Term
| How is the eyelid elevated and closed? What nerves are responsible for this movement? |
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Definition
| The tarsal plate of the eyelid is attached to the levator palpebrae superioris muscle that contracts and elevates the eyelid. It is closed by contraction of the palpebral fibers of the orbicularis oculi muscle (and gravity). Levator palpebrae superioris is innervated by branches of the oculomotor nerve (CN III) while orbicularis oculi is innervated by the facial nerve (CN VII). |
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Term
| Where are tears produced and how do they travel to the nasal cavity? What structures do they pass through? |
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Definition
| Tears are produced by stimulation of the lacrimal gland (parasympathetic fibers from facial) that flow through small ducts and enter the upper outer fornix area of the eye. They flow across the conjunctiva of the eyeball and eyelid toward the medial aspect. They exit through the superior and inferior puncta in the lacrimal papillae of the eyelids. The tears flow through small canaliculi to the lacrimal sac. The sac drains through the nasolacrimal duct that opens in the inferior meatus of the nose. |
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Term
| What are the conjunctiva, sclera, cornea, iris, lens, and pupil of the eye? |
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Definition
| The conjunctiva is the mucous covering of the eyeball and inner surface of the eyelid. The sclera is the connective tissue layer that makes up the wall of the eyeball (white of the eye) and is continuous with the cornea which is the clear layer through which light enters the bulb. The iris is the diaphragm at the front of the eyeball and the lens sits just behind and changes shape to focus the light on the retina. The pupil is the opening adjusted by movement of the iris. |
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Term
| What muscles either singly or together act to move the eye up, down, medially, and laterally? |
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Definition
| Medial movement – medial rectus muscle; lateral movement – lateral rectus muscle; movement up – superior rectus and inferior oblique muscles; movement down – inferior rectus and superior oblique. |
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Term
| What nerves innervate these muscles? |
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Definition
| Superior oblique – trochlear (CN IV); Lateral rectus - abducens (CN VI); all other oculomotor (CN III) |
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Term
| What are the layers of the eyeball? What is the ciliary body? |
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Definition
| The outer fibrous layer is composed of the sclera and cornea. The middle vascular layer that is made of the choroids, ciliary body, ciliary processes, and iris. The inner layer made up of the retina. The ciliary body is an anterior thickening of the middle layer containing muscles which control the shape of the lens, movement of the iris and serves as a point of attachment for suspensory ligaments of the lens. |
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Term
| What is the function of the retina? |
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Definition
| The function of the retina is to translate light into neural impulses for transmission through the optic nerve to the optic centers of the brain. |
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Term
| Where vision is the most acute? What is the blind spot? |
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Definition
| Vision is most acute in the fovea centralis of the macula lutea. The blind spot is the optic disc where the optic nerve and ophthalmic vessels enter the eyeball. It is not covered with a sensory layer. |
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Term
| How the blood is distributed to the orbit and eyeball? |
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Definition
| Blood enters the posterior of the orbit in the ophthalmic artery (branch of the internal carotid) through the optic foramen with the optic nerve. It then travels somewhat medially giving off branches to the posterior of the eyeball, the muscles and then ending with superior and medial branches. It also gives off the central artery of the retina that travels through the center of the optic nerve to emerge at the optic disc. |
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Term
| What are the major branches of the ophthalmic division of the trigeminal nerve in the orbit? |
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Definition
| Frontal with supraorbital and supratrochlear branches; lacrimal; nasociliary. |
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Term
| What nerve is sensory to the cornea? |
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Definition
| The ophthalmic division of the trigeminal by way of the branches from the nasociliary is sensory to the cornea. |
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Term
| How does the iris open and close? What muscles and nerves are responsible? |
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Definition
| What muscles and nerves are responsible? The iris is a diaphragm that is opened by radial muscles, dilator pupillae, innervated by postganglionic sympathetic fibers from the cervical sympathetic trunk. The iris is closed by circular sphincteric fibers, sphincter pupillae, innervated by parasympathetic fibers from the oculomotor nerve. These postganglionic parasympathetic fibers originate in the ciliary ganglion posterior to the eyeball. |
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Term
| How does the lens changes shape? What muscle and nerve is responsible? |
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Definition
| The lens is stretched into an elongated shape by tension on the suspensory fibers that connect it to the ciliary body. This shape is used for far vision. Contraction of the ciliary muscle in the ciliary body releases that tension and allows the lens to become rounded, the shape needed for near vision. The ciliary muscle is innervated by parasympathetic fibers from the oculomotor nerve (CNIII). |
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Term
| What structures focus light on the retina? |
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Definition
| Light is focused on the retina by the cornea, lens, and to a lesser extent by the vitreous humor. The lens is the only one that is adjustable. |
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Term
| What is relationship of the facial vein and the venous drainage in the orbit? |
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Definition
| The ophthalmic vein drains from the posterior orbit through the superior orbital fissure and then into the cavernous sinus. However it has numerous connections anteriorly with the facial vein. Thus it is possible for infection to travel from the facial vein into the ophthalmic vein and then to the cavernous sinus where it can expand and in some cases cause meningitis. |
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Term
| What are the openings in the posterior wall of the orbit and what passes through them? |
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Definition
| Optic foramen – optic nerve, ophthalmic artery; Superior orbital fissure – oculomotor, trochlear, abducens, and trigeminal (ophthalmic division), and ophthalmic vein. |
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Term
| What cranial nerves are found in the eye and orbit and in general what they do (Hint: CNII, CNIII, CNIV, CNV, CNVI, CNVII)? |
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Definition
| Optic nerve (CN II) – vision. Oculomotor nerve (CN III) – movement of muscles of the eye, parasympathetic fibers to the muscles in iris and ciliary body. Trochlear nerve (CN IV) – motor nerve to the superior oblique muscle. Trigeminal nerve (CN V) – ophthalmic division V1 is sensory to the skin over the orbit, the surface of the eyeball and cornea. Abducens nerve (CN VI) – motor nerve to the lateral rectus muscle. Facial nerve (CN VII) – small branch that provide parasympathetic fibers to stimulate the lacrimal gland to secrete, motor nerves to the orbicularis oculi. |
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