The role of the “second” instrument used during cataract surgery.
Modern phacoemulsification utilizes a fine, “second” instrument usually in the nondominant hand for a variety of effective manipulations during the procedure making surgery safer and more effective. This instrument came about in an effort to improve the efficiency during cataract surgery by applying mechanical segmentation to ultrasonic phacoemulsification. Utilizing a second instrument gained further acceptance in proportion to surgeons developing comfort with bimanual techniques while also recognizing the benefit from added efficiency with cracking and chopping techniques. All of this at a time when the equipment was much less efficient than it is today. Cracking and chopping denser nuclei offer the experienced surgeon a method of increasing surface area without using extensive ultrasound and potentially traumatizing corneal endothelium. A second instrument can also secure a nuclear segment between the instrument and the phaco tip techniques keeping it in place and also adding to the vacuum making the ultrasonic action more effective. This “backstop” produces more effective pulverizing and emulsifying of the crystalline lens. Otherswise, ultrasonic tip movement tends to push away nuclear fragments and even create so called “chatter” when the phaco power is out of proportion to the vacuum level.
More recently there have been some misunderstandings surrounding the second instrument particularly when it comes to being able to “hold back” the capsule and prevent contact with the phacoemulsifying tip. Frankly, I am unable to find a single manufacturer who claims or promotes posterior capsular protection by using any of the so called second instruments. Remember the posterior capsule is 3.5 microns thick centrally and this increases to 9 microns in the periphery. This represents only a third of the thickness of the anterior capsule. A Sinskey Hook, Osher Nucleus Manipulator, Drysdale Spatula, and Connor Wand have been suggested but looking closely at these designs, it becomes immediately apparent that they are not designed to keep the capsule protected.
Let’s take a more critical look at how the second instrument can be utilized to make cataract surgery a much safer procedure for patients. Effective use of the second instrument provides the following benefits during surgery:
a. A second instrument can help stabilize, manipulate, and position the eye for surgery while simultaneously performing phacoemulsification. However, I do not recommend using it in the paracentesis solely for the reason to stabilize the eye as this can lead to wound damage and leakage at the paracentesis if manipulation is too aggressive. When needing to stabilize the eye for example using a keratome to make an incision, I recommend grasping the conjunctiva 1 mm from the limbus using a 0.12mm forcep at the point of tenon’s insertion (this location avoids conjunctival tears and reduces subconjuntival hemorrhage.
b. Lens rotation and cracking, chopping, and disassembling can all be facilitated by the second instrument. Any technique that fragments the lens and effectively increases the overall surface area improves the efficiency of the surgery. (Remember the “engineering” concept behind phacoemulsification ultimately produces lens removal but begins with effectively increasing the surface area per given volume of remaining lens.)
c. Stabilizing lens fragments sandwiched between the phaco handpiece tip and the second instrument delivers a backstop for more efficient energy deliver while also reducing lens fragments potentially flying up against the endothelium. Consider the added impact of a jackhammer when you stand on it compared to trying to run it at arm’s length.
d. During cortex removal, on occasion, unseen nuclear and epinuclear fragments will appear and rather than changing out the handpiece, the second instrument can help pulverize the small fragments against the I&A handpiece tip for complete removal. This becomes a little harder with some of the newer flexible silicone tips.
e. The second instrument can help position an IOL completely in the bag and is particularly useful if axis alignment is needed for a Toric IOL for example.
f. The second instrument can provide a fulcrum strategically placed to minimize zonular stress while inserting an endocapsular tension ring.
g. With regard to protecting the posterior capsule, during what can be potentially higher flow and vacuum, the posterior capsule is protected by irrigation keeping the chamber deep, minimizing leakage by maintaining a reasonably closed system, and stabilizing nuclear fragments or plates against the posterior capsule. This spreads out the surface area which would be otherwise too small to safely protect the posterior capsule. Would never advocate placing the sharp end or even the sideways placement of a second instrument directly against the posterior capsule as protection against the phaco tip.
Misuses of the Second Instrument:
a) Relying on it to aggressively stabilize the eye of an uncooperative patient. Again, I prefer a safer and more effective method of securing the eye at the insertion of tenon’s capsule.
b) Allowing too much additional fluid to escape through the paracenteses causing chamber fluctuation and instability of the posterior capsule – causing both patient and surgeon concern and anxiety. Removing the second instrument in these cases often adds patient comfort and confidence by moving closer to a “closed” system with improved chamber stability and lower flow and turbulance.
Liyanage et al. showed substantial fluid loss through the paracentesis along with fluctuation of chamber depth and posterior capsule movement that improved with removal of the second instrument. Tee et al identified fluid utilization went from 75cc in a routine case that did not use a second instrument to 176cc with the addition of the second instrument. They also noted that this fluid loss occurred even when the instrument was “idle” which comprised a substantial amount of time. (92% of the time was “idle” in the hands of an experienced surgeon and 86% of the time with a less experienced surgeon) They concluded that the second instrument was best utilized in procedures that involved cracking or chopping, early on in the procedure but then removed the second instrument in cases where chamber stability and lower turbulence is beneficial. Combining all of this with an adequate capsulorhexis and cortical cleaving hydrodissection does seem to “front load” the benefits derived from the second instrument to the earlier aspects of surgery that focus on nuclear segmentation and chopping. Instrumentation, vacuum, tip design, vacuum levels, and advanced surge suppression all make one handed phaco, especially for the latter part of the procedure, an improved option for both patients and surgeons particularly as most of the larger fragments are removed.