The Eye Flashcards
What is the part of the eye which is the first point of focussing and has the greatest degree of refraction?
The Cornea
What is Astigmatism?
Surface of the cornea is uneven
What does laser correction surgery (LASIK) do?
Changes the degree of curvature of the cornea = light focussed to the retina
For fine focus the curvature of the lens is altered what is this known as?
Accommodation
When the ciliary muscle is relaxation, the lens is pulled taut (flat and thin) by intraocular pressure, there is therefore less curvature meaning the eye can focus , what is this known as?
Far vision
When the ciliary muscle is contracted, and the lens has a higher curvature, what system, what is this known as?
Near vision
What controls Near vision?
Parasympathetic nervous system
What controls far vision?
Sympathetic nervous system
When the lens is less flexible, and no longer able to become rounded therefore it is not possible to focus on near objects, what is this known as?
Presbyopia
When myopia occurs, meaning the eyeball is too long, and parallel light is focussed in the front of the retina, what is this known as?
Shortsightedness
When hyperopia occurs, meaning the eyeball is too short and near objects are brought to a focus behind the retina what is this known as?
Longsightedness
What do glasses do?
Change where the light is focussed
What part of the eye is the light sensitive part responsible for visual transduction?
The Retina
What are the sensory receptors of the retina?
The Photoreceptors
What is responsible for seeing of black and white?
The rods
What is responsible for seeing colour?
Cones
What is the function of the photoreceptors?
They change light energy, into electrical signals
What is the retina made up of?
Layers of neuronal cells with photoreceptors at the back of the retina
What part of the eye, detects light stimulus, is the most posterior part of the retina, consists of flattened, stacked, membranous discs and is turned over by the cells of the retinal pigment epithelium (RPE)?
The outer segment
Where is the metabolic centre in the eye?
The Inner Segment
What is the name of the synapse with the bipolar cells?
Synaptic terminal
What has a low sensitivity to light? cones or rods?
CONES
What has a high sensitivity to light and is required for night vision? cones or rods?
RODS
Where are cones the most abundant?
Fovea
Where are rods the most abundant?
In the periphery
What is the ratio of convergence of cones in the fovea?
no convergence 1:1 ratio of cone to ganglion cell = higher resolution of images
What is the convergence ratio of rods?
1 cell : 100 rods
Highly convergent many rods up to 100 feed into one ganglion cell = wider receptive field and therefore increased sensitivity
Why is visual acuity in the fovea the highest giving fine resolution of the image?
-More cones 1:1 coupling
-Lateral inhibition
-Other areas of the retinal are moved aside here, so light doesn’t travel though other layers of the retina
In the periphery, the signal is?
-Largely black and white,
-Very sensitive to movement and flashes of light *turn and look
What do photoreceptors contain which are able to capture the light energy and is the first step of signal transduction?
Photopigments
What does the photopigment consist of?
Protein - opsin and retinal and the chromophore
What type of receptor is Opsin?
GPCR
What is the ligand of Opsin?
Retinal
What vitamin is retinal derived from?
Vitamin A
What can a deficiency in vitamin A cause?
Night blindness
How many photopigments are there in rods?
1 - rhodopsin
How many photopigments are there in cones?
3 - sensitive to red, green and blue light
What changes shape from 11-cis-retinal to all-trans-retinal? and what causes this?
Retinal when activated by light
If a light is bright will more or less neurotransmitter be released?
The brighter the light the less glutamate released
‘graded’ system
When photopigments are activted what do they become?
‘bleached’ and remain unresponsive until recycling of the retinal has occurred
What takes the information to the brain from the eyes?
Ganglion cells
What are retinal cells described as in the dark?
Quiescent
What pathway takes information from the retina to the visual cortex?
-Retinal ganglion cells leave the eye at the optic disc and make up the optic nerve (cranial nerve II)
-These axons synapse in the thalamus (the lateral geniculate nucleus)
-Interneurons travel from the LGN to the visual cortex
What axons come from different halves of the visual field go to opposite sides of the brian?
RGC axons
Where do axons cross?
At the optic chiasm
Where does procession of visual information start ?
The retina and continues in the visual cortex and associated areas
Where does right sided vision come from?
The left side of the retina as it crosses the optin -> L side of brain vs versa
From a pharmacological point of view, explain the potential advantages of such sustained drug delivery product in comparison to traditional eye drop products for managing glaucoma?
1) Improved patient adherence
2) More consistent IOP control
3) Reduced side effects
4) Lower risk of contamination
What is Glaucoma?
Chronic eye disease that can cause irreversible damage to the optic nerve and lead to vision loss.
What is glaucoma managed by?
Eye drops that lower the intraocular pressure (IOP)
What are the potential impacts of poor patient adherence to prescribed IOP treatments?
1) Worsening of Glaucoma
2) Increased healthcare costs
3) Reduced QOL
4) Risk of medication side effects
5) Psychological Impacts
Why can’t eye preparations deliver drugs to the posterior chamber of the eye for diseases such as age-related macular degeneration?
1) Barriers to penetration
2) Rapid clearance and dilution
3) Limited retention time
4) Anatomical and physiological challenges
Explain how the Cornea is a barrier to penetration?
-Protective barrier for the eye, eye drops struggle to penetrate the cornea and reach the posterior chamber due to its limited permeability
Explain why Tear flow and drainage is an issue in rapid clearance and dilution of eye preparations?
Eye drops are often washed away by tear flow, limiting the time available for drug absorption
Explain why dilution in aqueous humor, is an issue in the rapid clearance and dilution of eye preparations?
Intracameral implants may face dilution within the aqueous humor of the anterior chamber before reaching the posterior segment
Explain why the blink reflex plays a part in the low bioavailability of eye preparations?
Frequent blinking and reflex tearing associated with eye drops can limit the retention time of the drug on the ocular surface, reducing the changes of effective absorption
Explain why implant displacement plays a part in the low bioavailability of eye preparations?
Intracameral implants may be subject to displacement or movement within the anterior chamber, affecting their ability to reach the posterior segment
Explain how the Vitreous humor plays a part in the anatomical and physiological challenges in drug delivery of eye drops?
The gel-like vitreous humor in the posterior segment can impede the distribution of drugs, making it difficult for them to reach the macula in sufficient concentrations
What is POAG?
Primary Open Angle Glaucoma
How do we treat glaucoma?
Reduction of IOP via medicine, surgery or laser
What are Latanoprost, Travoprosst, Bimatoprost and Tafluprost?
Prostaglandin Analogues
What are the common side effects of prostaglandin analogues?
-Lash growth
-Iris pigmentation
-Periocular skin darkening
-Conjunctivitis
Systemic (rare) - brittle asthma, induction of labour?! poss
What are the most potent ocular hypotensives?
Prostaglandin analogues
What group of drugs work by increasing uveoscleral outflow?
Prostaglandin analogues
What are the side effects of B-blocker eye drops?
Asthma/breathlessness, bradycardia, tiredness, depression, ED, hypotension and angina
What drug reduces the aqueous production in the eye?
Beta blocker eye drops
Timolol, Levobunolol and Betaxolol are examples of what group of eye drop?
Beta blockers
What eye drop group reduce the production of aqueous and are the least potent ocular hypotensive with fewer side effects?
Carbonic anhydrase inhibitors
How often do you need to give a carbonic anhydrase inhibitor?
TDS = poor adherence
Dorzolamide, and Brinxolamide are examples of what class of eye drop?
Carbonic anhydrase inhibitors
What eye drop is C/I to sulphonamide sensitivity?
Carbonic anhydrase inhibitors
Brimidine (Alphagan), Apraclondidine (Iopidine), are examples of what class of eye drop?
a2-agonists
What eye drop class must be avoided with use of MAOI’s and TCAs antidepressants?
a2-agonists
What is the main drug in combination eye drops?
Timolol +
What major risk factor does glaucoma eye drops look to act on?
Lowering intraocular pressure
What supplies nutrients to and removes waste products from the avascular organs of the anterior eye (lens and cornea)
The aqueous humour
What rate is aqueous humour produced at?
2-3ul/min
What is the conventional outflow pathway in regards to aqueous humour?
70-90% leave via, TM to SC
What is the non-conventional pathway, in regards to aqueous humour?
The uveoscleral pathway, (intracellular spaces between the ciliary muscle fibres, choroid and out via the sclera, this can be greater in patients with glaucoma!
What is the normal intraocular pressure of the eye?
10-20mmHg (mean 16mm/Hg)
How do drugs work to act on the intraocular pressure?
1) Decrease production of aqueous humour
2) Increase outflow of aqueous humour
What system controls the production of Aqueous humour?
Under autonomic sympathetic
What does stimulation of B2 receptors do in regards to Aqueous humour?
B2-receptors are stimulated (NA/Adr) causing an increase in AH production.
What does the stimulation of a2 receptors do in regards to aqueous humour?
It causes a decrease in AH production
Inhibition of carbonic anhydrase activity causes what?
A decrease in aqueous humour production.
Beta blocker eye drops are contraindicated in what?
Bradycardia and heart block
What is the MOA of beta blocker eye drops?
Reduce aqueous humor secretion
What is the MOA of A2-agonist and carbonic anhydrase inhibitor eye drops?
Reduce aqueous humour secretion
Can you use acetazolamide long term?
NO!!
Aqueous outflow via the trabecular meshwork is?
-Facilitated by constriction of the pupil
-Inhibited by dilation of the pupil
-Facilitated by contraction of the ciliary muscle
What is stimulated to cause contraction in the ciliary muscle?
ACh via muscarinic M3 receptors
What is stimulated to cause contraction of the radial smooth muscle?
NA via a1-adrenergic receptors
How do muscarinic agonists work? ‘pilocarpine’
Increases aqueous humour outflow via TM (miotics)
What drug stimulates M3 receptors?
Pilocarpine - muscarinic agonists
What does Pilocarpine do within the eye?
-Constriction of the pupil
-Contraction of the ciliary muscle
-Facilitation of drainage of AH via the canal of Schlemm
What eye drop can caused blurred vision and why?
Pilocarpine due to ciliary muscle contraction, the eye can’t focus
Which drug is not a prostaglandin agonist but does decrease intraocular pressure?
Bimatoprost
