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Lasers Saving Sight Teacher Sheet

Lasers Saving Sight Teacher Sheet Photo Credit: Clipart.com

Introduction

Your students should read the article, "Preserving the Miracle of Sight: Lasers and Eye Surgery," from Beyond Discovery, a project of the National Academies of Science, and answer questions on their student sheet. You can find answers to the questions on this sheet.


Name the two streams of research that contributed to the development of laser eye surgery.
Basic research in human anatomy and medicine and in physics intersected in the early 1960s to produce a revolution in ophthalmology that has saved hundreds of thousands of people from severe vision loss.

What eye problems can be treated with laser surgery?
When caught in time, the damaging changes in retinal blood vessels brought on by diabetes can be stopped—and in some cases even reversed—using the powerful, tightly focused beam of a laser. Precision lasers also can repair small tears in the retina that might otherwise lead to retinal detachment, and they are used in surgery related to cataracts.

Describe how the retina works. Why is it so vulnerable?
This thin layer of cells lining the back of the eye is akin to the film in a camera. If the film is damaged, no images are possible even if the rest of the camera is working perfectly. This biological film is actually an extension of the neural tissue of the brain itself. Early in the development of the embryo, the neural tube, which gives rise to the brain and the spinal cord, forms two optic vesicles, each of which folds inward to form an optic cup. A layer of cells, the neural epithelium, on the inner wall of the optic cup eventually becomes the retina. In the course of development, cells of the inner wall differentiate into all the retinal cells needed for vision. It is vulnerable because except for a few attachment points, such as around the optic nerve, the retina is held in place against the pigment epithelium and the back of the eye only by the fluid pressure of the vitreous.

What were some early techniques in treating a torn retina?
One early technique was called “ignipuncture.” This technique involved cauterizing the sclera (the eye’s opaque outer layer) with a hot instrument and deliberately perforating it to allow the subretinal fluid to escape. Diathermy, which involved applying a heat-generating electric probe to the retina, still required cutting into the wall of the eye. As the incision healed, the wall tended to shrink substantially. Not until the advent of cryotherapy, or freezing, in the 1960s did a technique become available that could treat retinal tears without damaging large areas of adjacent retina.

How did Einstein and Plank contribute to the procedure of laser surgery?
Albert Einstein published an article on a phenomenon he called “stimulated emission,” which would ultimately give rise to the laser. Einstein's idea built on work by German physicist Max Planck in 1900 and Danish theoretician Niels Bohr in 1913. Planck had theorized that accelerated atoms radiate energy in discrete packets, which he called “quanta.”

Describe Bohr’s model of the atom (briefly).
According to Niels Bohr's model of the atom, electrons occupy specific orbits around the nucleus that are determined by the atom's energy level. An atom can absorb only the exact amount of energy needed to kick an electron from one orbit up to a specific higher one, and it emits a specific amount of energy when an electron drops from a higher orbit to a lower one.

Describe how the work of physicists led to early laser technology.
The work of physicists like Planck and Einstein led to an understanding that light is made up of particles called "photons." According to Einstein, if atoms in an excited state are stimulated by an encounter with photons of light having the right amount of energy the encounter can trigger a kind of chain reaction of emission. Not only does the chain reaction amplify the intensity of the light passing through, but the emitted photons all head in the same direction as the incoming photons. The amplification of the light intensity by stimulated emission occurs only if more atoms in the population of atoms are in an excited state than in the ground state—the opposite of the normal situation. This idea was built on in 1951-53 when Charles Townes invents the maser, a device to harness stimulated emission to generate a focused microwave beam.

List the simultaneous research going on in the early 1960’s that lead to the first laser surgery on a human in 1961.
On the East Coast, Charles Koester and Charles Campbell begin research on the laser as a therapeutic device. At the same time on the West Coast, Milton Flocks and Christian Zweng, collaborating with Narinder Kapany, begin similar work.

Briefly summarize the main contributions of physics and human anatomy to the development of laser surgery.
In the physics field, Einstein's research on stimulated emission, which built on work by German physicist Max Planck in 1900 and Danish theoretician Niels Bohr in 1913, eventually led to work in the 1950s and 1960s on devices to harness stimulated emission to generate a focused microwave beam. Also in the 1950s, some researchers, like Charles Townes and Arthur Schawlow of Bell Laboratories publish their theory of how stimulated emission would work with much shorter wavelengths, including those of visible light—giving rise to the term “laser,” for light amplification by stimulated emission of radiation.

In human anatomy, techniques to deal with problems of the retina evolve over the course of the 20th century as medical researchers, from Jules Gonin and Gerd Meyer-Schwickerath to Stephen Trokel and R. Srinivasan develop techniques for using lasers to treat problems of the retina.

This teacher sheet is a part of the Lasers Saving Sight lesson.

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