vision Flashcards
what is sight
perception of objects in environment by means of the light they emit or reflect
name the accessory structures for vison
Eyebrows
Eyelids
Conjunctiva
Lacrimal apparatus
Six Extrinsic eye muscles
what is a sty
Inflamed ciliary gland of eyelash
what is a meibomian cyst
Infected oil-secreting tarsal glands
what is the Conjunctiva
Transparent mucous membrane, vascular
what is the Lacrimal apparatus
Gland & duct drain tears to nasal cavity
Tears contain bactericidal lysozyme
name the lacrimal structures
lacrimal gland (just above eye lid)
and
nasolacrimal canal (just a bit above hole of nose)
what do the Lacrimal gland & Nasolacrimal duct do
drain tears to the nasal cavity
how many extrinsic muscles of the eye are there
6
name the extrinsic muscles and the eye movements that they carry out
Superior rectus muscle:
- Upward, slightly outward
Inferior rectus muscle:
- Downward, slightly inward
Medial rectus muscle:
- Inward, toward the nose
Lateral rectus muscle:
Outward, away from the nose
Superior oblique muscle:
- Inward, downward
Inferior oblique muscle:
Outward, upward
describe the anatomy of the eye
Sphere with 3 principal components:
- Tunics: 3 layers that form wall
- Optical apparatus: admits & focuses light
- Neural apparatus: retina + optic nerve
Retina part of 1 & 3
Cornea part of 1 & 2
name the 3 tunics
Tunica fibrosa
Tunica vasculosa
Tunica interna
explain the Tunica fibrosa
sclera (white of eye) & cornea (transparent region; admits light into eye)
explain the Tunica vasculosa
uvea, under fibrosa (=choroid, ciliary body & iris)
Choroid = highly vascular, deeply pigmented layer behind retina
Ciliary body = thick extension of choroid, forming muscular ring around lens; supports iris & lens & secretes aqueous humour
Amount of melanin determines eye colour
explain the Tunica interna
retina
name the 3 layers of the eye (its outer surface surrounding the eye)
sclera (the most outer layer)
choroid
retina (most inner later of the eye layers)
what are the transparent elements of the eye and what are for
to admit/bend/focus light
- Cornea
- Aqueous humour
- Lens (if cloudy = cataract)
- Vitreous body = transparent jelly
where is the Aqueous Humor produced
by ciliary body
explain the Aqueous Humor in terms of what it flows through and what reabsorbs it
Flows through pupil into anterior chamber
Reabsorbed by ring-like blood vessel
- canal of Schlemm (= scleral venous sinus)
If reabsorption < secretion, pressure
- glaucoma
explain the structure of Optic Disc in Glaucoma
The pink rim of disc contains nerve fibers.
The white cup (in middle) is a pit with no nerve fibers.
As glaucoma advances, the cup enlarges until it occupies most of the disc area.
what cup to disc ratio indicated glaucoma
If cup to disc ratio >0.6, indicates glaucoma.
what shape is the lens of the eye
curved structure
‘Ellipsoid’ in shape, 10 mm across x 4 mm front to back
what is the crystalline lens
a clear disk behind the iris
flexible and changes shape to help you see objects at varying distances.
what does the lens of the eye do
Bends light and focuses it for the retina to help you see images clearly.
what happens to the eye lens as you age
the lens may become weaker or damaged.
what is cataracts
changes in proteins (crystallins), clumping.
cloudiness vision through pupil
explain the retina
Innermost layer; thin, transparent membrane
2 attachment points (optic disc & ora serrata [scalloped anterior margin])
Examine with ophthalmoscope
- Look for signs of hypertension, diabetes, atherosclerosis etc.
explain macula lutea
directly posterior to centre of lens, with central fovea centralis (mostly finely detailed images); no rods, only cones; highest concentration of cones
explain the optic disc
where all nerves & blood vessels pass
Creates ‘blind spot’ in vision
what is Proliferative Diabetic Retinopathy (PDR)
when Irregular new blood vessels form from the retina
this can cause black patches in vision
explain how an image is formed
Pupil admits light:
Diameter controlled by iris:
- Pupillary constrictor = concentric circles of SMC to narrow pupil
- Pupillary dilator = spokelike myoepithelial cells, widen pupil
Light is bent (refracted):
- By curvature of cornea towards centre of retina
- Refractive Index = measure of light retarded; lens merely fine tunes
The Near Response:
- Adjustment to close range vision
what does changing the curvature of the lens do
Light from a single point of a distant object and light from a single point of a near object being brought to a focus by this changing in curvature
what are the 3 processes involved to focus a near response image on retina
Convergence of Eyes:
- If problem, double vision
Constriction of Pupil:
- Screens out peripheral light rays that cannot be refracted well
Accomodation of lens:
- Change in curvature to focus
what is near response
the closest an object can still be in focus.
name some common defects of image formation
Hyperopia
Myopia
what is Hyperopia
Image (focal plane) behind retina
Correct with convex lens
Hyperopia = “Far sighted”
Image too far, behind eyeball
Can see far objects
correctedwith convex lense
what is Myopia
Image within vitreous
Correct with concave lens
Myopia = “short-sighted”
Image falls ‘short’ within eyeball
Can see near/short
explain Sensory Transduction in Retina
Conversion of light energy into action potentials occurs within retina
Consider:
- Cellular layout
- Pigments that absorb light
- What happens when light is absorbed
how many layer are there of the retina
5
name the 5 cellular layers of the retina
Pigment cell layer – retinal (RPE) absorb light (melanin) & reduce light scatter
Photoreceptor layer
- RODS – periphery, night
- CONES – centre of eyeball, day & colour
Bipolar layer
Ganglion layer
- largest neurons of retina
Nerve Fibre layer
what are the visual pigments in rods
RHODOPSIN (retinal+opsin)
(retinal is a pigment; opsin is a protein)
what are the visual pigments in cones
PHOTOPSIN (retinal+~opsin)
(retinal is a pigment; opsin is a protein)
what is retinol
a pigment
what is opsin
a protein
whats the shape of rods
long and thin
whats the shape of cones
short and wide
what is photochemical reaction
Cyclical process, same in rods & cones
cis-retinal (bent) absorbs photon of light, and with the requirement of ATP, it becomes trans-retinal (straight). which creates a nerve signal
trans-retinal can become cis-retinal by the dissociation from opsin
Colour Vision is based upon what
Based on 3 types of cones:
Blue
Green
Red
Perception of colour is based on what
on mixture of nerve signals from above
what do people with Dichromats do
confuse the colours of red and green
explain the visual pathway
the route of the visual image, from the retina through the optic nerve, crossing over at the optic chiasma, where the left field of vision is processed by the right side (& vice versa), moving along the optic tract to the thalamus, and on to the visual cortex (in the occipital lobe), where the brain interprets what is seen.
