Ординатура / Офтальмология / Английские материалы / LASIK and Beyond LASIK Wavefront Analysis and Customized Ablation_Boyd_2001

Fig 5-23. The Carriazo-Barraquer microkeratome.

The automated advance mode has a double traction: the crown of the head engages on crowns located at the end of the pivot on the ring, different from other automated Microkeratome. The motor gives the traction to the crown and the pivot ensures the guidance of the pivoting movement.

By using rings that pivot without a crown, the head can rotate freely around the pivot; this allows the surgeon to manually rotate the Microkeratome during the cut.

The head has a superior opening with an interior coil to set the motor.

It has a lateral groove that goes through and permits the introduction of the blade with the blade holder. It has a lateral curved guide that permits the sliding of the Microkeratome over the suction ring and maintains its correct position.

On the other side, it has a cylindrical vertical guide that has a rotational advance system in its interior.

The head has a fixed built-in plate located in front of the blade that applanates the cornea and determines the flap thickness.

In the center of the head is the blade housing, which is an opening that goes from side to side of the head at 300. The blade is made of stainless steel and comes sterile with a disposable blade holder.

MICROKERATOMES

Heads are available for cuts of 130, 160, and 180 microns flap thick nests.

The motor for automated advancement is electrical with two concentric shafts. The inner shaft rotates at 15,000 revolutions per minute (RPM) and activates blade oscillation. The outer shaft rotates at approximately 1000 RPM and, by means of a worm gear, connects to pinions located inside the head, which will transmit the pivot’s advance movement.

A nitrogen turbine can also be used. Turbine motors have a much higher torque than electrical motors. The turbine motor has only one shaft for driving the blade oscillation at 17,000 RPM. When the turbine is used, the Microkeratome is manually advanced.

The blade is made of stainless steel and comes sterile with a disposable blade holder. This holder has a protrusion that helps engage the blade in its housing without risk of damaging the cutting edge. The holder’s special shape has been developed in order to ensure a very accurate guide into its oscillations, for an accurate and predictable cut thickness.

The rings are very small in order to allow access to all types of eyes, including small and deep.

The Moria Evolution power unit powers the Carriazo-Barraquer Microkeratome. It is a batterypowered device. This unit can drive a nitrogen-pow- ered turbine motor or an electrical motor.

The nitrogen turbine motor can only be used for manual translation of the keratome head. The automated mode requires use of the electrical motor.

Both the turbine and electrical motor are supplied with the system in order to allow the surgeon a choice of the advancement mode.

The power unit provides the vacuum for the suction ring by means of two vacuum pumps. When the vacuum is activated by the corresponding footswitch, one pump is activated. The second will act as a back up and operates only if the control unit detects vacuum loss.

The unit has several safety devices such as alarms in case of vacuum loss, low battery charge, and deficient nitrogen pressure. It also has a low vacuum mode.

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Fig 5-23 A: The Disposable Carriazo-

Barraquer microkeratome.

Recently C. Carriazo modified the original Carriazo –Barraquer system for its disposable (Fig 5-23 A) and reusable use without gears in the head.

This Carriazo-Barraquer 2 Microkeratome (Fig 5-23 B) overcomes the inconvenient generated by the use of gears. It can be used manually or automatically.

In this model the ring handle has a special rotational system that allows different hinge sizes.

Moria ONE (Fig 5-24)

This manual Microkeratome is made mostly of stainless steel and is gearless. Its BI-faceted blade is also composed of stainless steel.

Because of its one-piece pre-assembled heads, the LSK-1 eliminates the risk often associated with presurgical assembly of the device, as a result of the manufacturer. Flap depth is dependent on the head selected and three depths are available: 130 m, 160 m and 180 m.

It brings a new power unit (Evolution II), and it is designed to work with the Moria Microkeratome and Carriazo-Barraquer. The versatility of this unit is particularly appealing for the surgeon who wants the option of using different types of microkeratomes.

Both the reusable and disposable One is powered by a nitrogen turbine giving high torque and

Fig 5-23B: The Carriazo-Barraquer 2 microkeratome

speed of 15,000 revolutions per minute (RPM) or 30,000 blade oscillations per minute.

The power unit has two powerful vacuum pumps. In normal conditions, only one pump is activated. In case of vacuum loss, the vacuum monitoring system will instantaneously activate the second pump in order to compensate the detected failure.

The low vacuum mode. This is one of the innovative features of this unit. It permits fixation of the eye by means of the ring handle (assisted fixation) during the laser ablation without compromising retinal vascular flow. It also allows the control

Fig 24. The Moria ONE.

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of peripheral bleeding in patients with peripheral corneal neovascularization.

Audible and visual alarms. The surgeon is alerted in case of loss of vacuum, low nitrogen pressure in the tank, or low battery charge.

Test mode. The surgeon is able to check the appropriate suction levels before the procedure.

.

Moria One Disposable (Fig 5-24 A)

The disposable one is the newer sibling of the original One. It has the same basic principles. It has a one-piece plastic molded head with one blade inserted, which, as a safety feature, cannot be removed from the head. The heads are available for cuts of 160 or 180 microns and are powered by the same turbine as the reusable one head, with an oscillation off 15,000RPM.

The rings are reassembled with the handle and aspiration tubing, and the two arms of the handle are opposite the head translation. This innovative ergonomic design improves sliding of the head and allows stabilization of the eye by opposing a force to the linear translation of the Microkeratome.

The location of the stopper just upward the ring allows complete visibility of the head position in relation to the stop during the cut. This avoids false stops due to the speculum or any other obstacle. The surgeon always knows the position of the head and can control the hinge size during the cut.

Fig 5-24A : The Disposable Moria ONE.

The Hansatome, like the ACS, relies on a gear drive to provide forward motion, but the number of tracks has been reduced to one, and the drive is now nasally located and slightly elevated, with some space between it and the patient’s eyelid and the speculum. This design prevents impeded forward progress or binding, while the single track allows smoother cuts. The system can create flaps of 8.5 mm to 10 mm.

It uses a disposable blade with an affixed

holder

The power supply unit has an internal diagnostic equipment, it verifies if the system is functioning properly before each procedure, and the system will not allow cutting to begin until the appropriate vacuum level is achieved. Cutting automatically stops if vacuum drops below the threshold, and an electronic compensation system delivers constant motor speed.

The Hansatome can create flaps of 160 m and 180 m in depth. The system involves hardware to adapt it to either left or right eyes. It is designed to create flap diameters of 9.5 mm.

Clear Corneal Molder (Fig 5-26)

This instrument consists of one single piece of 25 cm that involves one motor of double shaft, one suction ring and one applanation lens. The cutting blade is of thin metal in a plane of 00, has oscillatory movement, it slides between the suction ring and the applanation lens conducted by one electric motor. This feature allows a complete vision of the entire cut. There is only one suction ring, whose height in relation to the blade is adjustable and allows a resection of the flap between 7 and 10 mm. It has a fixed resection thickness.

The system can accept both stainless steel and diamond blades. Although diamond blades are not available for the system commercially.

This Microkeratome has a 0° blade-angle of attack on the cornea.

Blade speed is manually controlled up to 12,000 oscillations/min, and the keratome head advances manually across a single suction ring on gearless tracks. Separate electrical motors, controlled by a foot switch, perform each function.

Fig 5-26. The Clear Corneal Molder microkeratome.

The standard model has a fixed flap depth of 180 m, which is adequate for LASIK.

SCHWIND Keratome -Herbert

Schwind’s Microkeratome (Fig 5-27)

This is a single piece of automatic hand of 130degree weight and with a sapphire blade of 00 with oscillatory movement and two motors. The first one is for the advance of the blade, speed of 1.3-mm/sec and reverse speed of 3 mm/sec, and the other that supplies oscillation of 4.050 rpm of the blade.

Fig 5-27. The Schwind microkeratome.

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Both motors get placed in the control unit apart from the handle of Microkeratome. It has a dual suction ring in order to take the anterior sclera and the cornea; the sapphire blade slides between them to make one flap of 9mm diameter, with a fixed thickness of 150 microns. The control unit allows checking the pressure and the suction ring. This was the first Microkeratome with the handle independent from the motors.

It is the only Microkeratome in this survey that uses a sapphire blade, a cutting mechanism so sharp that it can create 300 or more corneal flaps before it needs to be replaced.

The fully automatic Microkeratome System relies on a motor located in its base console unit for both forward motion and blade oscillation. Power is supplied to a stainless steel hand piece through two plastic-coated drive shafts.

The system features a fixed depth plate that cuts at a consistent depth of 160 m. Globe fixation is achieved through a suction ring affixed to the limbs, while a smaller inner suction ring stabilizes the flap. Loss of suction automatically aborts the procedure and returns the blade to the home position. The system also features an emergency shut off knob that immediately stops all operations and shuts off the power supply. Releasing the foot pedal stops blade motion but maintains suction. If suction is not properly achieved prior to a cut, an audible warning sounds. The dual-position pedal can initiate a selftest and calibration prior to treatment, direct the blade to the home position and activate the vacuum pump to build suction prior to surgery.

The SCMD Turbokeratome (Fig 5-28)

This system features high-speed, high-torque nitrogen driven turbine motor that drives a reciprocating surgical blade at the ideal speed of 13,800 revolutions per minute (RPM). It is a manual, gearless Microkeratome.

The turbokeratome has an oscillatory movement and includes one inclined blade of 260 and produces a corneal resection of 150 microns thick.

It brings four applanator lenses provided with the turbokeratome system: 7.5 mm, 8.25 mm, 8.75 mm and 9.25 mm. Four different vacuum fixation rings control the diameter of the cornea that is ex-

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size, blade traverse distance, and advancement and oscillation speed of the blade by means of front panel settings on the control unit.

Based in the original Barraquer head, the major components of the SKBM are the control unit that involves operator controls, a microcomputer, a vacuum pump, and a back-up power supply a Microkeratome handpiece that contains motor for blade oscillation and advancement of Microkeratome head that has an oscillating steel cutting blade, four suction rings handle, and vacuum tube connector.

It is very important to know that in the motor shaft are three small pins. The center pin is the eccentric pin, which drives the blade oscillation. Dial the eccentric pin to the 6 or 12 o’clock position to allow the motor shaft to engage correctly with the Microkeratome head. If the Microkeratome head will not engage with the motor shaft press the extended pins on the side of the Microkeratome head and gently advance the head onto the motor shaft until it clicks.

Commendable only to realize nasal hinges due to its size and applanation plates.

A total of four suction rings are included with the SKBM: two rings with an outside diameter of 19 mm. The rings must be sterilized prior to every patient procedure. The rings are also marked as either # 3 or # 4 to indicate expected flap size. The # 3 size will normally produce the same diameter flap on both the 19 and 21-mm rings, as will the # 4 rings. The numbers used for flap size follow the original Barraquer nomenclature, whereby the lower the number, the larger the expected applanation and, therefore, the larger the flap diameter.

MICROKERATOMES

Suction rings marked # 3 have a shallower depth, so that they sit lower on the cornea. When these rings are used during a procedure, larger flaps (9.0 to 9.5 mm) are obtained.

It is important to note that the 19-mm rings do not protect the eyelids and drapes to the same extent as the 21-mm rings (because the steel blade oscillates approximately 0.85 mm beyond the wind of the Microkeratome head). The operator should carefully monitor the progress of the steel blade during the cutting phase to prevent possible injury to the eyelid when using the 19-mm ring.

Suction rings marked No 4 have a deeper depth, so that they sit higher on the cornea. When these rings are used during a procedure, a smaller diameter of cornea is applanated and smaller flaps (8.5 to 9.0 mm) are obtained.

In order to obtain a flap of the desired size, the meniscus of the cornea must correspond with the marking observed in the window of the Microkeratome head.

For example, if 8.5 mm of cornea is visibly applanated in the window and the panel setting is maintained at 9.0 mm for the cut diameter, the cut may be larger than the flap, causing a free cap. Similarly, if 9.5 mm of the cornea is visibly applanated in the window and the panel setting is maintained at 9.0 mm for the cut diameter, the cut will be smaller and the hinge larger than desired. If these do not correspond, adjust the panel settings.

The system’s blade angle of 26° is borrowed from the original Barraquer design, as is the depth plate, which is fixed on standard models at 160 m.

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Automatic Disposable Microkeratome

(A.D.K): (Fig 5-34)

The gear drive is in both sides of the keratome and is shielded by plastic skirts, allowing more symmetrical passage of the keratotomy and essentially eliminating the possibility of incarcerating material, such as cilia drapes, etc., into the gear drive. The keratome is installed in the suction ring at the factory to eliminate the awkward maneuver of putting the keratome in the suction ring already on the eye. The blade angle is 250 in keeping with Jose Barraquer’s tediously worked out principals. The suction ring has an aperture diameter of .488 inches and an outside diameter of .772 inches.

Because of a reduction transmission into which the motor is inserted, the gear drive runs at 5.5 mm per second and the blade oscillation speed is 7500 RPM. The keratome head is assembled at the factory, involving installation of a high quality, high power inspected blade. The blade is stainless steel. The suction handle serves as the stopper for the keratome.

The drive gear mechanism is covered, which should prevent tissue or eyelashes from interfering with the cut. The stainless steel blade oscillates at 10,000 cycles/min and advances at a rate of 4.5 mm/ sec. The device can create flaps from 9.0 to 9.5 mm in diameter.

The suction ring of the disposable unit has a narrow profile, which allows its application to virtually any eye, regardless of size or lid shape. The inside applanation diameter allows the creation of large flaps and decreases the chances of creating free caps in patients with extremely flat corneas.

The electric power console features reusable or disposable suction tubing and an internal alarm that alerts the surgeon to inadequate suction. The motorized drive mechanism can be attached directly to the keratome or can be situated remotely with an external drive cable. The motorized drive attaches to the keratome with a rapid coupling device.

of 0.9 mm and a variable advance rate of 1 to 4 mm/ sec. The oscillation rate is also variable up to 10,000 cycles/min. Flap diameter is variable from 8 mm to 10 mm.

The applanation plate is preset to 160 m and over the plate is a spring-loaded, disposable blade carrier that is supposedly easier to replace than a blade alone.

Other Mechanical Microkeratomes:

Amadeus. ( Fig 5- 36 )

Diamond Barraqueratome.

MicroPrecision

Microlamellar Keratomileusis System.

Med-Logics Microkeratome.

Femtosecond Laser Keratome (INTRALASE) (Fig 5-37)

A femtosecond laser is similar to a Neodymium YAG laser except that each laser pulse is approximately one hundred thousand times shorter in duration, lasting only about ten to the minus thir-

Fig 5-36. The Amadeus microkeratome.

Fig 5-37. The Femtosecond Laser Keratome.

teenth seconds. Each pulse creates a micro cavitation a few microns in size. Many pulses are required to create a surgical effect and these are delivered with a sophisticated computer controlled scanning system.

The possible advantages involved: The ability to make reproducible cuts no matter the shape of the eye. The ability to keep the intraocular pressure in the normal range at all times during the procedure. In this kind of system the side cut can be made at any angle or shape.

The accuracy and reproducibility of the femtosecond keratome has been tested in animal eyes with good results. Some technical characteristics are:

Laser source: Diode pumped pulsed ND-glass oscillator with a diode pumped regenerative amplifier (chirped pulse amplification, CPA), wavelength: 1052 NM. Pulse energy: 50 micro joules, Repetition rate: 7 kHz, (soon 10 kHz). Pulse length: ~600 fs. Treatment: Pulse energy: 4-5 microjoules, spot separation: 8-10 micrometers, pulse power: ~10 kW.

It is estimated that the cost of the laser Microkeratome system will be comparable with that of an excimer laser.

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