Eyes Flashcards
Three layers
Schleroid
* White of the eye
* Continuous with cornea
Choroid
* Blood vessel layer
* Iris and ciliary body
Retina
* Back and sides only
* photoreceptors
Vitreous and Aqueous Humour
Vitreous humour (behind lense)
-Gelatinous, thick
-Maintains shape of eye
Aqueous humour
-Provides nutrients to the cornea
- 5 mL/day, comes through front of lease
Glaucoma
-Blocked drainage duct
-Aqueous humour fluid builds
-Build-up of pressure, eye gets elevated pressure
- Can damage nerve
-throws off sizes and causes blurry vision
Iris and Pupil
Pupil
-Eye opening for light
Iris
-Colour of the eye
-Controls amount of light entering eye
- Circular muscles constrict pupil (get smaller, limit light)
- Radial muscles dilate pupil (pulls them open, done in dark)
Convex structures of eye produce
convergence of diverging light rays that reach eye
defracting pattern
- bent in
-diverging
Images formed on the retina are upside down and are only a small fraction of the object’s actual size
Refraction is a result of
Cornea, doesn’t bend
* Contributes most to refraction
* Refractive ability remains constant because curvature never changes
Lens
* Refractive ability can be adjusted by changing curvature as needed for near
or far vision
- allows focus of near/far
Accommodation
For far vision
-Light rays are parallel – need less bending
-Lens should be flatter, doesn’t need to be as strong
For near vision
-More bending needed, focus on retina
-Rounder lens, fatter and rounder
contracted = lower tension and more rounded lens
relaxed = higher tension and more flattened lens
Involves:
-Ciliary muscles - changes lens
-Suspensory ligaments - springs of trampoline
Near vs Far accommodation
For far vision
-Ciliary muscles relax
-Suspensory ligament are pulled taut (tight)
-Lens is flatter / weaker
For near vision
-Ciliary muscles contract
-Suspensory ligaments go slack
-Tension in lens causes it to become rounder/stronger
at rest=far vision
out of focus is going from far to near and light rays don’t bend in time due to changing lens shape
Lenses
Convex lens
-convergent
-Bends light rays in
-Eg. Lens of eye
Concave lens
-divergent
-Bends light rays out
Eye conditions
Emmetropia
-Normal vision
Myopia (can’t see far)
-Near-sightedness
-Lens is too strong or eye
too long (bending rays too much)
-Focus is in front of retina
-Corrected with a concave lens
- prescription makes lenses weaker
Hypermetropia or hyperopia
-Far-sighted-ness (only see far)
- Lens too weak or eye to short (not bending enough)
-Focus is behind retina
-Corrected with a convex lens
- prescription makes lenses stronger
-want focus on retina
Presbyopia
-Loss of near vision with age
Due to stiffening of lens
-Harder to become round
-Correct with reading
glasses
Light transduction
Light transduction occurs on the retina
- from light rays to electrical impulses
Photoreceptors
- Rods and cones
Bipolars
Ganglions
Optic nerve
From light waves to rods and cones then back to bipolar cells then ganglia and then out blind spot
Horizontal cells – lateral inhibition (acuity)
Amacrine cells – assist?
Retinal layers and Retina
Retinal Layers
-Light must filter through cell layers before hitting the rods and cones
- Blind spot – where optic nerve leaves eye
Retina:
Fovea
-Pinhead-sized depression in centre of retina
-Most distinct vision
-Has only cones (no filtering)
-no ganglia or rods
Macula lutea
-Area immediately surrounding
fovea
-High acuity
* cones only – but with overlaid
bipolars and ganglions
-2nd best visual
Macular Degneration
Macular degeneration
-Loss of cones in macula
- Lose central vision
- Leading cause of blindness
in western hemisphere (peripheral)
“doughnut” vision
Wet – more blood vessels – bleeding
Dry – atrophy of pigment
Properties of Rod and Cone vision
- Rods - peripheral vs Cones - central (fovea and macula lutea)
- Rods = 100 million per retina vs Cones = 3 million per retina
- Rods = vision in shades of grey vs Cones = colour vision, 3 main types
- Rods = high sensitivity, low acuity vs Cones = low sensitivity, high acuity
- Rods are night vision, Cones is day vision
- Rods = Much convergence in retinal
pathways vs Cones =Little convergence in retinal pathways
