Opthalmology - How we see Flashcards
(38 cards)
Why does refreaction happen?
As the light passes through different mediums it changes speed, so if at an angle will bend the light
Which 2 parts of the eye bend light?Whih one is more powerful?
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
How far away to get parallel rays reaching the eye? How do the rays hit if the object is closer?
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
Accommodation? Which 3 things? Innervated by whAT?
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)
Which muscle thicker: Lateral or medial rectus?
Usually medial rectus because we spend so much time looking at objects that re closer.
Emmetrope means what?
20:20 vision, can see and read the last line in the opticians
Myopia, what happens, what causes it usually, other symptoms, squint and treatment
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.
Hyperopia, what happens? Wh? Strains? Squint? treatment
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
Astigmatism? How does this present in treatment?
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
Presbyopia? What age? Teated with what?
long-sightedness of old age, needing reading glasses. Due to less mobile lense. Usually 40+
How can you end up with lazy eye
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)
Myopia numbers on glasses etc
Myopia has negative numbers
Glasses prescriptions:
BC
DIA
SPH
CYL
Axis
Add
BC -base curvature - how concave
DIA - diameter of the cornea
SPH - - = biconcave
CYL = cylindic - astigmatisic
Axis = axis for astigmatism
Add = reading glasses etc
Signs of vitamin A deficiency
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.
How do we see? (Inc. Phototransduction)
- 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
What is your visual filed?
How much you can see with one eye (inc. perhipery)
What is an automated perimetry
Test for field of vision testing
Visual field vs visual acuity
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)
How else can you do a simple visual field test?
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)
Where is the optic chiasm?
above the pituitary fossa
Journey of nerves eye-primary visual cortex
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
Right visual fieldis percieved where?
LHS of brian in the Primary visual Cortex (area 17 of Occipital cortex)
What do you see when:
a)Rght optic nerve is damaged
b)Optic Chiasma disrupted in the middle?
c)Right OPtic tract damageed
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)
up, down, laterally, medially looking words, left and right
Up=elevation
Down = depression
Laterally = abduction
Medially =adduction
Left =Levoversion
Right = Dextroversion
