Eye 1 Flashcards
Tears are produced by what
Lacrimal gland
Tears gather in
Tear sac
Tears exit through and reach
Tear duct and reach nasal cavity
Describe how tears drain
Tears drain through 2 puncta, openings on medial lid margin.
Tears flow through superior and inferior canaliculli
Tear film function
Maintains smooth cornea– air surface
O2 supply to cornea (as cornea has no blood vessels)
Removal of debris
Bactericide
3 layers of tear film
1) Superficial oily layer
2) Aqueous tear film
3) Mucinous layer on corneal surface to maintain surface wetting
Functions of each of the layers
Superficial oily layer -reduce tear film evaporation Aq tear film -Tear gland Mucinous Layer -On corneal surface to maintain surface wetting
Describe appearance Conjunctiva
Thin transparent tissue
Covers outer surface of eye
Covers visible part of eye and lies inside of eyelids
Nourished by tiny blood vessels
What is the average anterior-posterior diameter of the orbit?
24mm
Which bit of eye is responsible for 2/3rd of focusing power
Cornea
3 layers of eye?
Sclera
Choroid
Retina
Describe these layers
Sclera
- Hard and opaque
- High h2o cont
- Protective outer coat
Choroid
-Pigmented and vascular
Retina
-Neurosensory tissue
Describe appearance of cornea
- Transparent, dome shaped (convex)
- Front of eye
- Continuous w sclera
- Low water content
Function of cornea
Powerful retracting surface
Physical barrier
Infection barrier
5 layers of cornea
Epithelium Bowman's membrane Stroma Descemet's membrane Endothelium
Function of stroma
Regularity of stroma contributes towards transparency
Corneal nerve endings (cornea has no blood vessels)
Function of Endothelium
Pumps fluid out of endothelial cell
No regen power
Dysfunction may result in corneal oedema and corneal cloudiness
Appearance of cornea when hydrated
Turns white
Uvea function and location
Vascular coat of eyeball
Lies between sclera and retina
3 part of uvea
What happens when one part is diseased
Iris
Ciliary body
Choroid
Location of choroid
Between retina and sclera – part of uvea
Choroid composed of
Blood vessel layers that nourish back of eye
Part of eye that does’nt have blood vessels or nerves
Cornea
Part of eye with refactive power of remaining 2/3
Lens
Iris function
where
Controls light levels
Embedded w tiny muscles that dilate and constrict w pupil size
Lens appearance
Outer acellular capsule
Function of lens
Regulate inner elongated cell fibres – transparency
Refractive power
Accomodation-elasticity
Lens zonules appearance
-consists of?
lens suspended by fibrous ring
–> passive connective tissue
Retina
Structure
Function
Thin layer of tissue that lines inner part of eye
Capture light rays
Light impulses sent to brain for processing via optic nerve
Optic nerve
Function
Connects to eye near which structure
Visible part of optic nerve
Transmits nerve impulses from retina to brain
Connects to back of eye near macula
Optic disc
Structure in middle of retina, temporal to optic nerve
Macula
Function of macula
Small and highly sensitive part of retina responsible for detailed central vision
Fovea located where
Pit located at centre of macula
Macula located on retina, fovea located on macula
Anterior and posterior segments of eye separated by?
Lens
Anterior chamber
located where?
Contains?
Between cornea and lens
Filled w aq fluid – supplies nutrients
Ciliary body produces
Aq humour
Where is aq humour produced and where does it run into
Produced from ciliary bodies runs into anterior chamber
80% into canal of schlemm
20% into uveal scelal outflow
Glaucoma
Progressive death of what cell
Loss of what tissue
What happens to visual field
associated with progressive retinal ganglion cell death,
loss of nerve fibres and visual field loss
Glaucoma
Optic neuropathy w characteristic structural damage to the optic nerve, associated with progressive retinal ganglion cell death,
loss of nerve fibres and visual field loss
Glaucoma
Features of concern
Raised intraocular pressure
Retinal gang cell death
Enlarged optic disc cupping
2 types of glaucoma
Primary open angle glaucoma
Closed angle glaucoma
Describe the 2 types and affect they have on trabecular meshwork
Primary open angle glaucoma
- (Left) commonest
- Trabecular meshwork dysfunction
Closed angle glaucoma
- Can be acute or chronic
- Increased pressure pushing the iris/lens complex forward.
- Blocks the trabecular meshwork
Risk factor of glaucoma
Small eyes-hypermetropia
-Narrow angle at trabecular meshwork
How might someone with glaucoma present
Sudden painful red eye, w acute drop in vision
How can glaucoma be treated
W peripheral laser irditomy to create a drainage hole on the iris
Define optic nerve blindspot
Where optic nerve meets retina
-there are no light sensitive cells- blind spot
Most sensitive part of retina and how
Fovea (centre of macula thats located on retina)
Highest conc of cones and low rods
– Peripheral vision
Corresponding anatomic landmark for physiological blind spot
Optic disc
Which type of vision is responsible day vision Vv
Central vision
night -Peripheral vision
How can Central vision be assessed
Visual acuity assessment
How can peripheral vision be assesssed
visual field assessment
Central vision responsible for?
Colour vision fovea, reading, facial recognition
Peripheral vision responsible for?
Shape, movement
Retinal structure
3 layers and function
Outer -1st order neuron- detection of light Middle -2nd order neuron- local signal processing to improve contrast sensitivity, regulate sensitivity Inner -Retinal ganglion cells -3rd order neruon -Transmission of signal from eye to brain
Approximately how many rods and cones
120 million rods
6 million cones
Macula diameter
6mm
How long does it take for cone to adapt
7 mins
How long does it take for rod to adapt
30 mins (more rods as well) regeneration of rhodopsin
Macula Lutea appearance
Yellow patch
Macula in retina appearance
a pigmented region
Why does fovea form a pit
Due to absence of overlying gang cell layer
Which part of eye has highest conc of photoreceptors,what can it clinically be assess with
Fovea
OCT scan
Where are photoreceptors located
In retina
Rod and cone
Which photoreceptor is 100x more sensitive to light
Rod photoceptors
What are their responses to light like
Slow
What photoreceptors are responsible for night vision (scotopic)
Rod photoreceptors
Where is the highest conc or rod photoreceptors
20-40 degrees away from fovea
Test for colour perception
what colour deficiencies do they test for
Ishihara test
Green and red
Dark adaption how many phases
biphasic
Commonest form of colour vision deficiency in hujahs
Red green confusion
therefore ishihara test
2 types of lens
Converging diverging lens
Shape of converging and shape of diverging lens
function
Convex
Concave
Converging lens- take light rays and bring them to a point
Diverging lens-take light ray and spread outward
what sits in the limbus
corneal stemcell
Emmetropia
perfect focusing ability
Ametropi
Category of condition where light rays don’t fall on retina
Near sightedness
Myopia
Farsightedness
Hyperopia
Parallel rays converging at focal point posterior to retina leads to
Hyperopia
Excessive short glove (axial hyperopia) can lead to
Hyperopia
Insufferable refractive pwoer – refractive hyperopia lead to
Hyperopia
Asthenopic symptoms
Eyepain, headachein fronal region– where eyes are, burning sensation in eyes,
blepharoconjunctivities –asthenopic symptoms- tired eyes
Condition in which parallel rays come to focus in 2 focal lines rather than a single focal point
Astigmatism
Response triad is an adaption for?
Near vision
Near response triad consists of and function
Pupillary Miosis (Sphincter Pupillae) to increase depth of field – Convergence (medial recti from both eyes) to align both eyes towards a near object – Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision
cause of astigmatism
Cause : refractive media is not spherical–>refract differently
along one meridian than along meridian perpendicular to it–
>2 focal points ( punctiform object is represent as 2 sharply
defined lines)
Symptoms and treatment of astigmatism
Astigmatism
• Symptoms
– asthenopic symptoms ( headache , eyepain)
– blurred vision
– distortion of vision
– head tilting and turning
• Treatment
– Regular astigmatism :cylinder lenses with or
without spherical lenses(convex or concave), Sx
– Irregular astigmatism : rigid CL , surgery
Presbyopia
• Naturally occurring loss
of accommodation
(focus for near objects)
age 40 upwards
long distance fine
reading glasses
Accommodation Mechanism
Contraction of the Circular Ciliary Muscle inside the Ciliary Body – This relaxes the zonulesthat are normally stretched between the ciliary body attachment and the lens capsule attachment – Note that zonules are passive elastic bands with no active contractile muscle – In the absence of zonular tension, the lens returns to its natural convex shape due to its innate elasticity – This increases the refractive power of the lens • Mediated by the efferent Third Cranial Nerve
Accomodation is mediated by which cranial nerve?
3rd
• In accommodation, which one of the following events does not take place? – A) Relaxation of Circular Ciliary Muscle – B) Relaxation of Zonules – C) Thickening of Lens – D) Increase of Lens Refractive Power
– A) Relaxation of Circular
Ciliary Muscle
Intracollamer lens (ICL) can be used for which conditions
Astigmatism and myopia
