LASIK, or Laser-Assisted In Situ Keratomileusis, corrects vision by reshaping the cornea. Many people wonder if they will see the laser beam aimed at their eye. The straightforward answer is no; the patient cannot see the excimer laser used to reshape the corneal tissue. This invisibility is a function of the laser’s design and its physical properties.
The Invisible Wavelength
The therapeutic laser beam is unseen because of the specific type of light it emits. LASIK utilizes an excimer laser, which operates in the ultraviolet (UV) spectrum, typically at a wavelength of 193 nanometers (nm). This wavelength is far shorter than what the human eye can detect.
The visible spectrum of light, which humans can perceive, spans approximately 400 nm to 700 nm. Since the excimer laser operates below this limit, the energy it delivers is invisible to the patient. This UV light precisely removes microscopic amounts of corneal tissue through photoablation, without generating heat or damaging surrounding cells.
The Visual Experience During LASIK
While the therapeutic laser is invisible, the patient’s visual experience is not complete darkness. Before reshaping begins, you are instructed to fixate on a target light, often a small, colored light (such as green or red). This fixation light is intentionally within the visible spectrum and helps keep the eye steady and correctly aligned under the laser.
During the procedure, you may notice surrounding surgical lights appearing dim, distant, or blurred. As the surgeon prepares the eye, a suction ring is applied to stabilize it, which temporarily raises the internal pressure. This pressure causes a sensation known as a “gray out,” where vision momentarily dims or goes completely dark for a few seconds. This temporary dimming is due to the pressure, not the excimer laser.
Once the excimer laser begins firing, the visible fixation light may flicker or disappear entirely. This momentary visual change is caused by the microscopic tissue removal process, which creates a cloud of microscopic particles that temporarily scatter the light. The experience is brief, and vision returns to the dim, blurry view once ablation is complete.
How Focus is Maintained
Keeping the eye perfectly still during the brief laser application is a common concern, but advanced technology manages this. The small, colored fixation light serves as the initial guide, giving the patient a focus point. This light is positioned directly in the center of the laser’s path.
The primary method for maintaining precise focus is active eye-tracking. This advanced system uses high-speed infrared cameras to monitor the eye’s position hundreds to thousands of times per second. If the eye makes a tiny, involuntary movement, such as a microsaccade, the system instantly adjusts the laser’s aim to compensate.
If the eye moves past a safety threshold, the eye-tracking system immediately halts the laser emission. This ensures the laser only fires when perfectly aligned with the intended treatment zone, guaranteeing accurate corneal reshaping. The laser only resumes once the eye is back in the correct position, making the procedure safe even if you feel the urge to move your eye.