Vision 1 Flashcards
What is meant by accomodation?
How much we bend light rays
When is an object considered to have parallel rays of light?
Anything beyond 6 metres
What is meant by refraction?
Bending of light when it passes from one optical medium to another
What are the transparent parts of th eye?
Cornea, lens, aqueous humour and vitreous humour
What is the power of the cornea and the lens?
Cornea - 45 D
Lens - 15 D
What three things comprise accomodation?
Lens shape - becomes thicker and more spherical
Pupil constricts
Eyes converge
What is responsible for the lens becoming thicker?
Ciliary muscle contracts making the ciliary body bulge. Ciliary body contraction is under parasympathetic control.
The lens is normally under stretch
Ciliaris muscle is under control by the third cranial nerve
Which muscle is repsonsible for the constriction of the pupil when looking close up at an object? What is the innervation
Constrictor pupillae
It is the concentric muscle around the border of the pupil. Gets parasympathetic innervation from cranial nerve 3
Why are our medial rectus muscles thicker than our lateral rectus muscles?
Because humans spend a lot of time doing close work and it is our medial retus muscles that are responsible for convergeance
What is the definition of the following?
- Myopia
- Hyperopia
- Astigmatism
- Presbyopia
- Emmetropia
- Myopia – short-sightedness
- Hyperopia – long-sightedness
- Astigmatism – non-spherical curvature of cornea (or lens)
- Presbyopia – long-sightedness of old age
- Emmetropia - perfect vision
What is the cause of myopia?
Most common cause is that the eyeball is too long
What are symptoms of myopia?
Headaches
‘Can’t see blackboard/distant objects’
Infants and preverbal children have a divergent squint
Toddlers have a loss of interest in sports and people - more intersted in books and pictures
Child loses interest in class
What is the treatment for short sightedness?
Spectacles
Contact lenses
Laser eye surgery
What is the cause of hyperopia?
Eyeball is too short or cornea and lens is too flat
Where is the image formed in hyperopia?
Image is formed behind the retina
Why can’t people who are long sighted see objects close up?
They are aalready suing a large portion of their accomodative power at a relatively long distance
Their accomodative power eventually expires at a longer distance than normal
What are symptoms of long sightedness?
Eyestrain after reading/working on the computer in a young individual.
If a toddler has a convergent squint, it needs immediate correction with glasses/lenses to preserve vision in both eyes and prevent a lazy eye
What type of lenses are indicated for people with long sight?
Biconvex
What is an astigmatism?
Surface of the eye has different curvatures in different meridians - bending of light rays on one axis will never be the same as that of the other axis
What type of lens is needed for an astigmatism?
Cylindrical glasses - which are curved only on one axis
What is treatment besides glasses for an astigmatism?
Laser eye surgery
Toric lenses
What is presbyopia, and why does it occur?
Longsightedness of old age
Happens as a result of the lens becoming less mobile and elastic, when the ciliary muscle contracts it is less able to change its shape
When does presbyopia occur?
5th Decade of life
What is corection of presbyopia?
Using boconvex reading glasses
