Hydrodissection and hydrodelineation are sandwiched between the more glamorous phacoemulsification steps of capsulorrhexis and nucleus removal. Hydrodissection and hydrodelineation separate the nucleus from the surrounding cortex and are essential for safe nuclear rotation during phacoemulsification and nuclear delivery during standard extracapsular cataract extraction.
The goal is first to shear the attachments between the lens capsule and its surrounding cortex (hydrodissection) and then to separate the epinuclear bowl from its attachment to the lens nucleus (hydrodelineation). Successful completion of these steps will result in a lens nucleus that can be freely rotated during nucleus sculpture and division (thus minimizing stress on the zonule), an epinuclear bowl that protects the lens capsule during nucleus removal, and a cortex that can be more easily removed. Hydrodissection also loosens the nucleus and facilitates nuclear expression in standard extracapsular cataract extraction.
Hydrodissection is the great facilitator of cataract surgery. It is low-tech in terms of the instruments needed to complete this maneuver, thus it is an underappreciated step. Hydrodelineation, although not essential, is desirable because it separates the harder nucleus from the softer, adherent epinucleus. The resultant epinuclear bowl helps protect the lens capsule from instrument trauma as the nucleus is manipulated.
The instruments needed to complete this step are very simple: a 25- to 30-gauge cannula and a 3-cc syringe.
The 25- to 30-gauge cannula is typically angled or curved to facilitate placement under the anterior lens capsule. The tip may be flattened to allow it to slip under the capsule more easily. A J-tip cannula may be used to hydrodissect the subincisional cortex.
A 3-cc syringe is the ideal size for intraocular use. It can be handled easily with one hand and has good tactile feedback during the injection. A tuber- culin syringe (1 cc) does not allow enough injection force or fluid volume to achieve optimal hydrodissection. A 5 or 10-cc syringe may result in greater force with injection but less control during the maneuver.
If the anterior chamber (AC) is still filled with viscoelastic from the pre- ceding capsulorrhexis, partially empty the AC to make room for the increased fluid volume that will occur with this step. If a very dispersive/retentive vis- coelastic such as Healon 5 (Advanced Medical Optics) is used, tracks should be made in the material with the hydrodissection cannula to make a pathway for the balanced salt solution (BSS) to exit the eye. Otherwise, the expanded fluid volume in the AC can lead to blowout of the lens capsule or lens during this maneuver.
The hydrodissection cannula is placed on a 3-cc syringe filled with BSS. The tip of the cannula is then passed beneath the anterior lens capsule a suf- ficient distance to allow a forward wave of fluid during injection. Otherwise there is backflow into the AC and ineffective hydrodissection. Fluid must be injected with sufficient force to shear adhesions between the lens capsule and cortex. Repeat this maneuver 2 to 3 times at different locations to ensure com- plete dissection. Using the heel of the hydrodissection cannula, gentle depression of the nucleus after irrigating the BSS can be helpful to propagate the fluid wave completely and prevent capsular blowout.
For hydrodelineation, the cannula tip is placed into the edge of the epinucleus. The fluid must be injected with more force than during hydrodissection because the epinuclear-nuclear adhesion is stronger than the cortex-epinuclear adhesion. The fluid wave results in the appearance of a “golden ring,” which indicates successful epinuclear separation.
D. Potential Complications
The most feared complication of hydrodissection is damage to the lens capsule. Mechanical trauma from the cannula itself can occur if the cannula is placed too forcefully and peripherally under the anterior capsule and causes mechanical disruption of the capsule. In addition, if the capsulorrhexis is small and the nucleus itself blocks egress of the injected fluid from the capsule bag, the fluid can build up behind the nucleus, distend the capsule, and result in a posterior capsular rupture. This is more common with a large dense nucleus. This “intracapsular capsular block syndrome” can be avoided by tilting the nucleus with the cannula tip to allow egress of the injected fluid and by ensuring that the capsulorrhexis is at least 5 mm in diameter.
A lens with a fibrotic posterior subcapsular plaque is also at higher risk of posterior capsule rupture during hydrodissection because the capsule may be weak at the area of fibrosis and prone to tearing at the interface. Slow, limited hydrodissection may be more prudent in this case. In addition, concentrating more on hydrodelineation will allow mobilization of the lens while still protecting the capsule.
The cannula may also be inadvertently placed above the anterior capsule. The fluid will then be injected at the lens zonule and track back to the vitreous. This vitreous hydration increases posterior pressure and shallows the AC. If this occurs, decompress the AC and wait 5 to 10 minutes for the eye to re-equilibrate. Hydrodissection can usually be continued, but the AC remains shallow and the vitreous may need to be decompressed in some cases.
E. Special Technique: Cortical Cleavage Hydrodissection
1. Cortical cleavage hydrodissection
Fine described a technique called cortical cleavage hydrodissection, the purpose of which is to cleave the cortex from the lens capsule during hydrodissection so that more will remain attached to the epinucleus. Thus, cortex will be removed along with the epinuclear bowl and the amount of cortex remaining is minimized, thus decreasing the time needed for cortical cleanup. To achieve this, the cannula tip is used to tent up the anterior capsule and advanced so that the injection occurs near the lens equator. Care must be taken not to inject any fluid until the cannula tip is in position under the anterior capsule. After the injection, decompress the nucleus prior to initiating the next fluid wave.
2. Posterior polar cataracts
There may be a congenital absence of the central pole of the posterior capsule in posterior polar cataracts. Hydrodissection is often not recommended in these cases, and only gentle hydrodelineation is performed. Minimal ultrasound energy is used for nucleus removal, and viscodissection is used to mobilize the epinucleus and cortex, which helps prevent posterior capsular rupture and potential dislocation of the lens onto the vitreous cavity.
Hydrodissection is an essential step in safe phacoemulsification. The ability to freely rotate the nucleus is crucial to minimizing zonular stress during nucleus removal. As with all steps in cataract surgery, successful completion of each step facilitates the completion of the next.
*Dikutip dari Buku Essentials of Cataract Surgery 2nd Ed, halaman 101-104