Ophthalmology
Ophthalmology (lat., ophthalmos,
“eye”) is branch of medicine concerned with the study of the eyes, their
physiology and structure and the diseases and conditions affecting them. Unlike
optometrists, ophthalmologists are required to have a medical degree. In
addition to eye infections and other disorders, ophthalmologists are concerned
with refraction, orthoptics (the treatment of defective visual habits), the
prevention of blindness, and the care of blind people.
The letter was sent from the first
Afro-Asian Ophthalmology Congress in 1958
The eyes of Horus were regarded as a
symbol for light and darkness. His right eye is depicted as representing the
sun and his left eye the moon. Horus was the protective god from diseases.
The entire eye, often called the
eyeball, is a spherical structure approximately 2.5 cm in diameter with a
pronounced bulge on its forward surface. The outer part of the eye is composed
of three layers of tissue. 
The outside layer is the sclera, a
protective coating. It covers about five-sixths of the surface of the eye. At
the front of the eyeball it is continuous with the bulging, transparent cornea.
The middle layer of the coating of the eye is the choroid, a vascular layer
lining the posterior three-fifths of the eyeball. The choroid is continuous
with the ciliary body and with the iris, which lies at the front of the eye.
The innermost layer is the light-sensitive retina.
The cornea is a tough, five-layered
membrane through which light is admitted to the interior of the eye. Behind the
cornea is a chamber filled with clear, watery fluid, the aqueous humor, which
separates the cornea from the crystalline lens. The lens itself is a flattened
sphere constructed of a large number of transparent fibers arranged in layers.
It is connected by ligaments to a ring-like muscle, called the ciliary muscle,
which surrounds it. The ciliary muscle and its surrounding tissues form the
ciliary body. This muscle, by flattening the lens or making it more nearly
spherical, changes its focal length.
The pigmented iris hangs behind the
cornea in front of the lens, and has a circular opening in its centre. The size
of its opening, the pupil, is controlled by a muscle around its edge. This
muscle contracts or relaxes, making the pupil larger or smaller, to control the
amount of light admitted to the eye.
Behind the lens the main body of the
eye is filled with a transparent, jelly-like substance, the vitreous humor,
enclosed in a thin sac, the hyaloid membrane. The pressure of the vitreous
humor keeps the eyeball distended.
Albrecht von Graefe 1828 – 1870
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Graefe Point : Graefe
Operation : Graefe Reflex : Graefe
Syndrome : Graefe
Sign : |
Point near foramen supraorbitale, by pressing this point convulsion of
the eyelid. 1. Operation for
the correction of squint 2. Glaucoma operation Orbicularis phenomena Because of
degeneration in middle brain, paralysis both side of the eye musculature. Fall behind of eyelid, Sign of Basedow Disease. |
The retina is a complex layer,
composed largely of nerve cells. The light-sensitive receptor cells lie on the
outer surface of the retina in front of a pigmented tissue layer. These cells
take the form of rods or cones packed closely together like matches in a box.
Directly behind the pupil is a small yellow-pigmented spot, the macula lutea,
in the centre of which is the fovea centralis, the area of greatest visual
acuity of the eye. At the centre of the fovea, the sensory layer is composed
entirely of cone-shaped cells. Around the fovea both rod-shaped and cone-shaped
cells are present, with the cone-shaped cells becoming fewer towards the
periphery of the sensitive area. At the outer edges are only rod-shaped cells.
Where the optic nerve enters the
eyeball, below and slightly to the inner side of the fovea, a small round area
of the retina exists that has no light-sensitive cells. This optic disc forms
the blind spot of the eye.
Functioning of the Eye
In general the eyes of all animals
resemble simple cameras in that the lens of the eye forms an inverted image of
objects in front of it on the sensitive retina, which corresponds to the film
in a camera.
Focusing the eye, as mentioned
above, is accomplished by a flattening or thickening (rounding) of the lens.
The process is known as accommodation. In the normal eye accommodation is not
necessary for seeing distant objects. The lens, when flattened by the suspensor
ligament, brings such objects to focus on the retina. For nearer objects the
lens is increasingly rounded by ciliary muscle contraction, which relaxes the suspensor
ligament. A young child can see clearly at a distance as close as 6.3 cm, but
with increasing age the lens gradually hardens, so that the limits of close
seeing are approximately 15 cm at the age of 30 and 40 cm at the age of 50. In
the later years of life most people lose the ability to accommodate their eyes
to distances within reading or close working range. This condition, known as
presbyopia, can be corrected by the use of special convex lenses for the near
range.
Structural differences in the size
of the eye cause the defects of hyperopia, or long-sightedness, and myopia, or
shortsightedness. 
As mentioned above, the eye sees
with greatest clarity only in the region of the fovea due to the neural
structure of the retina. The cone-shaped cells of the retina are individually
connected to other nerve fibers, so that stimuli to each individual cell are
reproduced and, as a result, fine details can be distinguished. The rod-shaped
cells, on the other hand, are connected in groups so that they respond to
stimuli over a general area. The rods, therefore, respond to small total light
stimuli, but do not have the ability to separate small details of the visual
image. The result of these differences in structure is that the visual field of
the eye is composed of a small central area of great sharpness surrounded by an
area of lesser sharpness. In the latter area, however, the sensitivity of the
eye to light is great. As a result, dim objects can be seen at night on the
peripheral part of the retina when they are invisible to the central part
The mechanism of seeing at night
involves the sensitization of the rod cells by means of a pigment, called
visual purple or rhodopsin, that is formed within the cells. Vitamin A is
necessary for the production of visual purple; a deficiency of this vitamin
leads to 
night blindness. Visual purple is
bleached by the action of light and must be reformed by the rod cells under
conditions of darkness. Hence a person who steps from sunlight into a darkened
room cannot see until the pigment begins to form. When the pigment has formed
and the eyes are sensitive to low levels of illumination, the eyes are said to
be dark-adapted.
A brownish pigment present in the
outer layer of
the retina serves to protect the
cone cells of the retina from overexposure to light. If bright light strikes
the retina, granules of this brown pigment migrate to the spaces around the
cone cells, sheathing and screening them from the light, thereby making the
eyes light-adapted.
Georg Bartisch
1535 – 1607
Pioneer of operative
Ophthalmology
Subjectively, a person is not
conscious that the visual field consists of a central zone of sharpness
surrounded by an area of increasing fuzziness. The reason is that the eyes are
constantly moving, bringing first one part of the visual field and then another
to the fovea region as the attention is shifted from one object to another.
These motions are accomplished by six muscles that move the eyeball upwards,
downwards, to the left, to the right, and obliquely. The motions of the eye
muscles are extremely precise; the estimation has been made that the eyes can
be moved to focus on no less than 100,000 distinct points in the visual field.
The muscles of the two eyes, working together, also serve the important
function of converging the eyes on any point being observed, so that the images
of the two eyes coincide. When convergence is non-existent or faulty, double
vision results. The movement of the eyes and fusion of the images also play a
part in the visual estimation of size and distance.
Protective Structures
Several structures, not parts of the
eyeball, contribute to the protection of the eye. The most important of these
are the eyelids, two folds of skin and tissue, upper and lower, that can be
closed by means of muscles to form a protective covering over the eyeball
against excessive light and mechanical injury. The eyelashes, a fringe of short
hairs growing on the edge of either eyelid, act as a screen to keep dust
particles and insects out of the eyes when the eyelids are partly closed.
Inside the eyelids is a thin protective membrane, the conjunctiva, which
doubles over to cover the visible sclera. Each eye also has a lacrimal organ,
or tear gland, situated at the outside corner of the eye. The salty secretion
of these glands lubricates the forward part of the eyeball when the eyelids are
closed and flushes away any small dust particles or other foreign matter on the
surface of the eye. 
Normally the eyelids of human eyes
close by reflex action about every six seconds, but if dust reaches the surface
of the eye and is not washed away, the eyelids blink more often, producing more
tears. On the edges of the eyelids are a number of the Meibomian glands, small
glands which produce a fatty secretion that lubricates the eyelids themselves
and the eyelashes. The eyebrows, located above each eye, also have a protective
function in soaking up or deflecting perspiration or rain and preventing
moisture from running into the eyes. The hollow socket in the skull in which
the eye is set is called the orbit. The bony edges of the orbit, the frontal
bone, and the cheekbone protect the eye from mechanical injury by blows or
collisions.
Jules Gonin 1870 – 1935
He was world-famous with retina operations.
Eye Diseases
Eye disorders may be classified
according to the part of the eye in which the disorders occur. The most common
disease of the eyelids is hordeolum, known
commonly as a sty—an infection of the follicles of the eyelashes, usually
caused by infection by staphylococci. Internal sties that occur inside the
eyelid, not on its edge, are similar infections of the lubricating Meibomian
glands. Abscesses of the eyelids are sometimes the result of penetrating
wounds. Congenital defects of the eyelids occasionally occur, including
coloboma, or cleft eyelid, and ptosis, a drooping of the upper lid. Among
acquired defects are symblepharon, an adhesion of the inner surface of the
eyelid to the eyeball, which is most frequently the result of burns. Entropion, the turning of the eyelid inward towards
the cornea, and ectropion, the turning of the
eyelid outward, can be caused by scars or by spasmodic muscular contractions
resulting from chronic irritation. The eyelids also are subject to several
diseases of the skin such as eczema and acne, and to both benign and malignant
tumors. Another common eye disease is infection of the conjunctiva, the mucous
membranes covering the inside of the eyelids and the outside of the eyeball.
Conjunctivitis is an inflammation of the
conjunctiva of one or both eyes, characterized by redness, itching, and
discharge. Several different forms of this disorder exist and, in infective
cases, it may be caused by either bacteria or viruses. Similar symptoms can
also occur during an allergic reaction (for example, in hay fever).
Trachoma is contagious infection of the eye,
caused by a bacteria-like parasite named Chlamydia trachomatis, which is
related to the organism that causes psittacosis. Infection is spread by the
bite of a host fly. Characterized by hard pustules or granular excrescences on
the inner surface of the eyelids, inflammation of the membrane, and subsequent
involvement of the cornea, trachoma is a major cause of blindness in some
villages in northern
Cataract is opaque condition of the lens of
the eye or of its capsule. Its position behind the pupil readily distinguishes
it from opacities of the cornea. Cataract may affect the lens alone
(lenticular), or the front or back of the capsule of the lens (capsular), or
both lens and capsule (capsulolenticular). Cataract is painless and
unaccompanied by inflammation. It causes blindness by obstructing the passage
of light, but the patient can distinguish light from darkness.
Disorders of the cornea, which may
result in a loss of transparency and impaired sight, are usually the result of
injury. However, they may also occur as a secondary result of disease; for
example, oedema, or swelling, of the cornea sometimes accompanies glaucoma.
The choroid, or middle coat of the
eyeball, contains most of the blood vessels of the eye; it is often the site of
secondary infections from toxic conditions and bacterial infections such as
tuberculosis and syphilis. Cancer may develop in the choroid tissues or may be
carried to the eye from malignancies elsewhere in the body. The light-sensitive
retina, which lies just beneath the choroid, is also subject to the same type
of infections. The cause of retrolental fibroplasia, however—a disease of
premature infants that causes retinal detachment and partial blindness—is
unknown, but is associated with blood vessel abnormalities. Retinal detachment
may also follow cataract surgery. Laser beams are sometimes used to weld
detached retinas back onto the eye. Another retinal disease, called macular degeneration, which affects the central
retina, is a frequent cause of loss of vision in some older persons.
The optic nerve contains the retinal
nerve fibers, which carry visual impulses to the brain. The retinal circulation
is carried by the central artery and vein, which lie in the optic nerve. The
sheath of the optic nerve communicates with the cerebral lymph spaces.
Inflammation of that part of the optic nerve situated within the eye is known
as optic neuritis, or papillitis;
when inflammation occurs in the part of the optic nerve behind the eye, the
disease is called retro bulbar neuritis. When
pressure in the skull is elevated, or increased in intracranial pressure, as in
brain tumors, oedema and swelling of the optic disc occur where the nerve
enters the eyeball, a condition known as papilloedema.
Color Blindness is defect of vision affecting the ability to distinguish
colors, occurring mostly in males. Color blindness is caused by a defect in the
retina or in other nerve portions of the eye. The first detailed report on this condition was written by the British
chemist John Dalton, who was himself afflicted with it.
John Dalton 1766 – 1844
British chemist and physicist, who
developed the atomic theory upon which modern physical science is founded. He presented
a paper on color blindness, a condition from which
Corneal Transplants
Corneal tissue can be taken from
deceased persons for eye grafts. Blindness caused by cloudiness or scarring of
the cornea can sometimes be cured by surgical removal of the affected portion
of the corneal tissue. With present techniques, such tissue can be kept alive
for only 48 hours, but current experiments in preserving human corneas by
freezing give hope of extending its useful life for months. Vitreous humor, the
liquid within the larger chamber of the eye, can also be preserved and
distributed for use in treatment of detached retinas.
Carl Theodor 1839 – 1909
founded in 1896 ophthalmologic
hospital in
