Book of the Ten Treatises of the Eye
Encyclopedia
Hunayn ibn Ishaq
's Book of the Ten Treatises of the Eye is a 9th-century theory of vision
based upon the cosmological natures of pathways from the brain
to the object being perceived. This ophthalmic
composition is heavily derived from Galen
's De placitis Hippocratis at Platonis and De usu partium, both in terms of the anatomy
and physiology
being described. Hanayn's triumph comes from the systematic presentation of the parts of eye and the subsequent additions he made to the cosmological
aspects of the work. Its early translation to Latin also provided a means for medieval ophthalmologists in the West to come into contact with the work of Galen.
Hanayn relies on these principles to build up his conception of vision, which incorporates the anatomy of the eye in a way that makes discussion of one without the other unproductive.
, described as white, transparent, and luminous have a composition which lends itself to quickly receive colors. As opposed to Galen's more mathematical conception of flat-like lens, Hanayn opts a more spherical shape which allows for a larger field of vision. He describes the system behind the eyes that connects it to the brain, starting with the sclera
, a thick, hard membrane which protects the inner parts of the nerve
s from injury. The chorioid, a thin and soft structure filled with vein
s and arteries
, follows next and provides nourishment to the overall structure. Finally, the retina
transmits nutrient
s to the lenses themselves. Hanayn then presents the system responsible for protecting the eye. From the outermost level, these are the conjunctiva
, cornea
, and uvea
. While both the conjuctiva and cornea provide protection with minimizing hindrance to the lenses, the uvea has an extra function of concentrating the pneuma
exiting out of the eye to prevent it from being dissipated by light.
, voluntary movement, and free will
, is also described as the source of psychic pneuma. Starting out from the heart
as vital pneuma, it moves towards the brain where it is further refined into the specialized pneuma to be employed for vision. Hanayn also introduces the concept of a sense hierarchy, placing sight at the top of the list with the corresponding element of fire. In addition, he also describes three levels of this element: flame, red heat, and light, rationalizing the inclusion of light by describing the creation of flames after concentrating it via a magnetic glass. Hanayn connects all of these ideas by referencing the fact that the brain works directly to provide the eyes with the pneuma necessary to carry out its function, with light providing the illumination needed to discern the object being viewed.
. If one eye is closed and another is left open, the pneuma designated to the closed eye is instead redirected to the open one, causing the expansion of the pupil observed afterward. After collecting in the uvea, this pneuma then travels along the medium of air, causing a transformation that conforms to the shape around it, sending this signal back to the eye. An analogy
to describe this phenomenon is offered by Hanayn:
In other words, the air acts as the stick that allows the pneuma to identify the object, and transmit that back to the eye to produce sight as long as there is light. Both light and pneuma act together to eradicate barriers and direct the immediate transition of sensation to the eye, thus attaining vision.
Hunayn ibn Ishaq
Hunayn ibn Ishaq was a famous and influential Assyrian Nestorian Christian scholar, physician, and scientist, known for his work in translating Greek scientific and medical works into Arabic and Syriac during the heyday of the Islamic Abbasid Caliphate.Ḥunayn ibn Isḥaq was the most productive...
's Book of the Ten Treatises of the Eye is a 9th-century theory of vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
based upon the cosmological natures of pathways from the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
to the object being perceived. This ophthalmic
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
composition is heavily derived from Galen
Galen
Aelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
's De placitis Hippocratis at Platonis and De usu partium, both in terms of the anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
and physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
being described. Hanayn's triumph comes from the systematic presentation of the parts of eye and the subsequent additions he made to the cosmological
Cosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
aspects of the work. Its early translation to Latin also provided a means for medieval ophthalmologists in the West to come into contact with the work of Galen.
Overview
There are four essential doctrines that shape Hanayn's dissertation on vision and the anatomy of the eye:- Structural order – the individual components of the eye each have their own nature, and are arranged so that they are in cosmological harmony.
- Medical teleologyTeleologyA teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...
– the existence of each of these individual components is dictated by their ultimate purpose, vision. Their secondary purpose, guided by their immediate nature, dictates how vision will be achieved. - The elements – each of the four elements of earth, fire, air and water corresponds to a single sense. The fifth sense is a combination of two of the four elements described.
- Applicability of components – the effectiveness of each of the five senseSenseSenses are physiological capacities of organisms that provide inputs for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...
s depends largely on a component which is like the object of its sensation.
Hanayn relies on these principles to build up his conception of vision, which incorporates the anatomy of the eye in a way that makes discussion of one without the other unproductive.
Anatomy of the eye
The structure of the eye is presented as a hierarchy, starting first with the part that is most directly responsible for sight, and working down towards the parts which exists only to facilitate this function. The lensLens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
, described as white, transparent, and luminous have a composition which lends itself to quickly receive colors. As opposed to Galen's more mathematical conception of flat-like lens, Hanayn opts a more spherical shape which allows for a larger field of vision. He describes the system behind the eyes that connects it to the brain, starting with the sclera
Sclera
The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
, a thick, hard membrane which protects the inner parts of the nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s from injury. The chorioid, a thin and soft structure filled with vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
s and arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
, follows next and provides nourishment to the overall structure. Finally, the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
transmits nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
s to the lenses themselves. Hanayn then presents the system responsible for protecting the eye. From the outermost level, these are the conjunctiva
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...
, cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, and uvea
Uvea
The uvea , also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye. The name is possibly a reference to its reddish-blue or almost black colour, wrinkled appearance and grape-like size and shape when...
. While both the conjuctiva and cornea provide protection with minimizing hindrance to the lenses, the uvea has an extra function of concentrating the pneuma
Pneuma
Pneuma is an ancient Greek word for "breath," and in a religious context for "spirit" or "soul." It has various technical meanings for medical writers and philosophers of classical antiquity, particularly in regard to physiology, and is also used in Greek translations of the Hebrew Bible and in...
exiting out of the eye to prevent it from being dissipated by light.
Uses of the brain
The brain, being the source of perceptionPerception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
, voluntary movement, and free will
Free will
"To make my own decisions whether I am successful or not due to uncontrollable forces" -Troy MorrisonA pragmatic definition of free willFree will is the ability of agents to make choices free from certain kinds of constraints. The existence of free will and its exact nature and definition have long...
, is also described as the source of psychic pneuma. Starting out from the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
as vital pneuma, it moves towards the brain where it is further refined into the specialized pneuma to be employed for vision. Hanayn also introduces the concept of a sense hierarchy, placing sight at the top of the list with the corresponding element of fire. In addition, he also describes three levels of this element: flame, red heat, and light, rationalizing the inclusion of light by describing the creation of flames after concentrating it via a magnetic glass. Hanayn connects all of these ideas by referencing the fact that the brain works directly to provide the eyes with the pneuma necessary to carry out its function, with light providing the illumination needed to discern the object being viewed.
Function of pneuma and sight
Once concentrated in the brain, the highly fluid psychic pneuma travels along the network of the eye until it penetrates the forward region. The pneuma mixes with a preexisting aqueous humor, filling up the uvea and causing the stretches observed within the pupilPupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
. If one eye is closed and another is left open, the pneuma designated to the closed eye is instead redirected to the open one, causing the expansion of the pupil observed afterward. After collecting in the uvea, this pneuma then travels along the medium of air, causing a transformation that conforms to the shape around it, sending this signal back to the eye. An analogy
Analogy
Analogy is a cognitive process of transferring information or meaning from a particular subject to another particular subject , and a linguistic expression corresponding to such a process...
to describe this phenomenon is offered by Hanayn:
In other words, the air acts as the stick that allows the pneuma to identify the object, and transmit that back to the eye to produce sight as long as there is light. Both light and pneuma act together to eradicate barriers and direct the immediate transition of sensation to the eye, thus attaining vision.