Refraction and Accommodation Flashcards
Define Refraction
the bending of light when it passes from one optical medium to another to form sharp image on retina
Describe the effect of convex and concave lenses
Convex - bend light together
Concave - bends light away
What parts of the eye refract light
Cornea
Aqueous humor
Lens
What part of the light has the greatest bending power, and why
Cornea - 45D
Biggest difference in objects e.g. air - eye
The lens has a power of 15D but has the capacity to do what
Change its bending power
What happens to the lens when an objects distance decreases
Image rays are more divergent therefore lens needs to become spherical/thicker which increases the bending power so image can reach retina
Define accommodation
The ability to change focus from far off to near objects by changing how much we bend the light rays
What are the three ways the eye does accommodation
Lens thickening
Pupil constricts
Eyes converge
How does accommodation occur in the lens
In close objects the suspensory ligaments relax so lens is no longer being pulled therefore lens flops down becoming thicker and more spherical so can focus clearly on close objects
What innervates the lens accommodation
parasympathetic
How does accommodation of the pupils occur
In close objects the pupils constricts tallow only a few rays from object to pass through pupil
What muscle controls pupil accommodation
Spinchter pupillae
What innervates the spinchter pupillae
parasympathetic
What muscle is used in eyes converging in accommodation
Medial rectus in both eyes helps focus on close up objects as eyes converge to look at it
Why is the medial rectus shorter and ticker than the lateral
We use the medial rectus alot more than the lateral
What innervates the medial rectus for accommodation
Oculomotor nerve - IIIN
What is the name for perfect vision
emmertopia
What is 4 refractive errors
Myopia
Hyperopia
Astigmatism
Prebyopia
Define myopia
Short-sightedness
Distant objects not seen as clear
What occurs in myopia
Image is formed infant of retina as cornea and lens bends the rays to much for the eyeball
What effect does myopia have on close objects
When objects brought close the rays diverge and the bending power is useful as image is formed on retina without much curvature from lens
What is the most common cause of myopia
Long eye ball
What is the symptoms of myopia
Headaches
Divergent squint (infants, toddlers)
Loss of interest in school, sports etc
Complaining of not seeing distant objects
How is myopia corrected
Bending the light ray less so can focus on retina
Possible though biconcave lenses: spectacles, contacts
Laser eye surgery
