Accommodations of the eye

What is refraction?

The bending of light rays as they travel from one medium to another

What happens to the eye when focusing on a distant object?

1) Circular ciliary muscles relax so they have a longer diameter
2) Suspensory ligaments are pulled tight
3) The lens is stretched to become longer and thinner

What happens to the eye when focusing on a near object?

1) Circular ciliary muscles contract so they have smaller diameter
2) Loose pull on the suspensory ligaments
3) With less force on the lens its elasticity allows it to become fatter decreasing it focus length
4) Rays from the near object are brought to focus on the retina as light rays are refracted more

What are the issues with myopia?

Can't focus on distant objects caused by the eyeball being elongated

What is the correction for myopia?

A concave lens in front of the eye. Refracts the rays outwards and the convergent point is moved forwards so they meet a point on the retina

What are the issues with hyperopia?

Cant focus on near objects. Often related to old-age due to the loss of elasticity in the lens. The lens focuses the sharpest image behind the retina

What is the correction of the hyperopia?

Putting a convex lens in front of the eye. This refracts the light more so it moves the point of convergence forward so rays meet on the retina

New technologies to overcome myopia and hyperopia?

• Contact lenses
• Laser eye surgery
• Replacement lenses

How do contact lenses overcome myopia and hyperopia?

They are placed on the surface of the eye. Do the same job as glasses but can not be seen

What are some pros to contact lenses?

• Easier for playing sport and general activities
• Hard = last long
• Soft = flexible and more comfortable

What are some cons of contact lenses?

• Hard lenses = have to be removed overnight and kept sterile to prevent eye infection
• Sot lenses = don't last as long

How does laser eye surgery overcome myopia and hyperopia?

Once adults eyes stop growing and their vision has become stable. Lasers are used to treat myopia by reducing the thickness of the cornea so it reacts the light less strongly. The lens now focuses distant light on the retina instead of in front of the retina. To treat hyperopia

How do replacement lenses overcome myopia and hyperopia?

Adding another lens inside the eye itself to correct the visual defect permanently. Two main techniques -> 1) A permanent contact lens is implanted into the eye and the natural lens is let in place

What are the risks of lens replacement?

Damage to the retina