Amar Agarwal, MD has no proprietary interest in this report nor is he a consultant to MicroSurgical Technology. Phone: 91
44 2811 6233 Fax: 91 44 2811 5871 E-mail: dragarwal@vsnl.com
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San Francisco—Cataract removal using 0.7-mm instruments represents the latest development in the evolution of the bimanual phacoemulsification
technique, said Amar Agarwal, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.
"We first described bimanual phaco-emulsification through a 1-mm incision in 1998 and termed that procedure Phakonit," said
Dr. Agarwal, of Dr. Agarwal's Eye Hospital and Eye Research Centre, Chennai, India. "With this new instrumentation, surgery
through a sub-1-mm incision is now possible. This procedure, which we are calling Microphakonit, allows cataract removal through
the smallest incision described to date.
Figure 1 Microphakonit performed through a sub-1-mm incision.
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"Experience shows Microphakonit offers improved intraoperative control and is a safe and efficient method for use in routine
and complicated cases," he said. "We believe it has tremendous advantages, but the full extent of its benefits will be appreciated
only when IOLs become available that can be implanted through a sub-1-mm incision."
Microphakonit has become possible with the development of 0.7-mm instrumentation (MicroSurgical Technology), but use of gas-forced
infusion to increase fluid output is mandatory to maintain anterior chamber stability. The phaco needle that is used for Microphakonit
has been designed with thinner walls than standard phaco tips in order to increase the inner diameter.
Figure 2 Gas-forced infusion is mandatory for maintaining anterior chamber stability during Microphakonit. (Figures courtesy
of Amar Agarwal, MD)
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"With the modification of the needle design and a 30 angulation to the tip, the speed of Micro-phakonit surgery approximates
that achieved using a 0.9-mm phaco needle," Dr. Agarwal explained.
The 0.7-mm irrigating chopper features a sharp cutting edge that allows it to chop cataracts of any density using a karate
chopping or quick chopping technique. To maximize the amount of fluid coming out of the irrigating chopper and optimize fluidics,
it is designed with a single end opening rather than dual side openings. However, due to its small gauge, use of gas-forced
infusion is essential to increase fluid flow and maintain anterior chamber stability.
For that purpose, Dr. Agarwal uses the internal gas-forced infusion of the Accurus surgical system (Alcon Laboratories), although
an external system using an air pump purchased at an aquarium shop offers another alternative.
"With an internal system, we can regulate the amount of air entering the infusion bottle and titrate the system to avoid surge
and anterior chamber collapse," Dr. Agarwal explained.
The anterior vented gas-forced infusion system of the Accurus is composed of an air pump and regulator. The pump pushes air
into the irrigating solution bottle so that the fluid is pushed into the eye without adjusting bottle height. When performing
Microphakonit, Dr. Agarwal sets the infusion pump at 100 mm Hg. In a study measuring fluid flow from the 0.7-mm irrigating
chopper using that setting, he found the exit rate was 65 ml/min.
"For surgeons who use an external pump, we have found that setting the pump's regulator switch for high pressure results in
an irrigating chopper flow rate equivalent to that achieved when using the Accurus set at 100 mm Hg," Dr. Agarwal said.
The technique begins with injection of viscoelastic into the eye at the site where the side port incision will be made. The
clear corneal incisions are created between the lateral rectus and inferior rectus and between the lateral rectus and superior
rectus.
"Because of the use of gas-forced infusion, the surgeon should be careful to make the incision a bit long," Dr. Agarwal said.
"However, in contrast to Phakonit, valve construction is not very important because of the smaller incision."
Dr. Agarwal uses a needle for the capsulorhexis while holding a straight rod in the left hand to stabilize the eye. Hydrodissection
is done carefully to minimize the amount of fluid introduced.
"Compared with coaxial surgery, Microphakonit has the advantage of allowing hydrodissection to be performed from both incisions
and so enables hydrodissection of even the subincisional areas," Dr. Agarwal said. "However, with the smaller incisions, little
fluid exits the eye, and so caution is needed with respect to volume used."
For cataract removal, Dr. Agarwal uses settings of 50% ultrasound power, flow rate of 24 ml/min, and 110 mm Hg for vacuum
with a karate chop technique.
"While any flow rate can be used during Phakonit, the flow rate should not be set very high during Microphakonit," he said.
After nucleus removal is completed, irrigation/aspiration is performed with a 0.7-mm bimanual I/A set.
During his talk, Dr. Agarwal presented a video demonstrating the use of Micro-phakonit in a series of cases that included
eyes with hard brown, mature white, subluxated, and posterior polar cataracts, as well as in eyes undergoing combined glaucoma
surgery or vitrectomy.
