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This is the complete lecture note for OPT609 Paediatric Ophthalmology. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: OPT 609 Course title: Paediatric Ophthalmology Course credit load: 1 Unit Series 1: Extraocular Muscle Anatomy and Normal Ocular Alignment • Part 1.1: The Extraocular Muscles o Sub Part 1.1.1: The four recti muscles o Sub Part 1.1.2: The two oblique muscles o Sub Part 1.1.3: Innervation of the extraocular muscles • Part 1.2: Actions of the Extraocular Muscles o Sub Part 1.2.1: Primary and secondary actions of the recti muscles o Sub Part 1.2.2: Actions of the oblique muscles o Sub Part 1.2.3: Yoke muscle pairs and cardinal positions of gaze • Part 1.3: Normal Ocular Alignment o Sub Part 1.3.1: Defining normal ocular alignment o Sub Part 1.3.2: Binocular vision and fusion o Sub Part 1.3.3: Development of ocular alignment in infancy Introduction Confident assessment of the child with a suspected ocular alignment problem begins with a clear understanding of the extraocular muscles and the physiological basis of normal ocular alignment, the essential foundation for everything examined throughout the remainder of this course. The aim of this Series is to equip you with a thorough understanding of the normal anatomy of the extraocular muscles and normal ocular alignment. This Series begins with the extraocular muscles, before examining their actions. It concludes with normal ocular alignment.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Series Learning Outcomes At the end of this Series, you should be able to: • SLO 1.1: describe the four recti and two oblique extraocular muscles • SLO 1.2: describe the innervation of the extraocular muscles • SLO 1.3: describe the primary and secondary actions of the recti and oblique muscles • SLO 1.4: describe yoke muscle pairs and the cardinal positions of gaze • SLO 1.5: define normal ocular alignment and describe binocular vision and fusion, and • SLO 1.6: describe the development of ocular alignment in infancy. 1.1 The Extraocular Muscles 1.1.1 the four recti muscles Muscles arising from a common tendinous ring The four recti muscles, the superior, inferior, medial, and lateral rectus, discussed in relation to orbital anatomy in an earlier related course, all arise from the annulus of Zinn, a common fibrous tendinous ring surrounding the optic nerve at the orbital apex. Each rectus muscle inserts onto the sclera at a specific distance from the corneal limbus, discussed in relation to limbal anatomy in an earlier related course, with the medial rectus inserting closest to the limbus and the superior rectus inserting furthest, an anatomical pattern relevant to certain surgical considerations. Fill in the blank: The four recti muscles all arise from the annulus of Zinn, a common fibrous tendinous ring surrounding the optic nerve at the orbital ________. 1.1.2 the two oblique muscles Muscles with a distinct, indirect course to the globe The superior oblique muscle originates near the annulus of Zinn but passes through the trochlea, a fibrocartilaginous pulley in the superomedial orbit, before turning posteriorly to insert on the superotemporal sclera, discussed earlier in this Part. The inferior oblique muscle, by contrast, originates from the anteromedial orbital floor and passes beneath the inferior rectus to insert on the posterolateral sclera, meaning both oblique
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS muscles follow a genuinely distinct, indirect course compared with the more direct path of the recti muscles discussed earlier in this Series. Fill in the blank: The superior oblique muscle passes through the trochlea, a fibrocartilaginous pulley in the superomedial orbit, before turning posteriorly to insert on the superotemporal ________. 1.1.3 innervation of the extraocular muscles Three cranial nerves supplying six muscles The lateral rectus is innervated by the abducens (sixth) nerve, discussed in relation to ocular motor pathway anatomy in an earlier related course, and the superior oblique by the trochlear (fourth) nerve, while the remaining four muscles, medial, superior, and inferior rectus, and inferior oblique, are all innervated by the oculomotor (third) nerve. This innervation pattern, discussed earlier in this Part, is frequently summarised by the mnemonic "LR6, SO4, remainder 3", a useful memory aid directly relevant to interpreting the specific pattern of muscle weakness produced by an isolated third, fourth, or sixth nerve palsy. Fill in the blank: The innervation pattern of the extraocular muscles is frequently summarised by the mnemonic LR6, SO4, remainder ________.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Figure 1.1: Diagram illustrating the origins and insertions of the four recti and two oblique extraocular muscles. Pilot questions 1.1 1. Name the four recti muscles and their common origin. (Linked to SLO 1.1) 2. Describe the course of the superior oblique muscle. (Linked to SLO 1.1) 3. Describe the origin and course of the inferior oblique muscle. (Linked to SLO 1.1) 4. State which nerve innervates the lateral rectus and superior oblique. (Linked to SLO 1.2) 5. State the mnemonic summarising extraocular muscle innervation. (Linked to SLO 1.2) 1.2 Actions of the Extraocular Muscles 1.2.1 primary and secondary actions of the recti muscles Actions varying with the muscle's angle of pull The medial and lateral rectus muscles, discussed earlier in this Series, produce pure adduction and abduction respectively as their sole action, given their essentially horizontal line of pull,
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS while the superior and inferior rectus each produce a combination of elevation or depression together with secondary adduction and torsional actions. This more complex action pattern of the vertical recti, discussed earlier in this Part, reflects the angle between the muscle's line of pull and the visual axis, meaning their primary vertical action becomes most isolated and purely expressed specifically when the eye is positioned in abduction. Fill in the blank: The vertical recti's primary vertical action becomes most isolated and purely expressed specifically when the eye is positioned in ________. 1.2.2 actions of the oblique muscles Torsional and vertical actions from an angled insertion The superior oblique, discussed earlier in this Series, produces intorsion as its primary action, together with secondary depression and abduction, while the inferior oblique produces extorsion as its primary action, together with secondary elevation and abduction. As with the vertical recti discussed in the previous sub-Part, the specific vertical action of each oblique muscle becomes most purely isolated when the eye is positioned in adduction, given the specific angle of insertion relative to the visual axis in that particular gaze position. Fill in the blank: As with the vertical recti, the specific vertical action of each oblique muscle becomes most purely isolated when the eye is positioned in ________. 1.2.3 yoke muscle pairs and cardinal positions of gaze Coordinated muscle pairs producing conjugate eye movement Yoke muscles, discussed in relation to the ocular motor pathway in an earlier related course, are the specific pairs of muscles, one in each eye, that work together to produce conjugate movement into a given direction of gaze, such as the right lateral rectus and left medial rectus working together for dextroversion, gaze to the right. The cardinal positions of gaze, discussed in relation to ductions and versions testing in an earlier related course, are the six positions in which the action of a single specific muscle in each eye is most purely isolated, providing the essential clinical framework for testing and interpreting ocular motility. Fill in the blank: The cardinal positions of gaze are the six positions in which the action of a single specific muscle in each eye is most purely ________.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Table 1.2: Primary action of each extraocular muscle. Muscle Primary action Nerve Medial rectus Adduction Oculomotor (III) Lateral rectus Abduction Abducens (VI) Superior oblique Intorsion Trochlear (IV) Pilot questions 1.2 1. Describe the primary actions of the medial and lateral rectus. (Linked to SLO 1.3) 2. Explain when the vertical action of the superior and inferior rectus is most isolated. (Linked to SLO 1.3) 3. Describe the primary actions of the superior and inferior oblique. (Linked to SLO 1.3) 4. Define yoke muscles and give an example pair. (Linked to SLO 1.4) 5. Define the cardinal positions of gaze. (Linked to SLO 1.4) 1.3 Normal Ocular Alignment 1.3.1 defining normal ocular alignment Both eyes directed together toward the object of regard Normal ocular alignment, or orthophoria, discussed throughout this Series, describes both eyes being directed simultaneously toward the same object of regard, reflecting the coordinated, balanced action of the extraocular muscles and their yoke pairings discussed earlier in this Series. This alignment, discussed earlier in this sub-Part, must be maintained consistently across every direction of gaze and viewing distance, meaning genuinely normal alignment requires both accurate individual muscle function and precise, coordinated neural control of the entire ocular motor system. Fill in the blank: Normal ocular alignment must be maintained consistently across every direction of gaze and viewing distance, requiring both accurate individual muscle
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