The initial step is to introduce the endoscope through a standard sclerotomy9 to determine the ideal sites for the infusion cannula, the working instruments, such as the vitrectomy probe, and, possibly, the endoscope itself.10
The initial sclerotomy for the endoscope should be at no more than 3 mm from the limbus. This reduces, although does not eliminate, the risk of iatrogenic retinal injury during endoscope introduction.
8 This is significant when tissues with high resistance, such as mature cyclitic membranes, are encountered; tearing of the underlying ocular tissues (e.g., ciliary epithelium, iris root) is a real risk. With advances in technology, bimanual surgery will likely become possible in the future, making these maneuvers easier and less risky.
9 Preoperative B-scan ultrasonography, the UBM, or transcleral illumination may help identify the most optimal site for the initial entry (see Chap. 2.16).
10 i.e., if it is found that the initial entry site is not ideal.
• If the eye is hypotonous, intravitreal injection of BSS or air11 can restore the IOP and make endoscope insertion easier/2
Further difficulties" and important issues include:
• Loss of visibility of the normal anatomical landmarks
• Detachment of the ciliary body, choroid, and/or retina
• Anterior displacement of the vitreous base/retina
• Massive fresh hemorrhage that interferes with or completely blocks visualization
• A long (6 or 7 mm) infusion cannula should be used; it must be sharp" since choroidal, ciliary body, and retinal detachment, and thick, elastic cyclitic membranes adherent to the pars plana are not uncommon (Fig. 2.20.3). Self-retaining cannulas require special attention so they do not get expelled. ^
• Loss of view intraoperatively. If blood covers the probe's tip, the endoscope should be withdrawn and cleaned. This may have to be done repeatedly, if necessary.
• Number of sclerotomies. If the eye is phakic and the lens is to be preserved, a fourth sclerotomy may be needed to avoid lens injury. This is especially important if extensive manipulations at the vitreous base are required to prevent or treat an anterior PVR."
• Core vitreous. This is the initial step of vitrectomy. The direction of vitreous removal is antero-posterior (see Chap. 2.9), and it usually starts in the visual axis. In a severely traumatized eye, even without a purulent infection, it may difficult, if not impossible, to distinguish between a
11 This is a good advice for any eye with low IOP. The maneuver nevertheless requires experience so that the needle does not inflict further tissue damage and the fluid or air is not injected under the retina.
12 If visibility allows, an AC maintainer can also be used.
13 These are not necessarily specific to endoscopy.
14 The track created with the MVR blade can rapidly close due to tissue elasticity.
15 The risk is higher during EAV than in conventional vitrectomy because of the rotation of the eye during peeling at the vitreous base.
16 Obviously, complete scar removal takes precedence of lens preservation (see Chap. 2.9).
detached and necrotic retina and layers of vitreous tainted with streaks of blood and coated with fibrin (see Chaps. 2.12, 2.17). Preoperative ultrasonography may have been unfeasible, or yielded erroneous (see Fig. 1.9.5) or undecipherable information. With its high magnification, the endoscope has a good chance of allowing recognition of the retina17 before it is penetrated.
• Posterior cortical vitreous. Its detachment and removal is crucially important and represents the second step of vitrectomy. Separation may be aided by PFCL use. The endoscope-provided control increases safety and efficacy. The surgeon should also be familiar with the type, parameters, and settings of his vitrectomy machine. To avoid undue traction on the retina, a machine with flow control^ is preferred; when working in close proximity to the retina, the flow should be low (1-2 ml/m) and the cutting speed set at below 15 cpm or even "cut by cut."
• Peripheral vitreous. The last phase of vitrectomy is to remove as much of the vitreous, hemorrhage, fibrin, membranes, or scar tissue in the periphery as possible. Avulsion of the anterior vitreous base or ciliary detachment is not uncommon: the endoscopic hyaloido-capsulo-zonulo-ciliary dissection must therefore be performed cautiously to avoid injuring the zonular system or the ciliary epithelium. One of the surgeon's hands holds the endoscope that doubles as a light pipe while the other hand operates the usual vitrectomy instruments. A complete, 360° job can be accomplished by utilizing all sclerotomies and repeated switching of the hands as needed. The endoscope also allows complete cleansing of the sclerotomies, assuring that no tissue remains or gets incarcerated. The vitrectomy machine's settings may have to be similar to those described above. Helpful additional tricks include the following: - Blood, accumulated between various tissues, can be used as a marker to help delineating boundaries and cleavage plans, thus facilitating dissection.
17 Nevertheless, this may remain a challenge even for the experienced surgeon.
18 i.e., using a peristaltic, not Venturi, pump.
- Tissues and membranes located superiorly19 can be dissected under direct visualization by placing the endoscope in an inferior sclerotomy, or the area is approached tangentially by alternating the endoscope between the two superior sclerotomies.
- The membranes may be so thick and elastic as to allow true dissection at the level of the Wieger ligament or ciliary epithelium only if a flow-control vitrectomy machine is used. The cut rate and flow should be adapted to each individual case.
- Air or PFCL is often necessary to exert counter pressure on tissues to avoid iatrogenic injury to the ciliary epithelium or retina20 while performing complete dissection (see Chap. 2.9). The endoscope provides unique, high-magnification visual feedback.
- For the thick proliferative membranes the flow may have to be tripled to allow relieving at least some of the circumferential traction. The endoscope's high magnification and access to any intraocular space offers the best chance of freeing the ciliary body from cyclitic membranes and subsequent hypotony/phthisis (see Chap. 2.19). Radial cuts into the membranes may be the only option if the en-doscope-relayed image shows that dissection is impossible. Radial cuts can also alleviate the need for a prophylactic encircling scleral buckle.
In addition to removal of the vitreous and peripheral membranes, EAV also allows performing virtually the entire arsenal of intravitreal maneuvers, including:
• Removal of EMPs and the ILM21
• Removal of subretinal membranes and blood
20 Especially if the retina is detached.
21 Staining of the ILM is necessary.
• Cryopexy22, laser, diathermy, retinotomy, and retinectomy
• Exchanges between BSS, air/gas, silicone oil, PFCL as well as removal of these substances, even if trapped subretinally
• consider endoscopy/EAV in severely traumatized eyes if the cornea (AC, lens, pupil) interferes with visualization of the posterior segment
• create as many sclerotomies as necessary to do a complete job and avoid injuring a lens that would otherwise be preserved
• be thorough with the removal of vitreous, blood, fibrin, inflammatory debris, etc.
• make full use of the opportunity the endoscope offers to completely clean the vitreous base and ciliary body
• use the endoscope if you are inexperienced in both EAV and the vitrectomy management of severely injured eyes
• limit endoscope use to diagnostic purposes
• try to perform surgery on cases that would benefit from bimanual surgery
• operate blindly
Endoscopy provides a means to "bypass" a nontransparent anterior segment and thus allow for timely vitrectomy. The endoscope is not just a diagnostic tool: it can be utilized to perform virtually any and all maneuvers the vitreoretinal surgeon using the microscope would carry out. Endoscopy-assisted vitrectomy (EAV) requires the ocular traumatology expert to also be experienced in every aspect of endoscope use.
22 Cryopexy is to be avoided because of its risks of inducing PVR (see Chap. 2.9).
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