Contact lenses

The invention: Small plastic devices that fit under the eyelids, contact
lenses, or “contacts,” frequently replace the more familiar
eyeglasses that many people wear to correct vision problems.
The people behind the invention:
Leonardo da Vinci (1452-1519), an Italian artist and scientist
Adolf Eugen Fick (1829-1901), a German glassblower
Kevin Tuohy, an American optician
Otto Wichterle (1913- ), a Czech chemist
William Feinbloom (1904-1985), an American optometrist
An Old Idea
There are two main types of contact lenses: hard and soft. Both
types are made of synthetic polymers (plastics). The basic concept of
the contact lens was conceived by Leonardo da Vinci in 1508. He
proposed that vision could be improved if small glass ampules
filled with water were placed in front of each eye. Nothing came of
the idea until glass scleral lenses were invented by the German
glassblower Adolf Fick. Fick’s large, heavy lenses covered the pupil
of the eye, its colored iris, and part of the sclera (the white of the
eye). Fick’s lenses were not useful, since they were painful to wear.
In the mid-1930’s, however, plastic scleral lenses were developed
by various organizations and people, including the German company
I. G. Farben and the American optometrist William Feinbloom.
These lenses were light and relatively comfortable; they
could be worn for several hours at a time.
In 1945, the American optician Kevin Tuohy developed corneal
lenses, which covered only the cornea of the eye. Reportedly,
Tuohy’s invention was inspired by the fact that his nearsighted wife
could not bear scleral lenses but hated to wear eyeglasses. Tuohy’s
lenses were hard contact lenses made of rigid plastic, but they were
much more comfortable than scleral lenses and could be worn for
longer periods of time. Soon after, other people developed soft contact
lenses, which cover both the cornea and the iris. At present,many kinds of contact lenses are available. Both hard and soft contact
lenses have advantages for particular uses.
Eyes, Tears, and Contact Lenses
The camera-like human eye automatically focuses itself and adjusts
to the prevailing light intensity. In addition, it never runs out of
“film” and makes a continuous series of visual images. In the process
of seeing, light enters the eye and passes through the clear,
dome-shaped cornea, through the hole (the pupil) in the colored
iris, and through the clear eye lens, which can change shape by
means of muscle contraction. The lens focuses the light, which next
passes across the jellylike “vitreous humor” and hits the retina.
There, light-sensitive retinal cells send visual images to the optic
nerve, which transmits them to the brain for interpretation.
Many people have 20/20 (normal) vision, which means that they
can clearly see letters on a designated line of a standard eye chart
placed 20 feet away. Nearsighted (myopic) people have vision of
20/40 or worse. This means that, 20 feet from the eye chart, they see
clearly what people with 20/20 vision can see clearly at a greater
distance.
Myopia (nearsightedness) is one of the four most common visual
defects. The others are hyperopia, astigmatism, and presbyopia. All
are called “refractive errors” and are corrected with appropriate
eyeglasses or contact lenses. Myopia, which occurs in 30 percent of
humans, occurs when the eyeball is too long for the lens’s focusing
ability and images of distant objects focus before they reach the retina,
causing blurry vision. Hyperopia, or farsightedness, occurs
when the eyeballs are too short. In hyperopia, the eye’s lenses cannot
focus images of nearby objects by the time those images reach
the retina, resulting in blurry vision. A more common condition is
astigmatism, in which incorrectly shaped corneas make all objects
appear blurred. Finally, presbyopia, part of the aging process,
causes the lens of the eye to lose its elasticity. It causes progressive
difficulty in seeing nearby objects. In myopic, hyperopic, or astigmatic
people, bifocal (two-lens) systems are used to correct presbyopia,
whereas monofocal systems are used to correct presbyopia in
people whose vision is otherwise normal.Modern contact lenses, which many people prefer to eyeglasses,
are used to correct all common eye defects as well as many others
not mentioned here. The lenses float on the layer of tears that is
made continuously to nourish the eye and keep it moist. They fit under
the eyelids and either over the cornea or over both the cornea
and the iris, and they correct visual errors by altering the eye’s focal
length enough to produce 20/20 vision. In addition to being more attractive
than eyeglasses, contact lenses correct visual defects more effectively
than eyeglasses can. Some soft contact lenses (all are made
of flexible plastics) can be worn almost continuously. Hard lenses are made of more rigid plastic and last longer, though they can usually be
worn only for six to nine hours at a time. The choice of hard or soft
lenses must be made on an individual basis.
The disadvantages of contact lenses include the fact that they must
be cleaned frequently to prevent eye irritation. Furthermore, people
who do not produce adequate amounts of tears (a condition called
“dry eyes”) cannot wear them. Also, arthritis, many allergies, and
poor manual dexterity caused by old age or physical problems make
many people poor candidates for contact lenses.Impact
The invention of Plexiglas hard scleral contact lenses set the stage
for the development of the widely used corneal hard lenses by Tuohy.
The development of soft contact lenses available to the general public
began in Czechoslovakia in the 1960’s. It led to the sale, starting in the
1970’s, of the popular, soft
contact lenses pioneered by
Otto Wichterle. The Wichterle
lenses, which cover
both the cornea and the iris,
are made of a plastic called
HEMA (short for hydroxyethylmethylmethacrylate).
These very thin lenses
have disadvantages that include
the requirement of
disinfection between uses,
incomplete astigmatism correction,
low durability, and
the possibility of chemical
combination with some
medications, which can
damage the eyes. Therefore,
much research is being
carried out to improve
them. For this reason, and
because of the continued popularity of hard lenses, new kinds of soft and hard lenses are continually
coming on the market.