|Manipulate hydrodissection cannula|
|Stabilize dominant hand and push syringe plunger|
|Hydrodissection using a flat tipped cannula, note rapid posterior fluid wave.|
Hydrodissection plays a vital role in ensuring a freely mobile lens that is separated from its surrounding capsule. Incomplete hydrodissection can introduce unneccessary complications, and can make removal of the lens during phacoemulsification unnecessarily difficult.
A 3cc syringe is typically filled with balanced salt solution (BSS) to facilitate hydrodissection. Smaller syringes may not provide enough BSS, and larger syringes may be too bulky to handle. The cannula used is surgeon dependent, ranging from a round 25 to 30 gauge cannula, to a flat tipped cannula, to a J style cannula to reach the capsule under the wound. We prefer a flat tipped cannula, which allows easy access under the capsule, and minimizes fluid egress from the anterior capsular lip as well.
Prior to beginning hydrodissection, remove some viscoelastic from the anterior chamber by applying gentle pressure to the posterior aspect of the wound. This provides space for the ensuing fluid to occupy, without adding undue stress on the zonules.
Begin by directing the cannula under the anterior capsule at the location of choice. Often directly across from the main wound provides the easiest access. Maintain the syringe upright, paying particular attention in the case of flat tipped cannulas to have the flat portion of the cannula parallel with the anterior capsule. Failure to do so will create a larger gape between the capsule and lens, allowing more fluid to escape anteriorly and less fluid to be properly directed posteriorly. The tip of the cannula should be extended peripherally to allow for adequate anterior capsular coverage, again to ensure proper posterior delivery of fluid. This placement is critical and beginning surgeons are often hesitant to do so.
Next, lift up slightly with the cannula tip on the anterior capsule. While carefully maintaining the cannula tip in position, provide forceful injection of fluid. Enough force must be provided to sever the capsule-lens adhesions, with care to not over inflate the anterior chamber leading to posterior capsular rupture. Again, the cannula tip must be held in place, while the tendency to withdraw the tip must be overcome. Successful hydrodissection will be evident through visualization of a propagating posterior wave.
Press down gently on the lens using the hydrodissecting cannula to help distribute any posteriorly accumulated fluid, and promote complete hydrodissection. If a wave is not evident after continuous irrigation for a brief period, stop injecting, and re-direct the cannula to a new position for a repeat attempt. Any accessible area of capsule can be irrigated as needed.
The lens should be completely mobile prior to continuing on to phacoemulsification. This can be both assisted and tested by rotating the lens. The tip of the hydrodissecting cannula can be used for this step, or a specialized lens manipulator, Kuglen hook, or the like may be used. When using the hydrodissecting cannula, turn the cannula “upside down” such that the heel of the cannula (ie, the bend in the cannula) faces up. Then, engage the lens with the cannula tip starting at either the left or right of the wound (depending on the surgeon direction of rotation preference) in the far peripheral aspect of the lens. A tangential force is applied such that the cannula tip is dragged from one side of the wound to the other with minimal downward force to ensure lens traction. Care must be taken not to press down on the lens with force, as zonular compromise may ensue. Watch carefully for lens rotation, and repeat the process until the lens is clearly mobile, which may require 90 to 180 degrees of rotation. Less angular rotation may give a false sense of mobility, while adequate rotation will sever any remaining capsular-cortical attachments. Again, the lens must be engaged in the far periphery, as too central of an engagement will not generate enough tangential force for rotation.
Again, the lens should be completely mobile prior to continuing. Failure to do so will make lens removal difficult, as the lens may exhibit difficulty in cracking or quadrant removal due to remaining capsular-cortical attachments. If in doubt, hydrodissection should be repeated and the lens should demonstrate free rotation prior to moving on in the case.