(1)
Flinders University of South Australia School of Medicine, Adelaide, SA, Australia
Oculists, Spectacle Makers and Ophthalmologists
Models of eyes were used as votives by the Greeks and Romans when they sought divine intervention for relief from disorders affecting sight [1]. The models used for these early offerings often depicted the diseased eye of the sufferer but later Christian votives were models of a healthy eye [2]. Earthly treatment of eye conditions was offered by oculists, early specialists in disorders of the eye who travelled from town to town in search of business and often used astrology in determining the best course of treatment. Development of effective treatments for eye disorders and correction of refractive errors required an understanding of the structure and the function of the eye.
The Anatomy of the Eye
Early Illustrations
Around a thousand years ago the Islamic oculist Ibn Al-Haitham (965–1040), often referred to as Alhazen in Western literature, wrote the Kitab al-Manazir (Book of Optics), which included the first reasonably accurate illustration of the anatomy of the eye [3]. The astronomer Johannes Kepler (1571–1630) best known for his work on planetary motion1 read Alhazen’s book and applied his knowledge of optics to the eye. Kepler recognized that the lens focussed light from the subject on the retina so the image must be inverted and reversed and thought this was corrected in the “soul”. Kepler included a plate on the anatomy of the eye in Ad Vitellionem Paralipomena, quibus Astronomiae Pars Optica (The Optical Part of Astronomy), published in 1604 (see Fig. 8.1) [4]. The illustrations of the eye used by Kepler were actually from an earlier anatomy book by Felix Platter (1536–1514) published in 1583 [5].
Fig. 8.1
Anatomy of the eye from Johannes Kepler’s Ad Vitellionem Paralipomena, quibus Astronomiae Pars Optica [4]
Flaps
The first systematic text-book on eye disease Ophthalmodouleia: Das ist Augendienst by Georg Bartisch (1535–1606), a German oculist, was also published in 1583. Ophthalmodouleia covered the anatomy of the eye, diseases and their treatment, surgical instruments, the treatment of injuries and astrology [6]. Bartisch used flaps in some of the figures to depict the three dimensional structure of the globe of the eye and attachments (see Fig. 8.2) which was an advance on the multiple sections used by earlier authors such as Platter.
Fig. 8.2
Bartisch presented a detailed anatomy of the eye in Ophthalmodouleia: Das ist Augendienst which he published in 1583. Bartisch used flaps to reveal the internal anatomy of the globe and associated structures [6]
Bartisch has been called “the founder of modern ophthalmology” but he was very superstitious and thought eye disease was caused by sin or the work of the devil and used astrology to determine the best part of the year to perform operations. He believed short and long sightedness were signs of disease and a completely healthy eye would have good vision and need no aids and spectacles were actually harmful [7].
Jacques Fabian Gautier d’Agoty (1717–1785) is famous for colored mezzotints of anatomical dissections [8]. In Essai d’anatomie he drew flaps to de monstrate anatomical relationships such as the eye in the orbit and associated muscles (see Fig. 8.3).
Fig. 8.3
Muscles of the head and neck including the eye and orbit by Jacques Fabian Gautier d’Agoty [8]
Eye Models
Neils Stensen (1638–1686), also known as Nicolas Steno or Stenone, was a Dane who had travelled widely in Europe and in 1666 was a professor of anatomy at the University of Padua in Italy. Stensen had a reputation as a scholar in several disciplines including geology and paleontology as well as anatomy and was recruited by the Grand Duke of Tuscany Ferdinando II de’ Medici to collect and curate artifacts for a “Cabinet of curiosities”.2 Stensen was influenced by the writings of René Descartes and deduced it was important to study both how individual components of an organ worked and how these parts worked together [9]. On one occasion Stensen tried to show the Grand Duke the anatomy of the eye of a rabbit and sometime and after this Giovanni Battista Verle, a Venetian craftsman skilled in turning, received a commission from His Highness to make an Anatomia artifiziale dell’occhio umano, an anatomically correct imitation eye [10].
Verle outlined the background to the commission and how the eye was made in Anatomia artifiziale dell’occhio umano a small book first published in Italian in Florence in 1679 (see Fig. 8.4) [10]. Verle collaborated with Michelangelo Mollinetto, an anatomist in Padua, to construct the most accurate model of a human eye ever made. He had Venetian glassworkers create the transparent and colored parts of the eye and he turned wood and ivory to make the structural parts of the model [10]. An eye made by Verle is on display in the Galileo museum in Florence, Italy (see Fig. 8.5).
Fig. 8.4
Eye by Giovanni Battista Verle made from wood, glass and ivory. For transport the external part of the eye is put in the boxwood base and the cover is screwed onto the front of the eye
Fig. 8.5
The author examining an artificial eye at the Museo Galileo in Florence that had been made by Verle. The museum was very generous in giving access to the model especially as a previous visiting “scholar” had broken the iris
Verle noted an advantage of using an eye simulator for teaching was that it did not rot like cadaver eyes so could be used at any time [10]. In the last part of the book Verle sought commissions to make models of the eye and also of the ear. Verle claimed the ear was no less interesting than the eye but had more parts and would be more laborious to make. This was probably code for it being very expensive. Later, new materials and production techniques would make such model more affordable. Verle’s book on the eye simulator was also published in Latin in 1680.
Verle was not the only maker of artificial eyes around this time. Stephan Zick (1639–1715) of Nuremberg, Germany another ivory carver also made several model eyeballs in the second half of the seventeenth century (see Fig. 8.6).
Fig. 8.6
Eyeball simulators made by Zick and others. (Credit: Wellcome Library, London)
The artist Domenico Remps (1620–1699) specialized in trompe-l’oeil paintings which were popular although often dismissed by art critics. One of Remps’ famous paintings is “A Cabinet of Curiosities” which is on display in the Museo dell’Opifico delle Pietre Dure (Museum of Semi-precious stones) in Florence. On the middle shelf of the cabinet in Remp’s painting is a model eye on a stand.
Marcello Malpighi (1628–1694) improved knowledge of ocular anatomy when he used the magnifying glass on the body. Even smaller structures could be identified when Anthony Van Leewenhoek (1632–1723) discovered how a magnifying lens could be used to make a microscope. The early models of eyes and dissections were life size but when anatomical elements too small to see with the naked eye were discovered they were made visible through large scale models. Large scale models of the eye that could be taken apart to reveal the internal structure were made by Auzoux (see Fig. 8.7a, b). Some later models of the eye were made of plaster which were less expensive but more prone to damage. More recently models of the eye were made from hard rubber or plastic (see Figs. 8.8, 8.9, and 8.10).
Fig. 8.7
(a) An enlarged model of the eye inscribed “Anatomie Clastique du Dr Auzoux 1891”. (b) A series of hinged sections allow the eye can be taken apart. (Credit: photographs courtesy of phisick.com)
Fig. 8.8
A more recent “Anatomie Clastique” of the eye shown complete (a) and partly “dissected” (b). (Credit: photographs courtesy of phisick.com)
Fig. 8.9
Anatomical eye. (Credit: photographs courtesy of phisick.com)
Fig. 8.10
Anatomical model by Tramond. (Credit: University of Dundee)
The Whole Eye
The early anatomical models concentrated on the globe of the eye but the orbit and extraocular muscles are very important parts of the visual apparatus . Models of dissections of the head and neck often included the eye and associated structures (see Fig. 8.11) and models of anatomical sections were also made to show blood vessels, nerves, eyelids and surrounding parts (see Fig. 8.12).
Fig. 8.11
Wax model of the head showing the eyeball and orbit. (Credit: Science Museum/Science & Society Picture Library)
Fig. 8.12
Enlarged model of the eye showing the globe of the eye and the orbit. (Credit: Wellcome Library, London)
Physicians and surgeons also needed to understand the anatomy of the muscles that control movements of the eyeball. In the late seventeenth and early eighteenth centuries the skilled workers of Bologna and Florence produced wax copies of dissections that were anatomically correct and educational materials. One example of this is the table made by Anna Morandi to demonstrate the actions of the extra ocular muscles (see Fig. 8.13).
Fig. 8.13
Model of the extraocular muscles of the eye and their action on the eyeball made by Anna Morandi. (Credit: Museo di Palazzo Poggi, Bologna)
Functional Models: Eye Movements
The anatomical models couldn’t show movement and a new type of model was needed to understand the actions of the ocular muscles and how to use myotomy for correcting strabismus (squint). The first eye movement simulator, called an ophthalmotrope, was developed by Christian Georg Theodor Ruete in 1845 [11]. The eye of this ophthalmotrope was mounted in nested gimbals (see Figs. 8.14 and 8.15) and contained a camera obscura (see Fig. 8.16) so that the direction of gaze could be seen.
Fig. 8.15
Example of a Ruete-type 1 ophthalmotrope. (Credit: University of Dundee)
Ruete’s second ophthalmotrope had two eyes and was much more complicated than the first (see Fig. 8.17). In this new ophthalmotrope Ruete used weights and pulleys to represent the forces applied by the extraocular muscles [12]. There was a scale to measure muscle contraction or extension and both Donders’s and Listing’s laws could be demonstrated.
Fig. 8.17
Drawing of Ruete’s second ophthalmotrope [12, fig op p. 96]
Wilhelm Maximilian Wundt (1832–1920) constructed an ophthalmotrope that used springs and weights to represent the actual muscle forces (see Fig. 8.18). Wundt had calculated the forces applied by the muscles from postmortem measurements of their cross-sectional area and their length [13].
Fig. 8.18
Illustration of Wundt’s ophthalmotrope clearly shows the springs and weights that simulate the extraocular muscles [89]
An ophthalmotrope based on a rubber ball transfixed by knitting needles to show the principle axes was a simple simulator to learn about eye movements [14]. This simple simulator was improved by Edmund Landolt (1846–1926) (see Fig. 8.19) “who marked upon it the vertical and horizontal meridians, and the anterior extremity of the axes of rotation of the two oblique muscles (O) and the two vertical recti (R). The circle described on the ball about the point of O, with a radius from O to the center of the cornea, would indicate, for example, the path which the center of the cornea would follow if the globe were rotated only by the oblique muscles. Or, a circle described on the ball about the point R, with a radius from R to the center of the cornea, would indicate the path which the center of the cornea would follow if the globe were moved only by the superior and inferior recti.” Landolt also constructed an ophthalmotrope “whose object was the demonstration of the direction and the position which the eye takes under the influence of each of its muscles, and the position of the false image in the case of paralysis of a given muscle” (see Fig. 8.20) [15]. This simulator was first demonstrated in 1893 and a version was made by the E. B. Meyerowitz Company.
Fig. 8.19
Landolt’s “Rubber Ball” ophthalmotrope. The markings on the eye simulator are described in the text [14]
Fig. 8.20
An ophthalmotrope designed by Landolt to show the movements caused by each muscle. A schematic eye, represented by its vertical and horizontal meridians, its equator and the cornea, was set in two fixed rings and supported by the rotary axes of the muscles [14, p. 182]
Several other eye movement simulators were made in the second half of the nineteenth and early twentieth centuries including those of Donders, Zimmerman, Halle, Helmholtz, Snellen, Stephens and Knapp. The opthalmotrope designed by Hermann Jakob Knapp (1832–1911) is the one found most frequently in museum collections (see Figs. 8.21 and 8.22). In this simulator the muscles were represented by strings which were attached to small weights. When the eye was moved, it was easy to observe which muscles performed this action by the changes in position of the weights. This mechanism was also used in Howe’s ophthalmotrope (see Fig. 8.23).
Fig. 8.22
Knapp’s ophthalmotrope. (Credit: CUTVAP centre, Siena)
Functional Models: Formation of an Image on the Retina
Many early natural philosophers including Galen, Alhazen and Leonardo da Vinci thought the lens, then called the crystalline humor, was located in the center of the eyeball and was where light was perceived. Vesalius recognized that the retina was essential for vision but he continued to put the lens at the center of the eye in his anatomical illustrations. Research by René Descartes (1596–1650) confirmed an observation first made by Julius Caesar Aranzi in 1580, that the eye functioned as a Camera obscura [16]. Descartes made a vision simulator to demonstrate the formation of the image on the retina. Descartes removed the sclera and choroid from the back of eyes and when he directed these preparations at an object he could see an inverted image projected onto the semi-transparent retina. Descartes included a drawing of this experiment in La Dioptrique published in 1637 (see Fig. 8.24) [17].
Fig. 8.24
Illustration of a simulator made by René Descartes to demonstrate the formation of the image on the retina [17]
Descartes deduced that impaired vision caused by a derangement of the internal structure of the structure of the eye could only be corrected by external measures. In a discourse on Means for perfecting vision Descartes conceived a “contact tube”, an external apparatus to improve vision that was later discovered to be based on a key principle of contact lenses [18].
Development of Vision Simulators
Spectacles to correct presbyopia are thought to have been invented in Pisa, Italy towards the end of the thirteenth century and were then also made in Venice and Florence [19, ch. 1]. By the fourteenth century spectacles had spread throughout Italy and beyond including France, Germany and Britain [19, ch. 2] and spectacles to correct myopia were developed in the fifteenth century [19, ch. 3]. Also in the fifteenth century it was recognized that from around 30 years visual acuity declined with age and spectacles for 5-year age intervals began to be made. Italy lost its dominance in spectacle making in the sixteenth century and even began importing them [19, ch. 5.]
Christophorus Scheiner (1575–1650), a Jesuit priest and astronomer correctly described the structure and function of the optical parts of the eye in Oculus published in 1619 [20]. In the book Scheiner outlined how to make a simplified model of the eye (see Fig. 8.25),
F be a burning candle, ABC a hollow glass, bordered by spherical surfaces, LMN a complete vitreous or crystalline lens; in a similar way, ASC be the surface of a glass flash and these parts be connected with each other and arranged in such a way as the parts of the eye. The front sinus be filled up with common water, the rear sinus MS with pure and clear air, however. [21]
Scheiner’s major work, Rosa Ursina sive Sol published in several volumes between 1626 and 1630, was on sunspots and astronomy [22]. In the second volume of Rosa Ursina, Scheiner compared the eye to a telescope and explained how lenses corrected refractive errors in a table of figures [23] (see Fig. 8.26).
Fig. 8.26
Table comparing the eye to a telescope and how lenses can be used to correct visual errors [23]
Around 50 years later Claude-François Milliet Dechales (1621–1678), a Jesuit priest and teacher, conceived an eye model, an oculis materialis or physical eye , that could be demonstrate how near- and far-sightedness were produced and how these conditions could be corrected with appropriate lenses. Dechales included an illustration of this prototype eye simulator in a course on mathematics published in 1674 (see Fig. 8.27) [24, p. 360].
Fig. 8.27
Illustrations of the oculus materialis, a prototype eye simulator, from the section on optics in a course in mathematics by Dechales [24, p. 360]
The oculis materialis was a “simplified eye” in that the refraction at the cornea and the lens of the eye was produced by a single element. A paper diaphragm at the front represented the pupil and the anteroposterior diameter of the eye could be adjusted by sliding a cylinder with a paper screen representing the retina at one end inside a slightly larger cylinder mounted in the optical axis of the eye (see Fig. 8.27). A paper retina (labelled GL in the figure) was made translucent with oil so the image could be seen through the viewing tube at the back of the eye (labelled KL) that represented the optic nerve [25, pp. 336–340].
Johann Zahn (1641–1707), another cleric, made an improved oculis materialis (see Fig. 8.28) which he described in Oculus Artificialis Teledioptricus Sive Telescopium, an extensive work on optics published in 1702 [25, pp. 336–340]. Zahn’s simulator had a stand, leather caps with holes of different sizes to change the diameter of the pupil but the major improvement was a measuring scale engraved on the inner sliding cylinder. This facilitated experiments using the simulator to better understand the optics of the eye and the causes and correction of disorders of vision [25, pp. 336–340]. Zahn recognized the value of experiential learning and designed thirteen experiments that could be performed on the simulator to develop an understanding of the optics of the eye.
Fig. 8.28
Eye simulator by Johann Zahn from Oculus Artificialis Teledioptricus Sive Telescopium. It was a development of the earlier oculus materialis of Dechales on which is shown at the bottom of the plate [25]
A mathematical model of the optics of the eye was described by Christian Huygens in Dioptica published in 1702 [26]. This “simplified eye” was made from two concentric hemispheres of very different radii, the curved surface of the smaller represented the front of the eye and the other, three times larger, represented the back of the eye [26, pp. 211–214]. Robert Smith in A Compleat System of Opticks published in 1738 called this model a fictitious eye to differentiate it from the physical models (see Fig. 8.29) [27 p. 25–32].
In the middle of the eighteenth century the French surgeon Claude-Nicholas Le Cat removed the sclera and choroid from human and animal eye to investigate how the image was formed on the retina but he discovered that eyes handled this way soon lost their shape [28, p. 46].
To remedy the Inconveniences arising from the Softness and Variableness we have been observing in these eyes, [Le Cat] commissioned an Artificial Eye of more than four Inches Diameter, furnished with a Glass Cornea and Crystalline Humour, or with a Lens of Focus proportioned to this Diameter. [28]
From the last part of Le Cat’s description of the artificial eye it appears he understood the principle of a reduced eye model. Le Cat’s artificial eye was referred to in Rudiments of Physiology published in 1835 [29].
During the Enlightenment , also known as the Age of Reason, there was increasing interest in acquisition of knowledge and academies and institutes were established across Europe. Public lectures and demonstrations were popular and many compendia and encyclopedias were published. There was particular interest in physical phenomena including optics and models of the eye were produced explain how the eye worked and how lenses could improve vision.
Experiments in Physics by Pierre Polinière (1671–1734), a scientist and physician, was first published in 1709 [30]. In the book Polinière described a hundred experiments and included an eye simulator to demonstrate how an image was produced in the eye.
Christian Gottlieb Hertels included a model eye in a book on optical apparatus published in 1716 [31, pp. 112–115]. Hertels tried to make his model anatomically and optically correct to better explain the optics of the eye. It had an iris behind the glass cornea and behind the iris was a separate glass lens. The image could be viewed on a ground glass screen in place of the retina at the back of the eye which was shrouded by a conical tube meant to emulate the optic nerve.
The Cyclopaedia : or, An Universal Dictionary of Arts and Sciences by Ephraim Chambers (1680–1740) was published in London in 1728. The section on the eye in volume 1 included instructions for making an Artificial Eye (see Fig. 8.30) [32, p. 744] and a drawing of this model (see Fig. 8.31) was included in the table on “Opticks” in volume 2 [32, p. 318].
Fig. 8.30
Description of an artificial eye from Cyclopaedia: or, An Universal Dictionary of Arts and Sciences [32, p. 379]
Fig. 8.31
Illustration of an artificial eye from Cyclopaedia: or, An Universal Dictionary of Arts and Sciences by Ephraim Chambers [32]
The Dictionnaire universel de mathematique et de physique edited by Alexandre Julien Savérien (1720–1805) was published in 1753 [33]. Saverien included a description of a “machine d’optique ”, an artificial eye to demonstrate the optics of the eye (see Fig. 8.32). Also described was a larger model (see Fig. 8.33) that could be used to demonstrate the cause of myopia and the changes in the eye that occur with aging (presbyopia).
Fig. 8.33
An alternative eye simulator made from cylinders that could also be used to demonstrate errors of refraction, etc. [33]
The Encyclopedia , or a Systematic Dictionary of the Sciences, Arts, and Crafts edited by Denis Diderot and Jean le Rond d’Alembert was published in France between 1751 and 1772. This work appeared to recycle the figure of an artificial eye from the Cyclopaedia. (see Fig. 8.34) A dictionary of sciences, arts, and crafts edited by Charles-Joseph Panckoucke and published in Paris in 1780 included a reference to an “artificial imitation eye” made for a Sicilian physician called Masliari [34, p. 321]. Another version of an artificial eye was described in Elementa Opticae et Perspectivae by Jan-Frans Thysbaert (1736–1825) published in 1775 (see Fig. 8.35) [35]. This Oculus arteficialis was filled with water and used to demonstrate how an image was formed on the retina.
Fig. 8.34
Artificial eye from L’Encyclopédie, ou Dictionnaire Raisonné des Sciences, des Arts et des Métiers de Diderot et d’Alembert [90]
Fig. 8.35
Daniel Gabriel Fahrenheit (1686–1736) is most famous for his work on temperature but he also had an interest in optics and designed an eye simulator. It is known from his correspondence that Fahrenheit used scientific apparatus as “visual aids ” in his lectures [36, pp. 1–11] and he invented a model of the eye (see Fig. 8.36). The eye could be pointed at a subject and the resulting image formed on a screen in the eye representing the retina was observed through the conical tube at the back of the model (see Fig. 8.36c). A sliding mechanism on the top of the eye moved the retina to change the length of the eye for experiments on vision and correcting refractive errors. An eye model made by Hendrik Feyt (1699–1790) [37] that received favorable from Peter (aka Petrus and Pieter) Camper (1722–1789) in his doctoral dissertation on the optics of vision [38] appears to have been lost. After graduating from Leyden, Camper went to London where he was studied midwifery with Smellie [39] who used obstetric simulators in his courses. (See obstetric simulation in Britain section.)
Fig. 8.36
(a) Demonstration eye invented by Fahrenheit in the first quarter of the eighteenth century; (b) the top of the eye showing the sliding mechanism and the engraving; and (c) the inverted image on the glass “retina” seen through the conical viewing tube at the back of the model. (Credit: University Museum of Groningen, the Netherlands)
Jean Antoine Nollet (1700–1770), also known as l’abbé Nollet, was a French cleric with a deep interest in physics. In 1734 he visited London where he met John Desaguliers,3 a demonstrator at the Royal Society, who gave public lectures on physical principles. On his return to Paris wrote Leçons de Physique Expérimentale and began teaching physics [40]. Nollet developed an extensive collection of scientific apparatus to illustrate various physical principles and a catalogue of the collection published in 1765 listed 345 pieces [41]. One of the items in the collection was an artificial eye (see Fig. 8.37) which Nollet described in Leçon xvii of his course [40]. The frontispiece of volume 1 of Leçons is an engraving of Nollet teaching and the artificial eye is shown on a shelf behind him. Nollet also wrote L’art des experiences in which he detailed how to make the teaching apparatus including a “l’oeil artificielle” in volume 3 [42, p. 286]. Nollet popularized physics teaching and his biographer wrote that few men had made science more real than Nollet. Much of Nollet’s collection, including an eye simulator, was acquired by the Stewart Museum in Montreal, Canada [43].
Fig. 8.37
Nollet’s l’oeil artificielle. (Credit: Stewart Museum, Montréal (Québec)
London Eyes
“The optical effects of vision may be very pleasingly and satisfactorily illustrated by the instrument represented at Fig. 7, which is called an ARTIFICIAL EYE.” Adams (1889) [44, p. 50]. (Note. Fig. 7, the Artificial Eye, is reproduced as Fig. 8.39 below.)
Fig. 8.38
Model eye made by Benjamin Martin around 1765 now in the Harvard University Historical Collection of Scientific Instruments. (Credit: Harvard University)
Around 1765 Benjamin Martin (1704–1782), an optical instrument-maker of Fleet Street, London, made a model eye with a ground glass screen simulating the retina to demonstrate the optics of the eye. It is thought this model was made for Harvard University to replace equipment lost in a fire in 1764 and is now part of the Historical Collection of Scientific Instruments there [45]. Benjamin Martin’s invoice of instruments shipped to Harvard in August of 1765 included “an Artificial Eye in Brass” for £2.2.0. It is the only such model mentioned in any of the early inventories of College- owned equipment (see Fig. 8.38).
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