How we see 1

Question 1

What is refraction?

Answer 1

Bending of light when it passes from one optical medium to another

when those optical mediums have different refractory indexes

Question 2

In what parts of the eye is light refracted?

Answer 2

Cornea

Aqueous humor

Lens

Vitreous humor

Question 3

What is the refractive power of the cornea and lens of the eye?

Answer 3

Cornea = 45D (dioptres)

Lens = 15D but variable (this is what we focus with)

Question 4

As an object comes closer. How must the refractive power of the eye change in order to maintain a clear image?

Answer 4

More bending power is needed by the eye

To do this - the lens thickens thus becoming more powerful

Question 5

What is the image on the retina like compared to what we see?

Answer 5

Image on retina is the superimposition of the object

Question 6

What is accommodation?

Answer 6

Our eyes can change its focus for objects 20cm to infinity

The changes occurring in both eyes as it changes focus from a distant to a close object is called as accommodation

3 factors:

1. Lens shape
2. Pupil constriction/dilation
3. Eye convergence/divergence

Question 7

What is happening here and why?

Answer 7

Thickening of the lens to Increase refractive power (closer focus)

How it works:

• Parasympathetic stimulation causes Ciliary body to contract
  
  • (When it does this it weirdly bulges out)
• Suspensory ligaments become lax ∴ less stretching tension on the lens so it thickens

Question 8

Describe why our pupils constrict when objects move closer to us

Answer 8

Object close up ∴ need sharp focus

To sharpen focus, our pupil constricts to only let a few rays (those from the object) through

Question 9

Describe how our pupils constrict to focus on something close

Answer 9

Pupillary constrictor (sphincter pupillae) is a concentric muscle around the border of the pupil

Parasympathetic stimulation (via IIIn) causes it to constrict - decreasing the circumference of the pupil

Question 10

Describe why and how our eyes converge to focus on an object that’s close up

Answer 10

Pretty simple. You turn your eyes in when looking at something close up

We use our medial rectus muscles of both eyes to converge. (IIIn of both sides)

These are thicker than the lateral rectus because our eyes converge often

Question 11

What are the spicy names for short & long-sightedness and normal vision

Answer 11

Myopia = short-sightedness

Hyperopia = long-sightedness

Presbyopia = long-sightedness with old age

Emmetropia = perfect vision

Question 12

What is astigmatism?

Answer 12

non-spherical curvature of cornea (or lens)

Question 13

Describe how Myopia happens

Answer 13

Most common cause = eyeball is too long

Basically, the total refractive power of the cornea & lens is too much for that eyeball so the image focuses in front of the retina

When the object is brought really close up, the image is formed on the retina without the lens needing to change shape - thus the person can focus on close up objects (hence short-sighted)

Question 14

How would myopia present?

Answer 14

Complaints of:

• Not being able to see distant objects (no shit)
• Headaches
• Lack of interest in sports
• Loss of interest in class
• Increased interest in books/pictures (stuff thats close up)

Signs:

• Divergent squint
  
  • ^ in Infants/pre-verbal children

Question 15

What type of lens will correct myopia?

Answer 15

Biconcave

Spectacles or contact lenses

These reduce total refractive power

Laser eye surgery is other option

Question 16

What causes Hyperopia?

Answer 16

Hyperopia (far-sightedness) caused by the eyeball ‘being too short’

Refractive power of eye is too low, so focal point is behind the retina

Explanation:

The person will begin using the accommodative power of their eyes at a further distance than a normal person (so will be thickening lens at a distance when normal people would not be)

As the object gets closer, the eyes will be unable to accommodate it at a much greater distance than normal

Question 17

How does Hyperopia present?

Answer 17

Complaints of:

• Eye strain after reading/using computers etc (close up shit)
• Struggling to read and all that

Signs:

• Convergent squint (in the youngers)
• May have a lazy eye

Question 18

How is hyperopia treated?

Why is swift treatment important?

Answer 18

Biconvex glasses / contacts

Laser eye surgery

Children with Hyperopia need immediate correction with glasses/lenses to preserve vision in both eyes and prevent a “lazy eye”.

Question 19

How would astigmatism present?

What causes it?

Answer 19

Complaints of:

• Distant and close objects out of focus (hazy)

Cause:

• Surface of cornea (or lens) has different curvatures in different meridians (ie not spherical)
  
  • Light rays in one axis are bent more than light rays in the other

Question 20

What are the options for the treatment of astigmatism?

Answer 20

Glasses:

• Cylindrical glasses - which are curved in only one axis

Contact lenses:

• ‘Toric lenses’

Laser eye surgery - can also be used

Question 21

What causes presbyopia?

Answer 21

With age the lens gets less mobile/elastic - thus won’t change shape as easily/well

Accommodation to focus on nearby objects is impacted - reading etc becomes harder

Corrected using Reading glasses (Biconvex)