3 Rules for Maneuvering Instruments in the Eye

Intra-ocular procedures pose the surgical challenge of working within a very small space with limited room in which to maneuver instruments. In this regard, our eye instrumentation is very small with fine tips that are millimeters or less in dimension. Using these instruments within the eye, such as in cataract surgery but also applicable in posterior segment procedures, requires learning to pivot within our small incisions to avoid collapse or distortion of the anterior chamber. Our goal is a minimally invasive procedure with a low degree of surgically induced trauma so that the eye is quieter with less inflammation and a rapid recovery of excellent vision. These are the 3 Rules that Expert Cataract Surgeons always follow.

Rule 1: Pivoting is the key

Moving any instrument with a pivoting technique has the advantage of allowing a wide range of movement while inserting the instrument through a smaller incision. There is the additional benefit of increasing precision since a large movement on the outside of the pivot can give a small movement inside the eye.

Think of a row boat and a paddle with an oar lock. Though the part of the paddle in the water will move many yards each stroke, the handle portion of the oar moves only a few feet within the boat. With eye instruments, it is the reverse: a long handle outside the eye will move many centimeters while the short tips within the eye move just a few millimeters.

pivot in incision — By using the pivoting technique during capsulorhexis creation, this surgeon shows that a large 20 mm movement of the external instrument handle gives a very precise 1 mm movement of the internal tip of the forceps, thereby increasing precision.

This scaling allows for more precise control of intra-ocular instrumentation. And since the ocular incisions act like an oar lock, this pivoting movement can be accomplished through very small wounds.

The correct form is to pivot within the incision during surgery which means that the hand of the instrument will move to the right if you wish the tip of the instrument to move left. This keeps the corneal incision relatively closed and undistorted, allows viscoelastic to be retained within the anterior chamber to maintain depth, and gives maximal reach within the eye.

pivoting fig1 — Floating within the phaco incision and using a pivoting technique allows maximal reach and control during surgery.

The incorrect technique is to push against the incision walls, trying to move the instrument handle in the same direction as the instrument tip. This causes distortion of the cornea as the instrument pushes against the walls of the incision limited the view and allowing viscoelastic to escape from the eye, leading to collapse of the anterior chamber. The reach within the eye is also compromised if the surgeon does not employ the pivoting technique.

Rule 2: Float within the incision

Surgery is three dimensional and we must be able to move left and right (x axis), forward and backward (y axis), and anterior and posterior (z axis). These same principles of pivoting within the incision apply in all of these dimensions. In particular, a failure to properly pivot in the z axis can lead to extensive gaping of the phaco incision which causes loss of viscoelastic or saline solution and anterior chamber collapse during cataract surgery which makes a complication such as a posterior capsular rupture far more likely.

pivoting fig2 — The pivoting technique must be used in all dimensions: left-right movement (x axis), forward and back movement (y axis), and anterior-posterior positioning (z axis).

In addition to pivoting, we must also float within the phaco incision so that the eye stays in primary gaze. There is a tendency for beginning surgeons to lift up on the phaco incision which causes the eye to shift out of primary position. For temporal phaco incisions this causes the eye to move towards the nasal canthus which limits surgeon visibility and control, may cause patient discomfort, and predisposes to a phaco wound burn. When the phaco probe tip is forcefully pushed against the roof of the corneal incision, there is increased friction and heat from the ultrasonic vibrations in close proximity to the corneal stromal tissue without the benefit of adequate fluidic cooling. This leads to a phaco wound burn which can induce a large degree of irregular astigmatism and result in a poor visual result for the patient.

Also of importance is the surgeon’s non-dominant hand which controls instruments such as phaco choppers which are placed through the paracentesis incision. With the surgeon focusing much of his effort on the phaco probe in the dominant hand, the hand holding the chopper can have a tendency to wander or inadvertently place pressure on the paracentesis incision. This leads to distortion and increased fluidic leakage from the paracentesis which can be enough to upset the fluidic balance of the phaco machine.

Rule 3: Keep the eye in primary position

When the eye is moving towards the nasal canthus, gently bring the phaco probe downwards until the eye is back in primary gaze with the iris parallel to the floor. Remember that when instruments are inserted within the eye, it is the surgeon’s movement of these tools, and not the patient’s voluntary muscle control, which determines the position of the eye.

pivoting fig3 — If the surgeon lifts up on the temporal incision the eye will tend to move towards the nasal canthus (A.) which limits the view and control and poses a higher risk for a phaco wound burn. By lowering the phaco probe and allowing it to float within the incision (B.) the eye returns to primary position and provides a better view and control for the surgeon.

Keeping the eye in primary position gives you the best red-reflex which is helpful in seeing details such as the edge of the capsulorhexis. Looking at the reflection of the microscope lights on the cornea, make sure that this light reflex stays in the central corneal zone. The 1st Purkinje image is the reflection off the anterior corneal surface, the 2nd Purkinje image is the reflection from the posterior corneal surface, the 3rd Purkinje image is the reflection from the front of the lens, and the 4th Purkinje image is reflected from the posterior surface of the lens and it is inverted.

purkinje images — The blue arrows show the two strongest Purkinje images, the right arrow is the first Purkinje image from the anterior surface of the cornea while the left arrow is the fourth Purkinje image which is also inverted. When the eye is in primary position, these Purkinje images are close to each other or overlapping. In primary position the red reflex makes it easy to see details like the edge of the capsulorhexis.

By allowing our surgical instruments to gently float within the incisions and by using the pivoting method, we can keep the eye in its primary position and maintain good visualization throughout the surgery. These techniques can be challenging to learn for the beginning surgeon, but with practice they become second nature. And most importantly we can perform a safer surgery for our patients with less induced trauma and a faster recovery of good vision.