Today, most ophthalmologists use at least one laser every day in their practice.
Lasers are widely applied in both diagnostic and therapeutic devices. While few of us are laser physicists, it is helpful to understand a few principles regarding the therapeutic application of lasers.
The word laser is shorthand for light amplification by stimulated emission of radiation. Any wavelength of light can be amplified, whether in the ultraviolet, visible, infrared or other spectrum. Lasers in ophthalmology modify tissue primarily in three ways: coagulation, thermomechanical effects or photoablation. While all lasers generate heat when focused, the impact of the heat on tissue is modified by the time the laser is applied, as well as the rate and location of the laser applications. If we want to melt, burn or coagulate something, we apply a laser for a longer period of time. Thermomechanical and photoablation effects are achieved by utilizing short pulses of laser energy.
Simplistically, I think of the lasers we use in ophthalmology in the following way. First, the longer-pulse lasers in the visible spectrum coagulate tissue. These are the lasers we use to coagulate blood vessels or retinal tissue. Second, the shorter-pulse lasers in the infrared spectrum use optical breakdown to create a spark that has thermomechanical effects. This is how the commonly used Nd:YAG laser works in opening a posterior capsule. I think of it as a small depth charge focused to disrupt tissue. Heat is generated, but the pulse is so short there is no coagulation. Third, the pulsed lasers in the ultraviolet spectrum cause photoablation. Most familiar to us is the excimer laser. Pulsed excimer lasers cause tissue to disappear, converting it into its basic elements. So, very simply, our lasers either coagulate, disrupt or eliminate the tissue we focus them on.
Each type of laser/tissue interaction has valuable clinical applications. In the accompanying cover story, we focus on the femtosecond laser. The femtosecond laser is the ultimate short-pulse laser. It works by creating optical breakdown and is thermomechanical, but the pulses are extraordinarily short. They are so short, it is hard to conceptualize. A femtosecond is one quadrillionth of a second or one millionth of one billionth of a second. That is an ultra-short pulse, much shorter than a Nd:YAG laser. Because the pulse is so short, thermal damage is minimized, and the main effect is a mechanical one. One ultra-tiny explosion after another placed microns apart allows the femtosecond laser to cut like a diamond scalpel. If the pulses are too rapidly applied or too close together, tissue-damaging heat can be generated. Therefore, the focus, pattern and rate of application are critical.
Every clinician knows that some femtosecond lasers create a smoother cut than others. A smoother cut causes less inflammation and induced healing response, which, if excessive, can lead to undesirable haze or scarring. Femtosecond lasers today can be combined with optical imaging, artificial intelligence and robotics, which under a surgeon’s watchful eye can perform some surgical maneuvers very precisely. This has led to increased applications of the femtosecond laser in corneal refractive surgery, cataract surgery, lens-based refractive surgery and microtrabecular glaucoma surgery.
The opportunity for further application of both diagnostic and therapeutic lasers to benefit the ophthalmic surgeon and their patient is nearly limitless. I project, in combination with robotics and artificial intelligence, the impact of lasers in ophthalmology will grow exponentially, fertilized by significant infusions of human and financial capital.
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