U14W2: the eye Flashcards
(38 cards)
How does the eye transduce visual information to the brain?
Optic circuitry - happy.
How do photorecepotrs turn light changes into potentials?
happy
How does photoreceptors activity affect the activity of bipolar cells?
Increased PR activity in high light = hyperpolarisations = less glutamate release
1. Glutamate has an inhibitory affect at MGlur6 receptors on ‘on pathway’ bipolar cell - reduced inhibition increases activity down the on bipolar cell
2. Glutamate has an excitatory affect at AMPA receptors on ‘off pathway’ bipolar cell. Reduced activation decreases activity down the off pathway bipolar cell.
How does the activity of photoreceptors affect the activity of horizontal cells?
light = hyperpolarised PR = decreased glutamate
Glutmater norm activates horizontal cells - reduced activation of horizontal cells - horizontal cells have decreased activity - reduced inhibition from horizontal cells on neighbouring PR - neighbouring PR depolarises - perceived dark - inc contrast in the image.
What is the function of CN2 the optic nerve?
Is a specialised visceral afferent
Sense of vision - visual acuity, colour vision and afferent limb of pupillary reflexes.
What is the function of CN3 - the oculomotor nerve?
General somatic efferent - extraocular muscles
Efferent limb of the pupillary constriction reflex
General visceral efferent - Efferent limb of the lens accommodation reflex via contraction of the ciliary muscles.
What is the function of CNIV trochlear?
General somatic efferent - SO4 - motor innervation to superior oblique (an extraocular eye muscle)
What is the function of CN6 abducens?
General somatic efferent - for contraction of lateral rectus (one of the extraocular muscles of the eye) fo eye abduction.
How does RAPD (relevant afferent pupillar defect) test work?
Identifies damage to the afferent pathway of the pupillary reflex e,g the optic nerve.
On the side of the lesion will only show consensual contraction( as efferent pathway working) but will dilate/unconstrict when light is shone directly into the damaged eye (as the afferent pathway is not working).
Therefore the lack of light causing dilation in the non-affected eye, is stronger than the inactive constrictor reflex to light in the affected eye.
What does delayed evoked potential mean?
Evoked potential tests measure the electrical activity of area in your brain and spinal cord in response to stimulation. Often tested as response to visual auditory and electrical stimuli with elctodes position on the brain
Delayed = Slowed transmission of nerve signals, indicates damage to the nerve pathway, sometimes identifiable before patients start reporting symptoms.
What do the lumbar puncture results indicate in MS?
Analyses a sampe of CSF.
MS CSF will have - elevated wbc (autoimmune underpinning), neurofilaments and myelin basic protein (from myelin degradation) and oligoclonal bands (immunoglobulins) found in a protein gel.
What does an MRI show in a MS patient?**
Lesions (inflammation and odema) are best visible on a T2 weighted flair - appear as white
Can differentiate between old and new lesions using a T1 weighted MRI with gadolinium contrast, where older (non-enhancing) lesions will appear more black and newer (enhancing) lesions as a greyer colour as highlights inflammation
What is the use of beta interferon in the treatment of MS?**
Clinical: is a disease-modifying therapy for relapsing MS and in some cases used in secondary progressive MS treatment. Adminstered as an injection.
Is am immunomodulatory agent
Chem: recombinant human interferon
Pharm: Agonist at type 1 interferon receptors IFNAR1/2c, are tyrosine kinases, activation immunomodulatory nad antiviral responses via direct effect on gene expression.
Physio: suppresses inflammatory responses, including T cell activation and secretion of pro-inflammatory cytokines (shifts to anti-inflammatory cytokine phenotype).
Also encourages differentiation of neural stem cells to oligodendrocytes to repair damaged nerve cells.
What is the mechanism of action of methylprednisolone in MS?
Class - corticostreroid
Chem - methyl - enables injectable form and more potent than prednisolone
Pharm - glucocorticoid receptors Nuclear receptor agonist, hetero, sheet shock, transolcation, GRE, transcription factors, transactivation and transrepression.
Phyio - Inc Annexin A1 - inhibits PLA2, reduced prostaglandins, reduce TNFalpha, reduce COX, reduce pro-inflammoatry signals, increase INFy and IL-10 anti-inflammatory signals, Change to anti-inflammatory phenotype
Clinical - helps to reduce inflammation and speed up recovery during a relapse or exacerbation of MS symptoms. Can be given orally or IV.
What is a certificate of visual impairement?
A formal document completes by an consultant ophthalmologist to certify someone as either slightly impaired (partially sighted) or severely sight impaired (blind).
Based on personal visual acuity and field of vision.
This enables the individual to access support services, financial benefits and education resources including SEN in children.
Can now register with local social services, legal standing to access rehabilitation, mobility training and adaptation funding.
Why does beta interferon lose efficacy over time?
Sometimes whilst on treatment patients have a felt ineffectiveness of the drug when they experience worsening symptoms.
Thought to be due to production of interferon- neutralisng antibodies during therapy. Found in up to 40% of patients.
How does a Snellen Chart work?
Rows of letters getting gradually smaller, sizing of letters and the distance you are standing from the chart (norm use 6m chart and mirror) relates to your visual acuity
Compared to the average person can see at the same distance = 6/6 vision.
Identify deficits in vision is only able to see shorter distance sizing what other people can see at six meters for example 6/16.
How does being visually impaired affect a persons life?
Socially isolating
Stigma
Employment and education opportunities
Financial hardship - needs adaptations and support equipment.
Alters sense of identity.
Safety - alarms, cars, target for abuse.
What is the prevalence of MS?
2.3 million people in the world are thought to be living with MS.
Affects around 100,000 adults in the UK.
7,000 newly diagnosed a year
This equates to 1 in 500 people
What are some common refractive errors in the eye?
Short-sighted = myopic eye - refraction causes the focus point in front of the retina - blurred image on retina for long distance
Long sighted = hypermetropic eye - refraction error means focus point is behind the retina - blurred image on retina for short distance
Emmetropic eye - point focus on fovea - no need for corrective lenses.
What are the different types of corrective lenses for refraction disorders of the eye?
Myopic - or divergent (concaving shape) contact lenses - correct short-sighted vision by raising focal length of light before enters eye
Hypermetropic - or convergent lenses (convex shape) - correct long sighted vision - bling light together before it enters the eye.
What is often the problem underpinning diplopia?
What is diplopia?
Eyes are not in aligment causes object we are looking at to fall in the fovea in one eye but an extrafoveal location in the other eye.
Alters the degree of overlap between visual fields.
Results in two separates images being perceived.
Often neurological in origin (confirm by disappearance in monocular vision), causes defects in muscle movement.
Most common is ocular misalignment due to extraocular muscle dysfunction.
Where are the different nuclei for oculomotor, trochlear and abducens nerve found?
Oculomotor - midbrain
Trochlear - caudal midbrain
Abducens - pontomedullar junction
What is meant by the gaze centres of the brain?
The horizontal and vertical gaze centre are both part of the reticular formation.
They coo-ordinate activity of III,IV and VI to create smooth eye movements.