Lecture 3 and 4: Opthomology Flashcards
The eye lies inside the _____.
Orbit
What is the function of the orbit?
Allow movement of the eyes
Provides protection for the eyes
The eyes are always in a fixed position, we can learn good stereoptics (the ability to see in three dimensions)
Name the 7 bones which make up the orbit
What is the benefit of having multiple bones make up the socket?
1) Frontal
2) Lacrimal
3) Maxillary
4) Ethmoid
5) Sphenoid
6) Zygomatic
7) Palatine
Easier for development. It also helps make the fissures and openings allowing structures to go into/out of the ye.
What are the boarders of the orbit made up of?
superiorly by frontal bone,
medially by frontal process of maxilla,
inferiorly by zygomatic process of maxilla and zygomatic bone, and
laterally by zygomatic bone, frontal process of zygomatic bone, and zygomatic process of frontal bone.
Name the Extra-occular muscles
4 Rectus muscles (Superior, Inferior, Medial, Lateral)
-Superior and inferior work together, medial and lateral work together.
2 Oblique muscles (allow torsion to the yes)
The muscles are often paired.
Describe the innervation of the extra ocular muscles
Superior oblique: IV (Trochlear)
Lateral oblique: VI (Abducens)
Rest: III
Name the muscles of the eyelids (function and innervating nerve)
Orbicularis Oculi (closes eylids, innervated by facial nerve- CN VII)
Levator palpebrae (opens eyelids, innervated by Occulo-motor nerve - CNIII)
Describe the Anatomy of the eyelid (not the muscles)
Protective structures
1) Tarsal plate/tassus (rigidity and resistance to objects coming from outside)
2) Conjunctiva (lines inside of the eyelid and the bulbar side of the eye)
3) Fat (absorbs shocks)
Describe the features of the tear film
Very thin layer at the outside of the cornea. This is very thin but protective. Its function is to protect and l_ubricates eyes (moist),_ r_educe infection_, w_ash away foreign particles_, keep e_ye surface clear and smooth_ (unobstructed eyelid movements).
~10uL
There are lots of structures in place to prevent this from drying out. (deep to superficial)
1) Mucins (produced by the goblet cells, inside the conjunctiva)
2) Aqueous layer (produced by accessary lacrimal gland, which lubricate eyes and reduce infection)
3) Oily layer (produced by Meibomian (tarsal) gland, which reduces evaporation of tear film)
What is the lacrimal apparatus made up of? What is it’s function?
Lacrimal apparatus is made up of lacrimal gland, accessary lacrimal glands, canaliculi (via puncta), sac, duct.
It involves in the production, movement and drainage of aqueous fluid from the surface of the eyeball.
What is this?
What can cause this?
Subconjunctival Haemorrhage
1) Common
2) Typically idiopathic or after severe coughing, sneezing or vomitting
3) Rarely associated with anticoagulants or raised blood pressure.
Describe eyelid injuries
If your outside layer is damaged, it is fine. When eyelid margins are damaged, you must restore anatomy.
- Therefore, you close in layers (not altogether!) to retain function and minimise scar.
- Layers are skin, subcutaneous tissue, voluntary muscle, orbital septum, tarsus, and conjunctiva.
What are the layers of the eyelid?
Layers are
1) skin,
2) subcutaneous tissue,
3) voluntary muscle,
4) orbital septum,
5) tarsus, and
6) conjunctiva.
Describe Ptosis
Causes
Ptosis is dysfunction of levator palpebrae superiorus.
Its causes include:
1) Congenital
2) Involutional (old age)
3) Mechanical (e.g. tumour)
4) Myogenic (e.g. myasthenia gravis)
5) Traumatic
6) Neurogenic
- Parasympathetic ptosis (cranial nerve III palsy, e.g. brain tumour, aneurysm, diabetes)
- Levator palpebrae superiorus (upper lid) with ptosis
- Extraocular muscles involvement (with functional VI, IV)
- Pupil lost parasympathetic, hence mydriasis (dilated pupil)
- Sympathetic ptosis (Horner’s syndrome)
- Mullers (superior tarsal) muscle with subtle ptosis
- Pupil lost sympathetic, hence subtle miosis (constricted pupil)
Describe the possible neurogenic causes of ptosis
- Parasympathetic (cranial nerve III palsy, e.g. brain tumour, aneurysm, diabetes)
- Levator palpebrae superiorus (upper lid) with ptosis
- Extraocular muscles involvement (with functional VI, IV)
- Pupil lost parasympathetic, hence mydriasis (dilated pupil)
- Sympathetic (Horner’s syndrome)
- Mullers (superior tarsal) muscle with subtle ptosis
- Pupil lost sympathetic, hence subtle miosis (constricted pupil in the right eye)
Describe Orbital Haemorrhage
Orbital haemorrhage is worse when patients cannot open their eyes.
Haemorrhage can c_lose the eyelids and septum_, which increases intraocular pressure, which c_ompress optic nerve (ischemic),_ possibly loss vision.
Orbital cellulitis (top right figure) can also compress optic nerve.
Describe the Orbital blow out fracture
_Indirect traumatic injur_y that _displaces orbital wall_s is called a blowout fracture. (e.g. getting hit in the eye with a ball)
- Fractures of medial wall may involve the ethmoidal and sphenoidal sinuses, e.g. haemorrhage, airway obstruction, infection.
- Fractures of inferior wall (maxillary floor) may involve maxillary sinus, and orbital contents might fall down.
- Fracture of superior wall (stronger than medial and inferior walls) may involve a sharp object passing through it and enter frontal lobe of brain.
Signs include
1) black eye (haematoma),
2) infraorbital nerve anaesthesia (numbness),
3) double vision (affect upgraze and downgaze, e.g. patient’s left eye because muscles or fascia attaching muscles has fallen down).
- left eye cannot look down because the inferior rectus is trapped.
- the left eye also cannot look up because the inferior rectus and the buts of the septum have also fallen down.
Describe Thyroid Eye Disease
Thyroid eye disease may involve all orbital contents:
Signs:
- Lids changes as lid lag, lid retraction, lagophthalmos
- Ocular surface inflammation especially over horizontal recti muscles (e.g. MR)
- Proptosis of globe (abnormal protusion)
- Myopathy (strabismus)
- Optic neuropathy
CT scan features include:
- Thick extra-ocular (recti) muscles (thumb size)
- Proptosis, which is maximum diameter of globe extends beyond lateral orbital rim
- Tenting of optic nerve on right side
Describe Refractive Errors
Normally: The cornea and lens, together with fluids that bathe them, and iris diaphragm with variable aperture, constitute the optical system which focuses the image of the object (or target) at the foveola.
Long sighted- image forms behind the retina so the image is blurry.
Short sighted (myopia)- image forms in front of the retina.
Describe the Cornea
Top: front of the cornea
Important in focusing light.
Laminar layer that makes up stroma have a special space to allow light passage. This space in corneal stroma is dehydrated.
Endothelium is critical for maintaing the stroma.
2/3 of refractive power for the eye is done at the front surface of cornea.
- Curvature of cornea is important for refraction (fixed power lens, cannot alter focus properties).
- High difference in refractive index between air and cornea means light refracts/bends more.
Describe the Physiology of the Cornea
Laminar layer that makes up stroma have a special space to allow light passage. This space in corneal stroma is dehydrated.
- Endothelial layer has endothelial pump that pumps water out of stroma to create this space. Therefore, it maintains endothelial barrier between aqueous humour and stroma.
- If there is dysfunction of endothelial layer, water goes into the stroma and results in oedema in stromal space. This leads to opaque cornea and light can no longer get through.
In addition, there are no blood vessels in the cornea to prevent light refraction.
Refraction (Bending of Light)
2/3 of refractive power for the eye is done at the front surface of cornea.
- Curvature of cornea is important for refraction (fixed power lens, cannot alter focus properties).
- High difference in refractive index between air and cornea means light refracts/bends more.
What is Keratoconus?
Keratoconus is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape. This cone shape deflects light as it enters the eye on its way to the light-sensitive retina, causing distorted vision.
Aetiology
The exact cause remains unknown. Aetiology is probably multifactorial, or a final common pathway for a variety of different pathological processes.
- In an unknown proportion, one of aetiological factors is certainly genetic.
- In addition, suspected environmental components.
Therefore, two-hit hypothesis, i.e. genetic (predisposition) + environment (e.g. eye rubbing).
Prognosis
Natural history usually commences late puberty
Progression is rapid, gradual, or intermittent between 10-40 years (15-20% require transplant).
What is this?
Keratoconus.
It is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape. This cone shape deflects light as it enters the eye on its way to the light-sensitive retina, causing distorted vision.
What is this?
ptosis
Describe the Lens of the eye
Structure: Lens is almost completely cellular (fibre cells)
Most common pathology in the lens: Cataract
Lens is a transparent, biconvex structure that helps to refract light to be focused on retina.
Lens change shape (variable power lens) to change focal distance of eye so that it can focus on objects at various distances, thus allowing a sharp real image to be formed on retina. This adjustment of the lens is known as accommodation.
Lens sits behind iris and is connected to ciliary body by zonule fibres (suspensory ligaments). Lens has a thin extracellular matrix capsule encasing it, rest of the lens is all composed of cells (single layer of epithelium, then long fibre cells)
Central part of the lens is called nucleus (made of cells in-utero), and cortex of lens will continuously grow throughout life
What are Cataracts?
A cataract is a clouding of the lens in the eye which leads to a decrease in vision.
Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night.
2 Types:
1) Cortical cataract is clouding of lens cortex.
2) Nuclear cataract is clouding of lens nucleus (more severe, affecting visual axis centrally).
Aetiology: congenital, inherited, age-related (majority), metabolic (e.g. diabetes), toxic (e.g. corticosteroids).
What is this?
A cataract is a clouding of the lens in the eye which leads to a decrease in vision.
Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night.
Describe the Ciliary Body
Cilliary muscle is responsible for accommodation (focus power).
Circular muscle that is attached to the suspensory muscle.
- Relax (increased ciliary muscle diameter) means lens is pulled outward from equator (flattens), hence smaller pole to pole distance (anterior to posterior). Therefore, focus for farther objects.
- Contract (decreased ciliary muscle diameter, c.f. fist) means lens is more convex (much fatter), hence bigger pole to pole distance. Therefore, focus for closer objects (bend light more).
Ciliary body also has a ciliary epithelium part- which is responsible for producing aqueous homour
Aqueous humour is a transparent fluid similar to plasma, but containing low protein concentrations. It fills both the anterior and the posterior chambers of the eye.
What are the 2 types of cataracts?
1) Cortical cataract is clouding of lens cortex.
2) Nuclear cataract is clouding of lens nucleus (more severe, affecting visual axis centrally).
What happens when the Ciliary body contracts and relaxes?
Relax (increased ciliary muscle diameter) means lens is pulled outward from equator (flattens), hence smaller pole to pole distance (anterior to posterior). Therefore, focus for farther objects.
Contract (decreased ciliary muscle diameter, c.f. fist) means lens is more convex (much fatter), hence bigger pole to pole distance. Therefore, focus for closer objects (bend light more).
Describe the Acqueous Homour
Aqueous humour is a transparent fluid similar to plasma, but containing low protein concentrations. It fills both the anterior and the posterior chambers of the eye.
- Aqueous humour is secreted into posterior chamber by ciliary body (by ciliary epithelium).
- It flows through narrow cleft between front of lens and the back of the iris, to escape through pupil into the angle of the anterior chamber.
- It then drains out of the eye via trabecular meshwork (in angle of anterior chamber).
- Damaged trabecular network (impaired drainage) can cause increased intraocular pressure.
-
From here, it drains into Schlemm’s canal by one of two ways:
- Directly, via aqueous vein to the episcleral vein,
- Indirectly, through collector channels to episcleral vein by intrascleral plexus and eventually into veins of the orbit.
It is not to be confused with the vitreous humour, which is located in the space between the lens and the retina, also known as posterior cavity or vitreous chamber.
What is the Retina?
It allows visual sensation by the conversion of light images (photons) into nerve impulses.
Functions:
- To absorb photons of light
- Translate light into a biochemical message (photoreceptors)
- Translate biochemical message into electrical impulses.
- Transmit electrical impulse to the brain via ganglion cells
Areas:
Central or peripheral
1) Fovea
2) Macula Lutea
Is the retina back to front?
Why does the light have to travel through the ganglion cells and the bipolar cells before it hits the photoreceptors?
The retina is inverted such that innermost layer (towards middle of eyeball) is composed of cells that send nerve impulses via optic nerve to cerebral cortex, while the outermost layer consists of cells that contain photopigment molecules which capture light for conversion of signals to nerve impulses.
Therefore, l_ight must pass through all layers_ of the retina before being absorbed by photopigment. (and then information comes back again)
The retina is inverted because it is supported by retinal pigment epithelium (RPE), which is a layer of cells external to retina that are essential for formation of photopigments, renewal of photoreceptors (high energy requirement), reduction of damage due to scattered light and transportation of water and nutrients to the retina.
What is the fovea?
Fovea is a small, central pit composed of closely packed cones in the eye (direct light perception). It is located in the center of the macula lutea of the retina (no cell bodies of bipolar and ganglion cells- hits photoreceptors directly).
Fovea is responsible for sharp central vision, which is necessary for activities where visual detail is of primary importance.
What is the Macula Lutea?
Macula lutea is an oval-shaped pigmented area near center of the retina.
Because macula is yellow in colour, it absorbs excess blue and ultraviolet light that enter eye, and acts as a natural sunblock for this area of retina. Yellow colour comes from its content of lutein and zeaxanthin, which are yellow xanthophyll carotenoids, derived from the diet. These protect foveal cones from any light damage.
Describe the Optic Nerve
The optic nerve has no photoreceptors. This area cannot perceive light, thus blind spot. Due to binocular vision, we do not have blind spot in normal vision (each eye covers the other eye’s blind spot).
The optic nerve gathers all axons of ganglion cells to exit the eye to transmit signals to brain. This is also where central retina artery and vein enter and exits the eye (make use of a blind spot).
What are rods and cones?
and How are they distributed in the eye? (Photoreceptor density)
Cones: responsible for visual acuity and colour vision
Rods: Detect movement and night vision
More cones are found in the central area.
As you hit the fovea it is almost all cones
As you move away from the fovea, the cones disappear and there are more rods.
What is the Glaucoma?
Glaucoma is a group of diseases that damage the eye’s optic nerve and can result in vision loss and blindness. However, with early detection and treatment, you can often protect your eyes against serious vision loss.
Optic neuropathy
Glaucoma is an optic neuropathy with a specific pattern of axonal loss, which often may be associated with e_levated intraocular pressure (IOP_) and a typical pattern of visual field loss. It is extremely common in older age
Two types:
1) Open angle glaucoma (more common 95%) includes:
- Primary (presumed angle predisposition)
- Secondary (cells, inflammation)
- Only know you have this if you see an opthomologist. Caused by slow blockage of the drainage. Onset is slow.
- Gonioscopy can look at the angle of anterior chamber.
2) Closed angle glaucoma (5%) includes:
- Primary (narrow anterior chamber angle)
- Secondary (tumours, synechiae)
- Closed or narrow angle between the iris and cornea. This requires immediate medical attension.
*
What is this?
Diabetic Retinopathy (common retinal disorder)
What is this?
Age related macular degeneration (common retinal disorder)
What is the difference between open and closed angle glaucoma?
Glaucoma is an optic neuropathy with a specific pattern of axonal loss, which often may be associated with elevated intraocular pressure (IOP) and a typical pattern of visual field loss. It is extremely common in older age
Two types:
1) Open angle glaucoma (more common 95%) includes:
Primary (presumed angle predisposition)
Secondary (cells, inflammation)
Only know you have this if you see an opthomologist. Caused by slow blockage of the drainage. Onset is slow.
2) Closed angle glaucoma (5%) includes:
Primary (narrow anterior chamber angle)
Secondary (tumours, synechiae)
Closed or narrow angle between the iris and cornea. This requires immediate medical attention. Develops rapidly.
