Ophthalmic anatomy

The eye has six extraocular muscles

Cranial nerves and eye anatomy

CN 2 - Optic nerve

Receives information from the retina, carries retinal artery and vein into the globe

CN 3 - Oculomotor nerve

Innervates superior and inferior rectus muscles, the inferior oblique muscle, the medial rectus muscle, and the levator muscle of the upper eyelid

Parasympathetic fibers to the ciliary ganglion, which causes constriction of iris sphincter muscles

Sympathetic fibers from the carotid artery plexus cause contraction of the radial muscles and lead to papillary dilation

CN 4 - Trochlear nerve

Motor fiber to the superior oblique muscle (rotates eye toward the nose)

CN 5 – Trigeminal nerve

Sensory and motor

• Ophthalmic (pain, touch, temp to eye structures)
• Maxillary (pain, touch, temp to upper lip, nasal mucosa, and scalp muscles)
• Mandibular nerves

CN 6 – Abducens nerve

Motor function to the lateral rectus muscle

CN 7 - Facial nerve

Motor to face - To Zanzibar By Motor Car" (part of CN VII)

• Temporal (frontal) branch of the facial nerve
• Zygomatic branch of the facial nerve
• Buccal branch of the facial nerve
• Marginal mandibular branch of the facial nerve
• Cervical branch of the facial nerve

The Temporal and Zygomatic branches are most important for eye surgery

CN X – Vagus nerve

Efferent pathway for the oculocardiac reflex, which can result in bradycardia and dysrhythmias

Oculocardiac reflex

Trigeminal-vagal reflex generated by pressure to the globe, the optic nerve or the conjunctive, or by traction on the extraocular muscles.

The afferent pathway runs through the ciliary nerves to the ciliary ganglion, then along the ophthalmic division of the trigeminal nerve to the base of the 4th ventricle.

The efferent pathway is via the Vagus nerve to the cardio-inhibitory center.

This is most often seen in children getting eye muscle procedures.

Acute sinus bradycardia but may also see other arrhythmias.

Treatment

Surgeon to release pressure immediately

Assess oxygenation and ventilation

May need Atropine 2-3mg

Can pretreat with Glycopyrrolate or atropine just before surgery

The symptoms can reappear but seems to be fatigued with continued manipulations

Complications from eye surgery

Corneal abrasions due to drying of the exposed cornea or from direct trauma

Movement during ocular surgery is the most common mechanism of injury

Coughing and bucking.

Consider muscle relaxants

Chemical injury from cleaning materials Eddy

Lens

Located just behind the iris, the lens is one of the components that determines how the eye is focused and is also responsible for allowing the eye to see near objects. As we age, the lens becomes increasingly dense and inflexible, causing a continual decrease in the eye's focusing ability, known as presbyopia. The lens can develop cataracts due to age or injury or be present at birth.

Iris

This is the ring-shaped colored part of your eye and is responsible for controlling the amount of light that enters the eye. In the light, the iris constricts to make the opening in the iris, the pupil, smaller to decrease the amount of light entering the eye. In the dark, the iris dilates, increasing the pupil size and allowing more light to enter the eye.

Cornea

The cornea is a clear dome over the iris and is, on average, just 1/2 mm thick. It is one of the components that determines how the eye is focused. Contact lenses are worn on the cornea, and laser refractive surgery is performed here.

Pupil

This is the circular opening in the center of the iris, and it changes size in different lighting conditions. The pupil is usually black, but if the eye is lit up inside, such as when a camera flashes, the color of the eye's interior will be visible, and the pupil will appear red.

Aqueous

This fluid fills the area between the cornea and the lens and is continually produced and drained. The amount of aqueous in the eye determines the eye pressure, which varies at different times and on different days. If the eye pressure is too high for the eye tissues to tolerate, glaucoma can develop.

Conjunctiva

This thin layer of transparent tissue covers the white of the eye, the sclera. The conjunctiva contains many blood vessels, which fill with blood and expand if the eye is irritated, making the eye appear red.

Sclera

This is the white, tough outer casing of the eye, which gives the eye its shape and strength to resist damage.

Vitreous

This jelly-like fluid fills the area between the lens and the retina. Often, the vitreous contains fibers or clumps, which are seen as shifting black or translucent shapes in the vision and are called floaters. It is expected to notice an increase in floaters over time. The vitreous is contained within a capsule, attached to the retina at multiple points. At some point in life, usually in the 50s or 60s, the capsule of the vitreous pulls away from the retina and collapses into itself, much like a balloon deflating. This is called a vitreous detachment and is a normal part of aging.

Retina

This thin layer of tissue lines the inside of the eyeball and contains cells that receive light and transfer it into visual messages sent to the brain via the optic nerve. The retina also contains many blood vessels, which can break and bleed due to various eye conditions or diseases, causing vision loss. A retinal detachment occurs if the retina loses its attachment to a part of the eyeball, allowing it to come away from the wall of the eye.

Macula

This is an area in the central part of the retina that provides detailed vision. Diseases or injuries affecting this area almost always cause noticeable vision loss. Macular degeneration is one of the most common diseases affecting this part of the retina.

Optic Nerve

This nerve carries visual messages from the retina to the brain, interpreting them and perceiving vision. Glaucoma damages the optic nerve, causing individual nerve fibers to gradually die off, resulting in a subtle but progressive loss of vision.