Topic 9.2 eye Flashcards
1
Q
Describe the cornea
A
- Transparent
- Uniform structure
- Avascular
- Dehydrated
- Covered by 7–10 µm layer tears = smoothens optical irregularities + O2 supply
- Radius of curvature = 7.8 +/- 0.4
2
Q
Describe pupil
A
-1.5-10mm diameter
- In iris
- Diameter controlled by opposing pair of smooth muscle
3
Q
Describe crystalline lens
A
- Suspended + rests on posterior surface of iris
- Thickness = 4mm
- Diameter = 9mm
- Continues to grow as we age = new layers grow over old
4
Q
What determines formation of image on retina?
A
1) Indices of refraction of each component
2) Shape of elements surfaces
- Cornea = 2/3 focusing
- Crystalline lens = 1/3 focusing
5
Q
Describe rod cells
A
- 120 million per retina
- High sensitivity
- Low spatial acuity
- In periphery of retina
- Peak sensitivity = 500nm
- Vision = shades of grey
- Night vision + peripheral vision due to rods
- Diameter = 2 µm
- Far from fovea
- Connected to same nerve fiber
6
Q
Describe cone cells
A
- 6.5 million per retina
- Low sensitivity = 1000x lower than rods
- High spatial awareness
- Concentrated in fovea
1) Blue = 445
2) Green = 535
3) Red = 670 - Sharp vision + color vision due to cones
7
Q
Define photon
A
- Light packets
- Energy = hf
- Absorption occurs = when photons have energy in the ranges that can be absorbed by photosensitive molecules
8
Q
How much of visible incident light reaches retina?
A
- 50% to form an image
- Loss due to scattering in eye
9
Q
How much ligh is absorbed by crystalline lens?
A
300-400 nm
10
Q
Define Gullstrands exact eye
A
- Most complex
- 6 refractive surfaces
11
Q
Define Schematic eye 1
A
- Refractive index within crystalline lens = uniform
- 4 interfaces + 5 refractive indices
- Refractive power of each interface:
Pi + 1 = ni + 1 - ni / Ri + 1 - Total refractive power = 64.34
- Focal length = 20.8 mm
12
Q
Define reduced eye model
A
- Simplest model
- 1 refractive interface
- All distances are relative to single refractive interface
13
Q
What happens when you swin?
A
- Cornea doesn’t have refractive power under water
- Blurred images = focused image beyond retina
- Movement of water = variation of index of reaction
14
Q
Describe accommodation
A
- Ability to control focal length
- Crystalline lens = suspended by ligaments = tension controls curvature
- More tension = flattens + focal length max
- Relaxed = normal spherical shape
- Larger curvature = shorter focal length = clear image
15
Q
Define FP+ NP
A
- Max distance from eye where object form sharp images = ∞
- Nearest distance where objects are clear = 25cm
