the light pipe is moved onto the same side of the eye where the illuminated area is, the reflected light does not directly reach the surgeon’s eye. This vastly improves his visibility
6 Sometimes having to switch hands: the glare is worse, for instance, if the light is shone from the nasal side toward the temporal retina (see Fig. 22.1).
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at the vitreous base in a phakic eye) or because it offers better visualization of certain structures (e.g., determining the size of an EMP, working under air on the opposite side of the light pipe; see above).7
22.2Chandelier Systems8
The light is emitted from a device fixed at the sclerotomy. The options are the following:
•Incorporating the light into the infusion cannula.
•Stand-alone (independent; the much more commonly used version). It comes in a wide variety (single or dual fiber, twin, torpedo etc.).
Each of these devices is a stationary one, but they all allow some manipulation since the nurse can grab the extraocular portion (cable, tubing) and change the main direction of the illumination.
Regardless of type, these systems allow bimanual surgery. Use of a chandelier means that the light is much further away from the retina than it would be with the light pipe system, thereby greatly reducing the risk of phototoxicity – but at the cost of other potential disadvantages.
•Shadows cast by both working instruments.
•Light reflex (scatter, glare), which is more difficult to avoid than with a light pipe.
–Using multiple light sources may compensate for these shortcomings, but, obviously, this requires using multiple sclerotomies, however small they are.
•The light fixture may be too far from the posterior retina to provide ideal illumination for fine work.
22.3Light Built into the Handheld Instruments
The advantage of this option is that there is always light where the surgeon works – but the light may be too close to the retina for safety and comfort. Glare is another issue, as is shadowing. For these reasons, this option is rarely used nowadays.
7Which, naturally, means that the surgeon may be forced to use his nondominant hand for certain maneuvers; hence the need for at least some dexterity with this hand as well.
8May also be used in combination with each other and/or the light pipe.
The Checklist Before the First Cut |
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Table 23.1 provides a brief summary of the items the surgeon should check before the onset of the actual operation. As mentioned before, this list does not mean that before each surgery every item on it must be check-marked such as a pilot would do before flying the airplane. Much of the preparation becomes routine with time; however, the checklist is necessary initially to establish that routine.
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Table 23.1 The previtrectomy checklist |
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Item |
Comment |
More details in |
Surgical plan |
If the case is of average difficulty, the plan |
Sect. 3.1 |
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can be finalized just prior to the |
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operation. If it is expected to be more |
|
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complex and difficult, the plan is best |
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formulated the day before |
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Arrangement of the OR |
All major equipment, including the operating |
Chap. 16 |
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table, are in their desired position |
|
All cables and tubings are |
This includes the cables of the microscope |
Chap. 16 |
properly and securely |
and vitrectomy pedals (they are not |
|
connected; those linking the |
caught underneath the pedals themselves |
|
vitrectomy machine to the |
or the wheels of the surgeon’s chair)a |
|
tools used by the surgeon are |
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also fixed to the nurse’s table |
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so that they will not get in the |
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surgeon’s view |
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The patient is properly prepared |
It is impossible to be too cautious about |
Chap. 16 |
(anesthesia, medications etc.) |
this |
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and the correct eye marked for |
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surgery |
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Programming of the vitrectomy |
If necessary, changed from the standard |
Chap. 12, |
machine |
according to the expected actual |
Sect. 16.3 |
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situation |
|
Checking that all necessary |
Including all from the microscope to the |
Chap. 16 |
equipment, tools, and material |
intravitreal forceps. Especially crucial |
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are available and functioning |
for the surgeon is that he tests the |
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vitrectomy probe (in addition to the |
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testing [priming] done by the vitrectomy |
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machine). A stuck guillotine blade can |
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cause serious damage (aspiration without |
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cutting), and discovering it inside in the |
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vitreous cavity means it is too late |
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The laser filter must be attached to the |
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microscope but switched off/out until |
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neededb |
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Proper comfort for the patient |
Comfortably lying while maintaining a head |
Sect. 16.6 |
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position that is ideal for the surgeon’s |
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access to all of the vitreous cavity |
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Adjusting the microscope and the |
Posture for the surgeon (height of the |
Sect. 16.7 |
surgeon’s chair according to |
chair, distance from the operating table |
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the actual patient |
etc.). The chair’s wheels are to be locked |
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so that the chair cannot move as the |
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surgeon’s feet move |
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Initializing the BIOMc |
To ensure that the focus will need no |
Sect. 16.5 |
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readjusting unless F-A-X is required |
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Final adjustment of the view |
The BIOM lens at a distance of ~2 mm |
Table 16.3 |
through the microscope |
from the visco-coated corneal surface |
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and at a low zoom |
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aThis is why wireless pedals are so useful.
bOtherwise the colors inside the vitreous cavity are not realistic – neither for the surgeon nor for the video camera.
cObviously, this requires the light pipe to be inserted into the vitreous cavity.