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Mini- and Micro-incision Cataract Surgery – A Critical Review of Current Technologies
flattening effect increases significantly.
5
While SCIs, due to Figure 1: Design Characteristics of Slim-shaft
conjunctival healing, allow for permanent sealing within one week,
Strong-bevel Phaco Needles for Co-axial Mini- and
Micro-phacoemulsification (easyTip
®
2.2mm,
CCIs take months to do so, thereby exposing the patient to a risk of
easyTip
®
CO-MICS)
endophthalmitis for an extended time. However, corneal incisions
have become very popular since they are easy and fast to create,
Mono-/Microphaco needles
exclude intra-operative ballooning of the conjunctiva and are
A
0.45
cosmetically appealing while avoiding patient disturbances due to 1.25 0.95
conjunctival bleeding or foreign body sensations. However, to be safe
1.15 53º
CO-MICS 2
and astigmatically neutral CCIs must be further down-sized.
20G easyTip
®
How small must a safe CCI be? Deformation resistance of a CCI
1.25
0.7
depends on the width and length of the incision. The smaller the A
incision, the shorter the incision can be while providing for the same
0.6
30º
CO-MICS 1
amount of resistance against digital massage. Practically, a 2x1.5mm
0.9
incision should fulfil these requirements. Smaller incisions further
SSSB-design (top)
enhances inflow, suppresses
optimise safety, as long as they are not over-stressed during phaco 20G CMP
surge and increases
and IOL insertion. Topographical impact on the central corneal zone
holdability and power
has been shown to be negligible with a CCI size of 2.0mm or smaller.
6
Source: Oertli Instruments Inc.
What are the requirements for phaco and IOL technology? Phaco Figure 2: Post-occlusion Surge and Band of
should provide maximum safety and efficiency. Safety means
Steady-state Stability with Different Phaco Tips
Including Infusion Assistance
minimal incisional trauma and maximum chamber stability.
Efficiency means minimal phaco time and energy consumption. This Chamber stability
should be achieved through the smallest incision possible. IOLs 100
should provide easy and atraumatic insertion, auto-centration and
80
Surge
stable fixation within the bag, circumferential barrier function
60 (occluded
Band of stability
→
against lens epithelial cell (LEC) immigration and optimum optical
unoccluded)
(free flow)
40
performance. Implanting IOLs through smaller than appropriate
20
incisions may cause permanent tissue trauma, and compromises
the self-sealing properties.
7
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
-20
What incision sizes should be aimed for? Incision sizes are dictated
V
accum (seconds)
-40
by the IOLs to be inserted. Current IOLs may be divided into two -60
subgroups: mini-incision IOLs, which fit through a 2.2–2.4mm
-80
incision, and micro-incision IOLs, which fit through incisions smaller
-100
than 2mm. In conjunction with appropriate phaco equipment, the
-120
latter allow for what has been termed ‘sub-2mm’ or ‘micro-incision’
Time (seconds)
50ml/min, 500mmHg
cataract surgery (MICS).
SSSB design phaco tips: CO-MICS 2 infusion-assisted
easyTip
®
CO-MICS 2
MICS through 2.2–2.4mm incisions is achieved with current co-axial
Traditional design phaco tips: 19G accelerator 20G CMP
phaco and IOL technology. However, this is a trade-off. Simply
reducing the size of a standard phaco needle reduces holdability and theoretical advantage of this concept (Menapace et al., data on file). Of
energy output. Therefore, innovative phaco needle technology is the IOLs on the market, several fit through a 2.2–2.4mm incision.
mandatory (see Figure 1). When reducing the shaft diameter, higher However, most of these (e.g. Alcon Acrysof SN60WF, Zeiss-Acri.Tec
vacuum and flow settings may be used, at the same time suppressing AcriLyc 47LC) are one-piece acrylic IOLs with broad haptic–optic
post-occlusion surge. By increasing the bevel angle of the needle, junctions with the injector tip docked to, and not inserted into, the
holdability – a function of the area of the opening – is augmented. The incision. Broad junctions inherently interfere with capsular bending
transition between the broad needle-head and the slim shaft and thus compromise the barrier function against immigrating LECs,
increases the frontal projection area, which is proportional to the giving way to earlier and more pronounced after-cataract formation.
8
A
energy output. The slim shaft allows for a sleeve that runs almost singular exception is the HOYA AF-1 pre-loaded three-piece IOL, which
flush with the needle-head, which further reduces the incision size has recently been fitted with an exquisitely sharp posterior optic edge
required, and and avoids anteriorly directed infusion inflow, which and allows injection through a 2.4mm incision, if properly designed.
tends to push particles away from the front opening of the needle. Due to its slim junction design, the HOYA IOL may also be used in
Together, this slim-shaft–strong-bevel (SSSB) needle design fits into a conjunction with posterior optic button-holing for permanent
concept that optimises followability, holdability, energy transfer and eradication of any form of after-cataract formation.
9
With this
surge suppression (see Figure 2). three-piece IOL the injector tip must be inserted into the tunnel; by
contrast, it can be docked to the tunnel entrance with one-piece IOLs.
Such a needle has recently been released by the Oertli
®
Company: the While requiring a somewhat smaller incision width, docked injection is
easyTip
®
2.2mm (see Figure 1, left). A significant decrease in phaco less controlled and exposes the incision to distending and shearing
time and energy consumption in clinical tests has corroborated the forces. Parallel-walled incisions are therefore not recommended. A
EUROPEAN OPHTHALMIC REVIEW 53
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