structure and function of eye

Question 1

structure of eye on surface DIAGRAM

Answer 1

palpebral fissure between 2 eyelids, pupil black hole, with iris around it medial and lateral canthus the two sides of eye, and caruncle pink bit medially

Question 2

tear production- types of tears

Answer 2

basal tears, reflex tears from irritation, and crying tears

Question 3

lacrimal system DIAGRAM

Answer 3

produced by lacrimal gland- drains through puctum, then canaliculi into tear sac, which goes into nose cavity via tear duct

Question 4

tear film function and layers DIAGRAM

Answer 4

maintains smooth surface between air and cornea, supplies oxygen to cornea, and removes debris mucous layer (maintains surface wetting), aqueous layer, and superficial oily layer (reduces evaporation)

SAM

Question 5

conjunctiva DIAGRAM

Answer 5

thin tissue covering the outer surface of eye-starts at cornea, and lines inside of eyelids

Question 6

structure of eye and coats DIAGRAM

Answer 6

3 layers coating eye are sclera (hard), choroid (has vessels) and retina (neural tissue) optic disc is visual portion of optic nerve

Question 7

sclera and cornea and border between them

Answer 7

hard OPAQUE tissue protecting the eye with high water content- cornea is continuation of the sclera at front, with border known as LIMBUS; transparent part with low water content (ie becomes sclera if u hydrate cornea), giving 2/3rds of eyes focusing power

Question 8

layers of cornea

Answer 8

5 from in to out, anterior epithelium, bowmans membrane (basement membrane of epithelium), corneal stroma (helps with transparency), descement’s membrane (basement membrane of endothelium), endothelium

ABCDE

Question 9

UVEA

Answer 9

vascular coat of eye between sclera and retina- made up of iris, ciliary body (both anterior part of eye ie anterior to lens) and choroid (posterior part ie posterior to lens) choroid has blood vessels to supply retina iris- coloured part of eye which constricts/dilates pupil within eye using its muscles

Question 10

lens- functions

Answer 10

transparency and refraction (1/3rd)- done by ciliary muscles which are attached to lens by connective tissue called lens zonules when ciliary muscle contracts, it causes lens to bulge as lens zonules relax

also accomodation

TAR

Question 11

macula

Answer 11

in centre of retina- very sensitive for detailed CENTRAL vision- fovea is centre of macula: most sensitive part with highest conc of cones, but lowest conc of rods

Question 12

ciliary body and intraocular fluid DIAGRAM

Answer 12

not only needed to accomodate ciliary muscle, but also produces aqueous humour, which goes from posterior chamber to anterior chamber, then drains mostly into trabecular meshowork via canals of schlemm- rest passively absorbed via UVEAL-SCLERAL OUTFLOW needed to supply glucose to cornea (has no blood vessles)

Question 13

glaucoma DIAGRAM

Answer 13

sustained raised intraocular pressure (risk factor- not necessarily cause) also retinal ganglion cell death and enlarged optic disc (CUPPING)

Question 14

types of glaucoma

Answer 14

primary open angle glaucoma- problem with trabecular meshwork: develops SLOWLY, and asymptomatic until late

closed angle glaucoma- increased pressure pushing iris/lens forward, blocking trabecular meshwork: develops QUICKLY: very painful red eye

Question 15

blind spot of optic nerve

Answer 15

place where optic nerve meets retina (optic disc)- no light sensitive cells: tested using blind spot test

Question 16

central vs peripheral vision and how to test

Answer 16

central- colour vision and detailed vision eg reading, facial recognision due to fovea: damage= poor visual acuity peripheral vision- shape, movement, night vision: damage= unable to navigate in space

test central using visual ACUITY, peripheral using visual FIELD

Question 17

photoreceptor comparison DIAGRAM

Answer 17

rods are longer and more sensitive (hence needed for night vision)- also more abundant, but SLOWER cones less sensitive but faster, so needed for fine vision and colour vision distribution- most cones found in middle of fovea, most rods found 20-40 decreases away from fovea

Question 18

frequency spectrum and types of rods/cones DIAGRAM

Answer 18

S cones sense blue, M gree, L red- Rods, M and L cones overlap a lot in terms of wavelengths of light they detect

Question 19

test for colour blindness

Answer 19

ishiharda test- consists of plates filled with dots varying in size: only tests for RED-GREEN deficiencies (most common) those who are deficient cannot see number in middle

Question 20

light dark adaptation

Answer 20

dark adaptation is increase in light sensitivity in dark- cones adapt first, followed by rods, as they are more sensitive to light, so need more time light adaptation- from dark to light, where rod/cone function inhibited

Question 21

refraction DIAGRAM

Answer 21

converging (convex) lens takes light rays to a focal point (retina), with focal length distance between lens and focal point- not possible with concave lens

Question 22

emmetropiav vs ametropia

Answer 22

parallel light rays fall directly onto retina due to sufficient correlation between refraction and focal length in ametropia there’s a mistmatch, so light rays don’t fall onto retina= myopia, hyperopia, astigmatisms or presbyopia

Question 23

myopia (short sightedness) +symptoms and treatment

Answer 23

parallel rays converge in front of retina due to eye being too long (focal/axial length too big- more common) or too much refraction blurred distance vision (leading to squinting)= headache treatment- glasses, contact lenses orr intraocular surgery (replace lens)

Question 24

hyperopia (long sightedness) + symptoms

Answer 24

converge behind retina due to small eye or lack of refraction things near blurry- leads to eyepain, headache and burning sensation in eyes: also amblyopia (hyperopia in one eye as brain ignoring signals) treatment same as for myopia

Question 25

astigmatism- symptoms+ treatment

Answer 25

rays focus at 2 points rather than one, as cornea not spherical/dome shaped (one part of cornea steeper), so one side creates one focal point, the other creates another symtpoms- blurred vision, head tilting, headache/eye pain treatment is cylinder lense

Question 26

near response triad

Answer 26

this is adaptation for near vision- 1) miosis (sphincter pupillae causes pupil constriction) 2) convergence (aligns both eyes to near object) 3) accomodation (ciliary muscle causes lens to focus)

Question 27

presbyopia

Answer 27

age related occuring loss of accomodation (for near objects) due to stiffer lens- treatment is convex lenses to increase refractive power eg reading glasses

Question 28

types of intraocular fluid

Answer 28

aqueous humour (in front of lens) and vitreous humour (behind lens)

Question 29

normal intraocular pressure

Answer 29

12-20 mmHg

Question 30

aqueous vs vitreous

Answer 30

anterior and posterior segments divided by lens- vitreous in posterior, aqueous in anterior