(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_2) contains supplementary material, which is available to authorized users.
Irrigation/aspiration (often orally abbreviated to IA) is the application of fluid irrigation to maintain the anterior chamber, combined with surgeon-controlled aspiration to remove unwanted anterior chamber material. The two key materials that require removal include residual cortical soft lens material (SLM ) and viscoelastic . Irrigation/aspiration can be performed manually using a Simcoe cannula , bimanually (using separate fluid irrigation and aspiration instruments), or using coaxial IA (a single instrument that allows fluid irrigation and aspiration via separate ports).
The principles described can be applied when performing supervised surgery, or can be adapted if the surgeon is already familiar with IA. The following description is for a right-handed surgeon—transposition of instructions will be required for left-handed surgeons. Fundamental IA principles that describe the most common method (coaxial) are introduced below in a stepwise fashion. Though manual and bimanual techniques are not described, the fundamental principles of aspiration technique remain the same. Recommendations for Trainers are suggested at the end of the chapter.
When rear-ended modular training is applied to IA, it is recommended that novice surgeons gain skills in IA removal of viscoelastic material whilst simultaneously learning the IA probe movements required during SLM removal training. Continuity of performing training steps is maintained by progressing to the IOL implant insertion module after viscoelastic material IA removal training. Whilst competency in inserting the lens is achieved, the novice is recommended to continue performing IA tip movement practice above the inserted IOL in continued preparation for when actual SLM removal training commences. For clarity, this chapter deals with all of the IA probe movement training details whilst Chap. 3 relates to IOL insertion and Chap. 4 with SLM removal.
2.1 Irrigation/Aspiration Fundamentals
The technique requires four stages to be learned:
- 1.
Removal of viscoelastic after lens insertion.
- a.
Above lens implant
- b.
Removal of residual viscoelastic below IOL implant.
(Reduces risk of myopic shift)
- a.
- 2.
Probe tip movements necessary for SLM removal
(Performed above IOL implant)
- 3.
Removal of soft lens material
- 4.
Aspiration polish of the posterior capsule (if required to reduce the risk of posterior capsule opacification) and removal of epithelium remnants from the anterior capsule lens (if needed to reduce risk of capsule phimosis)
2.2 Terminology
2.2.1 Orientation
A system of orientation is required during surgery when making intraocular movements. This is especially true during training. Fixed reference points, for example the nose and the temple, can be used for nasal and temporal movements respectively. However, for other directions, a clock face description is commonly used, with positions on the cornea described by “hours”. Unfortunately, for novice surgeons, this may lead to confusion and hesitation. This is particularly true when the changing between the right and left eye, or if changing from superior to temporal based corneal incisions (or vice versa). To avoid this, when looking down a microscope it is suggested that the corneal incision, regardless of its position once created, is always deemed to be 12 o’clock. This ensures a fixed reference point is always used, even when changing from superior to temporal based incisions. The cardinal points of orientation (3, 6, 9, and 12 o’clock) can then be easily understood and matched by both Trainer and Trainee (Fig. 2.1).
Fig. 2.1
Cardinal points. Cardinal points (3, 6, 9, and 12 o’clock) of orientation. The corneal incision acts as a fixed reference for the 12 o’clock cardinal point regardless of where it is located
2.2.2 The ‘Safe Zone’
The safe zone is the deepest part of the anterior chamber and the centre of the capsulorhexis (Fig. 2.2). It is the area in which the risk of catching the iris or capsule is lowest, allowing maximum aspiration to be performed.
Fig. 2.2
The safe zone. Centre (star) of the capsulorhexis (dotted circle). Nucleus has been removed
2.2.3 Soft Lens Material
Following phacoemulsification of the lens nucleus, a thin layer of SLM remains adherent to the inner anterior and posterior surface of the capsular bag (Fig. 2.3). This is also referred to as the cortex layer. The SLM needs to be removed before the IOL implant is inserted.
Fig. 2.3
Cross section of anterior chamber. Direction of pull when peeling soft lens material (arrow), overhanging soft lens material (arrowhead) beyond capsulorhexis edge (solid black curvilinear line), division between (a) anterior and (p) posterior soft lens material (dotted line)
The SLM can be visualised as redundant material and creates an alteration in the red-reflex (Fig. 2.4). As SLM is removed, an area of clear red-reflex is produced. The effect of the SLM on the red-reflex appearance can be used to help identify an area of SLM to remove by intentionally grasping the redundant anterior portion that overhangs the capsulorhexis edge. The improvement in red-reflex can help the surgeon avoid accidental aspiration of the capsule where it is devoid of any SLM, reducing the risk of capsule damage or zonular dehiscence.
Fig. 2.4
Differences in red-reflex. Red-reflex differences allow outline of CCC and SLM to be distinguished. (a) Colour image (b) annotated image, CCC (dotted line), outline of SLM overhanging CCC edge (solid line), corneal incision (curved line). CCC capsulorhexis, SLM soft lens material
2.2.4 The Soft Lens Material Capsule Interface
Following removal of the lens nucleus a thin layer of soft lens material remains in situ, loosely attached to the inside of the lens capsule. The SLM capsule interface anchor points holding the SLM in place are easily overcome by pulling the SLM off the capsule surface.
2.3 Aspiration Control
The amount of aspiration control is determined by the amount of foot pedal depression. This is akin to foot pedal acceleration control whilst driving a car—the greater the depression the greater the aspiration. The maximum setting is pre-set by the surgeon, (Fig. 2.5). It is important to appreciate and recognise the sound the equipment makes when engaging irrigation/aspiration. Each machine will have a slightly different sound setting. However, in general, the pitch produced will alter in a linear fashion as the foot pedal is depressed (e.g. the louder the sound, the greater the aspiration). Maximum aspiration is commonly indicated by an intermittent beeping sound (Fig. 2.6).
Fig. 2.5
Aspiration foot pedal control. (a) Linear aspiration corresponding to pedal depression. (b) Linear aspiration scale with corresponding machine sounds and effect on soft lens material. H Holding aspiration, P peeling aspiration, F foot down maximum aspiration
Fig. 2.6
Aspiration foot pedal control sounds
2.3.1 Terms That Are Useful for Aspiration of SLM Include
“ Holding aspiration ”: the amount of aspiration that engages SLM into the probe aspiration port without fully removing the SLM from the anterior chamber.
“ Peeling aspiration ”: the amount of aspiration that can hold engaged SLM and allows the SLM to be peeled off the capsular bag as the probe is moved within the eye. Aspiration is just greater than the adhesive resistance of the SLM capsule interface anchor points but not enough to completely aspirate the SLM from the eye.
“ Foot down aspiration ”: the amount of aspiration required to actually remove material from the anterior chamber.
The aspiration is maintained at maximum or near maximum. Foot down aspiration should occur with the IA probe tip within the safe zone area, with the port kept away from the iris or capsule to avoid accidental damage.
Box 2.1 Aspiration Training Tip
In time, the sound produced by foot pedal depression will provide the surgeon with additional feedback, allowing them to carefully control the amount of aspiration.
There will be times when the IA tip fails to engage soft lens material, even despite high aspiration pressures. This may either be due to a higher “holding” aspiration amount being needed, or due to the port being blocked.
Tip: check the port tip for debris. The port can usually be cleared by applying maximal aspiration within the safe zone, or by removing the probe and wiping any occlusion away from the blocked port.
During supervision, Trainers can combine their observations with the sound of the IA in order gauge whether too much or too little aspiration is being used by the Trainee.
2.4 The Irrigation/Aspiration Instrument
Various coaxial IA probe tips are available, and each ophthalmic unit will stock those preferred by their surgeons. The IA probe is composed of a tip with an aspiration port on its superior aspect and irrigation holes on each side (Figs. 2.7 and 2.8). The 45-degree angled probe tip is the most commonly used; although both straight and 90° IA probe tips are also available.
