Words must have EXACT meanings.

This is some of the effort to define the fundamental eye
as the dynamic system -- that it is.

Thus the natural eye can have positive and negative
refractive STATES -- and not be "defective".

I moved this from the main page for house-keeping
reasons.

Otis

+++++++++++++++


HOW TO AVOID NEARSIGHTEDNESS

GLOSSARY


Accommodation

A blur controlled system that continuously monitors and
changes the internal lens of the eye -- too provide the
sharpest focus possible. The retina controls this
lens-system.

Accommodation, Average Value

The value of accommodation that is averaged over a 16 hour
day.

Analog Computer

Generally, a simulation of a physical or physiological system,
by using electronic operational amplifiers. The computer is
an analogy of the physical system being tested. This type of
computer is used when direct mathematical analysis is too
cumbersome or complicated to use.

Astigmatism

There is a "normal range" for astigmatism. It is between zero
and
two diopters. The FAA requires that you have 20/20 and less than
two diopters of astigmatism. If you have 20/20
there is no point to wearing glasses for astigmatism.

Black Box Testing

A type of testing where it is necessary to establish a
fundamental parameter of a previously untested system. In
general, you control one parameter, while monitoring the
effect on the second parameter.

Scientific Confirmation

Scientific testing in several different locations by different
scientists where the same result is always obtained. When the
results are consistent (as are tests conducted to determine
the fundamental behavior characteristic of the normal eye) the
result is considered to be an established fact.

Control System

A system, generally using power amplification, designed to
keep one parameter (i.e. the eye's desired focal state)
within tight limits with respect to another parameter (i.e.
average value of accommodation).

Corrective Lens

A term growing out of the Helmholtz-passive concept of the
eye. It means that if a normal eye has a focal state of + 1.0
diopter then the "corrective" lens for the normal eye should
be + 1.0 diopters. In a similar vein, if a normal eye has a
focal state of -1.0 diopters, the "corrective" lens should be
-1.0 diopters.

Cybernetics

The study of control systems in electronic and physiological
systems. The analysis and comparison of feedback systems in
man and machine.

Diopter

A unit of optical power. A focal length of one meter
(approximately on yard, or 39.4 inches). The reciprocal of
distance. A focal length of 1/2 meter represents a focal
power of 2 diopters.

Emmetropia

A focal state of exactly zero for the eye. (Under the
Helmholtz-passive concept, the only "normal" focal state of
the eye.)

Experiment

The explicit steps you must take to determine a fact. (In the
case of the eye, the explicit steps you must take to determine
the fundamental behavior characteristic of all normal eyes.)

Eye Acuity Testing

The type of testing whereby you are required to read the
standard Snellen eye chart at 20 feet. (The letters are 3/8
inch tall, and your successful reading of the chart indicates
20/20 vision.)

Eye

A dynamic system (similar to a camera) that controls light
rays so that they will form an image on the retina.

Facts

Explicit measurement results that can be repeated as many
times as desired. The entity to be tested, must be explicitly
identified (i.e. the normal eye) to get consistent results.
(You cannot run a test on the defective eye and reach a
conclusion about the normal eye's behavior.)

Farsightedness (Hyperopia)

A positive focal state of the natural eye.

Feedback Control

A method of linking (desired) output to (controlling) input.

First Class Medical

A Federal Aeronautics Administration (FAA) examination
required of you to be fully qualified as a professional pilot.
The chief visual requirement is the ability to read the 20/20
line on the eye chart. This represents a focal state of from
0 to +1.5 diopters. There is a visually less stringent
(20/50) 3rd class medical certificate issued by the FAA.

Focal Length

The point at which an image will form after light rays pass
through a lens, provided the object is located at a
considerable distance from the lens.

Focal Measurement

The process of determining the focal length of a lens, or the
focal status of the eye.

Focal Power

The ability of a lens to focus light rays. The shorter the
focal length, the greater the focal power.

Heuristic

Serving to discover or to stimulate investigation. Assisting
in the development of methods of demonstration which tend to
lead a person to investigate further by himself.

Hyperopia

A positive focal state of the normal eye. (Sometimes called
"Farsightedness". This is not a defect of the eye."

Infinity

For optical eye-testing purposes, a distance greater than 20
feet. Rays of light are considered to be parallel when the
object is located at infinity.

Magnifying Glass

A positive lens

Mathematical Model

A conceptual scheme developed to represent physical reality.
Mathematical models are essential to science, and are valued
for their practical technical accuracy and the elegance and
simplicity of their premise.

Model

A mechanical or electronic analogy of physical reality or a
physical system.

Myopia

See nearsightedness

Nearsightedness

A negative focal state of the normal eye. (As defined and
established in this book.)

Negative Lens

A lens that optically moves all objects closer to the eye.
Also called a diverging lens. A lens with a negative (or
virtual) focal length.

Noise

Unwanted or undesired perturbations in a system. Usually
defined as having a broad bandwidth.

Operational Amplifier

An amplifier specifically designed to perform some
mathematical operation: (e.g., integration, differentiation,
multiplication, division, addition, and subtraction.)

Ophthalmologist

A medical doctor specializing in diseases of the eye. He is
required to have four years of college, four years of medical
school, two years as an intern, and board certification as an
ophthalmologist.

Optometrist

A professional who has completed five years of specialized
college and is licensed to prescribe lenses for refractive
errors of the eye.

Paradigm

A conceptual scheme that has received broad acceptance by
scientists.

Perturbation

An unexpected and abrupt change to a system in a random
direction with random magnitude.

Physiological Optics

The application of optical analysis, using Snell's law. The
analysis of image formation in the eye and the representation
of the normal eye as a purely optical device.

Positioning Control System

A system, usually employing power amplification, designed for
the sole purpose of maintaining very accurate relative
position.

Positive Lens

A lens that optically moves all objects away from the eye. A
magnifying lens. A converging lens.

Presbyopia

A situation resulting from the stiffness of the internal lens
of the eye associated with old age. Sometimes (inaccurately)
called farsightedness.

Reading Glass

A magnifying glass, or positive lens.

Retina

The light sensitive surface on the back of the eye.

Science

The systematic assessment of facts. The theoretical and
experimental effort required to determine factual truth.

Servo System

A system, either mechanical or physiological, that "slaves"
the output to the input. (The normal eye continually adjusts
both its corneal power and relative length to maintain
accurate focus. The focal state of the normal eye is "slaved"
to its average visual environment.)

Statistical Testing

A mathematical method of organizing experimental data to
rapidly come to a reasonable conclusion about experimental
(factual) reality.

Testing

A systematic approach to confirming a physical fact concerning
some defined entity. (The normal eye is a defined entity.)

Theory

A concept developed over the years for explaining an
underlying physical reality.

Thought Experiment

A type of experiment that is designed to expose an old theory
to existing knowledge in a way that isolates the root of the
problem with a clarity that is unattainable in the laboratory.

Tonic Accommodation

A normal (and usually negative) neurological focal state for
the eye. It occurs any time the retina is unable to perceive
blur (which the accommodation system needs to focus properly)
in its field of vision. This is also referred to as
blank-field, or dark-focus accommodation.

Transfer Function

A mathematical function that relates the transformation of the
output response to the input signal. In the case of the
eye, "input" is the accommodation signal, and the "output"
is the measured focal status of the eye.

Verification Process

A method of repeated testing to determine factual
(experimental) truth.

Visual Acuity

In the normal human eye, visual acuity is given as 1 minute of
angle, or the ability to read 3/8 inch letters clearly at 20
feet. Also referred to as 20/20 vision. At night, the
resolving power (i.e. separation of stars) is about 3 to 5
minutes of arc. Some system refer 6 meters as the measurement
distance. Thus 20/20 is 6/6. A newer system uses this
fraction as the standard, thus 6/6 is 1.0, and 6/12 (20/40) is
0.5. The U. S. Army discovered (ca. 1914) that the 1 minute of
angle was an excessive requirement. A great many soldiers could
pass the 20/40 line -- but not the 20/20 line. They did not
wish to have a great mass of soldiers wearing glasses so they
set the standard at 20/40 -- and would not prescribe minus lenses
if the soldier could read better-than that line. This level
of vision has become standard throughout the world as the
DMV-Snellen standard. You must always pass this line if you
wish to avold wearing minus-lens glasses.