Chapter 3: Summary of the Gross Anatomy of the Extraocular Muscles

More documents

Recommendations

Info

$Vision and Refraction (PDF 3.31 MB) - Cyber-Sight - Orbis$

Summary of the Gross Anatomy of the Extraocular Muscles 45FIGURE 3–8. Tenon’s space shown by injection with Indiaink. (Modified from Charpy A: Muscles et capsulede Tenon. In Poirier P, Charpy A, eds: Traité d’anatomiehumaine, new ed, vol 5/2. Paris, Masson, 1912, p 539.)not clearly delineated; it is thin and more or lesscontinuous with the meshwork of the orbital fat.If the globe is enucleated, one can see theanterior orifice of Tenon’s capsule, the borders ofwhich were attached to the sclera before enucleation;the posterior orifice, which is fused withthe sheaths of the optic nerve; and the smoothinner surface with the slits of entry for the extraocularmuscles. The openings for the vortex veinsare small and not readily visualized (Fig. 3–9).Muscle Sheaths and TheirExtensionsThe extrinsic ocular muscles pierce Tenon’s capsule,enter the subcapsular space, and insert intothe sclera. Therefore, one can distinguish an extracapsularand an intracapsular portion of eachmuscle.In their extracapsular portions, the extrinsic eyemuscles are enveloped by a muscle sheath. Thissheath is a reflection of Tenon’s capsule and runsbackward from the entrance of the muscles intothe subcapsular space for a distance of 10 to 12mm. At the lower aspect of the entrance, Tenon’scapsule is reduplicated. At the upper aspect, itcontinues forward as a single membrane (Fig.3–10). The muscle sheaths of the four rectus musclesare connected by a formation known as theintermuscular membrane, which closely relatesthese muscles to each other (Fig. 3–11). In addition,there are numerous extensions from all thesheaths of the extraocular muscles, which form anintricate system of fibrous attachments interconnectingthe muscles, attaching them to the orbit,supporting the globe, and checking the ocularmovements. These will now be described in theiressential features.The fascial sheath of the superior rectus muscleclosely adheres in its anterior external surface tothe undersurface of the sheath of the levator muscleof the upper lid. In front of the equator thesheath of the superior rectus muscle also sends aseparate extension obliquely forward that widensand ends on the lower surface of the levator muscle.The fusion of the two muscles accounts forthe cooperation of upper lid and globe in elevationof the eye, a fact that must be kept in mind whensurgical procedures on the superior rectus muscleare being considered.The fascial sheath of the inferior rectus muscledivides anteriorly into two layers: an upper one,which becomes part of Tenon’s capsule, and aFIGURE 3–9. Anterior and posteriororifice of Tenon’s capsule shownafter enucleation of the globe. (Modifiedfrom Charpy A: Muscles et capsulede Tenon. In Poirier P, Charpy A,eds: Traité d’anatomie humaine, newed, vol 5/2. Paris, Masson, 1912, p539.)
46 Physiology of the Sensorimotor Cooperation of the EyesFIGURE 3–10. Check ligaments of medialand lateral rectus muscles. Reduplication ofTenon’s capsule, forming the muscle sheathof the rectus muscles.lower one, which is about 12 mm long and endsin the fibrous tissue between the tarsus of thelower lid and the orbicularis muscle (Figs. 3–11and 3–12). This lower portion forms part of Lockwood’sligament.The fascial sheath of the reflected tendon ofthe superior oblique muscle consists of two layersof strong connective tissue (Fig. 3–13). The twolayers are 2 to 3 mm thick, so the tendon and itssheath have a diameter of about 5 to 6 mm. Thepotential space between the sheath and the tendonis continuous with the episcleral space. Materialinjected into Tenon’s space therefore may penetrateinto the space between tendon and sheath. 2Many attachments extend from the sheath of thesuperior oblique muscle to other areas: to thesheath of the levator muscle, to the sheath of thesuperior rectus muscle, to the conjoined sheath ofthese two muscles, and to Tenon’s capsule, behind,above, and laterally. The numerous fine fibrils thatconnect the inner surface of the sheath to thetendon are an important feature (see Fig. 3–13).19, 29Some authors have rejected the idea of thesuperior oblique tendon having a separate sheathand favor the view that what appears to be sheathare actually reflections of anterior and posteriorTenon’s capsule. This concept is of interest inconnection with the etiology of Brown syndrome.The fascial sheath of the inferior oblique musclecovers the entire muscle. It is rather thin at theFIGURE 3–11. Intermuscular membranes and fascialextensions of the superior, lateral, and inferiorrectus muscles (right eye).
Page 1 and 2: CHAPTER3Summary of the GrossAnatomy
Page 3 and 4: 40 Physiology of the Sensorimotor C
Page 7: 44 Physiology of the Sensorimotor C

Chapter 3: Summary of the Gross Anatomy of the Extraocular Muscles

Create successful ePaper yourself

Delete template?

Save as template?