THE YAG LASER - Technical Description of How It Works
"The collagen proteins which make up the eye floaters are ideally destroyed by the laser, converted to water vapor, or other gases like carbon dioxide, and then dissolved into the solution of the vitreous fluid. Some floater types are more efficiently vaporized than others, and others types may require more and/or more aggressive treatment."
YAG LASER ORIGINS AND USES IN OPHTHALMOLOGY
The ophthalmic YAG laser has been used clinically since 1983. YAG lasers of various makes are are more commonly used to treat two conditions: A) Lens Capsule Opacification, and B) Narrow Angle Glaucoma
Not all YAG lasers are optimal or can be used at all to treat eye floaters. Even though the wavelength and frequency of the laser energy is similar across different manufacturers, the illumination light tower and other form factors make a big difference. I chose the Ellex Ultra-Q YAG laser for my work (note: I am intentionally NOT using the Ellex Ultra-Q Reflex model which is being touted as a floater-treatment laser). The Ellex Ultra-Q has a specific FDA labeling for treating vitreous membranes. Ultimately it is the surgeon’s choice, based on experience, which laser best fits their needs.
More important than the model of laser used is the doctor’s experience. If your local ophthalmologist suggests treating your floater, but it is not a significant part of their practice, be cautious. It is our opinion that the treatment of eye floaters is a very specialized skill set developed over the treatment of multiple hundreds of patients, thousands of treatments, and (for us) millions of individually aimed, assessed, and fired laser shots. If your doctor just bought the laser and “dabbles” with floaters, they may not be entirely committed to mastering the unique skills required to safely and successfully treat your eye floaters. Choosing an inexperienced doctor can have devastating implications.
YAG LASER PHYSICS
YAG lasers are solid-state lasers use Yttrium/Aluminum/Garnet crystals and are stable, self-calibrating, reliable, and accurate lasers that require little maintenance. Unlike lasers most people are accustomed to, the optics of our laser DOES NOT emit a single narrow beam.. The laser energy profile of the Ellex YAG laser has a cone-shaped beam. The YAG laser frequency is invisible to the human eye, but there are two red, visible, low energy red diode lasers that are always on and used as a focusing aid.
This cross-section schematic shows the cone-shaped pattern of the YAG laser energy profile. It is not a laser ‘beam’ in the more traditional sense. The energy is instead focused into one point in space. This is the only area where it is delivered. The laser energy can pass through the transparent tissues like the cornea and lens in the front of the eye, and importantly does not deliver any energy to the retina in the back of the eye – AS LONG AS the focused energy is kept a safe distance from these tissues.
The two red focusing lasers. the cone-shaped YAG treatment laser, and a few other optical mechanisms all coincide on one small spot where the energy is delivered. This allows the laser to pass though the cornea and lens without delivering any energy. The pulsed energy is only delivered where the apex (tip) of the cone-shaped energy profile where the focusing beams coincide. This also answers a question we are often asked: “What happens if you miss the target”? The answer is “Nothing”. The energy dissipates on the far side of the focus point and so no energy is delivered to the sensitive and important retinal tissue.
LASER ENERGY AND EYE FLOATER VAPORIZATION
A common misunderstanding among laser treatment naysayers and critics is the concern that the laser only breaks the floater into smaller pieces. They assume that having many small floaters would be worse than one large one. We have two answers to that concern: A.) Small floaters, if they are more than a couple millimeters from the retina may not cast any noticeable shadows and may be imperceptible and B.) The YAG laser, at appropriate energy levels not only breaks the floater into smaller pieces, but also vaporizes the collagen molecules directly to a gas so that at the end of a treatment, there should be less mass and less material present.
Floater molecules are not just broken up, but also converted to a small gas molecules which can exit the eye by passing across cell membranes just like oxygen and carbon dioxide molecules do with every breath you take.
With tight focus of the laser on the surface of the floater and appropriately delivered energy levels, there is a physical process called optical breakdown and plasma formation. There is a high frequency electrical field confined to an area of about 4-8 microns (4-8/1000’s of a millimeter). There is a combination of photochemical, thermal, thermoacoustic, and electromagnetic optical field effects which ionizes the molecules and forms plasma gases. For a duration of approximately 20-30 nanoseconds (0.0000002 seconds) the plasma becomes opaque and highly reflective acting like a shield preventing the energy from continuing towards the retina. With a good shot of the laser, both the surgeon and the patient will see a ‘spray’ of gas bubbles. The surgeon sees them rise to the top of the eye but the patient appears sees (what appear to be) small black dots sinking to the bottom of the visual field.
Since the floaters are inert and nowhere near nerves or other living tissues, the treatment is painless and there is no expectation for inflammation or healing in the traditional sense. More about the treatment experience (Here).
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