CAPSULORHEXIS

INSTRUMENTATION:
Rhexis can be performed with a cystitome or a capsulorhexis forceps. Using a cystitome is simple, be it selffashioned from a needle (preferably 26/27 gauge) or a pre-bent one. While fashioning the cystitome, the tip should be bent bevel up only at the very end. Having too long a bend can tear the corneal valve incision. Having a more oblique angle rather than an extreme right angle for the tip is preferable to be able to always visualise the tip during the rhexis. The shaft angle should be such that there is no distortion of the corneal incision secondary to excessive pressure on the anterior or posterior lip of the incision. For rhexis with forceps, either the Utrata forceps or microrhexis forceps may be used.

INCISIONS:
Whether performing a superior or temporal clear corneal phaco, the main port and the side ports should be made at a comfortable, ergonomic angle – ideally between the vertical rectus and the corresponding horizontal rectus. A common mistake is an anterior entry into the anterior chamber (AC) necessitating excessive posterior angulation of instruments with consequent stress on zonules. Excessively posterior incision can cause iris prolapse and conjunctival ballooning. The ideal incision should be a square tunnel just anterior to the limbus avoiding conjunctiva. Too short a tunnel can cause iris prolapse while an excessively long tunnel can cause oarlocking of instruments. For beginners, it is advisable to enter only partially so as to allow better retention of viscoelastic in the AC. The incision can be enlarged to its full extent after completion of rhexis.

SIZE OF RHEXIS:
The rhexis should be well centred. A uniformly dilated pupil may be used as a guide for centration and sizing. In small pupils, care should be taken not to make the rhexis too small. Ideal size is about 0.5 to 1mm smaller than IOL optic size. This allows the rim to overlap the optic on all sides and prevents posterior capsular opacification. It also allows easy optic capture of IOL in case of a posterior capsular rent.

RHEXIS WITH NEEDLE:
The AC should be kept deep throughout with viscoelastic and the anterior lens capsule flat. A shallow AC can cause the anterior lens capsule to be nicked while entering. It also allows the convex shape of the lens and intra-lenticular pressure to cause a run-away rhexis. Performing the rhexis without distortion of corneal wound allows better retention of viscoelastic inside the AC and hence better control over the rhexis. The bent cystitome is connected to a 1cc viscoelastic filled syringe to allow the surgeon to refill the AC without having to withdraw the cystitome. The microscope light is kept at coaxial and the cystitome is introduced through the incision keeping the bent tip horizontal to avoid incision tears.

Once inside, the AC is filled again and rhexis initiated by creating a tear in the anterior capsule from the centre outwards. Length of tear is kept just short of desired rhexis size as lifting the flap increases the size slightly. The tear is then continued in a circular manner aiming for a continuous curvilinear capsulorhexis. Pressure exerted against the capsule should be minimal. Digging and churning of cortex should be avoided to maintain optimal visualisation throughout. According to preference, rhexis may be continued so that the subincisional part of the rhexis is tackled either first or kept for last. The flap is always kept flat against the lens surface by injecting viscoelastic as and when required. The edge of the rhexis mirrors the curve of the capsular flap edge (Figure A). Turning the flap inwards or outwards can make the rhexis smaller or larger respectively. Once the desired size is obtained, the flap should be kept symmetric to the torn edge so as to get as circular a rhexis as possible. While nearing the main port, avoid the flap from sliding out through the incision which can lead to peripheral extension of rhexis. If the rhexis is smaller than desired, it is possible to go around a second time to enlarge the rhexis further. It is imperative to end the rhexis from outside in to avoid any weak spots. Once complete, inject viscoelastic again and turn the needle tip horizontal while exiting from the main port (Figure B). Finally, it is crucial to remember to enlarge the main port to its full extent prior to hydrodissection to avoid pressure build-up and a posterior capsule blow-out.

RHEXIS WITH CAPSULOR HEXIS FORCEPS:
The Utrata forceps requires full entry into the AC whereas a partial entry suffices for microrhexis forceps. Hence, the latter has the advantage of less viscoelastic loss and correspondingly better control. The initial radial cut is initiated either with a cystitome or with a sharp-tipped forceps. Flap edge is lifted up with viscoelastic (unlike in rhexis with cystitome where the flap is made to lie flat) in order to allow it to be grasped by forceps. It is grasped about a millimetre from the lifted edge for good control and the rhexis created (Figure C). Whenever required, the flap edge is released and regrasped closer to tearing edge for better control. Viscoelastic should be refilled whenever AC shallows to avoid a peripheral run-off. Spiral enlargement may be done if required (Figure D). As with needle, the rhexis is ended from outside in to avoid weak spots.

CAPSULAR DYE:
Using a capsular dye (Trypan blue 0.06 per cent) allows better visualisation of the capsular edge and is especially useful in cases without good red reflex such as white cataracts, dense nuclei, vitreous haemorrhage etc. Dye is injected prior to viscoelastic.

CONCLUSION:
Once a rhexis is created successfully, the rest of phacoemulsification can be continued. As you get more and more accustomed to making a rhexis, you will find that certain variations from this technique may feel better in your hands

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* 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.