PBL 14.1 Flashcards
1
Q
What is the bony orbit?
A
The bony orbit refers to the bones (7 bones) that form the walls of the orbit, the roof, medial and lateral walls and floor. The orbit contains the eyeball, nerves, muscles, eyelid, vasculature.
2
Q
What are the extraocular muscles?
A
They are extrinsic to the eyeball and are in the bony orbit and control movement of the eye and superior eyelid. There are 7 muscles divided in 2 groups:
-
Muscle that moves the upper eyelid
- Levator palpebrae superioris (LPS)
- Movement- moves eyelid superiorly
- Innervation- oculomotor
- Attachment- originates from the sphenoid bone to the superior tarsal plate of upper eyelid
-
Muscles that move the eyeball
- 4 recti muscles all originate from common tendinous ring that surround the optic canal and pass anteriorly to acatch to the sclera:
-
Superior Recti
- Movement- moves eyeball upward
- Innervation- oculomotor nerve
- Attachment- inferiorly to both ring and sclera of eyeball
-
Inferior recti
- Movement- moves eyeball down
- Innervation- oculomotor
- Attachment - inferiorly to both the ring and the sclera
-
Medial rectus
- Movement- adducts the eye
- Innervation- oculomotor
- Attachment- medial aspect of the ring and sclera
-
Lateral rectus
- Movement- abduction
- Innervation- abducens
- Attachment - lateral to both ring and sclera
- 2 Oblique (angular) muscles which don’t originate from the ring and attach to posterior aspect of the sclera
-
Superior oblique
- Attachment- originates from the sphenoid bone and it passes through trochlea and then attaches to the sclera superior to superior rectus
- Innervation- trochlear
- Movement- depression, abduction and medial rotation
-
Inferior oblique
- Attachment - from orbital floor to sclera
- Innervation- oculomotor
- Movement- abducts and laterally rotates
-
Superior oblique
3
Q
What are the 3 main parts of eyeball?
A
-
Fibrous
- __Outermost layer made of the sclera and the cornea
- Cornea is a centrally transparent smooth surface that refracts light
- Sclera provides attachment for extraocular muscles and is white
-
Vascular
- Below the fibrous layer and consists of the ciliary body, choroid and iris
- Iris circular structure with a central pupil which size is altered by smooth muscles
- Ciliary body has 2 parts the muscle and the processes (zonular fibre). The muscles are attached to the lens using the fibres which controls the shape. The ciliary body also produces aqueous humor
- Choroid layer is connective tissue with blood vessels that supplies nourishment to the retina layers
-
Inner
- Formed from the retina the light detecting component formed by multiple layers
4
Q
What are the main structures of the eyeball?
A
-
Vitreous body
- Transparent gel which fills the posterior segment of eyeball (behind the lens)
- Functions to magnify power of the eye, support the lens and holds layers of the retina in place
-
Lens
- Is between the vitreous body and the pupil. The shape is altered by the ciliary body changing the refractive power
-
Anterior and posterior chambers
- The chambers are filled with aqueous humor a clear plasma like fluid that nourishes and protects the eye.
- The fluid is produced constantly
5
Q
Explain the vasculature of the eyeball
A
- Mainly via the opthalmic artery the first branch off the internal carotid arising immediately distal to the cavernous sinus. The ophthalmic artery gives off many branches that supply different parts of the eye the central retinal artery of the retina is most important occlusion leads to blindness
- Venous drainage by the superior and inferior ophthalmic veins which drain into the cavernous sinus a dural sinus.
6
Q
Explain the lacrimal glands of the eye & vasculature & innervation
A
- An exocrine gland that produces lacrimal fluid that provides cleans lubrication and nourishment the cornea and conjunctiva
- In excess the fluid makes tears. Located lateral aspect of orbit in the lacrimal fossa
-
Lacrimal apparatus
- Drains fluid
- After it circulates eyes—->it gets to the lacrimal lake–>drains into the lacrimal sac using canals—>moves down the nasolacrimal duct—>fluid then drains into the nasal cavity
-
Vasculature
- Lacrimal artery branches from ophthalmic artery branching from the internal carotid
- Drained by superior ophthalmic vein —> empties into cavernous sinus
-
Innervation
- Sensory- via the lacrimal nerve branched from ophthalmic nerve that is a branch of the trigeminal
- Sympathetic innervation- deep petrosal nerve (from internal carotid plexus) inhibits fluid production
- Parasympathetic- greater petrosal nerve (from facial nerve) stimulates fluid secretion
7
Q
What is loss of facial recognition called and the different types?
A
- Prosopagnosia, also known as face blindness, means you cannot recognise people’s faces
- These individuals use alternate methods in order to recognise individuals e.g. hairstyles, voice or clothing
- These individuals usually avoid social contact and interaction and suffer from a social anxiety disorder
- Have problems with careers and trust leading commonly to depression
- Two types:
- Developmental prosopagnosia - has prosopagnosia without brain damage
-
Acquired prosopagnosia - develops prosopagnosia after brain damage (e.g. stroke/head trauma)
- Very rare
8
Q
What does bottom-up perception mean & what does top-down perception mean?
A
Bottom-Up perception
- Perceptions that start with an incoming stimulus and working upwards until a representation of the object is formed in our minds
- This suggests that perceptual experience is based entirely on sensory stimuli that we piece together using only data that is available from our senses
- Take energy from the environment and convert it into neural signs (sensation)
- Then our brains interpret these sensory signals (perception)
Top-down perception
- Involves the brain ‘sending down’ stored information to the sensory system as it receives information from the stimulus
- Hence, using the contextual information of things that we already know or have already experienced in combination with our senses to perceive new information
9
Q
Explain the histology of the eye
A
-
External structures:
- Eyelashes, tear film (aqueous, mucus, and oily secretions) eyelids, muscles, accessory glands (Apocrine glands of Moll, meibomian glands, lacrimal glands), and conjunctiva.
- Internal Structures (3 layers):
1) The sclera and cornea make up the exterior layers.
2) The uvea is a vascular layer in the middle -> subdivided into the iris, ciliary body, and choroid.
3) The lens, vitreous and retina make the innermost layer, made up of nervous tissue.
Layer 1 (outer)
- Sclera – the white of the eye
- Cornea- 5 layers-> epithelium (non-keratinized, stratified squamous epithelium), Bowman layer, stroma (also called substantia propria), Descemet’s membrane, corneal endothelium.
Layer 2 (middle)
- Uvea made of iris, ciliary body, and choroid.
- Iris- pigmented layer which prevents light penetrating so only light can pass through pupil, sphincter pupillae and dilator pupillae muscles connect to
- Ciliary body- contains the ciliary muscle which controls the structure of the lens
- Choroid- contains network of blood vessels to supply the eye.
Layer 3 (inner)
- Lens - separates the aqueous and vitreous chambers and refracts/ focuses light on retina
- Vitreous -> separating the retina and the lens
-
Retina:
-
Photoreceptors:
- Rods, in outer edge of retina, peripheral vision (scotopic vision)
- Cones, concentrated around retina + only photoreceptors in fovea (photopic vision)
- Horizontal cells –Acts synapses and relay info from photoreceptors and bipolar cells
- Amacrine cells- allow ganglion cells to send temporarily correlated signal to the brain and ensure two different ganglion cells send info to the brain at the same time.
- Bipolar cells- transmit signals from photoreceptors to ganglion cells indirectly or directly.
- Ganglion cells- have large axons which form the optic nerve, carry information to CNS.
-
Photoreceptors:
10
Q
What is the significance of myelination?
A
It insulates the nerve allowing for quicker transmission and also for protection of the nerve
11
Q
What is ptosis and what is it caused by?
A
- Pathological droopy eyelid
- May occur due to trauma, age (levator muscles stretch as age), various medical disorders
- Due to impact on the OCULOMOTOR nerve
12
Q
What is the purpose of the lacrimal gland & what does it innervate?
A
- Secretes lacrimal fluid (onto surface of eyeball)
- Lubricates & protects and provides nutrients to conjunctiva & cornea
- Drains into ducts
- Innervation:
-
Sensory
- From opthalamic nerve (lacrimal nerve)
-
Parasympathetic (stimulates secretion)
- From facial nerve
-
Sympathetic
- From internal carotid plexus
-
Sensory
13
Q
What is short sightedness & causes & solutions?
A
-
MYOPIA
- DISTANT objects appear blurred
- Due to refractive error (eye cannot focus light onto retina properly)
-
Causes
- Eyeball is too long OR cornea TOO curved
- Genetics
-
Solution
-
Concave (diverging) lenses
- Focuses them furtheer out = CLEARER image
-
Concave (diverging) lenses
14
Q
What is optic neuritis & causes & affect on vision & treatment?
A
- Inflammation affecting the optic nerve
-
CAUSES
- Demylination
- Infection
-
AFFECT on vision
- Eye pain (especially on movement)
- Few days = blurred vision
- Darkening of parts of fields
- Eventual visual loss
-
TREATMENT
- Usually naturally regenerate myelin
- Prednisolone (decreases inflammation = connection between eye & brain reformed)
15
Q
What are the differential diagnosis of optic neuritis?
A
- Uveitis
- Cataracts
- Retinal detachment
- Glaucoma
17
Q
What is the test for RAPD? (relative afferent pupil defects)
A
Swinging light test
- Bright light shone into one eye leads to an equal constriction of both pupils.
- When the light source is taken away, the pupils of both eyes enlarge equally. This is called the consensual light reflex.\
RAPD due to retinal/optic nerve disease
- Pupils of both eyes will constrict, but not fully. This is because of a problem with the afferent pathway.
- When the light is shone into the other, normal (less abnormal) eye, both pupils will constrict further. This is because the afferent pathway of this eye is intact, or less damaged than that of the other eye.
- When the light is shone back into the abnormal eye, both pupils will get larger, even the pupil in the normal eye.
18
Q
What is the light reflex pathway?
A
2 parts:
- The afferent part of the pathway (red) refers to the nerve impulse/message sent from the pupil to the brain along the optic nerve when a light is shone in that eye.
- The efferent part of the pathway (blue) is the impulse/message that is sent from the mid-brain back to both pupils via the ciliary ganglion and the third cranial nerve (the oculomotor nerve), causing both pupils to constrict, even even though only one eye is being stimulated by the light.
19
Q
Explain the visual pathway
A
EXTRACRANIAL
- The optic nerve is formed by the convergence of axons from the retinal ganglion cells. These cells in turn receive impulses from the photoreceptors of the eye (the rods and cones).
- Optic nerve leaves the bony orbit via the optic canal, a passageway through the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland).
INTRACRANIAL
- Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm. At the chiasm,fibres from the nasal (medial) half of each retina cross over to the contralateral optic tract, while fibres from the temporal (lateral) halves remain ipsilateral: (Remember it goes from left to right)
- Left optic tract – contains fibres from the left temporal (lateral) retina, and the right nasal (medial) retina.
- Right optic tract – contains fibres from the right temporal retina, and the left nasal retina.
- Each optic tract travels to its corresponding cerebral hemisphere to reach the lateral geniculate nucleus (LGN), a relay system located in the thalamus; the fibres synapse here.
- Axons from the LGN then carry visual information via a pathway known as the optic radiation. The pathway itself can be divided into:
- Upper optic radiation – carries fibres from the superior retinal quadrants (corresponding to the inferior visual field quadrants). It travels through the parietal lobe to reach the visual cortex.
- Lower optic radiation – carries fibres from the inferior retinal quadrants (corresponding to the superior visual field quadrants). It travels through the temporal lobe, via a pathway known as Meyers’ loop, to reach the visual cortex.
- Once at the visual cortex, the brain processes the sensory data and responds appropriately.
28
Q
What is meant by the primacy effect?
A
- The primacy effect relates to a person’s unconscious ability to recall information they receive at the start of a list/in the consultation better than in the middle.
- Thus, summarising good for recalling information
