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

25.1External 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).

25.1.1.1 The BIOM6

Make sure that:

•All optical surfaces have been cleaned.

•Both BIOM lenses have cooled off after sterilization (see Table 16.5).7

•All parts have been properly assembled and fixed onto the microscope.

•The focus has been set.

•The knob for the SDI, if it is to be set manually, is turned all the way.

25.1.2 The Contact Lens

Make sure that:

•The surface is not scratched.

•If the lens is reusable, it is completely transparent.8

3With most items on this list, the solution to the problem is obvious; where it is not, a solution is proposed.

4In addition to all that is listed here, be sure that the patient’s head is properly positioned (see

Fig. 16.5a).

5Perspiration can occur even when the OR temperature is low (see Sect. 16.10). This, incidentally, enhances the condensation risk.

6See more in Sect. 16.5.

7This problem can be eliminated by the disposable BIOM.

8Repeated sterilization can cause irreversible reduction in light transmission.

•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 illdefined 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.

9Move the lens toward 6 o’clock if what you want to increase the field of view toward 12 o’clock.

10A surface-coating visco is preferable; if a cohesive visco (e.g., Healon) is used, a drop of BSS on its surface helps smoothen it.