WEEK 7 - Topic 17 - Focusing Light on the Retina Flashcards
Which type of photoreceptors in the eye responds to the different wavelengths of the visible spectrum?
Cones
There are specific cones that respond to specific wavelengths of visible light. True or false?
True
All rods can respond to all wavelengths of visible light. True or false?
True
Which type of cones will respond to blue, green and red light?
Blue light - blue cones
Green light - green cones
Red light - red cones
What type of lens is our human lens?
Convex
What happens when light doesn’t hit the retina?
Image is blurred
How many times does the light bend as it enters our eye? List the areas.
3 times
- Entering the cornea
- Entering the lens
- Leaving the lens
What does the light move through in the eye when humans see shit?
Cornea Aqueous humour Lens Vitreous humour Entire neural layer of the retina
What are the light bending apparatus of the eyes?
Cornea
Aqueous humour
Lens
Vitreous humour
Which part of the eye accounts for the majority of the refractory power?
Cornea
Is the refractory power of the cornea constant or not?
Constant
Is the refractory power of the lens constant or not?
Not constant
Why is the refractory power of the lens not constant?
- The lens is highly elastic
- Its curvature and refractory power can actively change (accommodation) to allow fine focusing
Which part of the eye can change shape to focus light?
Lens
Human eyes are best adapted for distant or close vision?
Distant vision
What is accommodation?
The process of changing the refractive power of the lens of the eye to maintain a clear image (focus)
When is the refractory power of the lens at its lowest?
- During distant vision
- When lens is at rest
Define the “far point of vision”
The far point of vision is the distance beyond which no change in lens (accommodation) is needed for focusing.
What distance if the far point for normal eyes?
6 m or 20 feet
At 6 m, does the eye need to accommodate?
No.
When viewing objects that are distant, do our eyes need to make large or little adjustments for proper focusing?
Little adjustments
What happens during distant vision?
The light rays entering the eye from the distant object is nearly parallel.
Sympathetic input causes the
- Ciliary muscle to relax;
- Ciliary zonule tightens, pulls and stretches the lens into flattened shape
- Lens is as thin as possible, at rest and at its lowest refractory power
When does the ciliary muscle relax?
- During distant vision, as sympathetic input increases and parasympathetic input decreases
(REVISION) What type of muscle is the ciliary muscle?
Smooth muscle
When looking at an object at a distance, what are the light rays like?
Light rays from the distant object are nearly parallel
Why does the lens need to be flat when looking at a distant object?
Because the light rays from the distant object are nearly parallel.
What distance defines distant vision?
When an object is at or more than 6 m away from the eye.
What are the processes that must occur when focusing light from a close object? Just list the titles.
- Accommodation of the lenses
- Constriction of the pupils
- Convergence of the eyeballs
Outline accommodation of the lenses needed for close vision
Accommodation is the process of changing the refractory power of the lens of the eye to maintain a clear image (focus).
- During close vision, accommodation increases the refractory power of the lens.
- The ciliary muscles contract
- Ciliary zonule relaxes and releases tension
- Lens relaxes and bulges, becoming more spherical/convex
What controls the contraction of ciliary muscles?
Parasympathetic fibres of the oculomotor nerves
Outline constriction of the pupils needed for close vision
The pupillary reflex of the sphincter pupillae muscles of the iris constricts the pupil to prevent divergent light rays from entering the eye.
What is the pupillary reflex mediated by?
Parasympathetic fibres of the oculomotor nerves
Outline the convergence of the eyeballs needed for close vision
The medial rectus muscles converge, or medially rotate, the eyeballs towards the object being viewed.
What controls the convergence of the eyeballs?
Somatic motor fibres of the oculomotor nerves
When looking at an object up close, what are the light rays like?
The light rays are divergent
Outline the steps and processes that occur during close vision
- There is increased firing of parasympathetic fibres of the oculomotor nerves.
- Accommodation of the lenses
- The ciliary muscles contract
- Ciliary zonule relaxes and releases tension
- Lens relaxes and bulges, becoming more spherical/convex - Constriction of the pupils
- The pupillary reflex of the sphincter pupillae muscles of the iris constricts the pupil to prevent divergent light rays from entering the eye. - Convergence of the eyeballs
- The medial rectus muscles converge, or medially rotate, the eyeballs towards the object being viewed. This is controlled by the somatic motor fibres of the oculomotor nerves. - Through all these processes, near objects are brought into focus.
