Opthalmology - How we see

Question 1

Why does refreaction happen?

Answer 1

As the light passes through different mediums it changes speed, so if at an angle will bend the light

Question 2

Which 2 parts of the eye bend light?Whih one is more powerful?

Answer 2

Cornea (45 D) and lens (15D), the cornea is more powerful but the lens has the ability t chaneg its power and so is more useful

Question 3

How far away to get parallel rays reaching the eye? How do the rays hit if the object is closer?

Answer 3

6m and further away reach the eye as parallel, whereas if it is closer then will hit the eye as divergent and rely on a greater power from the lens

Question 4

Accommodation? Which 3 things? Innervated by whAT?

Answer 4

Accomodation is the ability of the eye to focus.

Due to:
-Lens changing shape (ciliary muscles in ciuliary body contract and bulge up like a bicep, releasing the tension on the suspensory ligaments and so the lens can retract and fatten.
-Pupils constrict, few rays allows for sharper focus (also parasympathetic innervation.Caued by the Pulpillary constrictor (Sphincter Pupillae)
-Eyes converging (looking towards close up object, external eye muscles)

Question 5

Which muscle thicker: Lateral or medial rectus?

Answer 5

Usually medial rectus because we spend so much time looking at objects that re closer.

Question 6

Emmetrope means what?

Answer 6

20:20 vision, can see and read the last line in the opticians

Question 7

Myopia, what happens, what causes it usually, other symptoms, squint and treatment

Answer 7

Short sightedness (think myopia is shorter word than hyperopia)

Caused by an eyeball that is too long, and so the image is formed before the back of the eye.

Struggle to see objects far away not close up because to form the close up image you need the refractive power and so just use less of it to form a clear image.

May present as children losing interest in things that are far away/sports etc but enoy close up things like books. May also have a headache.
Divergent squint

Treated with biconcave lenses or laser therapy.

Question 8

Hyperopia, what happens? Wh? Strains? Squint? treatment

Answer 8

Long sightedness, eyeball too short/light not refracte enough so image formed behind the eye.
Means that people are using their refractive power to look at objects that are far away and so there is less power available to look at objects that are close up.

Strains to look at close up objects eg reading/ocmputer work

convergent squint

Biconvex glasses/laser surgery are the treatment options

Question 9

Astigmatism? How does this present in treatment?

Answer 9

Funky shaped eyeball (think rugby ball rather than football) so gives a distorted image both short and long distance.

Treated with cylindrical galsses/ toric lenses, curved only in one axis
Laser eye surgery can also be used

Question 10

Presbyopia? What age? Teated with what?

Answer 10

long-sightedness of old age, needing reading glasses. Due to less mobile lense. Usually 40+

Question 11

How can you end up with lazy eye

Answer 11

If you have a divergent/covergent squint then one eye willl begin to be used less and les, leading to it being used less and less, atrophy of the muscles (especially if a divergent eye)

Question 12

Myopia numbers on glasses etc

Answer 12

Myopia has negative numbers

Question 13

Glasses prescriptions:
BC
DIA
SPH
CYL
Axis
Add

Answer 13

BC -base curvature - how concave
DIA - diameter of the cornea
SPH - - = biconcave
CYL = cylindic - astigmatisic
Axis = axis for astigmatism
Add = reading glasses etc

Question 14

Signs of vitamin A deficiency

Answer 14

Struggling to see at dusk/dawn/low light (it’s rods that it affects first, cones = colour, rods =light)

Bitot’s spots (white mini pimply mountain ranges on sclera of eye. Might take a while to clear up so may be from a prev. deficiency)

Corneal ulceration

corneal melting -> opacification of the cornea

Vit A is also used in a lot of epithelium.

Question 15

How do we see? (Inc. Phototransduction)

Answer 15

• We only see visable light (400-700nm)
  -Detected by photoreceptors rods/cones cell membranes (lamella)
  -Rhodopsin (in cell membrane) is split by the isometric change of 11-cis retinal (Cis->Trans), and activates, starting PHOTOTRANSDUCTION CASCADE and leads to bleaching
  -AT-Rol (vit A from liver) is needed to replenish the Rhodopsin becuase retinyl esters are made adn they can’t be used to replenish (it helps convert enough 11-cis-retinal
• Cascade hyperpolarises and becomes action potential in optic cell

Question 16

What is your visual filed?

Answer 16

How much you can see with one eye (inc. perhipery)

Question 17

What is an automated perimetry

Answer 17

Test for field of vision testing

Question 18

Visual field vs visual acuity

Answer 18

Visual field = how much you can see with one eye, whereas acuity is how well you’re able to see (acuracy, like a usual eye test)

Question 19

How else can you do a simple visual field test?

Answer 19

close one of your eyes and close patients, draw around where you can see with your eye (1 m away from patient so hand is in the middle, and they should be able to see roughy a simelar size etc)

Question 20

Where is the optic chiasm?

Answer 20

above the pituitary fossa

Question 21

Journey of nerves eye-primary visual cortex

Answer 21

so you have 2 nerves from both eyes, a nasal and temporal.
-Nasal will see laterally, wheras the lateral will see medidially (light goes in straight lines)
-SO Right eye lateral and L eye nasal will see the same thing, and Left eye lateral and right eye nasal will see the same thing.
-The lateral nerve goes all the way to the Lateral Geniculate body (LGB)
-The nasal nerves cross over to be with the nerve that has seen the same picture at the Optic Chiasma and then meets the lateral nerve at the Lateral Geniculate Body (LGB)
-One nerve comes out from LGB (Optic radiation) and this then stimulates the primary visual cortex.
-Lateral (sees medially) has no crossovers and so Left sided things is seen on the right side of the brain and right sided things are seen on the right side of the brain.

Optic nerve (both lateral and nasal from one eye) -> Optic Chiasma (laterals cross) -> Optic tract -> Lateral Geniculate Body (LGB) Superior Colliculus -> Optic radiation -> Primary visual cortex

Question 22

Right visual fieldis percieved where?

Answer 22

LHS of brian in the Primary visual Cortex (area 17 of Occipital cortex)

Question 23

What do you see when:
a)Rght optic nerve is damaged
b)Optic Chiasma disrupted in the middle?
c)Right OPtic tract damageed

Answer 23

a)Only out of left eye (Right eye blindness)
b) both nasals have the chop so can only see medially (bitemporal hemianopia)
c) Nothing on the left side contralateral homonymous hemianopia)

Question 24

up, down, laterally, medially looking words, left and right

Answer 24

Up=elevation
Down = depression
Laterally = abduction
Medially =adduction
Left =Levoversion
Right = Dextroversion

Question 25

Intorsion or extorion

Answer 25

Basically being able to keep field of vision upright whilst tilting the head

Extorsion = top of eye ball away from teh nose
Intorsiom = top of eyeball towards the nose

Question 26

Actions of individual eoms (external Orbital Muscles)

Answer 26

Remember RADSIN (Recti ADuctors, Superiors INtortors)
LR - abducts
MR - adducts
SR - elevates, adducts, intort
IR - depresses, adducts, extorts
SO - Inrots, depresses, abducts
IO - extorts, elevates, abducts

Question 27

Orbital vs optic axis

Answer 27

Orbital axis is the line the muscles follow, from centrally i the head out (45’ between devergent orbital axis, and the optic axis is the horrizontal line the way forward that our eyes look.

Question 28

Where do the oblique muscles attach on the eye and what effect does that have on the movements here

Answer 28

posteriorly almost in the lateral upper most quadrand of the posterior side of the eyeball., because behind, it means the the oblique inferior one will elevate and the superior oblique will depress as oposed to the superior and inferior rectus, which attach more on the anterior surface of the eye and so the superior will elevate and inferior depress.

Question 29

Esotrpia vs exotropia

Answer 29

squints:
Esotropia = convergent squint
exotropia = divergent squint

Can tell by shining a light on to the eyes, and if light not central then there is a squint.

Important to correct, can do with eye patch to make lazy eye work, otherwise can lead to lazy eye

Question 30

Amblyopia vs diplopia

Answer 30

Amblyopia = lazy eye (think about daisy ambling along)

Diplopia = double vision (di=2)

Question 31

3 intrinsic eye muscles

Answer 31

Ciliaris Muscle (ciliary body)
Constrictor Pupillae (in iris at pulpillary boarder)
Dilator Pupillae (radially running muscle in the eye)

Question 32

how to do the pupilary reflex

Answer 32

Dim room.
Shine light in one eye.
Both eyes should constrict
Move to other eye
Both eyes should stay the same

Question 33

What is the pathway of the light reflex

Answer 33

Optic nerve -> Optic Chiasma -> Optic tract !CHANGES HERE! -> Midbrain (IIIn nucleus), Edinger-Westphal nucleus (both sides go to both sides) ->Preganglioni parasympathetic nerves through IIIn into orbit, synapse in ciliary ganglion -> postganglionic fibres through short ciliary nerves o constricto pupillae ->constricted pupil

Question 34

Why do you get a bilateral reflex of nuclei

Answer 34

Because both sides of the optic tract go to the both sides of the Edinger-Westphal nucleus

Question 35

What can cause absent/abnormal pupillary reflex

Answer 35

Many varying conditions, anything that will cause damage to the nerves on their way

eg
Diseases of the retina – detachment/ degenerations or dystrophies
Diseases of the optic nerve – such as in optic neuritis (frequently seen in MS)
Diseases of III cranial nerve

Question 36

What is horner’s syndrome?

Answer 36

Malfunction in the sympathetic chain esp leading to the face. Often due to lung cancer in the apex (pancost tumour), and leads to dropPping eyelid, contriced pupil, no sweating.(Ptosis
Miosis
Anhidrosis)

Question 37

What is Anisocoria?

Answer 37

Pupils of different sizes

Question 38

What medical emergency do we suspect if reflex is absent?

Answer 38

cerebral artery anneyurism