Ophthalmology is the branch of medicine which
deals with the diseases of the eye and their treatment. The
word ophthalmology comes from the Greek roots ophthalmos meaning
eye and logos meaning word; ophthalmology literally means
"The science of eyes." As a discipline it applies
to animal eyes also, since the differences from human practice
are surprisingly minor and are related mainly to differences
in anatomy or prevalence, not differences in disease processes.
By convention the term ophthalmologist is more restricted
and implies a medically trained specialist. Since ophthalmologists
perform operations on eyes, they are generally categorized
as surgeons.
The eye, including its structure and mechanism,
has fascinated scientists and the public in general since
ancient times. The discovery of the eye went through two cycles
of limiting speculation and freeing observation, which led
to a dark age between Galen and Vesalius.
Arab scientists are some of the earliest to
have written about and drawn the anatomy of the eye—the
earliest known diagram being in Hunain ibn Is-hâq's
Book of the Ten Treatises on the Eye. Earlier manuscripts
exist which refer to diagrams which are not known to have
survived. Current knowledge of the Græco-Roman understanding
of the eye is limited, as many manuscripts lacked diagrams.
In fact, there are very few Græco-Roman diagrams of
the eye still in existence. Thus, it is not clear to which
structures the texts refer, and what purpose they were thought
to have.
The pre-Hippocratics largely based their anatomical
conceptions of the eye on speculation, rather than empiricism.
They recognised the sclera and transparent cornea running
flushly as the outer coating of the eye, with an inner layer
with pupil, and a fluid at the centre. It was believed, by
Alcamaeon and others, that this fluid was the medium of vision
and flowed from the eye to the brain via a tube. Aristotle
advanced such ideas with empiricism. He dissected the eyes
of animals, and discovering three layers (not two), found
that the fluid was of a constant consistency with the lens
forming (or congealing) after death, and the surrounding layers
were seen to be juxtaposed. He, and his contemporaries, further
put forth the existence of three tubes leading from the eye,
not one. One tube from each eye met within the skull.
Alexandrian studies extensively contributed
to knowledge of the eye. Aëtius tells us that Herophilus
dedicated an entire study to the eye which no longer exists.
In fact, no manuscripts from the region and time are known
to have survived, leading us to rely on Celsius' account—which
is seen as a confused account written by a man who did not
know the subject matter. From Celsius it is known that the
lens had been recognised, and they no longer saw a fluid flowing
to the brain through some hollow tube, but likely a continuation
of layers of tissue into the brain. Celsius failed to recognise
the retina's role, and did not think it was the tissue that
continued into the brain.
Rufus recognised a more modern eye, with conjunctiva,
extending as a fourth epithelial layer over the eye. Rufus
was the first to recognise a two chambered eye - with one
chamber from cornea to lens (filled with water), the other
from lens to retina (filled with an egg-white-like substance).
Galen remedied some mistakes including the curvature of the
cornea and lens, the nature of the optic nerve, and the existence
of a posterior chamber. Though this model was roughly a correct
but simplistic modern model of the eye, it contained errors.
Yet it was not advanced upon again until after Vesalius. A
ciliary body was then discovered and the sclera, retina, choroid
and cornea were seen to meet at the same point. The two chambers
were seen to hold the same fluid as well as the lens being
attached to the choroid. Galen continued the notion of a central
canal, though he dissected the optic nerve, and saw it was
solid, He mistakenly counted seven optical muscles, one too
many. He also knew of the tear ducts.
After Galen a period of speculation is again
noted by Arab scientists - the lens modified Galen's model
to place the lens in the middle of the eye, a notion which
lasted until Versalius reversed the era of speculation. He,
however, was not an ophthalmologist and taught that the eye
was a more primitive notion than the notion of both Galen
and the Arabian scientists - the cornea was not seen as being
of greater curvature and the posterior side of the lens wasn't
seen to be larger.
Understanding of the eye had been so slow to
develop because for a long time the lens was perceived to
be the seat of vision, not a tool of vision. This mistake
was corrected when Fabricius and his successors correctly
placed the lens and developed the modern notion of the structure
of the eye. They removed the idea of Galen's seventh muscle
(the retractor bulbi) and reinstated the correct curvatures
of the lens and cornea, as well as stating the ciliary body
as a connective structure between the lens and the choroid.
The seventeenth and eighteenth century saw the
use of hand-lenses (by Malpighi), microscopes (van Leeuwenhoek),
preparations for fixing the eye for study (Ruysch) and later
the freezing of the eye (Petit). This allowed for detailed
study of the eye and an advanced model. Some mistakes persisted
such as: why the pupil changed size (seen to be vessels of
the iris filling with blood), the existence of the posterior
chamber, and of course the nature of the retina. In 1722 Leeuwenhoek
noted the existence of rods and cones though they were not
properly discovered until Treviranus in 1834 by use of a microscope.
The establishment of the first dedicated ophthalmic
hospital in 1805 - now called Moorfields Eye Hospital in London,
England was a transforming event in modern ophthalmology.
Clincal developments at Moorfields and the founding of the
Institute of Ophthalmology by Sir Stewart Duke-Elder established
the site as the largest eye hospital in the world and a nexus
for ophthalmic research.
source: wikipedia.org
