Lightning

Most people unfamiliar with this procedure envision the laser taking a large floater and breaking it into hundreds of smaller floaters. That is not the case. Instead, the laser to a great extent obliterates the floater so that it no longer exists. However, especially with multiple floaters, at the end of the procedure there may remain some particles that are too near the retina to treat or are just too small to aim on.

A lightening strike is a familiar example of obliteration of matter under the influence of an intense electrical (optical spectrum) field. The mechanism for this obliteration is called "plasma formation" and "optical breakdown" which are terms known to students of laser physics. (Dr. Karickhoff was awarded "The Outstanding Physics Student" in college.)

Optical breakdown requires:

  1. a very high frequency (changing from plus to minus) electrical field in the optical region of the electromagnetic spectrum that
  2. is confined to a very small area.

When this is achieved, upon firing the laser, the clear vitreous and floater become opaque (plasma formation) at a microscopic point and they absorb the laser energy producing a micro lightening flash (optical breakdown). This flash obliterates the floater with a combination of photochemical, thermal, thermoacoustical and electromagnetic optical field effects. Each time optical breakdown occurs, the surgeon sees the micro lightening on the surface of the floater and both the surgeon and the patient hear the acoustical component (a micro thunder snap).

To focus this force on the floater and to control it:

  1. the surgeon has perfect microscopic viewing of the floater and the laser aiming beam,
  2. he has precise control of the laser power,
  3. the field size of the focused laser beam is only 8 microns wide in air and is much smaller than that when we use one of our three focusing contact lenses during surgery, and
  4. the laser pulse duration of our modern laser (produced in 1999) is only 4 nanoseconds (10 to the minus 9 seconds). Total duration of treatment per case is usually only about 160 nanoseconds.

It is safe to obliterate floaters with this localized force, these controls, familiarity with the laser, judgment, and experience.


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John Karickhoff, M.D. • 313 Park Avenue • Falls Church, VA 22046