L3: Young doctors guide to eye Flashcards
What are the 7 bones that make up the orbit (where the eyes sit).
Why is it good to have so many small bones
Frontal, lacrimal, Ethmoid, Maximillary, Palatine, Sphenoid, Zygomatic
Small bones can move and therefore facilitate growth more easily.
It allows for fissures/holes for vessels
Where do the extraocular muscles come from and attach to - not too important
All the muscles come from behind the orbit where they attach to a sheath around the optic nerve before attaching to the sclera around the circumference of the globe.
What are the 6 extraocular muscles, their movements and innervation. How does this movement work
Rectii muscles
- Lat+ Med: abduct and adduct
- Sup+ Inf: Up and down
Oblique muscles
- Sup : Down, abduct, intort.
- Inf: Up,abduct, extort
Innervation by CN3, except Sup ob (4) and Lat rectis (6)
The paired muscles work by increasing innervation to one and relaxing the other to bring about movement
What are the muscles of eyelid needed to close and open + innervation
- To close the eyelid: Orbicularis oculi - CN7
2. Open/lifting the eye lid: Levator palpebrae - CN3
What lines the globe and the eyelid
Conjunctiva
What is the 3 layers of the Tear film, producers and the function (for tear reflex)
A 3 layers of liquid:
(10 uL) from outside to inside,
Oil: Tarsal gland - slows down evaporation of tear film
Aqueous: lacrimal gland
Mucin: Goblet cells of the conjunctivis
Allows the eyelids to move smoothly over the cornea without injuring it.
Explain where tears start and go in the lacrimal system for tear reflex: foreign dirt)
- Lacrimal gland +accessory lacrimal glands produces tears on the upper lateral side, flows across the eye (helped by blinking reflex)
- to inner corner, draining through Punta which then drain into the lacrimal sac, then nasolacrimal duct
What is subconjunctival hemorrhage triggered by
- Common
Typically idiopathic or after severe coughing, sneezing or vomit.
Rarely associated with anticoagulants or high bp
How are eyelid injuries, lacerations treated
The eyelid has to be closed in layers to retain its function and minimise scarring
What does ptosis and 2 neurogenic causes
can also be caused by Congenital, involutional, myogenic, mechanical, traumatic,
Dysfunction of levator palpebrae superiorus: drooping lid. Have to treat it if its obstructing the pupil: 3mm-4mm
Causes:
Neurogenic cause: 1.CN3 palsy: upper lid ptosis, also most extraocular muscles not working so eye is down and out and big open pupil.
- Horner’s syndrome: damage to sympathetic innervation: small pupil (subtle miosis), Subtle ptosis (muller’s muscle)
What bones are broken in an Orbital blow out fracture,
how does it show on imaging and what are the signs
The floor of the orbit is thin (nasal, lacrimal and ethmoid).
It is broken with force which pushes eye and its contents back.
Shows a tear drop of muscle and fat- inf rectus getting trapped below on imaging.
Signs
- Can’t look up or down bc of inf rec trapped
- Black eye (haematoma)
- Infra-orbital nerve anaesthesia
- Double vision
What is Thyroid eye disease: signs, CT scan features and complications
Signs:
- Lid changes: lag (slow to close), retraction (see sclera), lagophthalmos- dry eye
- Ocular surface inflammation
- Proptosis of the globe: Maximum diameter of globe extends beyond the lat orbital rim on CT
Complication: corneal exposure treated with lubricants /taping eyelid shut
-Myopathy: can get double vision,
extra ocular muscle > rice size on CT: can lead to optic nerve compression leading to surgical intervention
-Optic neuropathy: Tenting of optic nerve on right side on CT
What are refractive errors and their correction of 3 Ametropia: hypermetropia, myopia, astigmatism
RE: The image of a distant target cannot be bough to focus by the lens system at the foveola leaving a blur circle
Hypermetropia: (Long sight) parallel light rays focus behind the retina. Corrected by convex lens
Myopia (short sight) : parallel light rays focus in front of the retina. Corrected by concave lens
Astigmatism: Two different focal planes of light
What are the cellular layers of the cornea from outside to in. What are the two jobs of cornea
- Epithelium
- Bowmans membrane
- Stroma: collagen, keratocytes
- Descemet’s layer
- Endothelium
Highly innervated to get dirt immediately out due to risk of scarring, infection,
Curvature does 2/3 of light focusing, maintained by the lamellar tension + intraocular pressure
How does the structure of the cornea’s layers help to keep it clear, right thickness
- Collagen lamellae arranged parallel to the eye with adjacent layers provides strength.
- Stroma also has hyaluronic acid = attracts water, altering distance of passage to light. This is compensated by
Endothelial pump pumps water out of the cornea to ant chamber retain the spacing of lamellae. - No blood vessels in the cornea
What is the most common condition for corneal transplant,
Keratoconus:
Shape of cornea becomes cone pointing out.
multifactorial or final common pathway for a variety of pathological processes.
- Two hit gene + environment hypothesis .
- generally commences late puberty
What structures does light pass through to get to the retina
- Cornea (40 diopters of focus)
- pupil
- lens (20 diopters of focus)
Describe the structure of the lens
Lens has epithelium on front surface. The body is made of fibre cells having laid in an annular pattern over time with nucleus having in utero cells.
The lens is connected to the ciliary body and held in place by suspensory ligaments of the lens (zonules). It is just behind the iris
The ciliary body contains ciliary muscle which surrounds the circumference of the lens. What is its job and how does it change with old age
Accommodation: the ciliary muscle contracts to increase curvature of the lens which refracts more light, this helps with near work. So better allows close focus.
Older age cannot accommodate as well as used to because of stiffer lens
Ciliary body produces aqueous humour. what is its purpose, What is the flow
Nourishes the lens and the cornea (avascular). The flow helps to maintain the shape of the anterior chamber and the pressure in the eye.
- Ciliary epithelium
- up in between lens and iris
- out the pupil
- away towards the angle of the anterior chamber.
- It drains through the trabecular meshwork
- Schlemm’s canal to veinous system.
How is cataract diagnosed and treated
- Using opthalmoscope + slit lamp microscope
- There will reduced visual acuity and significant lens opacity
Surgical:
- Intracapsular (developing)
- Phacoemulsification: most popular- removal of the cateract via a small incision, foldable and injectable intraocular lens
- Femtolaser assisted, - Extracapsular (sometimes developing)
What are the causes of cataract
- region cortical or nucleus
Majority: Aging: over time, the nucleus of fibre cells in the lens dissolves, therefore they cannot form new proteins, so break down and forming opacity within the lens.
Metabolic- diabetes
Toxic- oral corticosteroids
Traumatic- irradiation
Secondary - uveitis
What cellular layers does nerve signal generated by light hitting photoreceptor rods and cones go through
(Light first travels the opposite way)
- Retinal pigment epithelium
- Photoreceptor r&c
- Outer synaptic layer
- Connecting and processing cells (bipolar cells)
- Inner synaptic layer
- Ganglion cells.
- Retinal nerve fibre layers -> to the optic nerve
What is the function of Retinal pigment epithelium.
- why are photoreceptors at the back of the eye?
Retinal pigment epithelium (external to retina) helps 1.formation of photo pigments,
- renewal of photo receptors,
- transport of water and nutrients, 4.reduction of damage due to scattered light -
