structure and function of eye Flashcards
structure of eye on surface DIAGRAM
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
tear production- types of tears
basal tears, reflex tears from irritation, and crying tears
lacrimal system DIAGRAM
produced by lacrimal gland- drains through puctum, then canaliculi into tear sac, which goes into nose cavity via tear duct
tear film function and layers DIAGRAM
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
conjunctiva DIAGRAM
thin tissue covering the outer surface of eye-starts at cornea, and lines inside of eyelids
structure of eye and coats DIAGRAM
3 layers coating eye are sclera (hard), choroid (has vessels) and retina (neural tissue) optic disc is visual portion of optic nerve
sclera and cornea and border between them
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
layers of cornea
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
UVEA
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
lens- functions
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
macula
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
ciliary body and intraocular fluid DIAGRAM
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)
glaucoma DIAGRAM
sustained raised intraocular pressure (risk factor- not necessarily cause) also retinal ganglion cell death and enlarged optic disc (CUPPING)
types of glaucoma
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
blind spot of optic nerve
place where optic nerve meets retina (optic disc)- no light sensitive cells: tested using blind spot test
central vs peripheral vision and how to test
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
photoreceptor comparison DIAGRAM
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
frequency spectrum and types of rods/cones DIAGRAM
S cones sense blue, M gree, L red- Rods, M and L cones overlap a lot in terms of wavelengths of light they detect
test for colour blindness
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
light dark adaptation
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
refraction DIAGRAM
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
emmetropiav vs ametropia
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
myopia (short sightedness) +symptoms and treatment
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)
hyperopia (long sightedness) + symptoms
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
astigmatism- symptoms+ treatment
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
near response triad
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)
presbyopia
age related occuring loss of accomodation (for near objects) due to stiffer lens- treatment is convex lenses to increase refractive power eg reading glasses
types of intraocular fluid
aqueous humour (in front of lens) and vitreous humour (behind lens)
normal intraocular pressure
12-20 mmHg
aqueous vs vitreous
anterior and posterior segments divided by lens- vitreous in posterior, aqueous in anterior