YAG Laser Origins and Ophthalmic Uses
The first pulsed Yttrium-Argon-Garnet (YAG) lasers were developed in 1976 and the ophthalmic YAG laser has been used clinically since 1983. Dr. Franz Fankhauser of Switzerland was responsible for developing the Q-switched YAG laser used in treating vitreous pathology. Not all lasers have the specific optics necessary to treat in the vitreous chamber. We chose the Ellex Ultra-Q YAG laser for our work. The Ellex Ultra-Q has a specific FDA labeling for treating vitreous membranes. YAG lasers of various makes are quite common in a general ophthalmology clinic where they are more commonly used to treat two conditions: A) POSTERIOR CAPSULE OPACIFICATION, and B) NARROW ANGLE GLAUCOMA
POSTERIOR CAPSULE OPACIFICATION is a common condition post capsule that occurs after cataract (lens) removal and replacement with an artificial implant lens. The transparent capsule which surrounds the new, clear implant lens may cloud over and starts to resemble wax paper. The laser is very precisely focused onto this membrane and an opening is created and sequentially enlarged to once again restore clear vision. In this illustration, the cone-shaped beam is focused on the membrane behind the artificial lens. Here is a brief, 30 second YouTube video demonstrating where the laser is usually focused.
NARROW ANGLE GLAUCOMA | PERIPHERAL IRIDOTOMY (PI): There is a more rare version of glaucoma is sometimes treated or prevented by using the YAG laser. A small hole is created in the peripheral iris which allows for better communication of fluids between the front and rear chambers of the eye. A Laser Peripheral Iridotomy (LPI) is the name of the procedure and this photo shows the small opening. Below is a nice quality video showing the Laser Peripheral Iridotomy procedure. Note the high degree of precision and accuracy this laser is capable of.
YAG Laser Physics
YAG lasers are solid-state lasers using Yttrium/Aluminum/Garnet as the excitable doping material. They are stable, reliable, and accurate lasers that require little maintenance or worry. Unlike lasers most people are accustomed to, the optics of our laser does NOT emit a single narrow beam that many associate with lasers. As an example of the more common laser, this laser pointer light beam will continue in a straight line until it falls on an object or is dissipated by the atmosphere. The laser energy profile of the Ellex YAG laser is quite different. It has a cone-shaped beam as compared to the laser most people are familiar with. The YAG laser frequency is invisible to the human eye, but there are two red, visible, low energy red diode lasers used as a focusing aid.
The two focusing lasers, the cone-shaped YAG laser, and the surgeon’s narrow depth of field focus 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 to those important structures. The pulsed energy is only delivered where the apex (tip) of the cone 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. It is interesting that if the laser is focused adjacent to the floater into the clear vitreous or watery fluid, there does not appear to be any delivery of energy.
How accurate is the laser focus? The diameter of the YAG laser, when focused, is 4-8/1000 of a millimeter. This image shows the laser removing the top layer of ink off a printed tea bag. Please note, we are fully aware that there are faster ways of creating an outline-style font than using a laser. This was for illustration purposes.
LASER ENERGY AND EYE FLOATER VAPORIZATION: A common misperception 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 and hyaluronin 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). For a duration of approximately 20-30 nanoseconds ( 0.0000002 seconds) the floater becomes opaque and highly reflective acting like a shield preventing the energy from continuing towards the retina. There is a combination of photochemical, thermal, thermoacoustic, and electromagnetic optical field effects which ionizes the molecules and forms plasmas gases. 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 sees small black dots sinking to the bottom of the visual field.
Here is an Adobe flash video (sorry iPhone/iPad users) of gas bubbles clinging to the roof of the eye. This image is taken using the bottom mirror of the Goldmann lens reflecting upward. The bubbles, although transparent, cast a distinctly dark shadow adjacent and behind it. The patient perceives many dark round shadows for the first 15-30 minutes after treatment. These gas bubbles dissolve into the surrounding fluid and disappear completely.
So ideally, the floater material is vaporized and ablated into small gas bubbles which dissolve and resorb in the first 10-15 minutes after treatment. Some of the collagen is fragmented and disbursed which may need further treatment as explained in more detail on our “Expectations of Treatment” page.
