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15.13 Lens for Myopia -- Part 2
Light can only be accepted from a thin slice within the tissue and can't be reflected or scattered from other regions.
The device does produce magnified images, even though it does not look like a microscope.
A parallel beam of light is needed to illuminate the object.
The laser beam is reflected by a half-silvered mirror into the objective lens, which focuses the beam to a point inside the tissue.
The beam is brought to a point at the main focus of the lens because the light is parallel.
Changing the distance between the lens and the tissue can change the depth of this point.
Light is scattered and reflected from all points in the path of the entering light, and some of it is picked up by the objective lens.
Light coming from the focal point is the only light that comes out of the lens as a parallel beam.
The light passes through the half-silvered mirror and is picked up by the collecting lens.
The light is focused on the small exit of the collecting lens.
There is no parallel light at the exit.
A photomultiplier behind the exit is used to measure the light intensity transmitted through the exit.
The intensity of an electron beam is controlled by this voltage.
One spot on the screen of the oscilloscope glows with a brightness proportional to the reflectivity of one point inside the tissue.
To see a whole cell or region of cells, we must look at the region point by point.
The focal point is moved in its own plane so that it can see inside the tissue.
The light coming from the focal point of the objective lens is not affected by the motion of the lens.
The output of the photomultiplier and the brightness of the spot on the screen are proportional to the reflectivity of the point being scanned.
While the object is being scanned, the electron beam in the oscilloscope is moving with the objective lens.
The screen shows a picture of a very thin section.
The ratio of the electron beam excursion on the oscilloscope face to the scanning lens is the magnification of the microscope.
The electron beam may be adjusted to move 5 cm for a 0.1-mm excursion of the lens.
The magnification is 500.
The resolution of the device is determined by the size of the spot.
The resolution in conventional microscopes is the same as in the optimum resolution.
The first biologically significant observations with the confocal micro scope were those of endothelial cells on the inside of the cornea.
The light reflected from the front surface of the cornea makes it impossible to see the cells in a conventional microscope.
There are outlines in two of the cells.
Figure 15.19 was obtained by photographing the image on the screen.
Most biology laboratories use the confocal microscope.
The object is scanned with moving mirrors and the image is processed by computers in the newer versions of the instrument.
A wide range of medical applications use fiber-optic devices.
Their operation is simple.
This phenomenon has been known for a long time.
Before the phenomenon could be widely utilized, major breakthrough in materials technology was necessary.
The development of optical fiber technology made it possible to make glass fibers that can carry light over long distances.
Light trapping is increased by the coated fiber.
Light can be carried over twisting paths without significant loss.
A conventional microscope shows out-of-focus blur and a modern confocal microscope shows the sea urchin embryo.
They can be used to look at internal organs such as the stomach, heart, and bowels.
A fiberscope has two bundles of optical fibers tied together.
Each bundle has about 10,000 fibers.
The bundles can be up to 1.5 cm in diameter.
The bundles vary in length from 0.2 to 1.2 m.
Light is confined to travel inside a glass cylinder.
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