Lecture 21 Flashcards
The ____ divides the interior of the eyeball into two chambers
lens
What are the 2 chambers of the eye?
- Anterior/ Aqueous Chamber
- Posterior/ Vitreous Chamber
Where is the cornea located?
it is the transparent bulge at the front of the eye, continuous with the white of the eye, or sclera — the outer wall of the eyeball
What helps maintain the eyeball’s shape?
Behind is the vitreous chamber, filled with the vitreous body, a clear jelly
The role of the Cornea and Lens
focus light on the retina, the inner lining of the eye that contains the photoreceptors.
Where does light pass from the cornea to the lens?
Through a hole in the iris (the pupil)
In which order does light travel into the eye?
Cornea, pupil, iris, lens, retina
What is the Sclera?
the white outer coating of the eye
What is the role of the pupil?
- controls depth of field (the focus)
- helps to focus light
What controls pupil dilation?
- parasympathetic cells and sympathetic cells through the pupillary constrictor muscle and the radial pupillary dilator muscle of the iris
What happens when the eye is exposed to bright light?
- parasympathetic signals from the brain contract the pupillary constrictor muscle - - shrinking the pupil
What happens when the eye is exposed to the dark?
- sympathetic signals contract the radial pupillary dilator muscle of the iris
- dilating the pupil
What happens to our depth of field when the pupil is tightly constricted/ not dilated?
we have full depth of field, i.e. everything we see is equally in focus.
What happens to our depth of field when the pupil is dilated?
we have a shallow depth of field, i.e. only objects near one specific distance are in focus
How can we get a retinal image that is both bright and in focus?
By using refraction.
Refractive index
The ratio of the speed of light in a vacuum to its speed in a specific medium
The higher the refractive index the _______ the light travels
slower
What are our corneas made of?
clear collagen
Why does clear collagen allow for strong bending of light/ refraction?
because there is a big difference between the refractive indices of air and collagen
The cornea is responsible for ____ of the eye’s refraction, and the lens for ____
2/3
1/3.
How can the lens adjust the focus of light?
through change in shape
Why is refraction in water weak?
the refractive indices of collagen and water are similar
What is the lens?
It is a mesh of long cells without nuclei, packed with clear proteins called crystallins, and “zippered” together in concentric layers for flexibility
What makes up the lens?
clear cells and have no blood supply, but absorbs nutrients from the aqueous humor.
A convex lens
is fatter in the middle and thinner at the edges. It makes light rays converge to a focal point.
- ie: magnifying glass
Concave lenses
are thinner in the middle and fatter at the edges. They disperse light
- Ie: certain spectacles
How is the angle of incidence formed?
The angle depends on the shape of the lens and the direction of the light ray; e.g. in the simplest case, if a ray strikes the lens at right angles then it doesn’t bend at all.
What angle does refraction depend on?
the angle of incidence
4 results of the Parasympathetic nerve signals
- contract the ring-shaped, smooth ciliary muscle
- reduces tension in the zonules
- making the lens rounder, so light rays bend more
- focal point moves forward.
2 results of Sympathetic signals
- relax the ciliary muscle making the lens flatter
- allows for far vision
What is hyperopia?
farsightedness
- the focal point falls behind the retina
-
What is myopia
nearsightedness
- the focal point falls in front of the retina
- the lens is bending light rays too much
How is hyperopia treated?
a convex lens in placed in front of the light to help bend light rays more
What is accommodation?
Rounding of the lens for near vision
How is myopia treated?
a concave lens is placed in front of the eye to help spread out light rays
