Common problems of the eye Flashcards
What is accomodation?
The ability to change the shape of the lens to focus on near / distant objects
What is the lens surrounded by?
The ciliary muscle
How is the lens and ciliary muscle connected?
By fibres which are called suspensory ligaments
How can the ciliary muscle change the thickness of the lens?
By contracting or relaxing
What happens when the ciliary muscle contracts?
The suspensory ligaments loosen. The lens is now thicker and refracts light rays more strongly
What happens when the ciliary muscle relaxes?
The suspensory ligaments are pulled tight. The lens is now pulled in and only slightly refracts light rays
How much light is needed when focusing on distant objects?
Only a relatively small amount. The ciliary muscle relaxes and the suspensory ligaments are pulled tight
How much light is needed when focusing on near objects?
Light from near objects needs to be focused a large amount. The ciliary muscle contracts and the suspensory ligaments loosen
What is Hyperopia?
(Long sightedness) Can see distant objects but cannot focus clearly on near objects
What is the cause of hyperopia?
The eyeball is too short
How can hyperopia be treated?
Using glasses with convex lenses - partially focus the light before it enters the eye
What is Myopia
(Short sightedness) Can focus on nearby objects but cannot focus on distant objects
What is the cause of myopia
The eyeball is too long or the lens is too thick
How can myopia be treated?
Using glasses with concave lenses - partially unfocus the light before it enters the eye
What other things can we use instead of glasses?
- Contact lenses
- Laser eye surgery
- Replacement lenses
