The eye Flashcards
What is the consensual light reflex?
- Change in pupil size changes in both eyes if only one eye is stimulated
- Due to both Edinger-Westphal nucleus being innovated by sensory input from one eye
What is the function of the iris
- Contains muscles which control pupil size
What is the pupillay constrictor?
- Smooth, circular muscle on the inside of the iris
- Contracts to make pupils smaller
- Regulated by parasympathetic NS
What is esotropia?
- Convergence of the eyes
- Weakening of the outside muscles
What is glaucoma?
- A build-up of aqueous humor due to slowed uptake
- Increases intraocular pressure
- Compression of the optic nerve and blood vessels
- Progressive loss of vision from the periphery inwards
What is exotropia?
- Divergence of the eyes
- Weakening of the inside muscles
What is the difference between the light rays from near and distant objects by the time they reach the eye?
- Distant - almost parallel, requires less refractive power by the lens
- Near - not parallel, require more refractive power by the lens
What is the lens of the eye?
- Transparent structure behind the iris
- Can changes shape to adjust refractory power
- Connected to cillary bodies by zonal fibres
What is hyperopia?
- Longsightedness (can’t see close)
- Eye is too SHORT
- Light convereges after the retina
- Requires a convex lens to fix (converge light rays more)
What is the conjunctiva?
The membrane underneath the eyelids which connects to the sclera
As you get older are you more likely to get myopia or hyperopia?
Hyperopia as the refractive power of the lens decreases with age
What is cateracts?
- Clouding of the lens due to changes in the composition of the aqueous humor
- Not supplying the correct nutrients
- Increase with age, diabetes M, smoking
- Treatment is lens replacement
What are the zonal fibres?
- Ligaments which attach the cillary body to the lens
- Allows the lens to change shape and change refractive power
What is the optic disc?
- The ‘blind spot’ of the eye
- No photoreceptos
- Origin of blood vessels and the optic nerve
What is the sclera?
- The tough white part of the eye which is continuous with the cornea
What is refraction and when does it occur?
- Bending of the light as it travels from one transparent material to another
- Light travels easier in air than water
- Tries to bend light perpendicular to the interface
- Happens when light enters the aqueous humour, in order to focus light on the retina
When does pupil size change?
- Low light = large pupil
- Bright light = small pupil
What is the foeva?
- The centre of the macula
- Where the retina is the thinnest
- High concentration of cones found here
What is the focal distance?
- Distance between the cornea (refractive substance) and the retina (where the light rays converge)
- May be different in people - highlight disorders
What is the function of the pupil?
- Lets light into the eye
- Size changes
What happens to the lens when focusing on nearer objects?
- Ciliary muscles contract, zonal fibres relax, lens is more spherical
- Lens has more refractive power
Where does the most refraction occur in the eye?
In the cornea - 80%
Rest occurs by the lens - 20%
What is emmetropia?
- Ciliary muscles are relaxed, zonal fibres are stretched, lens is flattened
- When the eye is focused on an object more than 6m away (distant)
What is the vitreous humor?
- Viscous liquid inside the eyeball which keeps the eyeball spherical
Where is the aqueous humor secreted from?
The ciliary body (muscle)
What is the macula?
- Devoid (free of blood vessels) area
- Region of the retina for central visual processing
What is light?
Electromagnetic radiation in the visible region
What is the aqueous humor?
- Watery liquid infront of the lens and iris
- Providing nutrients to the lens and the cornea
What regulates light levels into the pupil?
The pupillay constrictor and pupillar relaxor muscles in the iris
What is refractive power measurements?
Diopters
What is the pupillay dilator?
- Smooth, radial muscle on the outside of the iris
- Contracts to make pupils larger
- Regulated by sympathetic NS
Where is the aqueous humor absorbed?
By the canal of schlemm (between the cornea and the sclera
What is myopia?
- Nearsightedness (can’t see far objects)
- Eye is too LONG
- Light converges before the retina
- Requires a concave lens to fix (to diverge light rays more)
What nerves is eye movement controlled by?
Oculomotor (III)
Trochlear (IX)
Abducens (XI)
How is refractive power calculated?
1/ focal distance(m)
