Eye Flashcards
How are the lateral and medial borders of the eye anteriorly called?
What is the name of the white part of the eye?
It is the sclera
How is the space between the two eyelids anteriorly called?
It is called the palprebral fissure
How is the remainant of the 3rd eyelid in the human eye called?
Caruncula
Why do we produce tears?
- Basal tears
- Lubrication of eye
- Relflex tears
- in response to irritation
- Emotional tears
What are the function of tear production?
- Smooth cornea-air surface –> O2 supply of cornea via oxgena in air
- Removal of debris
- Protection from infective agents
Explain the organisation of the tear film and respective function
- Mucous layer –> moisturise surface of cornea
- Aqueous part (secreted by lacrimal gland)
- superficial Lipid layer –> prevent evaporation
Explain the production and drainigae of tears
- Produced by lacrimal gland (PNS stimmulation)
- Absorbed medially via Punctum
- Via canaliculi into the tear sac
- And from there into tear duct –> nose
What is the conjunctiva?
Thin layer of tissue covering the outer layer of the eye (visible part+ inner parts of eyelids)
–> supplied by almost invisible blood vessels
What is the cornea?
What is its funciton?
Dome shaped window in front of eye
Main function: refraction –> covers 2/3 of focusing ability of eye
–> clear window to look through + physical and infectious barrier
Low water content
What is the structure and functio of the sclera?
It is the thogh, white connective tissue of the eye
Has a high water content
Main function: protection
What is the structure of the cornea?
- Epithelium
- Basement membrane Bowman’s Membrane
- Stroma –> regularity contributes towards transparency (non-vascular, supplied by corneal nerves)
- Basement membrane Descemet’s Membrane
- Endothelium –> pumps fluid out of cornea –> prevention of corneal edema –> (Cataract )
What happens if you hydrate the cornea?
It turns white
What is the Uvea?
Vascular part of eye that has three parts
- Iris
- Ciliary body
- Choroid
How do you call the vascular layer of the eye?
What does it contain?
Uvea has three parts:
- Iris
- Ciliary body
- Choroid
What is the funcition of the iris?
It controls size of pupil and hence amount of light in the eye
What is the choroid?
Part of the Uvea
- between sclera and retina
- supplies back of the eye
Explain the structure of the lens
Outer Capsule (acellular)
Regular inner elongated cell fibres – transparency
–> May loose transparency with age – Cataract
What is the function of the lens
it is transparent
1/3 of refraction of light
accomondation
How is the shape of the lens controlled?
By lens zonules –> connective fibres connected to ciliary body –> allows change in shape for e.g. accomondation
What is the optic disc?
the visible part of the optic nerve on the retina
What is the macula?
What is its funciton?
- located in the centre of the retina, temporal to the optic nerve
- part of the retina responsible for detailed central vision.
- Fovea= centre of macula
What is the fovea?
the centre part of the macula
What is the difference between the anterior and posteiror segment and the anterior and posteior chamber of the eye?
Anterior segment: Everything anterior to the lens
(posterior segment=everything posterior to lens
Anterior chamber : specific chamber between the lens and the posterior part of the cornea
Posterior chamber= Part of eye btween iris and lens (site of ciliary body)
Explain the production, route and drainige of the aqueous humor in the eye
Produced by the ciliary body in posterior chamber of eye –> goes into anterior chamber of eye
Drains into Trabercular meshword
- 90% into canal of schlemm
- 10% into via Uveal-scleral outflow
What is the funciton of the aqueous humour of the eye?
Mainly: It supplies nutrients to the cornea
Is also important in maintaining intra-occular pressure
Explain the role of intra-occular pressure and the role of the aqueous humor in maintaining it
It increased aqueous humour production of decreased absorbtion–> might be an increase in intra-occular pressure
- Intra-occular pressure is the single modifiable risk factor for glaucoma
- Might cause Retinal Ganglion Cell Death and Enlarged Optic Disc Cupping –> blindness
What is glaucoma?
Optic neuropathy with characteristic structural damage to the optic nerve, associated with progressive retinal ganglion cell death, loss of nerve fibres and visual field loss
What is the blind spot?
it is the spot on the retina where the optinc nerve meets the retina –> no visual fibres –> no vision
Explain the structural organisation of the retina
- Photoreceptors (cone+ rod cells) most posteriorly (because light is reflected at back of eye)
- Bipolar cells
- Local Signal Processing to improve contrast sensitivity, regulate sensitivity
- Ganglion cells
Explain the structure and the function of the fovea
Fovea forms the pit at the centre of the macula due to absence of the overlying ganglion cell layer
–> Fovea has the highest concentration of photoreceptors for fine vision
What is the function and characteristic of a rod cell?
- Longer outer segment with photo-sensitive pigment
- 100 times more sensitive to light than cones
- Slow response to light
- Responsible for night vision
- (Scotopic Vision)
- 120 million rods
–> Mainly located in lateral part of vision (mostly 20-40°)
What is the function, location and characteristics of the cone photoreceptors?
Less sensitive to light, but faster response
Responsible for day light fine vision and colour vision (Photopic Vision)
6 million cones
- mainly locared at centre of vision
What is deuteranomalie?
What is the cause for it?
bedingte Farbfehlsichtigkeit, bei der die Zapfenfür das Wahrnehmen von Grün das Opsin für Rot enthalten. Menschen mit Deuteranopie haben daher nur zwei statt drei verschiedene Zapfentypen.
How many different types of cones do we have?
what is their respective function?
Detect light at different frequencies:
Explain the concept of refraction
Light that enters a different medium that has differnt properdies gets refracted meaning
angle of incidence is > or < than angle of refraction
In convex lenses –> Light meets at one focal point
What is the importance of the focal point in vision?
If the focal point meets the retina –> we see a sharp picture
If it is before (Myopia) or behind the retina (hyperopia) the picture will be blurry
What is Emmetropia
focal point and distance on retina should be the same –> produces a sharp image
–> clear vision
What is Ametropia
Focal point does not reach retina –> blurred vision
- Nearsightedness (Myopia)
- Farsightedness (Hyperopia)
- Astigmatism (Hornhautverkrümminug)
- Presbyopia (Altersweitsichtigkeit)
What is Myopia?
What are possible causes for this?
Nearsightedness (Myopia)
focal point before retina due to
- excessive long globe (axialmyopia) (more common)
- excessive refractive power (refractivemyopia)
What is Hyperopia?
What are possible causes for this?
Farsightedness (Hyperopia)
- focal point not yet met when light reaches the retina
- excessive short globe (axialhyperopia):morecommon
- insufficient refractive power (refractivehyperopia)
What is Astigmatism?
Astigmatism (Hornhautverkrümminug)
refractory medial is not spherical–> two focal points on retina emerge
What is Presbyopia
Presbyopia (Altersweitsichtigkeit)
- Naturally occurring loss of accommodation
Explain the process of Accomondation
- Contraction of the Circular Ciliary Muscle inside the Ciliary Body
- This relaxes the zonules that are normally stretched between the ciliary body attachment and the lens capsule attachment
- –> 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
