Abstract
The eyes have fascinated scholars for millennia. From anatomy and disease to the process of vision, many have
contributed to the present understanding of optics. The difficulty lies in establishing the origins of discoveries.
Obtaining original manuscripts is arduous as texts have been lost in wars, conflagrations and disasters. Praise
for developments is sometimes ascribed to early scholars who may have inspired later academics. Greek
luminaries such as Aristotle and Galen laid strong foundations which the Arabs built upon, keeping the candle
of knowledge burning in the Middle Ages, a time when Europe was in darkness. This article aims to review the
Arab-Islamic impact on optics by presenting ancient theories, the contributions of prominent Arab scientists
exploring how the rise of Islam allowed them to flourish and influence optics.
Introduction
Historically, the study of the eye has often involved two
different but related approaches. Mathematicians,
physicists and even philosophers explored the physics of
light, vision, and optics whereas physicians sought to
understand the anatomy and related pathology.
Historically scholars acquired a wide knowledge base,
before focusing on specific interests. In fact, many were
generalists not oculists. Ophthalmology as a distinct
specialty only became recognised in the 19th century in
the United Kingdom.1
However, the medical treatment of the eye is referred to
in the Ebers Papyrus, an Egyptian scroll dating back
more than 3000 years.2 It is not until the ancient Greeks
that reliable records are found.
The ophthalmoscope was not invented until the 1800’s,
so a direct internal view was not possible to ancient physicians. They were limited to observing the external
eye or cadaveric dissection, therefore understanding of
the anatomy of the inside of the eye remained relatively
constant for centuries.3 Some authors have argued that the
Romans offered little new input and the encyclopaedias
of medicine they did gather, were described as “Not a
medium for the communication of an expanding
knowledge; rather, they were repositories for a static
body of ancient wisdom”.4
The Arab-Islamic empire, referred to by this name due to
the universally spoken Arabic language and Islamic
rulers, expanded substantially after the passing of
Prophet Muhammad (PBUH, 570-632 AD) reaching
India, North Africa and even Spain. At its height
physicians and scientists flourished with a particular
interest in the eyes.2
This paper will discuss the key figures in the Middle
Ages, between 500-1500AD and their influences.
Ancient theories
Alcmaeon of Croton c. 500 BC is thought to have been
the first to dissect the eye and describe its contents
although this is disputed as there is no remaining
evidence of his works.5 Herophilus, born 335 BC is
reported to have been the first to describe the layers of
the eye: an outer cornea and sclera, a grape-skin like iris
choroid and the inner retina.6
With regard to vision, Empedocles (c. 493
proposed that there were two different emanations: light
radiating from the eyes to the outside
referred to as the emission or extramission theory, and
also reflection from objects travelling to the eye, the
intromission theory. He was unable to explain how the
light in extramission and intromission were reconciled
into a singular image.4 Plato (c. 427-348 BC) believed in
the extramission theory but this was rejected by Aristotle
(c. 384-322 BC), arguing that emissions from the eye
itself would require a body of some kind which did not
exist or had not been discovered.7 Aristotle noted a
interesting concept whereby objects in direct contact with
the eyeball or in a vacuum could not be seen. This led
him to focus on the properties of the medium between the
eye and objects concluding that it must be transparent
and continuous with the surface of the eye such as air.
The eyeball must then contain a watery component
receptive to the incoming light and colour from the
external medium.4,7
Euclid (c. 300 BC) persisted on the path of extramission
optics but as a mathematician, devoted his atten
solely to the geometry and physics of vision, excluding
the anatomical components. It is said that Ptolemy in 2
Century AD Egypt did consider these components,
however his first book was lost in medieval times.
fragments of the work exist in Latin, translated from an
earlier Arabic translation of the original Greek text.
Galen, born 129 AD, developed Herophilus’ anatomical
theory and believed that the eye consisted of membranes:
cornea, sclera, choroid, retina and conjunctiva; internally
there were three sets of fluid: the albuminous, crystal and
vitreous fluid.8 In the literature it appears that Greco
Roman scientists after this time had little interest in
ophthalmology, although it may be that works were
destroyed in conflict or deemed unimportant to preserve.
The rise of Islam
The darkness in development was not restricted to
ophthalmology. By the 6th Century the Roman Empire
was a fracturing realm, Latin Western Europe losing connection to the Eastern Byzantine side rich in Greek
philosophy and science.9 Medicine was not mainstream,
and patients were susceptible to “quacks and
charlatans”.10 Conversely, Muslim armies post
Muhammad (PBUH, 570-632 AD) conquered swathes of
Western Asia and North Africa, gaining control of east
Byzantine.11
By 661 AD the Umayyad Caliphate transferred the
capital to Damascus but the integration between cultures
began with the accession of the Abbasids c. 750 AD
heralding the Islamic Golden Age particularly under
Caliph Al-Ma’mun (786-833 AD). He established ‘The
House of Wisdom’ in Baghdad in a significant endeavour
to translate Greek texts to broaden the Arab knowledge in
astronomy, science and maths. This translation
movement partly flourished because people in Arab
countries studied Greek to understand liturgical texts.
Historians have debated the motives behind the effort to
assimilate Greek learning. For medicine, the Arab
Caliphates were based on the teachings of Islam which
places emphasis on good health. Farag reports Europe at
the time was awash with charlatans capitalising on the ill,
whereas Islam condemned them. Ibn Majah reports the
teachings of Muhammad PBUH: “Whoever gives
medical treatment with no prior knowledge of medicine
is responsible (for any harm done)”. Furthermore, the
Quran states: “Whoever saves a life, it will be as if they
saved all of humanity”.15 Islam held physicians in high
esteem and encouraged the search for knowledge in all
regards. The Sufi sect placed unique significance on the
eyes, considering them to be mirrors to the soul
Politics and geography also played a crucial role in Arab
development. Nestorian Christians fleeing Byzantine
persecution sought refuge in Muslim lands bringing with
them Greek texts which they translated to Syriac and
Arabic.11 Shifting the capital from Damascus to Baghdad
meant a reliance on local Byzantine civil servants and
administrators further integrating the cultures and
enabling scholars from different backgrounds to
connect.13,17 The Caliphate’s tolerance to other religions,
encouraged research and empiricism, at a time when the
West was enforcing ‘dogmatism’. It is claimed that
between 800-1400 AD, the number of manuscripts
written in Arabic surpassed those in Latin, Greek and
European languages combined, with almost 30 books on
ophthalmology produced.19 The Greeks did not produce a
substantial ophthalmology textbook, only short works. It
was the Arabs who were the first to introduce detailed
encyclopaedic textbooks, with accurate descriptions of
the symptoms, methods of diagnosis and treatment of
diseases of the eye.20
Perhaps one of the most substantial driving forces was
disease. Egyptian Ophthalmia, otherwise known as
trachoma or contagious keratoconjunctivitis, plagued the
Middle East for millennia from the Pharaonic period to
Napolean’s arrival in Egypt in 1798 when tens of
thousands of French soldiers were infected during the
invasion.21-23 Trachoma was a major cause of blindless in
the Muslim world further increasing the interest in
ophthalmology. Individual aspirations were an additional
factor. Caliph al Ma’mun expressed a keen interest in
Greek medicine sending delegations to Alexandria and
Asia to obtain Greek manuscripts while taking esteemed
scholar Hunain Ibn Ishaq with him on campaigns against
the Byzantines.11 It became customary for Caliphs to
offer patronage to scholars and inviting them to position
at their courts. This enhanced the leader’s reputation
whilst also giving them a personal physician and learned
guide.9
The Islamic golden age
Despite the different religious backgrounds, Yuhanna ibn
Masawaih (Johannes, 777-857 AD) a Christian, was
appointed the Caliph’s court physician in Baghdad where
he authored the first recognised monograph on
ophthalmology in the Islamic world, Kitab Dagh
or Disorders of the eye.24
To aid his immense translation efforts, Al Ma’mun
employed philosopher Abu Yusuf Yaqub ibn Ishaq al
Kindi (Alkindus, 801-873) who went on to serve his
successors too.
Al-Kindi’s desire was to compile historical knowledge in
search of what he termed the truth. Although not an
oculist, he did have an interest in vision.4
In his work ‘De Aspectibus’, Al
Aristotle’s medium theory. Aristotle
vision involved external objects generating ‘motion’,
which travelled through a medium and ‘impressed its
form’ on the eye. However, Al
circular object in the same plane as the eye was seen as a
straight line and not circular meaning that the ‘motion’
produced did not mirror the object entirely.
that light and visual rays travel in a straight line and he
was also the first to explicitly state the concept that a
luminous body emits light rays in all dire
every point on its surface.4
A contemporary of Al-Kindi, Nestorian Christian Hunain
ibn Ishaq (Johannitius, 809-
Ibn Masawaih. He wrote the first systematic textbook of
ophthalmology covering anatomy, pathology and t
physics of vision. The ‘Book of the ten treatises on the
eye’, contains the first detailed drawing of the eye
including the optic nerve and the six extraocular
muscles.19 He remained upon the Galen school of thought
illustrating the outer layers as a co
meninges.16 Galen described the crystalline lens as an
anterior component however Ibn Ishaq incorrectly
positioned it in the centre of the eye suggesting all other
parts were designed to nourish it.
treatises discuss at length a multitude of eye diseases
including trachoma, corneal ulcers and cataract.
Explaining the optics of vision, Ibn Ishaq accepted Plato,
Aristotle, and Galen, proposing that a spirit is emitted
from the eye coinciding with light rays reflecting of
objects.25
revolution in optics
Abu Ali al Hasan ibn al-Haytham (Alhazen, 965-1039
AD) referred to as the father of optics, was arguably the
greatest writer in Arab ophthalmology. ‘Kitab al
Manazir’ or Book of optics, the most renowned of his
ninety texts, was an intrepid piece diverging from
preceding Euclid, Ptolemy and al-Kindi’s beliefs. Al
Haytham refuted the extra mission ideology raising
several critical objections. Firstly, light and visual rays
could not emanate from within the eye otherwise humans would be able to see in the dark. Similarly, focal light in
darkness only illuminates a fixed area. Lastly, we are
able to see distant objects such as stars immediately
without a delay which would be caused by light leaving
and returning to the eye. He presented his exposition of
the intromission theory using geometry to show that sight
required perception of light rays travelling from objects
towards the eyes not from them.26 It is important to note
here that Persian physician Al-Razi (865-925) did
possibly reject some of the prevailing theories about
vision earlier than al-Haytham, but the manuscripts
evidencing this have not survived.4
Interestingly, Ibn Sina (980-1037), a Persian polymath
had independently arrived at similar conclusions to al
Haytham at a similar time.4 Named Avicenna in the West,
he is regarded as one of the most influential figures of the
Islamic Golden Age. Often referred to as the ‘Prince of
Physicians’, he penned The Canon of medicine, an
encyclopaedia of medicine used as a standard and
reference across Europe until the 18th Century. His work
included a detailed description of the six extraocular
muscles, similar to ibn Ishaq, and their roles in eye
movement. Furthermore, he correctly stated that nerve
fibres only partially crossed over at the optic chiasm.
Quite possibly the most revolutionary yet overlooked
finding came from Ibn Rushd (Averroes, 1126-1198). In
both his works translated as ‘Colliget’ and ‘Epitome of
the Parva Naturalia’ he refers to the ‘final tunic’ and
‘innermost coat’ i.e., the retina as the ‘perceptive
faculty’, moving away from nearly a millennium of belief
that the crystalline lens was the region of primary
photosensitivity.4, 17 However, German scientist Johannes
Kepler (1571-1630 AD) is widely credited with the
discovery that light is focused by the lens onto the retina
then transmitted to the brain.4 Interestingly, Kepler was
inspired by Ibn al-Haytham who is considered to have
pioneered the modern scientific method. His systematic
recording and repeatable experimental designs are said to
have influenced Kepler.27
Clinical Contributions
Cataract surgery is one of the oldest invasive procedures
in history, yet tracing the origins is challenging due to the
lack of verifiable literature. The earliest authentic records
are of Sushruta, an ancient Indian from around 600 or
700 BC, referring to a method called couching whereby
the lens is forced out of the visual field using a curved
needle inserted at the limbus through the pars plana.
This method increased risks of glaucoma, posterior
capsular rupture and blindness.30 Nevertheless, the procedure was widely practiced in the world, until the
18th Century when Jacques Daviel performed a lens
removal procedure (1747).31 Eventhough he is credited
as the inventor of cataract extraction, Arabs had
developed this process much earlier. Al-Razi outlined the
technique of an earlier physician Antyllos (2
AD Rome) in which a hollow tube is used to remove the
lens. Ammar ibn Ali al-Mawsili in the 10th Century put
this into practice after inventing a hollow needle to
enable lens extraction and says he performed many of
these operations.13,28
Eyelid surgery was mentioned a great deal in the Arab
texts, and this often concerned the removal of various
tumours and cysts, including lacrimal abscesses and
fistulas. Symblepharon, (adhesion of eyelids) was also
treated surgically. Intricate procedures were used for
treating the consequences of Trachoma, including
trichiasis and entropion. The Arabs may have been the
first to describe peritomy to treat pannus caused by
trachoma; while an instrument was used to keep the eye
open, very small hooks were used for lifting and a very
thin scalpel, scissors or a needle were used for the
excision.30
Corneal surgery was also performed. El Zahrawi
(Albucasis, 936-1013 AD) described a technique to treat
pterygium which involved using a needle, horse-tail hair
and removing the part of the cornea with a sharp, smooth
blade.32
Another example of the Arab-Islamic contributions
non-surgical treatment of amblyopia. George Comte de
Buffon is often credited with the introduction of
occlusion therapy for amblyopia in 1743, however Thabit
Ibn Qurrah (836-901 AD), a polymath living in Baghdad,
described the method to patch the normal eye before him
in his book ‘Vision and Perception’. In fact, Paulus de
Aegina, a 7th century Byzantine, who was highly
regarded by the Arabs, had previously attempted to treat
strabismus using a perforated mask.
The practice of Medicine and Ophthalmology
Medicine has tried to distance itself from quackery for
centuries. The Arabs introduced the idea of qualifying
examinations for admission to the medical profession.
In the case of malpractice, the family could start
proceedings against the doctor, with witnesses and
written prescriptions being produced in evidence. If
found guilty, the doctor could be fined, barred from
practice or both.35 In ophthalmology, Al-Razi strongly disapproved of charlatans and called on authorities to
stop them.36 Itinerant oculists were considered to fit into
this category and Ibn Sina said that they “…go about
from place to place attacking men’s eyes with their
lancets and applying worthless ointments. There is no
honesty in them”.37 A Muhtasib, a type of ‘Censor who
was appointed by the Caliph, ensured that the interests of
the people were protected, and this included strict checks
on oculists. Only if they were satisfied could the oculist
continue in practice. One of their tasks was to examine
practitioners on their knowledge of ibn Ishaq’s Ten
Discourses on the Eye, and also a practical examination.
This tested competence in the handling of instruments,
such as a hooks (for the removal of growths within the
conjunctiva) and lancets for bleeding.37 Unlike some of
their predecessors, Arab Oculists were known for their
compassion. In his detailed description of cataract.
couching, Ali Ibn Isa, teaches to “speak kind words to the
patient so that his anxiety may be lightened”.
Conclusion
Sobotka described development in Europe during the
Middle Ages as stagnating, impeded by schoolmen. In
contrast Arab-Islamic scientists were willing to stand on
the shoulders of the giants that came before them. Al
Kindi states: “It is fitting then for us not to be ashamed to
acknowledge truth and to assimilate it from whatever
source it comes to us, even if it is brought to us by former
generations and foreign peoples”.4 He continues: “First to
record in complete quotations all that the Ancients have
said on the subject, secondly to complete what the
Ancients have not fully expressed”.4 The Arabs did not
simply translate ancient Greek knowledge. They
challenged existing ideas, developed theories, combined
the physics of vision with anatomy to elevate their
understanding and utilised their expertise in clinical
practice. Arabic medical and scientific textbooks were
translated into Latin and disseminated into Europe during
the Renaissance, and some continued to be used for
centuries.
The achievements of the Arab-Islamic world are
summarised well by eminent German ophthalmologist
and historian Julius Hirschbirg. In 1905, after 5 years of
research, he addressed the American Medical Association
remarking: “During this total darkness in medieval
Europe they lighted and fed the lamps of our science-
from the Guadalquivir to the Nile and to the river Oxus…
they were the only masters of ophthalmology in medieval
Europe.”38
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