Ophthamology #1 Flashcards
Describe the Orbit, and why is it made of these components.
Where the eye sits, halfway down the skull. Made of 7 bones, so that between the gaps of those bones
- Nerves/arteries can come through (eg; optic nerve)
- There can be growth of the orbit/skull
Describe the Extra-ocular Muscles
- 6 Eye muscles that sit in the orbit and attatch to the Sclera.
- Control eye movement; antagonistic pairs
Rectus Muscles: medial, lateral, superior and inferior
Oblique Muscles: Superior and inferior
Describe the direction of movement each ‘extra-ocular’ muscle allows?
Superior Rectus: up and medially
Inferior Rectus: Down and medially
**SR + IR can work with SO to straighten the eye movement!
LR6 SO4 3
Innervation of the Extraocular muscles
LR6 SO4 3
CN 6: Abducens n.
CN4: Trochlear n.
CN 3: Occulamotor n.
What controls the two muscles of the eyelids (protective layer)?
If you damage this you damageone of our most important senses. So it sits within the orbit, with the protective covering.
Protects against sleeping movement, abrasive objects etc
Controlled by two main muscles
- Orbicularis Oculi: closes the eyelids, innervated by CN 7 (facial n.)
- Levator Palpebrae: Opens the eye, innervated by CN 3 (Occular N.)
The eyelids aren’t just a flap of skin, they have several components.
Briefly describe these…
- *Muscles:** orbicularis oculi and Levator P.
- *Tarsus:** thick elongated plates of CT providing stiffness
- *Lashes:** on edge of lid
- *Congunctiva:** thin membrane that lines both the inside and bulbar side of eyeball.
What does the conjunctiva produce and why?
It’s a mucus membrane that produces Mucins for lubrication.
Therefore a problem with the systemic membranes, the Conjunctiva can’t produce mucins → dry eyes
Whats the tear film
A layer of liquid alway on th eye, <10-12microlitres.
This keeps eye moist, and allows the eyelids to pass over the eye with no damage to epithelial structures.
Made of three Layers:
- mucins produced from Goblet cells of Conjunctiva inner
- Aqueous produced from the Lacrimal Gland middle
- Oil on top produced by Meibomian glands at the lid margin outer
Why is the top layer of the tear film oil?
This stops evaporation of the aqueous layer so the eye doesn’t dry out, despite the small volume of fluid on eye
Big Lacrimal Gland is for _________, whereas the Accessory lacrimal Glands are for ________.
Big Lacrimal Glands: reflex tearing (watery when something in your eye etc)
Accessory Lacrimal Glands: responsible for the thin tear film
Explain the Lacrimal System, how it works and what it’s purpose is.
- Produce the tear layers within the Lacrimal glands (big tears) or accersory lacrimal glands
- these flow across the eye to little holes at the nasal side of the eye, the ‘Puncta’
- These can then drain out the Lacrimal canaliculi → sac → duct
This system allows us to carry away dirt/bacteria, continually washing the eye, and there are also immunogenic properties within tears with a protective effect
Subconjunctival (of the conjunctiva) Haemorrhage is from?
Typically idiopathic or from severe coughing, sneezing or vomiting (binge drinkers).
Rarely associated with anticoagulants or raised BP
Harmless to the patient.
What to do if someone has an eyelid injury.
- Restore anatomy
- Close in the 3 layers
- Retain Function
- Minimise scar
Don’t do if injury is to lid margins/ lid is divided as you could close the 3 layers eg mucous membrane! Get a senior doctor to do so!
Ptosis is?
Causes?
The “drooping lid”, due to a dysfunction of Levator Palpebrae Superiorus (LPS).
Many people have slight ptosis, but significant ptosis >1mm
Causes:
- Congenital
- Involutional: old age
- Mechanical: tumour
- Myogenic: myasthenia gravis
- Traumatic: rub eye too much, disinsert LPS muscle
- Neurogenic: **
What are the ways you can get Acquired Neurogenic Ptosis?
Cranial Nerve III Palsy
- LPS upper lid ptosis
- Extraocular muscles function lost so eye turns out.
- pupils parasympathetic lost > large pupil
Sympathetic: Horners Syndrome
- Subtle ptosis and miosis (small pupil)
Cranial Nerve III Palsy → Acquired neurogenic Palsy
Cranial Nerve III Palsy, which effects:
- LPS upper lid ptosis
- Pupils parasympathetic: get to neuro surgeon ASAP just in case of brain tumour, but its usually diabetes
- Jaundice due to metastatic disease of orbit
- Extraocular function gone
Sympathetic: Horner’s Syndrome
Sympathetic Palsy leading to
Mullers Muscle: subtle ptosis
Pupil: subtle miosis
What are the Orbital Contents?
What’s the septum
The orbit is a bony pyramid and dense white septum containing:
- Eye
- Muscles
- Optic Nerve
- Cranial Nerves
- Vessels
Orbital Septum: white 360º tough barrier between orbit and lid tissues, stretching from distal tarsus border to orbital rim. Anything abnormal (infection, haemorrage) in there will be contained → compression of the orbital contents.
Orbital Haemorrhage.
Which one is worst?
Worst one is bottom right, as eye has actually popped out, ruptured orbit, can lose vision
High Pressure Eye (top left): when the lids can’t even open, and you are at risk of compressing the optic nerve
Infected Eye (top right): These lids also can’t open.
How do you get an ‘orbital Blow out Fracture’?
(when the orbital floor deforms/fractures; the contents can fall down)
Usually due to high impact trauma. eg; a tennis ball or a fist
The thin maxillary wall cracks.
What are the signs/symptoms of an ‘orbital Blow out Fracture’?
(when the orbital floor deforms/fractures; the contents can fall down)
- Black eye (haematoma)
- Infra-orbital Nerve Anaesthesia ‘numbness’ due to damage
- Double Vision: impaired upgaze and downgaze, due to the trapping of muscle and/or fascia, can’t really look up or down
Thyroid Eye disease, very common
may involve all orbital contents
- -lids
- -Oculur surface
- -proptosis of the globe
Gives thick muscles.
Purpose of the Focussing Structures?
To take light from an object, and focus it on the Retina in order to get a good picture at the back of the eye.
What are Refractive errors?
The axial length (front to back) of the eye is ~2.5cm.
This correct length allows light to focus beautifully on the retina.
Variation in this length can lead to Refractive Errors.
Long-Sighted: ‘hyperopia’, shorter eye, so light focuses behind
Short-sighted: ‘myopia’, longer eye, so light focuses before the retina
Astigmatism: different focusing properities in different planes of the eye
Describe the cornea, and how do we examine it?
The Cornea is 600 microns (0.6mm)
Composed of several layers: Epithelium, Bowmans membrane, stroma, Descemet’s layer and endothelium
Slit Lamp is used to see the structures and thickness. A platform for seeing abnormalities and illness.
In vivo Confocal microscope: put up against a living eye and see the structures that compose the cornea
Why is the In vivo confocal microscope so good?
It allows you to see each layer of the cornea in a living eye!
‘Streak of lighting’: nerves of cornea, which are extremely sensitive to detect even tiny bits of dirt! this induces tears and gets it away from the cornea asap!
Why is the endothelial pump so important?
What happens if the endothelium is damaged?
The endothelial pump maintains the endothelial barrier between the aqueous and the stroma.
With no endothelial pump, water can shoot across into the stroma, the spacing between the lamellar swells and you get oedema.
The main thing the
The cornea turns opaque and light can’t get through anymore.
Importance of the Endothelial Structure!
Endothelial layer: looks like beeshive, has an endothelial pump, that maintains the barrier between the aqueous and the stroma by pumping water out.
The stroma needs to allow the passage of light, and this can occur by the actually anatomical structures themselves (blood vessels would disrupt this by refracting the light). Lamillar have a special spacing which can occur due to the relatively high dehydration of the cornea. With no Endo. Pump there’s no dehydration, as water can’t be pumped out.
Where does most of the bending of the light occur and how does it occur here so effectively?
Most of the bending of light is done at the frontal surface, 2/3 of the cornea.
So effective because of the curvature of the cornea!
The difference of refractive index between the outside air and our cornea means the light gets bent alot. Mammals bend light more then water-bound animals such as fish because of this!
Good function of the Cornea Requires what 3 things (and how can they go wrong)?
- Clarity: reduced by infection, scars, corneal dystrophies
- Regular Curvature: altered by disease; keratoconus (thins and bows forward like a rugby ball)
-
Controlled Thickness:
* Increased by endothelial Failure:* dystophies, intraocular surgery
* Decreased by disease;* keratoconus
Keratoconus definition and statistics
A progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape.
- Accounts for nearly half of cornea transplantation (also fuchus dystrophy)
Assessment of the Cornea
- IVCM Confocal
- Anterior OCT
- Computerised Topography: 10,000 datapoints show map of para (44)
- Biomechanical Corvis ST: shows biomechanical stretch of cornea
What causes keratoconus.
Progression of the disease
Multifactorial or a final common pathway for many different pathological processes.
- A propotion is always genetic
- There’s also suspected environmental components
The ‘Two-Hit hypothesis’: genetic + _______ (eyerubbing etc)
Usually commences late puberty
Progession: Rapid, gradual or intermittent, between 10-40 yrs
15-20% require transplant
Corneal Transplant
The oldest transplantation technique.
Now we can transplant a specific layer!
If you just do the inner layer you dont even need stitches! (roll ndothelial layer out then blow it with air to stick it to the cornea)
