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refraction

bending of light rays when passing between compartments of different density, as from air into the cornea of the eyes

How does focus of light rays take place?

Light rays enters eye at an inward angle because of the eye's curved surface.
-falls on cornea, here light is refracted
-Incoming light is bent in opposite directions on the retina.
-then falls on lens, changes shape, and refracts light to point of acute vision on retina

How are images formed on the retina?

They are upside down and are only a small fraction of the object's actual size.

Point of acute vision is located?

retina

Is it easier to see far away objects or closer objects? Why?

Far away objects. There is less work for the eye because contraction of the ciliary muscles

Contraction state of ciliary muscles determines what?

amount of tension that the zonular fibers exert on the lens.

Contracted ciliary muscles?

lower tension, rounded lens

Relaxed ciliary muscles?

higher tension, flattened lens

accommodation

process by which the eye adjusts the shape of the lens to keep objects in focus, using convergence and emmetropia.

What is Convergence?

CLOSE looking at close objects like reading a book. ciliary muscle is contracted,releases tension on zonular fibers which allows natural elasticity of lens to return to more spherical shape or rounded and pupil restricts.

What is emmetropia?

DISTANT normal vision, ciliary muscle is relaxed in distant vision. Pupil is dialated, no accommodation or diversion
ciliary muscle relaxes
zonular fibers pull lens into flattened lens

In summary if you want to look at something closer,

Contraction happens, making the lens rounder

The lens is attached to the ciliary muscle by

inelastic ligaments (zonules)

Accomodation for year vision happens how?

a) in focus-light rays from distant objects are more parallel, they focus onto retina when lens is less curved.

b) out of focus-diverging light rays from near objects do not focus on the retina when the ciliary muscles are relaxed.

c) bringing into focus-firing of parasympathetic nerves, contracted ciliary muscles, slackened zonular fibers, rounded lens. Accomodation increases the curvature of lens, focusing the image of near objects onto the retina.

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