130; Eye Week Flashcards
What assessments are involved in a 6(7) point eye examination?
- Visual acuity
- Eye movements
- Pupils
- Visual fields
- External inspection / anterior segment
- Fundoscopy
- (intraocular pressure- if equipment available)
List potential causes of ocular neuropathy.
- Compression
- Infection
- Ischaemia
- Inflammatory
- Congenital
- Hereditary
*
What is Leber’s hereditary optic neuropathy?
Mitochondrially inherited degeneration of the retinal ganglion cells.
It causes sequential painless loss of vision in late teens - 20s
males > females
*Only transmitted through the mother; only the oocyte contributes mitochondrial DNA to the embryo (different to nuclear DNA)
Why does this mitochondrial defect affect the retina?
Mitochondrial disease affects tissues with high energy turnover; the retina is the most metabolically active tissue in the body
What are the main cell layers of the retina? (from the choroid inwards)
- RPE
- Photosensory cells (rods & cones)
- Bipolar cells
- Ganglion cells
List, in detail, the layers of the neurosensory retina.
- RPE
- Photoreceptors (rods & cones)
- Outer limiting membrane; Inner horizontal branches of Muller cells
- Outer nuclear layer; Cell bodies of Rods & Cones
- Outer plexiform layer; synapse of R&C with Bipolar cells
- Inner nuclear layer; Cell bodies of Bipolar cells
- Inner plexiform layer; Synapse of Bipolar and Ganglion cells
- Ganglion cell layer; Cell bodies of ganglion cells
- Nerve fibre layer; axons to optic nerve
- Inner limiting membrane; inner border of Muller cells
- Basement mambrane
Describe the distribution of Rods and Cones at the retina.
Generally there are far greater Rods in the retina
*Fovea has v.high density of Cones*
What are the differences between Rods and Cones?
Rods
- 3 types of photosensitive pigments
- Colour vision
- Req higher light intensity
- Dense at fovea
- Visual acuity
- Highly metabolic
Cones
- 1 photosensitive pigment; not distinguish colour
- Active at lower light intensity
- Peripheral vision
- Night vision
What happens to the photoreceptor when stimulated by light?
- At rest it is depolarised
- When stimulated it becomes hyperpolarised
- Reduction in glutamate release
- Bipolar cells regulate the signal from photoreceptors and transmit to Ganglion cells
- Ganglion cells transmit this to retinal nerve fibres –> optic nerve
Where does the neural processing of vision occur?
At the retina
What are the 3 different types of cone cells?
Defined by their specific opsins which have peaked sensitivity at particular wavelengths
- Blue
- Lower wavelength detection
- 450 nm
- Green
- 550nm
- Red
- 600nm
What is the most common colour vision defect, and who is predominately affected?
Red-green colour blindness; 99%
Males > Females
It is an X-linked defect
What are the 2 sub-types of red-green colourblindness?
Protanopia- Red weakenss
Deuteranopia- Green weakness
What is the cause of Blue colourblindness?
Tritanopia; caused by chromosome 7 defect
Autosomal dominant disease; Males = Females
Name the different types of Photoreceptors.
- Rods
- Cones
- Photosensitive retinal Ganglion cells
What photosensory pigment does the photosensory retinal ganglion cell contain?
Melanopsin
What is the role of photosensory RGCs?
Non-image-formatting cells
Provide info on ambient light intensity; control pupil size
Role in Circadian rhythms; Regulate melatonin production
What tract do photosensory RGCs project information?
Retinothalamic tract
Where is melatonin produced and what is its role?
Produced in the pineal gland
and skin, retina, GIT
A hormone thet regulates circadian rhythms
Alos an antioxidant that protects DNA
What is miosis?
Pupil constriction
Describe the Afferent route of pupillary reflex fibres.
Light hits retina…
- Optic nerve
- Optic chiasm
- Optic tract
- Fibresdiverge to pretectal nucleus
- Bilateral projections to occulomotor n. nucleus
Describe the Efferent route of pupillary reflex fibres
- Occulomotor nerve nuclei
- Occulomotor nerve
- Ciliary ganglion
- Short ciliary nerves
- Sphincter pupillae
What is the direct and consensual pupillary response?
Direct; Pupil constriction in eye that sensed the light
Consensual response; Pupil constriction in contralateral eye
What is the swinging light test?
Light moved from one eye to the other and pupil reaction and size noted.
Abnormality indicates relative afferent pupilary defect.
**Lesion anterior to chiasm**
What is the pupillary near response?
aka Accommodation reflex
It is a combination of vergence, lense shape and pupil size
What is the Afferent route of the pupillary near response?
CN II route to the occipital lobe
What is the efferent route of the pupillary near response?
Occipital projections to frontal eye field
Bilateral projections to main and accessory occulomotor nuclei
- Occulomotor nerve to extraocular muscles
- Occularmotor –> Short ciliary nerve to pupil
What are the signs and symptoms of dorsal midbrain syndrome.
- Light-near dissociation
- No reaction to light; Pupil constriction to near response
- Failure of upgaze
- Nystagmus
What can cause Dorsal midbrain syndrome?
Pineal tumour
What is the Lateral Ganiculate Nucleus?
It is a part of the thalamus between the optic tract and optic radiation.
Primary relay center for visual information.
What are the different parts of the optic radiation?
- Meyer’s loop
- Superior part
Which part of the visual field does Meyer’s loop process?
Superior part
Which part of the visual field does the Superior part of the optic radiation process?
The inferior visual field
Where is orientation information processed?
Cortical neurones
List some factors that provide anti-microbial protection to the eye.
Tears
- Lactoferrin
- Complement
- Lysozyme
- IgA IgG
- Leukocytes
Conjunctiva
- Lymph tissue
What is Mydriasis
Dilation of the pupil
What is hyphaema?
Blood in the anterior chamber of the eye
Disease to which areas of the visual system can cause sudden visual loss?
- Cornea
- Anterior chamber
- Lens
- Vitreous humour
- Retina
- Optic nerve
- Higher pathways
What is Uveitis?
Acute intraocular inflammation
What may cause people to see flashing lights?
Retinal detachment
Migranes (flashing usually bilatereal here)
How can you test weather the visual pathways up to the optic chiasm are functional?
Pupillary reflex
What is phenylepherine
A sympathomimetic drug
â1 adrenergic receptor agonist
- Pupil Dilation (Mydriasis)
What are the side effects of Phenylepherine?
Photophobia
Blurred vision
Stinging
Acute glaucoma
Arrhythmias & hypertension
*Not as effective in DM, dark iris or elderly*
Give some examples of Antimuscarinics
Atropine
Cyclopentolate
Tropicamide
How do antimuscarinics work?
Muscarinic Ach receptor antagonists
- Cause Mydriasis= pupil dilation
What is Tropicamide used for in practice?
Mydriasis in eye exams
What is Cyclopentolate used for in practice?
Uveitis- relaxes the ciliary muscle
Wat are the side effects of antimuscarinics?
- Photophobia & Blurred vision
- Stinging and raised IOP
- Dry mouth
- Confusion
- Flushing
What are the symproms for acute angle-closure glaucoma?
- Blurred vision
- Headache
- Red, painful eye
- Nausea & vomiting
Name a parasympathomimetic drug
Pilocarpine
How do Parasympathomimetics work?
Muscarinic Ach receptor agonists
Cause Miosis, pupil constriction
Open up drainage channels in trabecular meshwork
Treatment for Glaucoma
What are the side effects of Pilocarpine?
Headache / browache
Stinging on application
Myopia (short sighted)
Retinal detachment
Name a ß blocker used in ocular pharmacology
Timolol
What are the uses of Timolol
It is a ß blocker; prevents the production of aqueous humour (aqu. in the anterior compartment)
Treat Glaucoma
Name carbonic anhydrase inhibitors used in ocular pharmacology
- Acetazolamide; oral/IV
- Dorzolamide; topical
Used to treat Glaucoma
Give one example of artificial tears
Hypromellose
Name a staining agent for the eye
Fluorescin
Shows up damage to conjunctiva or cornea
Give an example of an anaesthetic agent for the eye
Lidocaine
Name an agent used to treat superficial eye infections
Chloramphenicol (antibiotic)
Here are examples of systemic drugs causing ocular side effects:
- Digoxin toxicity – disturbance in colour vision
- Amiodarone – halos, especially affecting night-time driving, optic neuropathy
- Anti-psychotics – blurred vision, corneal deposits
- Ethambutol – optic neuritis causing loss of visual acuity and macular degeneration
- Rifampicin – orange staining of tears
- Tricyclic antidepressants – anticholinergic effects (blurred vision, disturbance of accommodation, increased IOP)
- Opioids – miosis
- Ipratropium – anticholinergic – care with nebulisation
- Anti-malarials – various effects
- Corticosteroids – cataracts in long-term use, increased IOP
- Antihistamines – blurred vision, reduction in tears
What are the 3 stages involved in Phototransduction?
- Light activates visual pigments (rhodopsin)
- Activated molecules stimulate cGMPphosphodiesterase
- This enzyme reduces [cGMP]
- cGMP reduction closes cGMP-gated channels; hyperpolarising the cell
What os the visual pigment in Rod cells?
Rhodopsin
Opsin is the protein protion, embedded in the disk membrane
Retinal is the light-absorbing portion; a derivative of VitA
What is the non-activated and activated form of Rhodopsin?
Non-activated –> 11-Cis
Activated –> all-Trans
What neurotransmitter is releasd by Rod cells?
Glutamate
An inhibitory neurotransmitter;
In dark Rods are depolarised, releasing glutamate to bipolar cells. Following hyperpolarisation (LIGHT) glycine release ceases and the bipolar cells no longer inhibited.
