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Review
, 10, 649-62
eCollection

A Medieval Fallacy: The Crystalline Lens in the Center of the Eye

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Review

A Medieval Fallacy: The Crystalline Lens in the Center of the Eye

Christopher T Leffler et al. Clin Ophthalmol.

Abstract

Objective: To determine whether, as most modern historians have written, ancient Greco-Roman authors believed the crystalline lens is positioned in the center of the eye.

Background: Historians have written that statements about cataract couching by Celsus, or perhaps Galen of Pergamon, suggested a centrally located lens. Celsus specifically wrote that a couching needle placed intermediate between the corneal limbus and the lateral canthus enters an empty space, presumed to represent the posterior chamber.

Methods: Ancient ophthalmic literature was analyzed to understand where these authors believed the crystalline lens was positioned. In order to estimate where Celsus proposed entering the eye during couching, we prospectively measured the distance from the temporal corneal limbus to the lateral canthus in 30 healthy adults.

Results: Rufus of Ephesus and Galen wrote that the lens is anterior enough to contact the iris. Galen wrote that the lens equator joins other ocular structures at the corneoscleral junction. In 30 subjects, half the distance from the temporal corneal limbus to the lateral canthus was a mean of 4.5 mm (range: 3.3-5.3 mm). Descriptions of couching by Celsus and others are consistent with pars plana entry of the couching needle. Anterior angulation of the needle would permit contact of the needle with the lens.

Conclusion: Ancient descriptions of anatomy and couching do not establish the microanatomic relationships of the ciliary region with any modern degree of accuracy. Nonetheless, ancient authors, such as Galen and Rufus, clearly understood that the lens is located anteriorly. There is little reason to believe that Celsus or other ancient authors held a variant understanding of the anatomy of a healthy eye. The notion of the central location of the lens seems to have arisen with Arabic authors in 9th century Mesopotamia, and lasted for over 7 centuries.

Keywords: anatomy; cataract couching; crystalline lens; medical history.

Figures

Figure 1
Figure 1
The lens (L) positioned anteriorly in the schematic horizontal section of the right eye. Abbreviations: C, cornea; Cc, corpus ciliare; Ch, chorioidea; Co, conjunctiva sclerae; Cor, corona ciliaris; D, dural sheath; F, fovea centralis; G, vitreous; Hk, posterior chamber; I, iris; Lc, lamina cribrosa; Li, limbus; Mc, musculus ciliaris; N, nasal side; O, nervus opticus; Or, orbiculus ciliaris; Os, ora serrata; P, pigment epithelium; R, retina; Rl, musculus rectus lateralis; Rm, musculus rectus medialis; S, sclera; Se, sulcus sclerae externus; T, temporal side; Vk, anterior chamber; Z, zonula ciliaris.
Figure 2
Figure 2
The anatomy of the eye with an anterior lens according to Walter Spencer’s 1938 interpretation of Celsus’ writings (lens location ratio 0.23). Notes: (A) Depicts the healthy eye with the locus vacuus, or empty space, denoted “a”, between the lens and iris. (B) Depicts the eye during couching, with a suffusion, or cataract, denoted “b”, anterior to the lens.
Figure 3
Figure 3
The anatomy of the eye, with an anterior lens (lens location ratio 0.18), according to a modern interpretation of the writings of Rufus of Ephesus.
Figure 4
Figure 4
The anatomy of the eye, with an anterior lens (lens location ratio 0.30), according to Hugo Magnus’ interpretation of Galen’s writings.
Figure 5
Figure 5
The macaque eye in cross section. Notes: Image courtesy of Richard Dubielzig, DVM, of the University of Wisconsin. The lens is located anteriorly: this specimen’s lens location ratio of 0.22 is similar to that of a composite eye (0.23).
Figure 6
Figure 6
The eye of a pig in cross section. Notes: Image courtesy of Richard Dubielzig, DVM, of the University of Wisconsin. The lens is thicker, but its equator still lies anteriorly. This specimen’s lens location ratio of 0.35 is similar to that of a composite eye (0.33).
Figure 7
Figure 7
The anatomy of the eye, with the central lens, according to Hugo Magnus’ interpretation of Celsus’ writings (lens location ratio 0.47).
Figure 8
Figure 8
During cataract couching, as depicted by George Bartisch in 1583. Notes: The patient seems to be gazing straight ahead. Copyright © 1995. JP Wayenborgh. Reproduced from Bartisch G, Blanchard DL (translator). Ophthalmodouleia. That is the Service of the Eyes. Ostend, Belgium: JP Wayenborgh; 1995:7–63.
Figure 9
Figure 9
In couching of cataracts, as depicted by George Bartisch in 1583. Notes: The needle appears to be placed on the eye about halfway between the limbus and the lateral canthus, and then passes posterior to the iris. Copyright © 1995. JP Wayenborgh. Reproduced from Bartisch G, Blanchard DL (translator). Ophthalmodouleia. That is the Service of the Eyes. Ostend, Belgium: JP Wayenborgh; 1995:7–63.
Figure 10
Figure 10
The ciliary region of the eye. Notes: Added lines show the possibility of a couching needle passing through the sclera (as far posteriorly as the rectus muscle insertion), the ciliary body, the posterior chamber, and the iris–lens channel, while remaining posterior to the iris and anterior to the vitreous. The absolute limbus to rectus muscle distance, and the ciliary body length, are both 20%–23% less in the medial region, depicted here, compared with the lateral region, which is involved with the couching technique of Celsus, pseudo-Galen, and Paulus Aegineta. Nonetheless, the relative length of internal and external structures is unchanged. Abbreviations: b, border of Bowman’s membrane; qB, vitreous base; Cs, corneoscleral limbus; Co, conjunctiva sclerae; d, Descemet’s membrane; Es, episcleral tissue; f, contraction furrows; vG, anterior border of the vitreous; hG, posterior border of the vitreous; Gk, vitreous nucleus; k1, ciliary and k2 pupillary crypts; Lhc, ligamentum hyaloideo-capsulare; Mr, medial rectus tendon; iZ, innermost; cZ, circular; vZ, anterior; qZ, middle; hZ, posterior zonula fibers; Z, zonular cleft.
Figure 11
Figure 11
Diagram of the eye with a central lens, from Hunain Ibn Ishak’s Ten Treatises on the Structure of the Eye (c. AD 860), taken from an AD 1197 manuscript, as copied and labeled by Polyak.

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