SAFE PHACOEMULSIFICATION

Hydrodissection and hydrodelineation are vital for safe phacoemulsification and it is important to understand the forces involved. These are performed preferably using a 27-gauge cannula mounted on a 2cc syringe filled with balanced salt solution (BSS). Hydrodissection refers to the fluid wave in the cortical plane that separates the cortex and capsule from the nucleus. This allows rotation of the nucleus and its mobilisation which helps later in nucleus disassembly. Hydrodissection is performed by introducing the cannula into the outer layers of the cortex and injecting fluid gently. This allows the epinucleus and endonucleus to be separated from the cortex.

Partial entry

The cannula is introduced through the main port. It is important to create the main port incision up to the full extent of the keratome before performing hydrodissection. A partial entry/high viscosity OVD blocking egress of fluid, mature cataracts, small rhexis, rapid hydrodissection and using large volumes of fluid are some of the factors that can lead to fluid build-up behind the nucleus in the capsular bag and within the anterior chamber (AC) causing a very high IOP which can ultimately lead to a capsular block syndrome (CBS) and a blow-out of the posterior capsule. This may also occur more commonly in mature cataracts, posterior polar cataracts and myopic eyes. Thus, it is vital to always allow fluid to simultaneously exit from the eye during hydrodissection.

CBS can be avoided by using small bursts of fluid as well as by depressing the posterior lip of the main port to allow fluid egress. The fluid wave causes the nucleus to float up against the anterior capsular rim, creating a seal and causing accumulation of fluid within the capsular bag. It is important to tap the nucleus gently down to break this seal and allow fluid trapped behind the nucleus to flow out. This is also important in microincision coaxial phaco and bimanual phaco where the incisions are smaller and the nucleus should be tapped down gently and the fluid burped out.

Cortical cleaving

Cortical cleaving hydrodissection is a technique first used by Howard Fine (Figures A and B). The tip of the cannula tents up the anterior capsular rim before injecting BSS. This causes a wave of fluid to flow under the capsule, cleaving the cortex all around from the capsule. It helps in easy cortex removal as the cortico-capsular adhesions are lysed. Cortical cleaving hydrodissection allows separation and aspiration of cortex in large sheets. Multi-quadrant and focal cortical cleaving hydrodissection described by Vasavada et al are also important to lyse various types of corticocapsular adhesions (anterior, posterior and equatorial) and make nuclear rotation easier. This becomes especially important in complex situations such as small pupil cataract surgery, subluxated cataracts etc, and it facilitates both ease and rapidity of surgery (Figure C).

Hydrodelineation

Hydrodelineation refers to separation of the epinucleus from the endonucleus. Multiple fluid waves can be used to generate multiple epinuclear shells. These shells are seen as one or more golden rings (Figure D). Hydrodelineation is done by inserting the cannula into the substance of the lens and injecting BSS into the substance of the nucleus. This generally requires more forceful irrigation as compared to hydrodissection. Creation of an epinuclear shell allows safe phacoemulsification of the endonucleus within this protective shell. The size of the lens fragment that is brought out into the AC and emulsified is decreased. The shell also holds the bag open and prevents aspiration of the capsular bag into the phaco probe. In very soft nuclei, the degree to which the cannula is introduced into the epinucleus may be limited in order to avoid a very small endonucleus and very thick epinucleus.

Hydroprolapse

Hydroprolapse of the nucleus can be achieved during hydrodissection by performing the tilt and tumble technique described by Dr Richard Lindstrom. Hydromanoeuvres are used to prolapse the pole of the nucleus opposite the incision out of the capsular bag. Fluid is injected continuously but gently until the fluid wave is seen to proceed along the posterior capsule and lift up the edge of the nucleus from within the capsular bag following which it is emulsified. Excessively vigorous manoeuvres should be avoided in order to avoid increased pressure build-up posterior to the nucleus leading to a capsular blow out.

Hydrodissection

Hydrodissection is completely contraindicated in posterior polar cataracts as the fluid wave can cause a rupture of the weak posterior capsule. A hydrodelineation is done in these cases to mobilise the nucleus. Viscodissection may also be done. OVD is gently injected under the anterior capsule to prevent an accidental fluid wave from entering the sub-capsular plane. Viscodissection/viscoeexpression may also be used after removal of the nucleus and mobilisation of the posterior plaque from the capsule to bring out the epinuclear shell from the bag into the AC.

A good cortical cleaving hydrodissection is especially important in subluxated cataracts where a capsular tension ring (CTR) implantation is planned. This facilitates easy aspiration of cortex trapped beneath the CTR.

Hydromanoeuvres should be done very carefully in mature cataracts as the nucleus almost completely fills the bag and the chances of a CBS are greater. Vigorous cortical cleaving hydrodissection is not required as the cortex is minimal in such cataracts. Multifocal gentle hydrodissection is more appropriate in such cases.

Different approach

With the advent of femtosecond laser-assisted cataract surgery, it is important to know the differences in approach for hydrodissection. Femtosecond disruption occurs with creation of bubbles. Intra-lenticular gas is thus produced during laser fragmentation and this together with laser-induced cortical changes can increase the intra-capsular volume. Vigorous hydrodissection without decompressing these bubbles from behind the lens can cause a posterior capsular blow-out.

Recommendations include decompression of the AC and the capsular bag by removing high-viscosity OVD and by tapping the nucleus; gradual, gentle and multi-quadrant hydrodissection and pre-chopping of hemispheres before hydrodissecting to allow bubbles as well as fluid to escape.

* Dr Soosan Jacob is a senior consultant ophthalmologist at Dr Agarwal's Eye Hospital, Chennai, India and can be reached at: dr_soosanj@hotmail.com