Lecture 15- The Eye: How we see

Question 1

light must reach andf be focused onto the

Answer 1

macula

Question 2

features of the eye that help us to see

Answer 2

• transparent
• regulate light entry
• refract to bring into focus
• shape of eye ball

Question 3

transparency of the eye

Answer 3

nothing interferes with light getting through

• Tear film
• Cornea
• Anterior and posterior chamber fluid
• Vitreous jelly

Any pathology effecting the transparency of these will impede light

Question 4

Regulate light entry and retract to bring into focus

Answer 4

• Light will only be able to pass through via the lens once it has entered the pupil–> iris will not allow light to pass through
• Strongest point of refraction- the cornea –> tear film air interface –> scattered eye waves will be bent
• Focused through the pupil
• Further refraction as it passes through the lens

Question 5

Shape of eyeball

Answer 5

• Too long – short sighted- myopic
• Too short- long sighted- hypermetropic

Question 6

myopic

Answer 6

short sited- eyeball too long

Question 7

hypermetropic

Answer 7

too short- long sighted

Question 8

Accommodation reflex aim

Answer 8

Focusing near objects requires greater refraction of light

Question 9

outline the Accommodation reflex

Answer 9

light from near-objects more divergent- greater refraction required to focus onto retina, beyond capability of the cornea (which is in a fixed shape)

Eye accomodates

1. pupils constrict (limits amount of light coming through
2. eyes converge (to ensure image remains focused on same point of retina in both eyes)
3. lens becomes more biconvex (fatter) by contract of ciliary muscles

Question 10

presbyopia

Answer 10

harder to focus on close object

Lens tend to stiffen with age- less able to change shape presbyopia age related inability to focus near object

Question 11

When the ciliary muscle is relaxed

*

Answer 11

• Ligaments pulled tight
• Pulls the lens thinner good for looking at distant objects

Question 12

When ciliary muscle is constricted (parasympathetic fibres of oculomotor nerve)

• Tension removed from ciliary muscles
• Rounder, fat lens
• Good for looking at nearby objects

Question 13

Age related macular degeneration

Answer 13

Thinning and atrophy of the macula affects central vision

• Visual loss
• Gradual
• Some types are more rapidly

Question 14

• When light received by the retina (rods and cones) ligght waves are

Answer 14

are converted to action potentials and received by the ganglion cells which converge to form the optic nerve

Question 15

• Rods

Answer 15

• Active at lower light levels, do not mediate colour vision
• Abundant in peripheral parts of retina

Question 16

• Cones

Answer 16

• High definition
• Colour vision
• Active at high light levels
• Concentrated within macula of retina
• Fovea= only cones

Question 17

When light hits the retina

Answer 17

1. Photoreceptors convert light signals into Ap
2. Interneurons communicated with ganglion cells
3. Action potentials propagated via retinal ganglion cells
4. RGC axons collect in area of optic disc–> form optic nerve
   
   1. Blind spot= no photoreceptors
5. AP propagated along visual pathway to occipital lobe for interpretation

Question 18

optic disc-

Answer 18

-> form optic nerve

Blind spot= no photoreceptors

Question 20

decreased visial acuity… pathology affecting…

Answer 20

• transparency of structures anteiror to retina e..g opcity of lens such as a cataract
• refractive ability of strutures anteiror to retina e..g irregularity of corneal surface (astigmatism), ability of lens to change shape (presbyopia), shape of eyeball
• retina (inc macula) or optic nerve e.g. retinal detachment, age-related macular degeneration, optic neuritis

Question 21

cataracts

Answer 21

cloudy lens- replaced with artificial lens

Question 22

astigmatism

Answer 22

irregularity of corneal surface

Question 23

what can be used to assess vision

Answer 23

snellen chart

• stand 6m away
• Record the line they can read to for both eyes
• E.g 6/8 (if read up to 8^th line)

Question 24

snellen chart can be used to tell if problem is a

Answer 24

refractive or non-refractive problem

Question 25

refractive or non-refractive problem using Snellens chart

Answer 25

• Refractive – corrected with pin-hole testing
• Non-refractive- not corrected with pin-hole (optic nerve problem

Question 26

error of redraction is correted with

Answer 26

pin hole testing

Question 27

not corrected with pin hole indicates

Answer 27

pathology involving retina or optic nerve

Question 28

acute angle closure glaucoma

(closed angle glaucoma)

Answer 28

opthalmological emergency

• older patient 55+
• acutely painful red eye
• irregular oval shaped pupil (fixed)
  blurring of vision
• Halos around light (due to corneal oedeme)
• nausea and vomiting

Question 29

fluid in the eye provides

Answer 29

• Provides intraocular pressure
• If problem with drainage If pressure rises in the eye -> can be transferred to the back of the eye- damage to the back of eye

Question 30

Production of aqueous humour

Answer 30

• From the ciliary processes in ciliary body
• Passes into posterior through the pupil into anterior –> provide cornea nourishment

Question 31

Drainage of aqueous humour

Answer 31

• Drains via the iridocorneal angle
• Via trabecular meshwork into canal of Schlemm
  
  • Circumferential venous channels draining into venous circulation

Question 32

glaucoma is related to

Answer 32

• Problem with fluid drainage

Question 33

outline glaucoma

Answer 33

• Problem with fluid drainage
• Causes optic nerve damage secondary top raised intraocular pressure

Can develop chronically or acutely

Question 34

chronic glaucoma

Answer 34

• most common (open-angle glaucoma)
  
  • Normal iridocorneal angle
  • Trabecular meshwork deteriorates as age
  • Many asymptomatic (eye screening)
  • Increased IOP  increased optic nerve cupping

Gradual loss of peripheral vision

Question 35

• Acute – closed angle glaucoma

Answer 35

• Narrowing of iridocorneal angle
• Ophthalmological emergency