Vision 1 Flashcards
What is refraction?
Bending of light in order to see an image on the retina
When is light bent?
Light bends when it passes from one medium to another
Which images need to be bent to be seen on the retina?
When an object is far away the rays will not need to be bent- usually parallel to the image
When an object is up close- then the rays need to be bent more
How does refraction occur?
How does it work:
Light bends when it reaches the cornea
Light bends more when it reaches the lens
When an image is closer?
Lens needs to be thicker
This increases the bending power of the lens
What property of the cornea allows it to bend light?
Transparency
Which is the most powerful bender of light?
The Cornea.
However the lens has the ability to change the power of bending.
What is accommodation?
Change in focus on images away or up close by changing how much the image is bent
How does accommodation occur?
Lens changes shape and thickens
Pupil constricts
Eyes converge
How does the lens change shape and thicken?
- Lens is attached to ciliary body via suspicion ligaments
- Ciliary body contracts= causes lens to become thicker and more spherical
- Thicker lens is more powerful and therefore able to focus better
How does the ciliary body contract?
Ciliary muscle contracts Causes ciliary body to bulge Reduces length of suspension ligaments Lens is no longer stretched Lens becomes thicker
How does the pupil constrict
Contraction of the papillae constrictor
Allows only a few rays of sunshine to pass through
How do the eyes converge?
Medial rectus muscle constricts
what is a refractive error?
When there is an error with how much we bend the rays
What is myopia
Short-sightedness: Close objects are clear, far away objects are hazy
what is the cause of myopia?
Due to the eyeball being to long compared to the socket
Rays of light are bent to much compared: they do not reach the retina
symptoms of myopia?
- Divergent Squint: particularly in infants and children- eyes do not look straight
- Loss of interest in books/sports- in toddlers/ young children
- Headaches
Treatment for myopia
Need to decrease bending power
- Biconcave lens
- Spectacles, contacts
- Laser eye surgery
What happens in laser eye surgery
Take away a flap of the Cornea to expose the stroma, Machine can be used to say how much of the stroma needs to be burnt away. Should only be performed on people who struggle a lot with glasses, contacts - machine will not be able to give accurate results on people who have small defects
What is hyperopia?
Long-sightedness= can see far away but not up close
What is the cause for hyperopia?
Eyeball is too short for the orbit
Image forms behind the retina - it is not bent enough
Symptoms of hyperopia?
- Eyestrain after reading/working in young individuals
- Convergent squint in toddlers/children - need to connect straight away in order to prevent damage to eyes
Treatment for hyperopia
Biconvex glasses
Contact lenses
Laser eye surgery
What is astigamatism?
Images close up and far away both appear hazy
Surface has different curvatures in different meridians
Treatment for astigmatism?
Special glasses : cylindrical
- Special contact lenses : Toric
