How LASIK Works


Young woman smiling after LASIKThe excimer laser is a type of laser used in refractive surgery to correct nearsightedness, farsightedness, and astigmatism. This laser is used to reshape the surface cornea in order to decrease the patient’s reliance on glasses. This laser is used in both PRK and LASIK. Our Sacramento LASIK center currently uses a scanning slit and spot beam laser with wavefront optimized profiles to achieve the best clinical results.

Laser-Assisted In Situ Keratomileusis (LASIK)

LASIK is now the vision correction procedure of choice for many ophthalmologists worldwide. Instead of removing the surface epithelium with the laser and exposing many nerve endings (as in PRK), the surgeon performing LASIK uses a motor-powered microkeratome to create a “flap.” The flap is then lifted and reflected back, allowing a computer-guided Excimer laser (cold laser) to use light pulses to remodel the corneal tissue underneath. Afterward, the flap is gently positioned back onto the cornea. Since this procedure is less traumatic to the outer surface of the eye, vision is restored more quickly and the patient’s discomfort is reduced. Most patients report greater comfort after surgery and can generally drive two to three days after the surgery.

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If you have any questions about LASIK surgery, feel free to contact Dr. Liang’s Sacramento office at 916-446-2020.

Allegretto Wave Eye-Q

The ALLEGRETTO WAVE EYE-Q laser system performs customized LASIK treatment using data provided by the WaveLight® Topolyzer™ VARIO.  These procedures are called “Topo-guided” or topography-guided Custom Ablation Treatments. The Topolyzer system measures the height data of the patient’s cornea and generates the required topography data for planning and carrying out topo-guided treatments. This data is transferred to the ALLEGRETTO WAVE EYE-Q laser system where it is used to plan and perform the customized corrections to the eye.

It is the fastest laser system for LASIK surgery in the United States today, using PerfectPulse Technology to safely and accurately control every single laser pulse from start to finish. The system was designed to perfection based on knowledge and experience. It represents a new generation of refractive technology conducting High-Performance Vision Correction that patients can rely on night and day.

The Allegretto Wave Eye-Q offers a customized treatment that incorporates wavefront principles to patients with nearsightedness and even farsightedness.

Dr. Liang works with patients to tailor it to their corneal curvature and refraction with the intention to preserve the natural aspheric cornea shape and to maintain or improve the quality of vision and visual acuity.

Allegretto Wave-Front technology


Available in our Sacramento LASIK center, the laser makes surgery a breeze. In one second the system applies 400 fine laser pulse on the cornea. In fact, one diopter only takes 4 seconds to correct (at a 6.5mm true optical zone). That means that the average patient treatment with about less than 3 diopters takes only ten seconds. The time it takes you to pour yourself a cup of coffee.


Such a high-speed laser must also have an ultra-fast eye-tracking system to follow eye movement during the procedure. The Allegretto Wave Eye-Q captures the current position of the eye 200 times per second. It then only takes the laser a fraction of a second to reposition the laser putting it exactly into the desired location on the eye. Should the eye ever move too fast or out of range, the laser will automatically stop and wait until the eye is back in position. So you can simply relax, knowing that your eye is being followed at all times.

Eye Doctor performing a LASIK Eye Exam
Perfect Pulse Technology

PerfectPulse Technology means that every laser pulse is completely controlled as it is applied to the eye using intelligent pulse management.

This is critical as the ALLEGRETTO WAVE EYE-Q operates at high speed with 200 laser pulses per second. Every laser pulse thinner than your fingernail in order to precisely sculpt the corneal surface.

Therefore, PerfectPulse Technology uses advanced high-speed eye-tracking to follow the eye’s fastest movements and ensures accurate placement of every laser pulse. During the treatment, the energy stability of every pulse is controlled with a smart energy control program. This program automatically balances the energy levels during the treatment to ensure that every laser pulse creates the same result.

More about PerfectPulse Technology

PerfectPulse Technology comprises many different technological components all aimed to control the laser pulse.

Smart Energy Control measures the energy of each pulse three times while the pulse travels through the laser system. If at any of the three checkpoints the laser pulse’s energy does not meet the desired energy during the LASIK surgery, then the system will automatically adjust itself.

Energy is heat and if two hundred pulses of energy are applied on the eye per second, this could potentially cause heating which is not desirable. PerfectPulse Technology makes sure that only every fifth laser pulse overlaps the first and therefore reduces the chances of any kind of heating effect.

PerfectPulse also means that the Allegretto Wave Eye-Q precisely sculpts the cornea in order to create an even ablation. With a pulse diameter of less than 1mm and a so-called Gaussian beam profile, PerfectPulse Technology creates very fine, smooth pulses.

The eye can move at extreme velocities. Therefore it is critical to follow the eye movements and place the pulses into the desired location. Active-track automatic eye-tracking technology ensures that this is the case. Our eye-tracking system checks the position of the eye 200 times per second – as many times as laser pulses reach the eye. Once the position of the eye is determined, the laser system automatically adjusts all internal mirrors to place the next pulse into the right location. Right before that pulse is launched, the system reconfirms that the eye has not moved in the meantime. Only if that is confirmed will the system release a laser pulse. The total reaction time from the detection of the eye position to the release of the next pulse is called response time and the Allegretto Wave Eye-Q response time is only 4-6ms depending on the moving speed of the eye.

You can rely on PerfectPulse Technology to control every laser pulse from start to finish. This gives you the benefit and comfort of an ultra-fast treatment and less time to worry.


The Allegretto Wave Eye-Q was designed with the understanding that the human cornea is not a simple optic. Based on extensive empirical research, WaveLight developed a proprietary treatment that is adjusted to the patient’s individual corneal curvature.

Imagine a glass ball. If you took a flashlight and aimed it directly at the top of the ball, the light would form a circular shape on the surface of the ball. If you now aimed the flashlight towards the side of the ball, the light would form an elliptical shape and not seem as bright anymore. This is because the same amount of light is suddenly distributed over a larger area and some of the light is reflected away due to the angled surface of the glass ball.

Understanding these effects, the Allegretto Wave Eye-Q applies additional laser pulses into the periphery, with the intention to compensate for reflection to maintain the natural curved shape of the cornea. In addition, Wavefront principles are applied in order to address the induction of spherical aberrations.

As a result, the Allegretto Wave Eye-Q creates very smooth and functional optical zones. Large, true optical zones are important in laser vision correction, especially for patients with large pupils.

During the day, the pupil is very small because of the bright daylight, but at night or under dim light conditions, the pupil opens up. A large, functional optical zone will support good vision even under dim light conditions.

Large Optical Zone, small pupil, Daylight Conditions (Simulation)

Large Optical Zone Daylight Conditions

Large Optical Zone, large pupil, Night Conditions (Simulation)


In the US clinical trials, more than 1000 eyes were treated successfully with PerfectPulse technology and patients reported improved quality of vision especially in regards to night driving glare.

If you have any questions about the Allegretto Wave Eye-Q or would like to schedule a consultation with Dr. Liang – Center for Sight, contact our Sacramento office.

Our Location

Center for Sight
3160 J Street
Sacramento, CA 95816-4403