IC-45: MICROINCISION CATARACT SURGERY:
TIPS & TRICKS
Microincision cataract surgery (MICS) was developed at the turn of the 21st century. The goal
was to achieve a minimally invasive procedure, with increased safety, faster visual recovery and
less surgically induced astigmatism. Initially, MICS was only performed through two sub-2-mm
incisions. It was a bimanual approach using sleeveless phaco probes with a separation of the
irrigation and the aspiration lines. More recently, several companies have modified their phaco
platforms to develop a microcoaxial approach, with sleeved phaco needles used to provide
irrigation and aspiration through one sub-2-mm incision. According to a recent European survey,
almost 35% of cataract surgeons have transitionned to MICS in 2008. This percentage is
increasing as the industry is following the same trend, providing sophisticated MICS phacoplatforms and micro-instruments, as well as new implants compatible with a small incision.
Today, the industry contributes to the development of MICS and performs extensive research to
optimize the MICS platforms, instruments and intraocular lenses adapted to small incisions.
MICROINCISION CONSTRUCTION
The construction of a microincision is a crucial first step as it influences the safety, effectiveness
and refractive outcome of the procedure. A well constructed incision provides an optimal wound
stability during and after the surgery, and decreases the risk of infection. Precalibrated
microblades, ranging from 1.2 to 1.8-mm are required to perform a stable microincison. They
allow for a precise diameter and tunnel length.
A square geometry optimizes the stability of the wound. Studies have shown that rectangular
incisions have lower resistance to deformation pressure. A long tunnel can induce corneal folds,
decrease the probe motion, and increase the surgically induced astigmatism. A short tunnel
contributes to intraoperative and postoperative leakage, with increased risk of endophthalmitis. If
limited, wound-stretch during the procedure has negligeable consequences. However, excessive
stretching linked to the use of an unproper calibrated blade or lateral intraoperative movements
may lead to an ovalization of the incision and compromize its self-sealing properties.
Thermal burns rarely occur with sleeveless phaco tip used during bimanual MICS. An adequate
setting of the machine with low ultrasound power levels and pulse mode decreases the incidence
of complications. The accurate architecture of a microincision leads to increased safety and
comfort during the surgery as the surgeon works in a closed environment. Postoperatively,
several studies have shown that MICS stabilizes the optical quality of the cornea, prevents
surgically induced astigmatism, avoids corneal aberrations and provides faster visual recovery.
MICS INSTRUMENTS
The reduction of the incision size requires a perfect calibration of the instruments used during the
procedure. As mentioned in the previous paragraph, microblades are necessary to obtain an
incision size slightly larger than the US and I/A probe. Trapezoidal blades with 1.6 x 1.8 mm size
allows for equilibrated inflow of fluid with limited friction of the probe during the different steps
of the surgery. This incision size is compatible with a wound-assisted implantation of most MICS
intraocular lenses.
The capsulorrhexis is easily performed either with a bent needle or microforceps specifically
designed for sub-2-mm incision.
Irrigating choppers or dividers with large bores positioned in the front or laterally are used to
chop or divide the nucleus during bimanual MICS. Several types of vertical or horizontal
choppers are available. Irrigating and aspirating probes are also designed to complete the I/A
part of phacoemeuslification and facilitate the aspiration of the cortex, particularly under the
incision site.
PHACO PLATFORMS
Today, most phaco platforms are developed to be MICS compatible. Several technical points
have been adjusted to optimize the results of the phaco machine used in conjonction with
microincisions. Smaller incision sizes imply the use of microphaco tip. Twenty-gauge phaco tips
are currently used with all types of machines. The smaller inside diameter of the phaco tip
reduces the holding power of the tip. However, special tip designs such as flared tips counteract
this limitation. In addition, the restricted inner phaco tip diameter can slow down surgery speed.
Thus, the use of smaller phaco tips requires higher vacuum settings to perform an effective
phacoemulsification.
Fluidics is regulated by peristaltic or venturi pumps but today, the latest pumps are mixed pumps,
which offer the best of the two systems to equilibrate the inflow and the outflow. The goal is to
obtain a stable anterior chamber all along the different steps of phacoemulsification. The inflow
of fluid is mainly regulated by the height of the bottle. The inflow should always be superior to
the outflow to avoid surge. Antisurge tubings and algorythms as well as anticlogging filters are
currently available. These technological advances reduce the incidence of clogging and
postocclusion surge and improve anterior chamber stability even with higher levels of vacuum.
The modulation of ultrasounds and the lower frequency of the phaco handpiece have limited the
temperature at the incision site and decreased the energy delivered into the eye. This is
particularly advantageous in bimanual MICS where a sleeveless phaco probe is used. Most
machines allow for customized ratios of "on-time and off-time power settings", called duty cycle,
and variable power intensities to minimize the total amount of phaco energy delivered into the
eye. The modulation of ultrasound with the onset of pulses and bursts has transformed
phacoemulsification from an ultrasound, power driven technique to an aspiration, manual
chopping driven technique. Continuous and high levels of ultrasounds which could cause thermal
trauma to the incision and endothelial damage are no longer necessary. Effective fluidics control
and power modulation softwares have contributed to a widespread acceptance of MICS,
shortened the learning curve and improved the effectiveness and safety of the procedure.
SURGICAL TECHNIQUES
Microincision cataract surgery can be performed with two different techniques: bimanual (BMICS) and coaxial (C-MICS).
In the B-MICS, a sleeveless phaco probe provides the US and aspiration and a separated
irrigating instrument is used through a second incision. The fluidics of B-MICS are particularly
advantageous for an effective phacoemulsification. The separation of aspiration and irrigation
lines allows for a synergetic work of the two functions. Irrigating instruments need to provide
sufficient inflow to balance high vacuum settings. The learning curve of B-MICS is steeper than
for the C-MICS, and could explain why the majority of cataract surgeons perform coaxial
phacoemulsification. In C-MICS, a sleeved phaco probe provides aspiration and irrigation
through one incision. The only difference with a standard coaxial phaco is the reduction of the
incision size which explains why there is almost no learning curve with C-MICS.
The divide and conquer technique is compatible with MICS. Specific irrigating dividers are
available to accomodate the scuplture of the lens. Chop or stop & chop techniques allow for a
faster and more effective nucleus extraction with less intraocular energy delivered. Stop & chop
facilitates the transition from divide and conquer to chop technique.
The manipulation of the sleeveless phaco probe and the irrigating chopper requires particular
attention to avoid incision and Descemet's membrane damage. The phaco tip is inserted with the
bevel down and the chopper horizontal. They are rotated clockwise in the anterior chamber. To
maintain the inflow of fluid and the anterior chamber stability, the irrigating instruments are
always pulled out of the eye after the phaco probe and the aspirating tip.
Power and fluidics settings vary according to the machine, technique and cataract grades. This
includes the height of the bottle, vacuum, flow rate, ultrasound power and mode (duty cycle,
pulse, burst) during the different steps of the procedure and for some machines, the adjustment of
the pedal's dual linear control. The choice between longitunal, torsional or elliptical ultrasounds
depends on the phaco machine and surgeon's preferences. These ultrasound delivery systems aim
at optimizing the effectiveness of the procedure with improved followability, efficiency and
safety.
Hydrodissection is a crucial step in MICS as the small size of the incison limits the amplitude of
the maneuvers and prohibits lateral movements during the surgery. Partial removal of viscoelastic
substance is necessary before the beginning of hydrodissection to avoid an over-inflated anterior
chamber. Minimal volume of fluid is injected to obtain hydrodissection and hydrodelineation.
The cannula is inserted under the capsulerrhexis border, the capsule is slightly raised and the
fluid is directed in the capsular bag to separate the capsule from the lens and the epinucleus from
the nucleus.
MICS INTRAOCULAR LENSES
An increasing number of MICS IOLs are now available on the market. Hydrophilic IOLs
represents the majority of lenses as they are more easily implantable through sub 2-mm incisions.
Intraocular lens implantation is performed with a wound-assisted technique through a 1.6 mm
incision size. Specific cartridge and syringe type injectors garantee a safe and reproducable
implantation with no need for incision enlargement. Complete removal of viscoelastic substance
is required at the end of the procedure to minimize the risk of IOL dislocation. MICS IOLs are by
definition thinner than standard ones and their in-the-bag implantation needs to be secured and
stabilized at the end of the surgery. Studies have shown that MICS IOLs provide excellent optical
performances and stable refractive results. Some of the lenses have multifocal optics and can also
correct astigmatism at the same time.
The interest in microincision cataract surgery is constantly growing with the industry
encouraging this evolution. In fact, technological improvements of the phaco platforms with
optimized fluidics and power modulation control facilitates the transition and improves the safety
and effectiveness of phacoemulsification. Specifically designed microinstruments enable easy
maneuvers during the procedure and shorten the learning curve. The availability of high-quality
MICS IOLs with reliable injecting systems completes the surgical arsenal. Over the years, there
has been a consistent reduction in cataract incison size and this trend should continue in the
future.
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