Vision Flashcards
What is refraction?
Bending of light when it passes from one optical medium to another
The bending of light rays to form a sharp image on the retina
What is accommodation?
The focusing of a far off or near object by how much we bend the light rays
What is a refractive erros?
When there is a mismatch of bending the light rays
Which components of the eye are transparent?
Cornea
AH
Lens
VH
What are the two main benders of light in the eye?
Cornea
Lens
What is the most powerful bender of light?
Cornea
What are the 3 things that cause accommodation?
Pupil constricts
Eyes converge
Lens changes shape
What is the sequence of events that occur to thicken the lens?
o Want to thicken the lens – ciliary muscle
o Ciliary muscle contracts making the ciliary body bulge
o Space in the middle decreases and the suspensory ligaments become lax
o This means the lens is no longer being pulled
o Basically just flops down and becomes more spherical (thicker)
o This bends the divergent rays
Do eyes converge or diverge when an object is up close?
Convege
Which muscles causes convergence?
Medial Rectus
Which CN controls the medial rectus?
CN III
Which muscle is thicker medial or lateral rectus?
Medial
Which of the 3 aspects of accommodation is examinable?
Pupillary constriction
Which part of the NS controls the constriction of pupils?
Parasympathetic innervation
What is myopia?
Short sightedness
What is hyperopia
Long sightedness
What is a astigmatism?
Non-spherical curvatures of the cornea
What is prebyopia?
Long sightedness of old age
What is short sightedness?
When close objects appear clear and distant ones hazy
What is the most common cause of myopia?
Eyeball is too long
Where does the image form in myopia?
In front of the lens
What are the symptoms of myopia?
Headaches
Complain of not being able to see board or distant objects
What are infant symptoms of myopia?
Loss of interest in sports/people
More interested in books/pictures
What is the treatment for myopia?
Bi concave lenses
Spectacles
Contact lenses
Laser eye surgery
What is long sightedness?
When distant objects appear clear
Close objects appear hazy
What is the main cause of hyperopia?
Eyeball is too short
Or lens is too flat
Where is the image formed in hyperopia?
Behind the retina
Why can accommodation not just be used to correct hyperopia?
Use more and more power for seeing close up until all accommodative power has gone
What are the symptoms of hyperopia?
Glasses
Contact lenses
Laser eye surgery
What can be seen in children with hyperopia?
Convergent squint
Why is immediate correction of convergent squint in children necessary?
To preserve vision
and prevent a lazy eye
What is astigmatism?
When close and distant objects appear hazy
What contact lenses are needed in astigmatism?
Toric lenses
Which glasses are neededin astigmatism?
Cylindricallens
What is the cause of presbyopia?
With age the lends becomes less elastic
Accommodation power weakens
When does presbyopia usually start?
In the 5th decade of life
What is phototransduction?
The conversion of light energy to an electrochemical response by the photoreceptors
What are the 2 types of photoreceptors?
Rods and cones
What do the phototransduced rods and cones need to activate?
Optic nerve neurons
To generate and AP
What is the visual pigment in rods?
Rhodopsin
What is the visual pigment in cones?
Opsin
What are the 3 types of cones?
S, M and L
What do the 3 different types of cones all respond to?
Different wavelengths of light
What does rhodopsin consist of/
Opsin + 11-cis Retinal
Where is vitamin A supplied?
Through the diet
What is rhodopsin?
Integral transmembrane helical protein
What is retinal?
Chromophore
What is retinal derived from?
Vitamin A
What is opsin?
A G-coupled protein
What are the 2 conformations of retinal?
Cis and trans
What happens when light hits retinal?
Changes from cis to trans conformation
Why does rhodopsin split?
Because not all trans-retinal can fit into the opsin
How is visual pigment regenerated?
Dietary vitamin A goes back to form 11 cis -retinal
This then joints the opsin
Forms rhodopsin
Why is a constant supply of vitamin A require?
because not all vitamin A is regenerate to form retinal
some of it does not combine with opsin and gets used instead to form an ester
In what conditions can vitamin A deficiency occur?
Coeliac
Sprue
What is your visual field?
Everything you see with one eye including the periphery
How are images of objects in your filed of vision formed?
Upside down
Where are upside images inverted?
on the retain
Where is the left half of the visual field seen?
On the right side of the retina
Where is the right visual field seen?
On the left side of the retina
Where do fibres from the optic nerve pass?
The optic chiasma
At the optic chiasma which fibres cross?
Medial ones
Which fibres cross over at the chiasma nasal or temporal?
Nasal
Where do fibres from the optic tracts synapse?
At the LGB of the thalamus
Where do optic fibres pass from the LGB?
Behind the internal capsule to reach the primary visual cortex
What is area 17?
Primary visual cortex
Where is area 17 located?
Occipital lobe
Which cortex sees the left half of the visual field?
Right cortex
Which cortex sees the right half of the visual field?
Left cortex
When the right optic nerve is damaged what do you expect to see?
Blindness in the right eye
Entire eye has been affected
When the optic chiasma is interrupted in the middle what do you expect to see?
Bitemporal hemianopia
Naso fibres are affects meaning lateral vision is lost
When the right optic tract is damage what do you expect?
Left side blindness
Contralateral homonymous hemianopia
What is the function of intrinsic muscles of the eye?
Control pupil diameter an alter lens curvature (accommodation)
What is the function of extrinsic eye muscles?
To move the eyeball
What are the muscles of the eye?
MR LR SR IR IO SO
Where do the recti muscles arise from??
Apex of the orbit from an annular fibrous ring
Where does the SO muscle arise?
The roof of the orbit posteriorly
Where does the IO arise from?
The roof of the orbit anteriorly
Which is the only eye muscle to originate anteriorly?
IO
Which muscle lies just above the SR?
LPS
Levator palpebrae superioris
Which muscles closes the eyelid?
LPS
Where do the recti muscles insert?
Onto the sclera anteriorly
Where do the oblique muscles insert?
On to the sclera posteriorly
Which CN supplies the extrinsic muscles of the eye?
SO CN IV
LR CN VI
and everything else by CN III
What term is used to describe eye movements of both eyes?
Binocular
What is meant by uniocular?
Movement of 1 eye
When LR has abducts the eye what does SR and IR cause?
SR - elevation
IR - depression
When MR has adducted the eye what does SR and IR cause?
SR - intorsion
IR - extorsion
When the eye ball is adducted what does SO and IO cause?
SO - depression
IO - elevation
When the eyeball is abducted what does SO and IO cause?
SO - intorsion
IO - extorsion
What is the primary action of the extrinsic eye muscles?
MR - adduction LR - abduction SR - elevation IR - depression SO - intorsion IO - extorsion
What is the secondary action of SR, IR
SO, IO?
SR - adduction
IR - abduction
SO - depression
IO - elevation
What is the tertiary action of SR, IR, SO ,I O?
SR - intorsion
IR - Extorsion
SO - Abduction
IO - adduction
What is esotropia?
Convergent squint
What is exotropia?
Divergent squint
What is amblyopia?
Lazy eye
Where brain supresses the image of one eye leading to poor vision in that eye
How is amblyopia treated?
With an eye patch to try and stimulate the lazy eye
What is diplopia?
Double vision
What are the intrinsic muscles of the eye?
Ciliaris muscle
Constrictor pupillae
Dilator pupillae
What is the ection of the cilaris muscle?
Muscles that contracts to make the lens thicker
Where is the constrictor pupillae found?
In the iris at the pupillary border
What is the action of the constrictor pupillae?
Constrict the pupil
Which part of the NS innervated the constrictor pupillae?
Parasympathetic
Where is the dilator pupillae found?
Radially running muscle in the iris
What is the action of dilator pupillae?
Works to dilate the pupils
What is the pupillary reaction to increased illumination?
- parasympathetic system innervated
- both pupils constrict
What is the pupillary reaction to decreased illumination?
Sympathetic system innervated
Both pupils dilate
How do you elicit the pupillary reflex?
Start in dimly lit room
Put pen torch in front of the eye
Both pupils should be dilated
Where is CN III nuclei located?
In the midbrain
Where do fibres destined to activate the pupillary reflex go?
Leave the optic tract and go to the midbrain where CN III nuclei is located
DO fibres destined to activate the pupillary reflex go to the LGB?
No
What are common causes of absent/abnormal pupillary reflex?
Any abnormality of the afferent, centre of efferent part of the reflex
Diseases of the retina
Diseases of the optic nerve
Diseases of CN III
Where is optic neuritis commonly seen?
MS
Which is the afferent limb of the pupillary reflex?
CN II
Which is the efferent limb of the pupillary reflex?
CN III
What is anisocria?
Pupils of different side
What is ptosis?
Drooping of the eyelid
Which segment of the NS has thoracolumbar outflow?
Sympathetic
What is horners syndrome?
Horner syndrome is a combination of signs and symptoms caused by the disruption of a nerve pathway from the brain to the face and eye on one side of the body.
What are the common symptoms of horners syndrome?
Typically, Horner syndrome results in a decreased pupil size, a drooping eyelid and decreased sweating on the affected side of your face.
