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By: A. Hogar, M.B.A., M.D.
Associate Professor, Western Michigan University Homer Stryker M.D. School of Medicine
Astigmatic aberration is an undesired side effect that is present whenever one looks through a lens at an oblique angle antibiotics for acne singapore purchase zyvox with a visa. This phenomenon should be distinguished from astigmatic or toric lenses antibiotics for acne for 6 months 600 mg zyvox amex, which correct for astigmatism of the eye when the patients looks through them along the optical axis antibiotic nomogram cheap 600mg zyvox visa. Curvature of Field this means that the magnification of the image changes as one approaches the periphery. Convex or plus lenses produce pincushion distortion; concave or minus lenses produce barrel distortion. However, it appears to the observer that the object is shifted toward the apex of the prism (dotted line). This form of strabismus may occur as monocular strabismus, in which only one eye deviates, or as alternating strabismus, in which both eyes deviate alternately. This form differs from concomitant strabismus in that the angle of deviation does not remain constant in every direction of gaze. Esotropia (convergent strabismus) occurs far more frequently than exotropia (divergent strabismus) in Europe and North America. Concomitant strabismus usually occurs in children, whereas paralytic strabismus primarily affects adults. This is because concomitant strabismus is generally congenital or acquired within the first few years of life, whereas paralytic strabismus is usually acquired, for example as a post-traumatic condition. All of these muscles originate at the tendinous ring except for the inferior oblique muscle, which has its origin near the nasolacrimal canal. Superior rectus Superior oblique Medial rectus Inferior oblique Trochlea Tendon of the superior oblique Superior oblique Lateral rectus Inferior rectus Inferior oblique Optic nerve Tendinous ring Lateral rectus Superior rectus Inferior rectus Medial rectus. The four rectus muscles insert on the superior, inferior, nasal, and temporal sclera. The insertion of the muscles determines the direction of their pull (see Table 17. Other important anatomic structures include the lateral and medial check ligaments comprising the lateral connections of the orbital connective tissue and the ligament of Lockwood. This is comprised of the ligamentous structures between the inferior rectus and inferior oblique that spread out like a hammock to the medial and lateral rectus muscles. These anatomic structures and the uniform nerve supply to the extraocular muscles (like acting muscles have like nerve supply) ensure ocular balance. All other extraocular muscles have a secondary direction of pull in addition to the primary one. Depending on the path of the muscle, where it inserts on the globe, and the direction of gaze. The primary action of the superior rectus and superior oblique is elevation; the primary action of the inferior rectus and inferior oblique is depression. Nerve supply to the extraocular muscles: the oculomotor nerve (third cranial nerve) supplies all of the extraocular muscles except the superior oblique, which is supplied by the trochlear or fourth cranial nerve, and the lateral rectus, which is supplied by the abducent or sixth cranial nerve (see Table 17. The extraocular muscle nuclei are located in the brain stem on the floor of the fourth ventricle and are interconnected via the medial longitudinal fasciculus, a nerve fiber bundle connecting the extraocular muscles, neck muscles, and vestibular nuclei for coordinated movements of the head and globe. The location of the muscle nuclei and knowledge of the visual areas are important primarily in gaze paralysis and paralytic strabismus and of particular interest to the neurologist. For example, the type of gaze paralysis will allow one to deduce the approximate location of the lesion in the brain. All extraocular muscles except for the superior oblique and lateral rectus are supplied by the oculomotor nerve. The optic nerve and visual pathway transmit this information in coded form to the visual cortex. The sensory system produces a retinal image and transmits this image to the higher-order centers. The motor system aids in this process by directing both eyes at the object so that the same image is produced on each retina.
Reduction and rigid fixation of the nasomaxillary buttress and piriform aperture requires a maxillary gingival buccal approach antimicrobial flooring cheap zyvox 600mg online. Clinical experience antibiotics for acne cons discount 600 mg zyvox with visa, along with current literature antibiotic not working order 600 mg zyvox with amex, supports the use of fewer and smaller plates than previously employed. As originally described, four-hole or five-hole inferior orbital rim, piriform, and superior plates were used to fixate the fragments. If the angular process of the frontal bone has only a greenstick pattern in combination with a displaced inferior segment, then only a single inferior rim or piriform plate is required. Inferior stabilization must be followed with superior fixation at the angular process to the stable nasal process of the frontal bone; a three-hole plate typically suffices. Inferior stabilization is identical, with a single four-hole plate on each side of the piriform aperture or both inferior orbital rims. However, the complete posterior and inferior displacement of the internal angular process here necessitates a single four-hole or five-hole Y-type plate. A combination of coronal, lower eyelid, and upper gingival buccal incisions provides sufficient space for miniplate and wire fixation. Integral to this exposure is identification of the medial orbital rim bone, into which the medial canthal tendon inserts. Meticulous dissection must be applied to avoid inadvertent stripping of the medial canthal tendon. Specifically, approaching from the nasal side may assist in more easily and safely identifying this segment. The nasal bones must be temporarily dislocated or removed to allow visualization of the medial orbital wall during this technique. This also allows easier placement of transnasal wires and an accurate assessment of reduction. The exact transnasal wiring technique depends on the shape and size of the central fragment. Most surgeons prefer to drill two holes in a vertical fashion 4 to 5 mm apart (using a 1. Dislocating the central fragments anteriorly and laterally can facilitate drilling these holes. The two ends of a 28-guage wire are passed through the holes and twisted together on the nasal or medial side. This end and the contralateral side are then twisted together in the midline until reduction of the fragments is complete. Junctional miniplate or microplate fixation with a three-hole plate at the internal angular process of the frontal bone further stabilizes the reduction. However, fixation at the inferior aspect is not important; it provides only contour without further stabilization. Surgeons must avoid placing plates around the anterior canthal area; therefore excluding an inferior plate may be more beneficial in this technique. Management of the medial canthal tendon in nasoethmoid orbital fractures: the importance of the central fragment in classification and treatment. Unless sharp penetrating trauma was involved, the medial canthal tendon is almost never completely avulsed. Careful examination of the medial canthal tendon, its insertion, and the bony segment must be performed. Any partial avulsion of the tendon demands reinforcing it with wire to the medial orbital wall at the posterosuperior aspect for a combination transnasal wire reduction/stabilization and canthopexy. However, the central fragment rarely contains enough surface area for two drill holes to be placed 4 mm apart, and a bone graft is almost always needed to provide adequate skeletal support. Bone graft donor sites, such as a larger local medial orbital rim segment or distal parietal skull outer table, may substitute as a central fragment. Reduction starts by detaching the canthal tendon and properly arranging the bone graft and other segments. A 4 mm horizontal incision at the eyelid commissure facilitates passing a 3-0 braided suture to secure the lateralmost aspect of 296 Part Two Regional Management the canthal tendon with a modified Kessler stitch. The suture is connected to a pair of transnasal wires that are subsequently placed in the central bone graft as described previously. Up to four sets of transnasal wires may be required: one for medial orbital rim reduction (because plates anterior to the canthal tendon can be detrimental), one for each canthus, and one for an external nasal bolster.