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Difference between 'Orbit' and 'Globe' in eye anatomy?

Difference between 'Orbit' and 'Globe' in eye anatomy?


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What's the difference between 'Orbit' and 'Globe' in eye's anatomy. Do they refer to the same ? I encountered this in this text:

… ciliary ganglion, which is approximately 3 mm in size, and located 2-3 mm posterior to the globe and lateral to the optic nerve,…


I've found a rough answer myself:

The globe of the eye, or bulbus oculi, is the eyeball apart from its appendages

http://en.wikipedia.org/wiki/Globe_%28human_eye%29

… the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents.

http://en.wikipedia.org/wiki/Orbit_%28anatomy%29


Since only a small part of the eye called the fovea provides sharp vision, the eye must move to follow a target. Eye movements must be precise and fast. This is seen in scenarios like reading, where the reader must shift gaze constantly. Although under voluntary control, most eye movement is accomplished without conscious effort. Precisely how the integration between voluntary and involuntary control of the eye occurs is a subject of continuing research. [2] It is known, however, that the vestibulo-ocular reflex plays an important role in the involuntary movement of the eye.

Origins and insertions Edit

Four of the extraocular muscles have their origin in the back of the orbit in a fibrous ring called the annulus of Zinn: the four rectus muscles. The four rectus muscles attach directly to the front half of the eye (anterior to the eye's equator), and are named after their straight paths. [2] Note that medial and lateral are relative terms. Medial indicates near the midline, and lateral describes a position away from the midline. Thus, the medial rectus is the muscle closest to the nose. The superior and inferior recti do not pull straight back on the eye, because both muscles also pull slightly medially. This posterior medial angle causes the eye to roll with contraction of either the superior rectus or inferior rectus muscles. The extent of rolling in the recti is less than the oblique, and opposite from it. [2]

The superior oblique muscle originates at the back of the orbit (a little closer to the medial rectus, though medial to it), getting rounder as it [2] courses forward to a rigid, cartilaginous pulley, called the trochlea, on the upper, nasal wall of the orbit. The muscle becomes tendinous about 10mm before it passes through the pulley, turning sharply across the orbit, and inserts on the lateral, posterior part of the globe. Thus, the superior oblique travels posteriorly for the last part of its path, going over the top of the eye. Due to its unique path, the superior oblique, when activated, pulls the eye downward and laterally. [3]

The last muscle is the inferior oblique, which originates at the lower front of the nasal orbital wall, and passes under the LR to insert on the lateral, posterior part of the globe. Thus, the inferior oblique pulls the eye upward and laterally. [3] [4] [5]

The movements of the extraocular muscles take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit. The extraocular muscle pulley system is fundamental to the movement of the eye muscles, in particular also to ensure conformity to Listing's law. Certain diseases of the pulleys (heterotopy, instability, and hindrance of the pulleys) cause particular patterns of incomitant strabismus. Defective pulley functions can be improved by surgical interventions. [6] [7]

Blood supply Edit

The extraocular muscles are supplied mainly by branches of the ophthalmic artery. This is done either directly or indirectly, as in the lateral rectus muscle, via the lacrimal artery, a main branch of the ophthalmic artery. Additional branches of the ophthalmic artery include the ciliary arteries, which branch into the anterior ciliary arteries. Each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The exact number and arrangement of these ciliary arteries may vary. Branches of the infraorbital artery supply the inferior rectus and inferior oblique muscles.

Nerve supply Edit

The nuclei or bodies of these nerves are found in the brain stem. The nuclei of the abducens and oculomotor nerves are connected. This is important in coordinating the motion of the lateral rectus in one eye and the medial action on the other. In one eye, in two antagonistic muscles, like the lateral and medial recti, contraction of one leads to inhibition of the other. Muscles show small degrees of activity even when resting, keeping the muscles taut. This "tonic" activity is brought on by discharges of the motor nerve to the muscle. [2]

Development Edit

The extraocular muscles develop along with Tenon's capsule (part of the ligaments) and the fatty tissue of the eye socket (orbit). There are three centers of growth that are important in the development of the eye, and each is associated with a nerve. Hence the subsequent nerve supply (innervation) of the eye muscles is from three cranial nerves. The development of the extraocular muscles is dependent on the normal development of the eye socket, while the formation of the ligament is fully independent.

Movements Edit

Below is a table of each of the extraocular muscles and their innervation, origins and insertions, and the primary actions of the muscles (the secondary and tertiary actions are also included, where applicable). [8]

Muscle Innervation Origin Insertion Primary action Secondary action Tertiary action
Medial rectus Oculomotor nerve
(inferior branch)
Annulus of Zinn Eye
(anterior, medial surface)
Adduction
Lateral rectus Abducens nerve Annulus of Zinn Eye
(anterior, lateral surface)
Abduction
Superior rectus Oculomotor nerve
(superior branch)
Annulus of Zinn Eye
(anterior, superior surface)
Elevation Incyclotorsion Adduction
Inferior rectus Oculomotor nerve
(inferior branch)
Annulus of Zinn Eye
(anterior, inferior surface)
Depression Excyclotorsion Adduction
Superior oblique Trochlear nerve Sphenoid bone
via the Trochlea
Eye
(posterior, superior, lateral surface)
Incyclotorsion Depression Abduction
Inferior oblique Oculomotor nerve
(inferior branch)
Maxillary bone Eye
(posterior, inferior, lateral surface)
Excyclotorsion Elevation Abduction
Levator palpebrae superioris Oculomotor nerve Sphenoid bone Tarsal plate of upper eyelid Elevation/retraction

Movement coordination Edit

Intermediate directions are controlled by simultaneous actions of multiple muscles. When one shifts the gaze horizontally, one eye will move laterally (toward the side) and the other will move medially (toward the midline). This may be neurally coordinated by the central nervous system, to make the eyes move together and almost involuntarily. This is a key factor in the study of strabismus, namely, the inability of the eyes to be directed to one point.

There are two main kinds of movement: conjugate movement (the eyes move in the same direction) and disjunctive (opposite directions). The former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is usually triggered by the nearness of the target object. A "see-saw" movement, namely, one eye looking up and the other down, is possible, but not voluntarily this effect is brought on by putting a prism in front of one eye, so the relevant image is apparently displaced. To avoid double vision from non-corresponding points, the eye with the prism must move up or down, following the image passing through the prism. Likewise conjugate torsion (rolling) on the anteroposterior axis (from the front to the back) can occur naturally, such as when one tips one's head to one shoulder the torsion, in the opposite direction, keeps the image vertical.

The muscles show little inertia - a shutdown of one muscle is not due to checking of the antagonist, so the motion is not ballistic. [2]

Examination Edit

The initial clinical examination of the extraoccular eye muscles is done by examining the movement of the globe of the eye through the six cardinal eye movements. When the eye is turned out (temporally) and horizontally, the function of the lateral rectus muscle is tested. When the eye is turned in (nasally) and horizontally, the function of the medial rectus muscle is being tested. When turning the eye down and in, the inferior rectus is contracting. When turning it up and in the superior rectus is contracting. Paradoxically, turning the eye up and out uses the inferior oblique muscle, and turning it down and out uses the superior oblique. All of these six movements can be tested by drawing a large "H" in the air with a finger or other object in front of a patient's face and having them follow the tip of the finger or object with their eyes without moving their head. Having them focus on the object as it is moved in toward their face in the midline will test convergence, or the eyes' ability to turn inward simultaneously to focus on a near object.

To evaluate for weakness or imbalance of the muscles, a penlight is shone directly on the corneas. Expected normal results of the corneal light reflex is when the penlight's reflection is located in the centre of both corneas, equally. [9]


Moran CORE

Name: Paul D Chamberlain, 4 th year medical student, Baylor College of Medicine Reese Feist, Chief Resident, University of Utah Moran Eye Center.
Topic: Preseptal vs Orbital Cellulitis
Terminology and Anatomy

Differentiating orbital from preseptal cellulitis is extraordinarily important given that orbital cellulitis has the potential to cause a compartment syndrome within the eye socket resulting in irreversible vision loss to the affected eye. The orbital septum is a membranous sheath extending from the periosteum of the orbit to the tarsal plate located in the eyelid, and is the key anatomical structure in differentiating preseptal from orbital cellulitis. The orbit (eye socket) is the bony structure in which the globe (eyeball) is housed, and it also contains extraocular muscles, fat, and the blood vessels and nerves that supply these structures. Orbital cellulitis (Image 1), also called post-septal cellulitis, is inflammation of the soft tissues (muscles, fat, and connective tissue) of the orbit most commonly from infection. It is important to remember that in orbital cellulitis, the globe itself is not infected or inflamed. Because the orbit is surrounded by the frontal, ethmoid, and maxillary sinuses, infection often results from extension of a sinus infection.

In comparison, pre-septal cellulitis (Image 2), also known as peri-orbital cellulitis, is an infection of the eyelids and surrounding soft tissues that are anterior to the orbital septum. Both orbital cellulitis and preseptal cellulitis are more common in children, and preseptal cellulitis is much more common that orbital cellulitis.

A patient with orbital cellulitis. Note: orbital cellulitis can take on a variety of clinical manifestations and this image should not be taken as a gold standard to which an examiner compares a patient.

A patient with preseptal cellulitis.

Clinical Manifestations

A number of signs may alert the examiner to the presence of orbital cellulitis (table 1). Patients typicall present with erythema and edema of the eyelids. In orbital cellulitis, they erythema and edema can abruptly stop at the arcus marginalis, where the orbital septum inserts into the periosteum. Preseptal cellulitis typically expands beyond this landmark. Patients may present with eye pain, especially with eye movements due to irritation of inflamed muscles. Partial or complete ophthalmoplegia (inability to move the eye in one or more directions) and associated diplopia (double vision) due to inflammation of extraocular muscles or associated cranial nerves. In orbital cellulitis, inflammation and/or an orbital abscess can displace the globe, often pushing it forward or outward which is called proptosis. The presence of proptosis is a medical emergency to evaluate for compartment syndrome. The eyelids can be swollen and in severe cases swollen shut. Eyelids being swollen shut can be present in either orbital or preseptal cellulitis, and is not as helpful in distinguishing between the two. Visual acuity may be decreased but is often unaffected, and a normal visual acuity should not rule out orbital cellulitis. There is often a history or sinusitis or dental abscess. However, there may be no clear source of inflammation, and it may not even be infectious, as with idiopathic orbital inflammatory syndrome.

Preseptal cellulitis is much more common than orbital cellulitis and also presents with eye pain and erythema of the eyelid and surrounding skin and soft tissue. The inflammation may be great enough to tightly close the eyelids as well (image 3), and they should be opened for a visual inspection. Pre-septal cellulitis does not cause loss of vision and if visual acuity is decreased it is likely because of a poor exam or a more severe infection. Preseptal cellulitis may also arise from sinusitis, but may also arise secondary to local trauma, foreign body, or bug bite (Image 4).

Preseptal cellulitis with mechanical ptosis or droopy eyelid due to edema and erythema of the eyelids. Note that there is no proptosis and the erythema doesn’t abruptly stop at the orbital rim, making it clinically less likely to be orbital cellulitis.

A patient with preseptal cellulitis secondary to a bug bite.

Orbital cellulitis. Note the bullous, edematous conjunctiva (conjunctival chemosis), proptosis and the delineation of swelling around the orbital rim. This patient underwent an urgent lateral canthotomy/cantholysis.

Table 1: Comparison of clinical, historical, and diagnostic characteristics of preseptal and orbital cellulitis.

Characteristic Preseptal Cellulitis Orbital Cellulitis
Eye pain May be present Yes
Eyelid erythema and/or tenderness Yes Yes
Pain with eye movements No May be present
Ophthalmoplegia ± diplopia No May be present*
Proptosis No May be present*
Vision loss No May be present*
RAPD No May be present*
Fever Usually not present Usually present
Intraocular Pressure (IOP) Normal May be elevated*
Resistance to Retropulsion None Present*
History of sinusitis May be present, but often not Present more often than not
CT or MRI imaging Shows inflammation only anterior to the orbital septum Show post-septal involvement of the inflammation.
Blood Cultures Very rarely has bacteremia Bacteremia may be present
*Emergent signs and symptoms that might warrant immediate lateral canthotomy/cantholysis

Work-up and Treatment

As previously discussed, the first step is to determine whether a patient has orbital cellulitis, which requires orbital imaging, admission, blood cultures and IV antibiotics. Begin with a thorough ophthalmologic exam, with particular attention to visual acuity, pupillary testing for a relative afferent pupillary defect (RAPD), intraocular pressure, and assessment of proptosis and eye motility. In cases of question, Computed tomography (CT) with and without contrast of the orbits and sinuses should be ordered to look for evidence of post-septal involvement. If a diagnosis of orbital cellulitis is made, the patient needs to be immediately assessed monitored for signs of compartment syndrome and optic neuropathy which would warrant an emergent lateral canthotomy/cantholysis. This procedure allows for anterior expansion of orbital contents which relieves pressure within the orbit in restores blood flow to those structures. Even after initiating antibiotics the swelling may increase for the first 24-48 hours, so frequent re-evaluation is warranted. Immediate surgery may be indicated if there is evidence of a subperiosteal abscess, orbital abscess, or extension of the infection into the cranium. Consider consulting an otolaryngologist for management of sinus disease.

Patients whose history and examination are consistent with preseptal cellulitis without symptoms of orbital cellulitis may be treated as an outpatient with oral antibiotics. Patients with preseptal cellulitis who are appropriately treated typically recover completely without any permanent sequelae. If treated appropriately, patients with orbital cellulitis also often have good outcomes. However, failure to diagnose and treat orbital cellulitis in a timely manner may result in permanent vision loss. An ophthalmologist should be consulted in all cases of orbital or preseptal cellulitis. However, assessing for vision threatening orbital cellulitis should not be postponed until an ophthalmologist is available as an irreversible ischemic optic neuropathy can occur in less than 90 minutes.

Amin N, Syed I, Osborne S. Assessment and management of orbital cellulitis. British Journal of Hospital Medicine. 2016 77(4):216-20.
Hauser A, Fogarasi S. Periorbital and orbital cellulitis. Pediatrics in Review. 2010 31(6):242-9.
Meara DJ. Sinonasal disease and orbital cellulitis in children. Oral Maxillofacial Surgery Clinics of North America. 2012 24(3):487-96.
Rashed F, Cannon A, Heaton PA, Paul SP. Diagnosis, management and treatment of orbital and periorbital cellulitis in children. Emergency Nurse. 2016 (24(1):30-5.


Orbit Anatomy

The bony orbit borders and anatomical relations. The cavity surrounds and provides mechanical protection for the eye and soft tissue structures related to it.

Anatomy Of The Orbit Of The Eye Medmovie Com

Eye anatomy in human eye.

Orbit anatomy. Orbit anatomy in anatomy the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. Orbit can refer to the bony socket or it can also be used to imply the contents. Orbital process of the frontal bone orbital process of the zygomatic bone.

The orbit can be thought of as a pyramidal structure. The orbit is a feature of the face and contains the globe and its supporting structures as well as many nerves and vessels. Fig 11 diagram of the arterial supply to the eye.

Superior orbital fissure lies between the lesser and the greater wing of sphenoid. Fig 12 the major openings into the orbit. Gross anatomy in the adult the orbit has a volume of approximately 30 ml of which the globe occupies 65 ml.

The contents of the orbit are separated and supported by multiple. The orbit which protects supports and maximizes the function of the eye. The orbit the eye is protected from mechanical injury by being enclosed in a socket or orbit which is made up of portions of several of the bones of the skull to form a four sided pyramid the apex of which points back into the head.

By definition the orbit bony orbit or orbital cavity is a skeletal cavity comprised of seven bones situated within the skull. In the adult human the volume of the orbit is 30 millilitres 106 imp fl oz. 101 us fl oz.

Pathways into the orbit. The lacrimal system produces distributes and drains tears. Inferior orbital fissure lies between.

This fissure allows the passage to the nerves iii iv vi branches of the v1 and ophthalmic veins.

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Inflammatory Eyelid Processes

HORDEOLUM

A hordeolum, or stye, is a well-defined, often painful mass at the eyelid margin, commonly caused by bacterial infection of the follicle of the eyelash.14 , 21 A hordeolum is an infection of the internal meibomian (sebaceous) gland, whereas a stye (external hordeolum) is an infection of the external Zeis (sweat) gland.1 , 21 , 22 These localized masses appear as papules and furuncles located distally at the lid edge.1 , 21 , 22 They typically resolve spontaneously within a few days or weeks, and warm compresses can help.1 , 21 Chronic hordeola can lead to chalazia.22

CHALAZION

A chalazion is a noninfectious mass surrounding the meibomian gland within the midportion of the eyelid.1 , 14 , 22 Chalazia tend to present for longer than two weeks compared with the shorter natural history of sties or internal hordeola.1 Chalazia may develop from hordeola or when sebum clogs the gland.22 The skin of the lid appears unremarkable without findings such as a papule.1 The resultant erythema of the mass effect can be confused with cellulitis however, chalazia are not painful.14 , 23 Surgical intervention with incision and drainage can be considered for very large chalazia.1 , 14 , 22 Intralesional steroid injections have also been used for treatment if conservative management with time and warm compresses is ineffective.24 , 25

BLEPHARITIS

Blepharitis is inflammation at the base of the eyelashes that can be chronic or acute, and is associated with dry eyes, seborrheic dermatitis, rosacea, and Demodex mite infestation. Symptoms are often worse in the morning. Treatments include warm compresses, gentle massage, washes with diluted baby shampoo, topical antibiotics, topical steroids, oral antibiotics, and combinations of these therapies.26

DACRYOADENITIS

Dacryoadenitis is inflammation of the lacrimal glands, whereas dacryocystitis is inflammation of the lacrimal sac in the inferior lid.1 Both conditions can be caused by viruses or bacteria. Bacterial infections tend to be tenderer to palpation than viral infections.1 Staphylococcus , Streptococcus , and gram-negative organisms are common pathogens. Clinically, these processes may mimic preseptal cellulitis.


Retinal Detachment

The retina consists of two layers: inner and outer. The inner layer, or neurosensory retina, includes the photoreceptors. The outer layer is the retinal pigment epithelium and attaches to the inner surface of the choroid (12). The term retinal detachment refers to separation of the inner and outer layers. The most common mechanism of retinal detachment is tearing of the inner layer. Traction or pulling on the retinal hole in conjunction with vitreous fluid entering the hole can create a potential space as the inner and outer layers separate. Retinal detachment is a surgical emergency, and treatment is necessary to prevent complications, such as retinal ischemia and blindness. The aim of surgical treatment is apposition of the two retinal layers. Several procedures are available in ophthalmologists’ armamentarium to repair retinal detachments, including scleral buckling, pars plana vitrectomy with subsequent intraocular tamponade, and retinopexy. These interventions may be used simultaneously or in succession for the same eye, as needed.

Scleral buckling surgery causes an indentation of the wall of the globe, which decreases the vector forces pulling on the retina. Scleral buckles encircle the eye either in total (360°) or in a segmental fashion (less than 360° of the total globe circumference) if they are oriented perpendicular to the rectus muscles. They may also be radially oriented (parallel to the rectus muscles). Any combination of these arrangements may be applied to the eye (13). Scleral buckles are usually permanent and are removed only if complications arise. Scleral buckle devices are usually composed of silicone material, either solid silicone rubber or a porous silicone sponge. Solid silicone rubber devices are hyperattenuating at CT, whereas silicone sponge devices appear as a structure with air attenuation deforming the globe. At MR imaging, both solid silicone and silicone sponges have low signal intensity on T1- and T2-weighted images, and they can be difficult to detect (Fig 8). Indentation of the eye may be the only clue to their presence at MR imaging. Regardless of their composition, all current scleral buckle devices are MR imaging safe. In the past, tantalum clips were used to hold scleral buckle devices in place, although, currently, sutures alone are preferred. Tantalum clips are seen on radiographs and CT images as radiopaque structures, and they create susceptibility artifact at MR imaging. Tantalum is a nonferromagnetic metal and, thus, is considered MR imaging safe (14).

Figure 8a Scleral buckle devices for treatment of retinal detachment in two patients. (a) Coronal CT image obtained in a 67-year-old man shows a a solid silicone rubber scleral buckle, which is seen as a thin hyperattenuating structure (arrow) encircling the right globe. (b) Axial CT image obtained in an 80-year-old woman shows a silicone sponge (arrowhead) sutured to the lateral sclera of the right globe in a radial configuration, which is seen as a structure with air attenuation. A solid circumferential silicone rubber buckle device (arrow) is also seen. (c, d) Sagittal T2-weighted (c) and axial contrast-enhanced T1-weighted (d) MR images obtained in the same patient as in b show that both the solid (arrows ) and sponge (arrowhead) silicone devices have low signal intensity.

Figure 8b Scleral buckle devices for treatment of retinal detachment in two patients. (a) Coronal CT image obtained in a 67-year-old man shows a a solid silicone rubber scleral buckle, which is seen as a thin hyperattenuating structure (arrow) encircling the right globe. (b) Axial CT image obtained in an 80-year-old woman shows a silicone sponge (arrowhead) sutured to the lateral sclera of the right globe in a radial configuration, which is seen as a structure with air attenuation. A solid circumferential silicone rubber buckle device (arrow) is also seen. (c, d) Sagittal T2-weighted (c) and axial contrast-enhanced T1-weighted (d) MR images obtained in the same patient as in b show that both the solid (arrows ) and sponge (arrowhead) silicone devices have low signal intensity.

Figure 8c Scleral buckle devices for treatment of retinal detachment in two patients. (a) Coronal CT image obtained in a 67-year-old man shows a a solid silicone rubber scleral buckle, which is seen as a thin hyperattenuating structure (arrow) encircling the right globe. (b) Axial CT image obtained in an 80-year-old woman shows a silicone sponge (arrowhead) sutured to the lateral sclera of the right globe in a radial configuration, which is seen as a structure with air attenuation. A solid circumferential silicone rubber buckle device (arrow) is also seen. (c, d) Sagittal T2-weighted (c) and axial contrast-enhanced T1-weighted (d) MR images obtained in the same patient as in b show that both the solid (arrows ) and sponge (arrowhead) silicone devices have low signal intensity.

Figure 8d Scleral buckle devices for treatment of retinal detachment in two patients. (a) Coronal CT image obtained in a 67-year-old man shows a a solid silicone rubber scleral buckle, which is seen as a thin hyperattenuating structure (arrow) encircling the right globe. (b) Axial CT image obtained in an 80-year-old woman shows a silicone sponge (arrowhead) sutured to the lateral sclera of the right globe in a radial configuration, which is seen as a structure with air attenuation. A solid circumferential silicone rubber buckle device (arrow) is also seen. (c, d) Sagittal T2-weighted (c) and axial contrast-enhanced T1-weighted (d) MR images obtained in the same patient as in b show that both the solid (arrows ) and sponge (arrowhead) silicone devices have low signal intensity.

Vitrectomy is the process of removing the vitreous gel from the eye. Removal of the vitreous is necessary because it strongly adheres to the retina, resulting in a constant pull. Pulling on the retina allows the liquid vitreous to enter the intraretinal space in the setting of a tear of the inner retinal layer, causing separation of the two layers. At the end of the vitrectomy procedure, the eye is filled with either a long-acting gas, such as sulfur hexafluoride, or silicone oil, which serves to plug the retinal hole and prevent additional fluid from entering. However, the initial vitreous fluid that infiltrated the intraretinal space remains. One of the functions of the retinal pigment epithelium is to pump water out of the intraretinal space and into the choroid. By draining this vitreous fluid, the two retinal layers are able to reapproximate over time, relieving the retinal detachment. After intraocular gas tamponade, air attenuation is seen in the vitreous cavity at CT, with or without air-fluid levels (Fig 9). Corresponding areas of hypointensity are seen on T1- and T2-weighted MR images because of the presence of air. When silicone oil is used, it appears hyperattenuating at CT (15). Differentiating intraocular hemorrhage from an injection of silicone oil is possible by measuring the attenuation values (in HU). Typically, silicone is more than 100 HU, and blood is less than 90 HU, although these values may vary depending on CT scanning parameters (16). The imaging characteristics of silicone oil are somewhat variable at MR imaging because of manufacturing differences in its viscosity. Hyperintensity on T1-weighted images and iso- to hypointensity on T2-weighted images are the most commonly reported findings (17). Chemical shift artifact can be seen at the oil-water interface after injection of silicone oil (Fig 10) (18).

Figure 9a Vitrectomy followed by intraocular gas tamponade for treatment of retinal detachment in two patients. Sagittal CT image obtained in an 18-year-old man (a) and axial CT image obtained in a 34-year-old man (b) show an area of air attenuation within the globe (*), which represents injected sulfur hexafluoride gas. The presence of an air-fluid level (arrowhead in b) should not be mistaken for a postoperative infectious process. Solid silicone rubber scleral buckle devices (arrows) are also present.

Figure 9b Vitrectomy followed by intraocular gas tamponade for treatment of retinal detachment in two patients. Sagittal CT image obtained in an 18-year-old man (a) and axial CT image obtained in a 34-year-old man (b) show an area of air attenuation within the globe (*), which represents injected sulfur hexafluoride gas. The presence of an air-fluid level (arrowhead in b) should not be mistaken for a postoperative infectious process. Solid silicone rubber scleral buckle devices (arrows) are also present.

Figure 10a Vitrectomy followed by intraocular silicone oil tamponade for treatment of retinal detachment in two patients. (a) Axial CT image obtained in a 19-year-old man shows an area of homogeneous hyperattenuation (arrow) in the right globe, a finding that represents silicone oil. A silicone rubber buckle device (arrowhead) is also present. (b, c) Axial T2-weighted (b) and sagittal T1-weighted (c) MR images obtained in a 79-year-old woman show silicone oil (arrow) within the left globe. Silicone oil is mildly hypointense relative to the contralateral right vitreous humor on T2-weighted images, with corresponding intermediate signal intensity on T1-weighted images. Chemical shift artifact (arrowhead), which is seen as crescent-shaped, parallel bands of low and high signal intensity on both T1- and T2-weighted images, is seen at the oil-water interface. (d) Axial fluid attenuation inversion-recovery image obtained in the same patient as in b and c shows silicone oil, which is hyperintense (arrow), whereas the normal right vitreous fluid is dark (*).

Figure 10b Vitrectomy followed by intraocular silicone oil tamponade for treatment of retinal detachment in two patients. (a) Axial CT image obtained in a 19-year-old man shows an area of homogeneous hyperattenuation (arrow) in the right globe, a finding that represents silicone oil. A silicone rubber buckle device (arrowhead) is also present. (b, c) Axial T2-weighted (b) and sagittal T1-weighted (c) MR images obtained in a 79-year-old woman show silicone oil (arrow) within the left globe. Silicone oil is mildly hypointense relative to the contralateral right vitreous humor on T2-weighted images, with corresponding intermediate signal intensity on T1-weighted images. Chemical shift artifact (arrowhead), which is seen as crescent-shaped, parallel bands of low and high signal intensity on both T1- and T2-weighted images, is seen at the oil-water interface. (d) Axial fluid attenuation inversion-recovery image obtained in the same patient as in b and c shows silicone oil, which is hyperintense (arrow), whereas the normal right vitreous fluid is dark (*).

Figure 10c Vitrectomy followed by intraocular silicone oil tamponade for treatment of retinal detachment in two patients. (a) Axial CT image obtained in a 19-year-old man shows an area of homogeneous hyperattenuation (arrow) in the right globe, a finding that represents silicone oil. A silicone rubber buckle device (arrowhead) is also present. (b, c) Axial T2-weighted (b) and sagittal T1-weighted (c) MR images obtained in a 79-year-old woman show silicone oil (arrow) within the left globe. Silicone oil is mildly hypointense relative to the contralateral right vitreous humor on T2-weighted images, with corresponding intermediate signal intensity on T1-weighted images. Chemical shift artifact (arrowhead), which is seen as crescent-shaped, parallel bands of low and high signal intensity on both T1- and T2-weighted images, is seen at the oil-water interface. (d) Axial fluid attenuation inversion-recovery image obtained in the same patient as in b and c shows silicone oil, which is hyperintense (arrow), whereas the normal right vitreous fluid is dark (*).

Figure 10d Vitrectomy followed by intraocular silicone oil tamponade for treatment of retinal detachment in two patients. (a) Axial CT image obtained in a 19-year-old man shows an area of homogeneous hyperattenuation (arrow) in the right globe, a finding that represents silicone oil. A silicone rubber buckle device (arrowhead) is also present. (b, c) Axial T2-weighted (b) and sagittal T1-weighted (c) MR images obtained in a 79-year-old woman show silicone oil (arrow) within the left globe. Silicone oil is mildly hypointense relative to the contralateral right vitreous humor on T2-weighted images, with corresponding intermediate signal intensity on T1-weighted images. Chemical shift artifact (arrowhead), which is seen as crescent-shaped, parallel bands of low and high signal intensity on both T1- and T2-weighted images, is seen at the oil-water interface. (d) Axial fluid attenuation inversion-recovery image obtained in the same patient as in b and c shows silicone oil, which is hyperintense (arrow), whereas the normal right vitreous fluid is dark (*).

Retinopexy is the creation of a chorioretinal scar surrounding the retinal tear to prevent re-separation, and it can be performed with photocoagulation (laser), cryotherapy, or heat. Recently, pneumatic retinopexy has gained popularity because it can be performed in an outpatient setting. It involves the use of laser or cryotherapy retinopexy to cause adhesion between the retina and the retinal pigment epithelium surrounding the retinal breaks followed by injection of intraocular gas. Postprocedure CT or MR imaging findings of pneumatic retinopexy are similar to those of gas tamponade after vitrectomy.


Clinical relations

Fractures

The most common clinical conditions related to the orbit are fractures. Any of the walls can be affected, but most commonly it’s the floor, followed by the medial wall (because of the fragility of thin ethmoidal cells). When the orbital floor is affected, the inferior rectus muscle is often dragged into the fracture line which results in an inability to move the eyeball upwards in the affected eye (known as upward gaze diplopia).

On the other hand, the ethmoid bone and its labyrinth are usually affected in medial wall fractures. This usually results with creating continuity (craniosinus fistula) between the ethmoid paranasal sinuses and the orbit and is clearly visible in radiographs. The craniosinus fistula enables leakage of the cerebrospinal fluid from the cranium through the nose which leads to a drop in intracranial pressure (hypotension) and manifests as headache, nausea, vomiting, and difficulty concentrating. In addition to this, bone fragments can physically damage the eye and cause blindness and nasal deformity.

Inflammatory and neoplastic processes

When it comes to the contents of the orbit, any inflammatory processes such as conjunctivitis, or even neoplastic processes, like chorodial melanoma, that affect the eye or its accessory structures show a tendency to spread into the cranium through orbital openings as they provide a direct communication between the orbit and cranial fossae. Depending on the nature of the process, it may result either with inflammation of the meninges (meningitis), or with creation of metastatic masses (cancer) within the brain tissue.

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Eye shape reveals whether an animal is predator or prey, new study shows

The eyes say it all. They answer questions about a creature’s social scale, and its place in the pecking order. The geometry of the eye indicates whether an animal is the hunter, or the hunted – and how tall it walks.
Scientists from the Universities of California Berkeley and Durham in Britain have
discovered just how much they can learn from pupils. As every householder knows, when the domestic cat narrows its eyes to slits, it does so vertically. Sheep, deer and horses however have eyes with horizontally elongated pupils.

Martin Banks, professor of optometry at Berkeley and Gordon Love, director of the Centre for Advanced Instrumentation at Durham, have learned something else. So important is it for a grazing animal to keep an eye on the ground that when it drops its head, the pupil rotates by up to 50 degrees to stay horizontal.
“The first key visual requirement for these animals is to detect approaching predators, which usually come from the ground, so they need to see panoramically on the ground with minimal blind spots,” said Professor Banks. “The second critical requirement is that once they do detect a predator, they need to see where they are running. They have to see well enough out of the corner of their eye to run quickly and jump over things.” The two scientists and their colleagues report in the journal Science Advances that they looked at the eyes of 214 closely-studied animals, all terrestrial vertebrates. These included Australian snakes, every species from the cat and dog families as well as hyenas and mongooses, and domestic grazing animals as well as tapirs and rhinoceroses. The challenge was to see if they could predict a relationship between an animal’s ecological niche and the shape formed by the pupil in its eye.
They found a pattern. The smaller ambush predators – those little creatures that lie in wait for their lunch – are more likely to have pupils that narrow vertically. Hunters that prowl by day or night need to make the most use of available evening light yet exclude the glare of the sun, which is why the eyes must narrow dramatically. The mouse-hunting domestic cat can change the area of its pupil gaze 135-fold and the insectivorous gecko 300-fold. Round-eyed humans – that is, with circular pupils – can reduce them 15-fold. But humans walk tall. So do lions and tigers, and they too have round eyes and circular pupils. The big cats are “active foragers”: they hunt down their prey. The researchers included 65 ambush predators with eyes in the fronts of their heads for this study. Of these, 44 had vertical pupils and 82% had shoulder heights less than 42 cms or 16.5 inches. So the reasoning is that binocular vision and vertical slit pupils together make it easier for small animals to pounce, by using the difference between close focus on the innocent dinner and the out-of-focus or blur beyond and before it, to judge the distance precisely. The team started with a classic 1942 text on the physiology of the eye that proposed that slit-shaped pupils allowed for different musculature and a greater range of light entering the eye. But the theory did not explain why the eye slits could be sometimes vertical, sometimes horizontal. When a grazing animal lifts its head, its eyes are elongated horizontally. But surely, when it drops its head to crop grass, the eyes would appear near vertical to the ground? The scientists set out to observe the eyes swivel to stay parallel with the ground. Professor Love began research in astronomical technology but joined the eye project years ago. “The physics of huge telescopes, microscopes, and eyes is all rather similar so it wasn’t such a big jump,” he said. Professor Banks went to Oakland Zoo in California to observe at first hand, and Professor Love took his camera to the Yorkshire Dales to record changing pupil shapes in the field. “The photography part was new and fun and took more time than I care to remember,” he said. “You might think that sheep would be easy to photograph. I now have eternal respect for David Attenborough and his colleagues.”


Difference between 'Orbit' and 'Globe' in eye anatomy? - Biology

Function . (See also vision .) The refraction or bending of light rays so that they focus on the retina and can thus be transmitted to the optic nerve is accomplished by three structures: the aqueous humor, a watery substance between the cornea and lens the lens, a crystalline structure just behind the iris and the vitreous humor, a jelly-like substance filling the space between the lens and the retina. Unlike the lens of a camera, the lens of the eye focuses by a process called accommodation. This means that when the eye sees something in the distance, muscles pull the lens, stretching it until it is thin and almost flat, so that the light rays are only slightly bent as they pass through it. When the object is close, the muscles relax and the elastic lens becomes thicker, bending the light rays and focusing them on the retina.ƒ

Because the eye must function under many different circumstances, there are two types of nerve cells in the retina, with different shapes: the cones and the rods . They cover the full range of adaptation to light, the cones being sensitive in bright light, and the rods in dim light. The cones are responsible for color vision. There are three types of cones, each containing a substance that reacts to light of a different color, one set for red, one for green, and one for violet. These are the primary colors in light, which, when mixed together, give white. White light stimulates all three sets of color cells any other color stimulates one or two.

The optic nerve, which transmits the nerve impulses from the retina to the visual center of the brain, contains nerve fibers from the many nerve cells in the retina. The small spot where it leaves the retina does not have any light-sensitive cells, and is called the blind spot.

The eyes are situated in the front of the head in such a way that human beings have stereoscopic vision, the ability to judge distances. Because the eyes are set apart, each eye sees farther around an object on its own side than does the other. The brain superimposes the two slightly different images and judges distances from the composite image.

Disorders of the Eye . If the eyeball is too short or too long, the lens focuses the image not on the retina but behind or in front of it. The former condition is called hyperopia (or farsightedness) and the latter myopia (or nearsightedness). An irregularity in the curvature of the cornea or lens can cause the impaired vision of astigmatism . strabismus (or squint or crossed eyes) is usually caused by weakness in muscles that control movement of the eyeball. conjunctivitis is an inflammation of the membrane that covers the front of the eyeball and lines the eyelids. When small pieces of the retina become detached from the underlying layers, the result is a retinal detachment surgery may be necessary to prevent blindness. presbyopia (usually taking the form of hyperopia) occurs in older persons and develops as the lens loses its elasticity with the passing years. Correction is easily made with properly prescribed eyeglasses.ƒ

Foreign bodies in the eyes are common occurrences. Protective eyewear should be worn by individuals at risk. Cinders, grit, or other foreign bodies are best removed by lifting the eyelid by the lashes. The foreign body will usually remain on the surface of the lid, and can easily be removed. Particles embedded in the eyeball must be removed by a qualified health care professional.

Eyestrain is fatigue of the eyes caused by improper use, uncorrected defects in the vision, or an eye disorder. Symptoms may include aching or pains in the eyes, or a hot, scratchy feeling in the eyelids. Headache, blurring or dimness of vision, and sometimes dizziness or nausea may also occur.

artificial eye a glass or plastic prosthesis inserted in the eye socket to replace the eyeball most are designed to be worn day and night. When patients become debilitated and unable to care for such a prosthesis, they must depend on members of the health care team to give proper care according to the chosen preferred routine.ƒ

Cleaning of a prosthetic eye is similar in principle to care of dentures both are handled with care to avoid damage and are cleansed according to good hygienic principles. The prosthesis is removed while the patient is lying down so that it falls into the hand and is not likely to be dropped and broken. It is removed by depressing the lower eyelid, allowing the prosthesis to slide out and down. Mild soap and water are most often used for cleansing the prosthesis. Alcohol or other chemicals can damage prostheses made of plastic. If it is not replaced in the socket immediately after cleansing, it is stored in water or contact lens soaking solution. Insertion of the prosthesis is done by lifting the upper eyelid with the thumb or forefinger and placing its notched edge toward the nose. It is placed as far as possible under the upper lid and then the lower lid is depressed to allow it to slip into place. The process can be made easier by first moistening the prosthesis with water. If it is necessary to wipe the eye area of a patient wearing a prosthesis, one should gently wipe toward the nose in order not to dislodge the prosthesis.

Anatomy

The eyeball has three layers: the inner retina, which contains the photoreceptors the middle uvea (choroid, ciliary body, and iris) and the outer sclera, which includes the transparent cornea. The eyeball contains two cavities: the anterior cavity and the posterior cavity. The smaller anterior cavity is in front of the lens and is further divided by the iris into an anterior chamber, filled with aqueous humor, and a posterior chamber, filled with the vitreous. Behind the lens is the larger posterior cavity, which contains the vitreous. The lens is behind the iris, held in place by the ciliary body and suspensory ligaments called zonules. The visible portion of the sclera is covered by the conjunctiva. Six extrinsic muscles move the eyeball: the superior, inferior, medial, and lateral rectus muscles, and the superior and inferior oblique muscles.

Nerve supply: The optic (second cranial) nerve contains the fibers from the retina. The eye muscles are supplied by the oculomotor, trochlear, and abducens (third, fourth, and sixth cranial) nerves. The lid muscles are supplied by the facial nerve to the orbicularis oculi and the oculomotor nerve to the levator palpebrae. Sensory fibers to the orbit are furnished by ophthalmic and maxillary fibers of the fifth cranial (trigeminal) nerve. Sympathetic postganglionic fibers originate in the carotid plexus, their cell bodies lying in the superior cervical ganglion. They supply the dilator muscle of the iris. Parasympathetic fibers from the ciliary ganglion pass to the lacrimal gland, ciliary muscle, and constrictor muscles of the iris.

Physiology

Light entering the eye passes through the cornea, then through the pupil, and on through the crystalline lens and the vitreous to the retina. The cornea, aqueous humor, lens, and vitreous are the refracting media of the eye. Changes in the curvature of the lens are brought about by its elasticity and by contraction of the ciliary muscle. These changes focus light rays on the retina, thereby stimulating the rods and cones. The rods detect light, and the cones detect colors in the visible spectrum. The visual area of the cerebral cortex, located in the occipital lobe, registers them as visual sensations. The amount of light entering the eye is regulated by the iris its constrictor and dilator muscles change the size of the pupil in response to varying amounts of light. The eye can distinguish nearly 8 million differences in color. As the eye ages, objects appear greener. The principal aspects of vision are color sense, light sense, movement, and form sense.

Patient care

When injury to the eye occurs, visual acuity is assessed immediately. If the globe has been penetrated, a suitable eye shield, not an eye patch, is applied. A penetrating foreign body should not be removed. All medications, esp. corticosteroids, are withheld until the patient has been seen by an ophthalmologist.

The patient is assessed for pain and tenderness, redness and discharge, itching, photophobia, increased tearing, blinking, and visual blurring. When any prescribed topical eye medications (drops, ointments, or solutions) are administered, the health care provider should wash his or her hands thoroughly before administering the agent. The patient's head is turned slightly toward the affected eye his or her cooperation is necessary to keep the eye wide open. Drops are instilled in the conjunctival sac (not on the orb), and pressure is applied to the lacrimal apparatus in the inner canthus if it is necessary to prevent systemic absorption. Ointments are applied along the palpebral border from the inner to the outer canthus, and solutions are instilled from the inner to the outer canthus. Touching the dropper or tip of the medication container to the eye should be avoided, and hands should be washed immediately after the procedure.

Both patient and family are taught correct methods for instilling prescribed medications. Patients with visual defects are protected from injury, and family members are taught safety measures. Patients with insufficient tearing or the inability to blink or close their eyes are protected from corneal injury by applying artificial tears and by gently patching the eyes closed. The importance of periodic eye examinations is emphasized. Persons at risk should protect their eyes from trauma by wearing safety goggles when working with or near dangerous tools or substances. Tinted lenses should be worn to protect the eyes from excessive exposure to bright light. Patients should avoid rubbing their eyes to prevent irritation or possibly infection. See: eyedrops artificial tears


Contents

The bony orbit contains the eyeballs and their associated structures:

Fig 1.1 – Diagram of the arterial supply to the eye.

Extra-ocular muscles – These muscles are separate from the eye. They are responsible for the movement of the eyeball and superior eyelid.

  • Eyelids – These cover the orbits anteriorly.
  • Nerves: Several cranial nerves supply the eye and its structures optic, oculomotor, trochlear, trigeminal and abducens nerves.
  • Blood vessels: The eye receives blood primarily from the ophthalmic artery. Venous drainage is via the superior and inferior ophthalmic veins.

Any space within the orbit that is not occupied is filled with orbital fat. This tissue cushions the eye, and stabilises the extraocular muscles.


How to use orb in a sentence

It has been a terrible year on so many metrics, no matter where on this celestial orb you live.

Scientists have observed the planets and moons in our solar system for centuries, and have flown spacecraft past the orb s for decades.

Its shape is more similar to a spinning top than a basketball or other orb , and it’s not very big—about a third of a mile wide at its widest point.

When moved next to text, the faint gray orb signifying your mouse cursor transforms into a blinking editing variant, letting you highlight and copy or paste whatever you’re hovering over.

Materia, orb s of immense power, grant the ability to cast spells.

There is something to the challenge posed by that dimpled orb that creates great distraction.

Unbeknownst to him, the orb contains an Infinity Stone, which holds within it the power to destroy entire planets.

Guardians centers on Peter Quill/Star-Lord (Chris Pratt), an intergalactic smuggler who swipes an orb .

One day, he stumbles across a mysterious orb whose very existence threatens the future of the universe.

Quite frankly, the custom made Sealegs craft knocks the spots off the orb he got given by the Pope the other day.

The morning crawled past, the sun mounted until I could see the golden orb near zenith.

The moon rose majestically above the distant trees her full, round, and yellow orb cast a mellow light upon our group.

The orb of the sun, already near the horizon, seemed enormous and of purple hue.

They prayed devoutly before sunrise but until the orb had risen they never spoke of worldly matters.