|Create main wound with keratome|
|Stabilize the eye (with Thornton ring, cotton tip, .12 forceps, or other)|
|Corneal main wound creation with a 2.75mm keratome blade, and the eye stabilized with a Thornton fixation ring. Note manipulation of the blade heel to ensure proper entry.|
A well-constructed, self-sealing, corneal main wound is critical in maintaining chamber stability, providing for adequate instrument maneuverability, and preventing post-operative wound leaks. Attention is drawn to the following points.
The non-dominant hand should stabilize the eye, using one of a variety of available instruments (see discussion in the “Paracentesis” section). Additionally, given the presence of the paracentesis, some surgeons use .12 forceps to gently grab the anterior lip of the paracentesis for stabilization, although this maneuver may stretch the side port wound and lead to post-operative leakage if not performed with caution.
The main wound must be wide enough to allow passage of the phacoemulsification tip and subsequent folded intraocular lens while narrow enough to prevent excess fluid egress around the tip during surgery. We currently use a 2.75mm (which specifies blade, and therefore wound, width) disposable metal keratome for coaxial phacoemulsification. Other surgeons prefer smaller or larger blade widths depending upon available instrumentation such as microcoaxial phacoemulsification setups. Other surgeons also prefer diamond blades, which may produce cleaner tissue planes but introduce higher initial cost and subsequent maintenance requirements.
As in paracentesis creation, the main wound incision needs to be placed appropriately to provide comfortable access and mobility for subsequent instrument manipulation. Closely spaced wounds should be avoided to prevent “oar locking”, and we thus typically space the main wound about 90 degrees away from the paracentesis.
There are many variations on corneal main wound creation, including the location of entry (scleral, limbal, or true clear corneal) and architecture (with or without initial groove). Some surgeons prefer scleral tunnel incisions, which will not be discussed here. The initial groove can be of varying depths, or not performed at all. Our preference is typically for grooveless, limbal corneal incisions.
After stabilizing the eye with the non-dominant hand, the keratome blade is introduced at the near corneal limbus with the dominant hand. The blade is angled parallel to the surface of the eye, with the blade heel down to point the blade tip slightly upwards to match the orientation of the stromal lamellae. The blade should be advanced to produce a 2mm long wound. A short wound will increase the likelihood of wound leakage both during the surgery (promoting a shallow chamber) and after the surgery (possibly necessitating sutured closure). An excessively long wound will make instrument manipulation difficult with the introduction of corneal striae during surgery, possibly limiting visibility as well. Of note, a dull blade or an inadequately pressurized eye (ie, too little viscoelastic) will promote longer wounds so attention should be given to these factors.
Once an adequate wound length is achieved, the heel of the blade is lifted up from the surface of the eye, to point the blade tip towards the anterior chamber for entry. When using a metal blade, this “dimple down” maneuver may require a gentle increase in force to penetrate Descemets membrane. The eye must also be stabilized sufficiently to avoid eye rotation during this process. The resistance will quickly dissipate upon entry, and thus caution should be exercised to avoid disrupting the anterior capsule with the blade tip. Complete entry of the blade to the blade shoulders will ensure an appropriate internal wound width. Be careful to maintain blade positioning until the blade is completely removed from the eye, to avoid undesirable widening of the wound from a misguided blade edge while exiting.