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The Nervous System: The eye > Refraction and Accommodation > Flashcards

Refraction and Accommodation Flashcards

1
Q

Define Refraction

A

the bending of light when it passes from one optical medium to another to form sharp image on retina

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2
Q

Describe the effect of convex and concave lenses

A

Convex - bend light together

Concave - bends light away

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3
Q

What parts of the eye refract light

A

Cornea
Aqueous humor
Lens

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4
Q

What part of the light has the greatest bending power, and why

A

Cornea - 45D

Biggest difference in objects e.g. air - eye

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5
Q

The lens has a power of 15D but has the capacity to do what

A

Change its bending power

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6
Q

What happens to the lens when an objects distance decreases

A

Image rays are more divergent therefore lens needs to become spherical/thicker which increases the bending power so image can reach retina

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7
Q

Define accommodation

A

The ability to change focus from far off to near objects by changing how much we bend the light rays

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8
Q

What are the three ways the eye does accommodation

A

Lens thickening
Pupil constricts
Eyes converge

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9
Q

How does accommodation occur in the lens

A

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

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10
Q

What innervates the lens accommodation

A

parasympathetic

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11
Q

How does accommodation of the pupils occur

A

In close objects the pupils constricts tallow only a few rays from object to pass through pupil

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12
Q

What muscle controls pupil accommodation

A

Spinchter pupillae

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13
Q

What innervates the spinchter pupillae

A

parasympathetic

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14
Q

What muscle is used in eyes converging in accommodation

A

Medial rectus in both eyes helps focus on close up objects as eyes converge to look at it

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15
Q

Why is the medial rectus shorter and ticker than the lateral

A

We use the medial rectus alot more than the lateral

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16
Q

What innervates the medial rectus for accommodation

A

Oculomotor nerve - IIIN

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17
Q

What is the name for perfect vision

A

emmertopia

18
Q

What is 4 refractive errors

A

Myopia
Hyperopia
Astigmatism
Prebyopia

19
Q

Define myopia

A

Short-sightedness

Distant objects not seen as clear

20
Q

What occurs in myopia

A

Image is formed infant of retina as cornea and lens bends the rays to much for the eyeball

21
Q

What effect does myopia have on close objects

A

When objects brought close the rays diverge and the bending power is useful as image is formed on retina without much curvature from lens

22
Q

What is the most common cause of myopia

A

Long eye ball

23
Q

What is the symptoms of myopia

A

Headaches

Divergent squint (infants, toddlers)

Loss of interest in school, sports etc

Complaining of not seeing distant objects

24
Q

How is myopia corrected

A

Bending the light ray less so can focus on retina

Possible though biconcave lenses: spectacles, contacts

Laser eye surgery

25
Q

How does laser eye surgery work in correcting myopia

A

Flatten out stroma and reshape cornea decreasing power

26
Q

Define hyperopia

A

Long sightedness -close objects not seen as clear

27
Q

What occurs in hyperopia

A

Image is formed behind the retina as use up accommodation power to objects far away, making lens thicker, so when looking at objects up close they appear hazy as al lens power has been used up

28
Q

What is the common cause of hyperopia

A

Eyeball to short or cornea

Lens to flat

29
Q

What is the symptoms of hyperopia

A

Convergent squint (children, toddlers)

eyes strain after reading

30
Q

How is hyperopia corrected

A

Make lens fatter so can bend light rays more and focus on the retina

31
Q

What is used to help correct hyperopia

A

Biconvex glasses - focus on distant objects and rest accommodative power

contact lenses

Laser eye surgery

32
Q

Define Astigmatism

A

Non spherical curvature of cornea so close and distant object appear hazy

33
Q

What occurs in astigmatism

A

Surface has different curvature in different merdians so the bending of light rays along one axis will never be the same as another axis therefore image formed is hazy no matter the difference

34
Q

How is astigmatism corrected

A

Cylindrical (special) glasses - curved only in one axis

Toric lenses

Laser eye surgery

35
Q

Define presbyopia

A

Long sightedness occurring in old age (5th decade)

36
Q

What occurs in presbyopia

A

With age the lens fibres are less elastic so can no longer to floppy movement as well so when ciliary muscles contract its not as capable to change shape

37
Q

How is presbyopia corrected

A

Biconvex - reading glasses

38
Q

What is OD and OS

A

OD - Right eye

OS - Left eye

39
Q

What is CYL and when is it prescribed

A

Cylinder correction

prescribed for astigmatism

40
Q

What is also included with CYL

A

AXIS

41
Q

What does SPH stand for and when is it prescribed

A

Spherical contraction - the amount of lens power

Myopia/hyperopia

42
Q

What is BC and DIA

A

Base curve 8-10cm

Diameter of lens

The Nervous System: The eye (11 decks)

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