title: Double insertions of extraocular rectus muscles in humans and the pulley theory.
abstract: Recent studies have promoted the concept that rectus muscles pass through connective tissue pulleys located near the equator of the eye and act, in effect, as the muscle origins. Orbital muscle fibres (facing bone) terminate in pulleys, permitting adjustment of their position independent of the global fibres responsible for rotating the eye. The structure of pulleys (or muscle sleeves) and the passage taken by their muscle fibre insertions are unclear, and a detailed description is presented here together with a review of the active pulley hypothesis. Segments including the full width of single muscles were removed from the full orbital contents of dissection room cadavers and fresh perfusion-fixed rhesus and cynomolgus monkeys and prepared for light microscopy. Thin longitudinal sections were cut as facets from resin-embedded tissue blocks and montages assembled. Interrupted serial sections of selected regions of both species and ultrathin sections of monkey material were prepared for light and electron microscopy, respectively. Slender tendons leave the orbital surface of rectus muscles at intervals, aggregating and entering sleeves in humans and monkey; less frequently, tendons pass from the global surface to sleeves or insert directly in the posterior fascia bulbi. The orbital sides of sleeve rings are continuous with the fascial canopy of the globe and are 5-6 times as thick as the global sides; sleeve structure differs in the four recti. Medial rectus sleeves are the thickest, and contain smooth muscle, whereas little or none is present in the other rectus sleeves. Superior rectus sleeves are variable in structure and relatively insubstantial. A narrow interval separates muscles from the surrounding connective tissue equatorially in some preparations, consistent with a capacity to slide, but the tissues are contiguous in others, especially in monkey material. The structural organization of sleeves and their tendons, together with other presented factors, is inconsistent with a facility for the separate adjustment of sleeve position. The results favour the theory that sleeve tendons have just one role, to counter the viscoelastic resistance of global fascia - ocular and sleeve muscle fibres acting in unison. Whether the fragile sleeve structure can meet the physical demands of pulleys is questionable; but otherwise the veracity of the pulley hypothesis cannot be assessed from the structural relations of muscles and fascia bulbi reported.
authors.affiliation: Department of Optometry and Visual Science, City University, London, UK.
authors.forename: Gordon L
authors.initials: GL
authors.lastname: Ruskell
authors.forename: Inga-Britt
authors.initials: IB
authors.lastname: Kjellevold Haugen
authors.forename: Jan Richard
authors.initials: JR
authors.lastname: Bruenech
authors.forename: Frans
authors.initials: F
authors.lastname: van der Werf
mesh_terms: D000818:Animals; D003238:Connective Tissue / Q000033:anatomy & histology*; D005133:Eye Movements / Q000502:physiology*; D006801:Humans; D008252:Macaca fascicularis; D023421:Models, Animal; D009130:Muscle, Smooth; D009801:Oculomotor Muscles / Q000033:anatomy & histology*; D009915:Orbit / Q000033:anatomy & histology; D012590:Sclera / Q000033:anatomy & histology; D013710:Tendons / Q000033:anatomy & histology
references.citation: Invest Ophthalmol Vis Sci. 1996 Feb;37(2):468-72
references.pmid: 8603853
references.citation: Eye (Lond). 1988;2 ( Pt 2):130-4
references.pmid: 3197870
references.citation: Vision Res. 1989;29(2):223-40
references.pmid: 2800349
references.citation: Ophthal Plast Reconstr Surg. 1994 Jun;10(2):87-91
references.pmid: 8086368
references.citation: Anat Rec. 1996 Nov;246(3):415-22
references.pmid: 8915464
references.citation: Arch Ophthalmol. 1982 Aug;100(8):1313-8
references.pmid: 7103816
references.citation: Invest Ophthalmol Vis Sci. 2001 Aug;42(9):1986-92
references.pmid: 11481262
references.citation: Invest Ophthalmol Vis Sci. 2002 Sep;43(9):2923-32
references.pmid: 12202511
references.citation: Trans Am Ophthalmol Soc. 1950;48:443-86
references.pmid: 16693522
references.citation: Br J Ophthalmol. 1962 Jul;46(7):397-403
references.pmid: 18170795
references.citation: Invest Ophthalmol Vis Sci. 2000 May;41(6):1280-90
references.pmid: 10798641
references.citation: Invest Ophthalmol Vis Sci. 1995 May;36(6):1125-36
references.pmid: 7730022
references.citation: J Neurophysiol. 2003 Dec;90(6):3809-15
references.pmid: 12944533
references.citation: Am J Ophthalmol. 1948 Dec;31(12):1539-53
references.pmid: 18103814
references.citation: Invest Ophthalmol Vis Sci. 2000 Nov;41(12):3787-97
references.pmid: 11053278
references.citation: Invest Ophthalmol Vis Sci. 2001 Jan;42(1):10-6
references.pmid: 11133842
references.citation: J Anat. 1961 Jul;95:371-85
references.pmid: 13776596
references.citation: J Neurophysiol. 2000 Aug;84(2):639-50
references.pmid: 10938292
references.citation: Invest Ophthalmol. 1975 Nov;14(11):801-25
references.pmid: 1184315
references.citation: Arch Ophthalmol. 1985 Jan;103(1):124-8
references.pmid: 3977665
references.citation: Exp Brain Res. 2002 Feb;142(4):439-62
references.pmid: 11845241
references.citation: Invest Ophthalmol Vis Sci. 1997 Apr;38(5):884-92
references.pmid: 9112984
references.citation: J Neurophysiol. 1998 Jun;79(6):3197-215
references.pmid: 9636119
references.citation: J Neurophysiol. 2001 Oct;86(4):1877-83
references.pmid: 11600647
references.citation: J Neurophysiol. 1988 Dec;60(6):1874-95
references.pmid: 2466962
references.citation: Invest Ophthalmol Vis Sci. 1997 Aug;38(9):1774-85
references.pmid: 9286266