General Ophthalmology Flashcards
What is hypermetropia?
Long-sighted ness
What is myopia?
Short-sightedness
What is astigmatism?
Unevenly curved cornea causing a refractive error
What is presbyopia?
Age-related long-sightedness
What two structures of the eye are responsible for refracting light onto the retina?
Cornea and lens
What structure controls the concavity of the lens?
The ciliary body and zonules (ligaments)
Is the refractive error positive or negative for short-sightedness?
Positive
Why do Pancoast tumours cause the symptoms of ptosis, anhydrosis and miosis?
Due to disruption of the sympathetic fibres to the head and neck, including occulosympathetic fibres.
A patient presents with partial right-sided ptosis, a dilated right pupil with deviation of that eye inferiorly and laterally oriented. What is likely to be wrong?
Occulomotor nerve palsy (eye moves in direction of the one remaining intact muscle: the lateral rectus, not innervated by the occulomotor nerve)
Why might you want to x-ray a patient presenting with partial unilateral ptosis, miosis and anhydrosis?
Because you may need to rule out a more sinister cause for those symptoms such as a Pancoast tumour
What is the Edinger-Westphal nucleus and what does it supply?
It is the accessory parasympathetic nucleus of the oculomotor nerve (CN III). It supplies the constricting muscles of the iris and the ciliary muscles.
What is emmetropia?
Normal sight
What causes myopia (short-sightedness)?
The eye grows to become too long (front to back) which means the light doesn’t reach the retina so distant objects appear blurred.
What sort of sight are most babies born with?
Hyperopia. The eyes continue to grow and elongate until around the age of 8 years. Children before this point are able to accommodate to overcome this though (not possible with short-sightedness)
From what germ layer does the retina originate?
The ectoderm
The retina is considered an out-pouching of what organ?
The brain
How does aqueous humour drain from the anterior chamber to the circulating blood?
Via the trabecular meshwork and Canal of Schlemm
What are the 3 layers of the meninges (outside-in)?
Dura mater
Arachnoid
Pia mater
Which anatomical feature of the eye has the greatest number of pain receptors?
The choroid
Damage to the Canal of Schlemm can result in what?
Glaucoma
What is the emergency eye service in Wales called?
Rapid Access Clinic for Eyes (RACE)
How do you test visual acuity?
Using a Snellen chart or Logmar
How do you test eye movements?
Get patient to look at you finger / held object and keeping head still follow the object in an ‘H’ formation
How do you test visual fields?
First both eyes: wiggle finger individually at 10, 2, 4 & 8 o’clock then both together (10 & 2) and (4&8). Then cover one eye at a time: bring in a red tipped pin / pen from bottom and top diagonals starting out of peripheral vision. Test against your own peripheral vision.
What is acuity?
The ability to see fine detail
When recording a Snellen result what do both the numerator (top number) and denominator (bottom number) represent?
Numerator = distance from the chart in metres Denominator = lowest line read
What would testing VA with a pinhole do?
Correct refractive error
What is the driving standard for Snellen results?
6/12
What is considered normal visual acuity?
6/6 (Snellen) or 0.0 (LogMAR)
How do you test for a relative afferent pupillary defect?
With the swinging light test
How can a relative afferent pupillary defect (RAPD) be detected with the swinging light test?
In a normal swinging light test both pupils with constrict initially with light and then relax a little. With RAPD when shining the light in the affected eye both pupils dilate rather than constrict.
What pathologies can be seen when assessing the red reflex?
Ocular media abnormalities: foreign bodies, cataract, haemorrhage, floaters
Retinoblastomas
Why might a VDRL be performed in the case of sudden visual loss?
To test of syphilis (which can cause blindness)
Why might you test for antinuclear antibodies in the instance if sudden visual loss?
To test for SLE (systemic lupus erythematosis) which can attack any bodily organ
In the presence of light are rod cells switched on or off?
Off
What does the phototransduction cascade achieve?
It is a series of molecular steps that result in turning off rod cells. In-so-doing informing other cells that light is present. These messages get converted into neural impulses to inform he brain
Which type of cell is more sensitive to light - rods or cones?
Rods
Where a rods most concentrated?
In the periphery of the retina
Where are cones most concentrated?
Fovea / macula
Which have slower absolute refactory periods rods or cones?
Rods (so it takes a long time for eyes to adjust to sudden dim light)
What molecule in rhodopsin is altered by light contacting it?
Retinal
When light changes retinal’s shape what occurs next?
The shape of rhodopsin changes too and binds to a molecule called transducin
What does transducin do in the phototransduction cascade?
Its alpha unit binds to phosphodiesterase which inturn converts cGMP to GMP
What impact does the reduction of cGMP have in the phototransduction cascade?
It closes Na+ channels on the rod cell causing hyperpolarisation therefore switching off the rod cell.
Explain the final stage in the phototransduction cascade with regard to bipolar cells.
When a rod cell is switched off ‘ON-centre’ bipolar cells switch ON. They activate retinal ganglion cells which sends impulses down the optic nerve to allow brain to recognise that light is entering the eye.
What does guanylate cyclase do?
Catalyses the conversion of GTP to cGMP
What change does light manifest in retinal?
Changes it from 11-cis retinal to all-trans retinal
What separates the alpha unit from transducin for it to bind to phosphdiesterase?
Activated opsin
Which neurotransmitter it’s released in photoreceptor action potentials?
Glutamate (excitatory)
What three types of cone cell are there? List in order of wavelength at which they are stimulated
Blue, green, red. Red = being the longest wavelength
Deficiencies in production of what accounts for colour vision defects?
Opsins
99% of red-green deficiencies are coded on which chromosome?
X (hence more common in men but still present in some women if both X chromosomes carry the fault)
What is protanopia?
Red weakness
What is deuteranopia?
Green weakness
Which chromosome is associated with blue weakness and what is this weakness called?
Chromosome 7; tritanopia
Autosomal dominant, males = females, rare!
What might you use to detect a colour deficiency in a patient?
Ishihara plates
What is the 3rd and least abundant type of photoreceptor?
Retinal ganglion cell (2%)
What do retinal ganglion cells contain?
Melanopsin (photopigment blue)
How do RGCs project and what do they regulate?
Via retinohypothalamic tract - regulate melatonin production
What is melatonin and where is it produced?
Hormone which regulates circadian rhythms and acts as an antioxidant (intracelluarly, protects DNA).
Produced in pineal gland, skin, retina, GIT
Where in the brain is the primary visual cortex?
The occipital pole
If a patient has a RAPD in their left eye where has the lesion occurred? Is this anterior or posterior to the chiasm?
The left optic nerve. Anterior to the chiasm
