(1)
Newcastle Eye Centre Royal Victoria Infirmary, Newcastle upon Tyne, UK
Electronic Supplementary Material
The online version of this chapter (doi:10.1007/978-3-319-59924-3_5) contains supplementary material, which is available to authorized users.
Continuous curvilinear capsulorhexis (also referred to as the rhexis ) is performed by creating an aperture in the anterior capsule. The most common manual technique is made by initially puncturing the capsule surface, creating a capsule flap that is then dragged circumferentially to create a central, circular aperture [1]. Experienced surgeons can perform a capsulorhexis quickly, adapting intraocular movements and adjusting the direction of the tearing force to create an ideal rhexis aperture (well centred and of a size that is small enough to just overlap the lens optic). Mimicking the proficient, rapid movements of expert surgeons may be daunting for Trainees who may not appreciate the sequence of movements that are required. However, once the technique broken down into steps, these movements become simple and reproducible. It should be acknowledged that novice surgeons will not always achieve a rhexis that is well centred and of perfect size or shape. Indeed, in everyday practice, capsulorhexis perfection is something all cataract surgeons strive for.
The term rhexis in cataract surgery has several interchangeable meanings that require clarification for the novice surgeon. It refers to any part of the cut edge of the incomplete, or completed, continuous curvilinear capsulorhexis aperture. For example, during phacoemulsification, care is taken not to damage the rhexis. It also refers to the specific point at which the capsule is torn during the creation of the capsulorhexis aperture. Loss of control of the rhexis implies the rhexis tear is extending outwards towards, and potentially under, the iris margin.
This chapter will describe the principles involved in creating a manual rhexis. Femtosecond laser capsulorhexis formation is also possible, but is not discussed. Terminology and steps are explained with the aid of diagrams highlighted with a “cartoon” capsule. This will allow the steps to be visualised. Concepts will be introduced in stages throughout the chapter and it will be necessary to read the whole chapter for a full understanding. During training, novice surgeons will be shown various modifications of the described technique. The principles underlying basic technique remain the same.
Assumptions for this module are shown in Box 5.1
Box 5.1 Assumptions Made in Relation to this Training Module
The anterior chamber is pre-filled with viscoelastic.
Viscoelastic top-up is applied as required.
The Trainee is right-handed. For left-handed Trainees, an anti-clockwise direction may be applied and the instructions are reversed. The Trainer may prefer to initiate the rhexis at a different position, or even perform the capsulorhexis clockwise. The fundamentals remain applicable.
The chapter describes the use of a short orange needle to start the rhexis flap, but a cystotome or equivalent can be used if preferred. If using a cystotome, remember to rotate the tip during insertion and removal to prevent “catching” the section.
Adhering to the rules described facilitates performing rhexis in a routine fashion. The basic rules can be broken as experience is gained.
Breaking the rules too early will lead to a higher rate of take-over by Trainer.
The Trainer will provide specific guidance to novice surgeons during each rhexis attempt, slowly withdrawing instruction as technical skills are gained.
It is assumed the novice does not know where to hold the flap nor the direction of movements required.
5.1 Fundamentals of Capsulorhexis
5.1.1 Anatomical Orientation
To facilitate surgical instruction, a common anatomical surgical orientation between the Trainer and novice surgeon should be used. One method is to consider the eye as a clock face with four cardinal reference points, namely the 3, 6, 9, and 12 o’clock positions. To avoid confusion, the corneal incision is always designated the 12 o’clock cardinal position (Fig. 5.1). This ensures that the corneal wound once created acts as a fixed reference point for the surgeon, even when changing the location of the incision or switching from the left to the right eye.
Fig. 5.1
Cardinal points of orientation. Corneal incision (solid line), cardinal points (3, 6, 9, and 12 o’clock) with joining imaginary cross hairs (dotted lines)
5.1.2 Viscoelastic Fill
Viscoelastic material is needed to protect the internal ocular tissues, maintain the anterior chamber depth and tamponade the capsule surface. It aids visualisation and facilitates controlled rhexis surgery. At the end of intraocular lens training it is a simple matter to fill the anterior chamber with viscoelastic. To recap: expel a small amount of viscoelastic before entering the eye to ensure any potential trapped air bubbles in the syringe hub are removed. A side-to-side movement of the cannula during insertion will allow the cannula to navigate the corneal wound. Continue to inject viscoelastic and direct the cannula towards the 6 o’clock position. Noodle-like streams of viscoelastic will start to fill the eye and then coalesce together to form a bow wave. This bow wave of viscoelastic moves towards the cornea incision as the anterior chamber is filled. The cannula can then be slowly withdrawn whilst further viscoelastic is injected. Once the chamber is completely filled the viscoelastic will start to leak from the wound. At this point stop injecting and remove the cannula.
Experienced surgeons are able to complete the rhexis without a top-up of viscoelastic. Novice surgeons are more likely to require a viscoelastic top-up during surgery, as it is common to inadvertently depress the posterior lip of the corneal wound whilst forming the rhexis. This will allow viscoelastic to escape. This is not a major concern during the initial stages of rhexis creation as ample viscoelastic is present. In the later stages, however, as additional viscoelastic escapes, a top-up may be required. This will ensure the viscoelastic tamponade of the capsule is maintained.
5.1.3 Creation of Capsule Flap
Depending on surgeon preference, initial puncture of the capsule surface can be implemented with a variety of instruments. This includes: a keratome tip, a cystotome (pre-formed, or created by the surgeon by bending a needle tip into a cystotome shape), capsulorhexis forceps, or 25-gauge needle tip. Novice surgeons will be guided by the Trainer’s teaching preference. The chapter will describe the use of a 25-gauge needle (attached to an empty syringe) to breach the capsule and create a flap. Subsequent rhexis completion is described with capsulorhexis forceps.
A short, 25-gauge needle (Fig. 5.2) in the bevel up position is used to make the capsular flap (Fig. 5.3). The flap is needed for controlled tearing of the rhexis. The needle-tip has sharp edges and a round-bodied shaft attached to the needle hub.
Fig. 5.2
25-gauge needle. Lateral view (main image), superior view (insert). Needle tip (arrow), cutting edge (arrow head), non-cutting round bodied shaft (open arrow)
Fig. 5.3
Capsule flap orientation . Flap (large arrow), edge of tear (short arrow), capsule surface (black star), exposed lens surface (white star)
The initial flap creation has three components :
- 1.
The needle-tip is used to stab and breach the capsule surface.
- 2.
Its sharp edge used to slice the capsule open.
- 3.
The tip is used to push and fold the capsule over itself to create the initial flap.
Before insertion into the eye, preparation of the needle shaft is required (Fig. 5.4). Keeping the needle bevel facing upwards, the shaft is bent upwards using applied finger pressure. Bending the needle shaft facilitates the angle of entry into the eye.
Fig. 5.4
Bent needle. (a) Bent needle side profile, (b) Bent needle superior view
Insertion of the needle into the eye may initially be met with resistance due to the difficulty of navigating the stepped corneal incision. This can be exacerbated if the needle tip is rotated slightly within the corneal section. It is recommended the tip is held so that the cutting edges remain horizontal. One approach is to place the tip to one side of the corneal section (rather than the centre of the wound) and then perform a side-to-side movement whilst navigating the wound. This encourages the stepped corneal incision to open slightly and allows the needle tip access into the anterior chamber without catching the corneal tissue or creating false passage (Fig. 5.5). Occasionally, novice surgeons may need to lift the upper lip of the corneal wound using forceps, in order to insert the needle. However, with practice this is usually is not required.
Fig. 5.5
Needle insertion. Corneal incision (arrow), horizontal movement of needle (double headed arrow)
5.1.4 Capsule Stab
Once the needle has been inserted into the anterior chamber, it is advisable to pause and determine the ideal centre for the rhexis. Imagining crosshairs connecting the four cardinal points will act as an aid. The preferred point for the initial stab that breaches the capsule surface is just lateral and off-centre (Figs. 5.6 and 5.7). If the stab is made too centrally, the rhexis may extend outwards towards the iris when the flap is created.
Fig. 5.6
Capsulorhexis initial stab. Incision site (star), imaginary cross hairs (dotted lines) along cardinal points (12 to 6, and 3 to 9 o’clock), corneal incision (solid line)
Fig. 5.7
Needle tip poised to stab capsule
Breaching the capsule surface requires a bold stabbing motion, (Fig. 5.8). The needle tip should be aimed obliquely downwards (as if aiming for the posterior pole of the eye) during the stab. Once the capsule is breached, the needle should be lowered closer to the horizontal to avoid disturbing too much cortex material during the next movement. If the stab is done too slowly, then the capsule will stretch under the force, before it is breached. This should be avoided as it results in unnecessary downward force being applied to the lens.
Fig. 5.8
Needle tip stabbing capsule
Adjustment of the tip is now required. Pull the tip back so that the sharp edge of the tip is used for the next stage (Fig. 5.9). Pull-back ensures the round body of needle shaft is not inadvertently used to cut and slice capsule (Fig. 5.10). If the shaft is used it will stretch the capsule and may result in an irregular, uncontrolled tear when the next step is performed (usually towards the 10 o’clock position directly underneath the needle shaft). Should this occur, withdraw the shaft and start to create the capsule flap using the eccentric tear.
Fig. 5.9
Correct needle tip sharp-edge positioning. After stabbing the capsule the needle tip is pulled back (arrow) so cutting edge is ready to slice the capsule
Fig. 5.10
Incorrect needle tip positioning. Here the needle is incorrectly positioned, and the shaft of the needle (arrow) will cause an uncontrolled tear
5.1.5 Capsule Flap Creation
Once positioned, the cutting-edge of the needle tip is ready to slice open the capsule. Both oblique and horizontal movements may be used, but an oblique direction will result in predictable tearing of the capsule when flap is folded over. An in-and-out sawing action, using the needle tip edge as a blade, will facilitate making the cut. Once proficient in the movement, a sliding action alone will work. The slide should not go right out to the iris, but instead leave a reasonable margin (Fig. 5.11).
Fig. 5.11
Capsule slice. Capsule slice (arrow) ends a reasonable distance from iris margin (arrow head)
The capsule now needs to be folded over to create a flap. Novice surgeons can be nervous about the capsule tearing in an uncontrolled fashion. This concern can be reduced with good visualisation and the knowledge that a predictable tearing of the rhexis is possible. To help visualise the flap origin and the direction in which the initial capsule tear will extend, the needle tip needs to retreat a fraction along its original path. This allows visualisation of the outer peripheral edge of the recently made cut (Fig. 5.12).
