Once the capsulorhexis has been created, it is helpful to use balanced salt solution to loosen and separate the cataract from the capsular bag in order to facilitate its removal. The two primary techniques are hydro-dissection and hydro-delineation, both of which are performed using a blunt 27 gauge cannula on a 3cc syringe filled with balanced salt solution.
Hydro-dissection is performed between the capsule and the cataract cortex in order to free the adhesions of the cataract from the capsular bag and allow it to rotate fully. Care is taken to place the blunt cannula under the edge of the anterior capsulorhexis and towards the lens equator. You should stop shy of the lens equator as you do not want to puncture the lens capsule or damage the zonules. Keep the cannula still so that it forms a tight seal between the capsule edge and the cataract. If you move too much and loosen this seal, the fluid will come back towards you and not go forwards.
Next, gently press on the plunger of the syringe in order to send the balanced salt solution around the posterior aspect of the cataract. You want to see at least one fluid wave propagated around the cataract, and more waves are better. As the waves propagate, they will loosen the cataract from the capsular bag and some fluid may become trapped behind. To release this fluid, use the cannula to gently tap on the center of the nucleus and the fluid will be pushed anterior. The key here is to be gentle so that force is not used as this could cause the capsule to rupture and the nucleus to sublux into the vitreous.
How much force is used? Very little, since the key is slow and steady. To give you an idea of the force used, if you take the 3 cc syringe with the 27 gauge cannula and inject it outside of the eye, it would form a gentle arc of fluid that would extend only a few inches. If your level of force causes the fluid to shoot across the room, you are being much too forceful. This requires a steady hand and a good sense of fluid control.
Hydro-delineation is to separate the endo-nucleus from the epi-nucleus. The central endo-nucleus is of a higher density and requires more ultrasound energy to remove, while the epi-nuclear shell is softer and easier to remove. This is an optional step that is performed with the idea that the epi-nuclear shell can act to protect the posterior capsule during phacoemulsification of the endo-nucleus. Many surgeons do not perform this step, and instead prefer to remove the entire nucleus without separating it into these layers.
To prevent the fluid from the cannula from going between the capsule and the cataract, which was already performed during hydrodissection, the tip of the cannula should be placed within the edge of the capsulorhexis and not beyond it. Dig the tip of the cannula into the nuclear material while keeping it within the confines of the 5 mm capsulorhexis. This will allow proper hydrodelineation and a successful fluid wave will result in the “golden ring” appearance at the area of separation.
Once the cataract has been freed from the capsule with hydrodissection and split into endo-nuclear and epi-nuclear sections with hydrodelineation, we are ready to perform nucleus removal using the ultrasound energy from the phaco probe. If you wish to read more about these techniques, I can recommend this article by Howard Fine MD and his associates.
Click below for both hydro-dissection and hydro-delineation in cataract surgery:
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