(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
The VR surgeon is exposed to various types of feedback.
Tactile feedback is occasionally felt during intravitreal work, such as from a strong subretinal strand, but this has an insignificant role in tactical decision-making.1 Pushing an instrument against the sclera (see Sect. 33.3) is also instantly felt by the surgeon.
Audible feedback can be heard when the laser power is too high and the tissue “pops.” Such a strong laser delivery is to be avoided because it can cause retinal bleeding or a rupture in Bruch’s membrane, with the risk of secondary neovascularization.
Olfactory feedback is possible if a very significant bleeding occurs on the ocular surface.
Pearl
All of the VR surgeon’s tactical, and some of his strategic, decisions are based on visual feedback: appreciating the default situation and detecting the tissue reaction to his actions.
This all means that virtually the only type of feedback the VR surgeon2 has of the consequences of his actions is visual.
Maintaining the clearest view possible throughout the entire operation is thus crucially important for the VR surgeon. There are many elements to this puzzle, most of which is discussed below; this helps the surgeon find and fight the cause of suboptimal image clarity.3
25.1 External Factors4
25.1.1 The Microscope
Make sure that:
You have adequate but not-more-than-minimally-necessary brightness.
All optical surfaces are clean.
There is no fogging: condensation on the eyepiece because the surgeon is sweating5 or the mask allows the exhaled air to be streamed onto it. For this reason, I wear the mask only over my mouth, not over my nose; another option is to tape it to the bridge of the nose.
Adjust the focus to the needs of the video camera; then readjust the eyepieces so that each of your eyes has maximal sharpness (see Sect. 12.4).
25.1.2 The Contact Lens
Make sure that:
The surface is not scratched.
If the lens is reusable, it is completely transparent.8
The lens is properly centered on the cornea. If the lens slides, the image may get distorted and the visual field reduced.
If the area to observe is slightly off-center, move the contact lens in the opposite direction of the area desired to be viewed.9
25.1.3 The Corneal Surface
Make sure that:
The corneal epithelium is not edematous.
If it is, placing a piece of cotton saturated with 40% glucose is sometimes able to reduce the edema. This may also help with stromal edema.
If the edema persists, the epithelium may have to be scraped (see Table 45.3).
In the presence of edema, all intraocular instruments look “foggy”, with ill-defined borders.
The visco is evenly distributed10 and covers the entire surface.
There are no air bubbles, however small, on the visco surface.
Q&A
Q
What is the correct technique of scraping the corneal epithelium?
A
Use the hockey knife, which is ideally angled and has just enough sharpness. Start from the corneal epicenter and move in a centrifugal direction first. Once you have a small denuded area, move toward it from all directions – avoid returning to areas that already have been scraped. Do not wet the cornea until you are done – it is easier to see the denuded area if it is dry. Do not scrape more than you need to, and avoid the corneal margin (close to the limbus). Do not leave loose epithelium behind.
Pearl
Air bubbles in the visual axis can cause major interference. The more anterior the bubble, the more it interferes with visualization: the same size of air bubble is more bothersome if it is on the surface of the visco than behind the lens capsule.
The cornea rapidly dries: this is why we blink every ~5 s and why it is highly advisable to use visco during vitrectomy. Requiring the nurse to “squirt” the cornea ever so often is cumbersome, may cause fluid droplets to splash back and smear the BIOM front lens, and increases the risk of corneal edema, which in turn may require scraping.
25.1.4 The Corneal Stroma
The following abnormalities can lead to decreased light transmission.
Stromal edema due to a posteriorly still open wound.
Corneal wounds of the injured eye should be closed with full-thickness sutures (see Sect. 63.4).
Elevated IOP.
The high pressure can lead to not only epithelial but also stromal edema. If the edema is not long standing and the IOP is normalized, the cornea may “dry out” rather fast.
Low IOP may cause folds in Descemet’s membrane. Inflating the AC with visco can be helpful, but this requires the presence of the crystalline or artificial lens with intact zonules.
Q&A
Q
In eyes with severe hyphema, at what IOP should the blood be evacuated to prevent corneal bloodstaining?
A
There is no magic number regarding the IOP value as the risk also depends on the duration of the pressure elevation as well as on the “tolerance” of the individual patient’s endothelium. My general suggestion is to remove the blood from the AC if, even on maximal topical/systemic antiglaucomatous therapy, the IOP exceeds 30 mmHg for 3 days. Err on the side of being too “aggressive.”
25.2 Internal Factors
25.2.1 AC
Several materials can interfere with light transmission:
25.2.2 Pupil
The BIOM represents a huge advantage over the contact lens by allowing adequate visualization of the retina even if the pupil is small. Still, a wide pupil has tangible benefits for the surgeon. There are several methods to achieve pupil dilation on the operating table if the preoperative medication has been ineffective or the drugs used during general anesthesia caused secondary miosis.
25.2.2.1 Mechanical Forces Preventing Pupil Dilation
A fine retropupillary membrane or fibrin may be the culprit. In such cases, gentle pulling on the iris margin with forceps (see Fig. 48.1c, d) or blunt dissection with a spatula may help. The surgeon must carefully observe how the tissues behave to avoid tearing the iris or rupturing the anterior lens capsule if posterior synechia is present, and switch to a sharp instrument if there is a risk.
A retroiridal fibrinous membrane is dangerous to forcefully pull on since the surgeon has no visual feedback about the consequences of his action until it may be too late.
If fresh posterior synechia are present (see Sect. 39.4), usually a blunt spatula is utilized to break it. However, especially after trauma, it may be preferable to use scissors and cut the tissue responsible, sometimes preceded by endodiathermy12 to prevent bleeding.13 Limited amounts of visco can be injected to create space for the scissors between the iris and the capsule or control the bleeding.
Pearl
Never inject visco under the iris in order to try to break posterior synechia or separate a fibrinous membrane from the iris back surface: by doing so, you simply give up control over events (see Sect. 3.2). The visco will go wherever the resistance to its flow is the weakest, tearing some tissue (where it wants to, not where you would prefer it to) or disappear posteriorly.
25.2.2.2 Intracameral Adrenalin or Visco
If it is not synechia or a membrane (see above) that prevents iris dilation, intracameral adrenalin14 usually works. Repeated injections of the drug, however, do not help: the effect is typically one time. In older patients adrenalin occasionally constricts, rather than dilates, the pupil.
Visco may dilate the pupil and keep it so, but may also interfere with visualization (see above, Sect. 25.2.1).
25.2.2.3 Iris Retractors15
These are very potent weapons to widen the pupil and keep it wide throughout the case, and they can be used even in the phakic eye. A few caveats are worth mentioning.
The angle at which you created the paracentesis with the needle16 is crucially important. The retractor is too delicate to allow substantial modification to its trajectory once you pushed it past the intracorneal channel you just prepared.
When you create the channel, keep in mind the parallaxis phenomenon. Viewing from above, the instrument inside the AC gives the false impression that the tool is at a shallower angle (closer to the cornea) that it really is. Compensate for this when deciding the angle of penetration.
Do not use toothed forceps to grab the retractors.
Upon insertion, hold the retractor close to its hook (the working end) to avoid bending it. Never grab the hook itself.
Keep the disc on the retractor close to the proximal (nonworking) tip of the retractor, never at the distal end: not all retractor types allow reinsertion of the shaft into the disc if it has been accidentally pulled off.
Save time by creating all17 paracenteses first, then place all retractors on the conjunctiva, and finally insert them.18
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