Lecture 2 How We See Flashcards
Define refraction
• Change of speed when light passes from different mediums
When light passes through the cornea and lens
Light waves from an object ben at the cornea, and ben some more at the lens to form a clear image on the retina
Between the Cornea and Lens which one can change their power
The Ciliaris muscle can make the lens more powerful to allow the eye to see objects up close and make the lens biconvex
When an object comes closer what does the eye need to do
The eye needs more bending power to focus on the object- the becomes more thicker and rounder
Define accommodation
Eyes ability to focus for distant to close objects
What 3 things happen silmultaneously during accommodation
o Lens changes shape (becomes thicker & more spherical)
o Pupil constricts
o Eyes converge
What causes the lens to become more rounder and fatter when the eye focuses on close objects
Ciliary body contracts
What CN brings parasympathetic innervation to the eye muscle
CN III
What muscles causes the eyes to converge and move inwards
Medial rectus
Between the lateral recti and medial recti what muscle is thicker and why
Medial recti
Humans spend a lot more time ding close work
Name the 4 types of refractive errors
Myopia
Hyperopia
Astigmatism
Presbyopia
What is Myopia
Can see images up close but not far away (short sightedness )
In myopia where does the image seen by the eye form
Forms in front of the retina because the eyeball is too long
Does not need accommodation to see objects up close
What are the consequences of myopia
Divergent squint
not using accommodating power that would normally cause your eye to converge, instead it diverges
Symptoms of myopia
Headaches
Not being able to see blackboard
Loss of interest in sports/people
More interested in books
Myopia correction
o Bending power needs to be decreased. o Biconcave lenses o Spectacles o Contact lenses o Laser eye surgery
What is Hyperopia
Cant see objects up close, but can see objects far away
Image forms behind retina as eyeball is too short
What is the consequence of hyperopia
The person starts to use accommodation power automatically- using lens power to see far off things
When looking at close objects all their power is used up
Can lead to convergent squint
Symptoms of Hyperopia
o Symptoms of eyestrain after reading/ working on the computer in a young individual.
o Convergent squint in children/ toddlers
Correction of Hyperopia
o Biconvex glasses alleviates use of glasses for focussing distant objects and ‘rests’ the accomodative power
o Contact lenses
o Laser Eye surgery
What is Astigmatism
up close or far away still blurry
• More bending in axis than the other
• 2 images formed and cannot bend to focus on one
• Can be behind or in front of the retina
Correction of Astigmatism
- Cylindrical lenses- one axis more bent than the other
- Laser eye surgery can also be used to correct the defect.
- Need special contact lenses called toric lenses
What is Presbyopia
- Lens becomes less elastic and more rigid
- Lens is not able to become more spherical when you want to see something up close
- So when the ciliary muscle contracts, it is not as capable as before to change shape
- Usually starts in 5th decade of life.
How is Presbyopia corrected
Biconvex reading glasses
