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BRS Year 2 > Optics of the Visual System > Flashcards

Optics of the Visual System Flashcards

1
Q

Describe the phenomenon of refraction

A

When light travels through one medium to another it changes velocity causing the ray to refract, this makes it bend

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2
Q

What is the equation for calculating index of refraction?

A

Speed of light in a vacuum/speed of light in the medium (n= c/Vn)

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3
Q

What should the index of refraction always be?

A

Greater or equal to 1 because the denominator is always smaller than the numerator

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4
Q

When the light goes from less dense to more dense where does it bend?

A

Towards the normal

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5
Q

How many types of lens are there? What are they called?

A

2 types:
Concave
Convex

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6
Q

Describe the properties of a convex lens

A

Converging lens that causes light rays to come together at a point

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7
Q

Describe the properties of a concave lens

A

A diverging lens that causes light rays to spread away from each other

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8
Q

What is ametropia?

A

Refractive error, there is a mismatch between axial length and refractive power
This means parallel rays don’t fall on the retina and there’s no accomodation

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9
Q

What is the medical name for near sightedness?

A

Myopia

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10
Q

What is the medical name for far sightedness?

A

Hyperopia

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11
Q

What are the types of ametropia?

A

Myopia (nearsightedness)
Hyperopia (farsightedness)
Astigmatism
Presbyopia

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12
Q

What happens to light rays in those with myopia?

A

Light rays converge at a point anterior to the retina

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13
Q

What are the types of myopia? Describe them

A

Axial myopia= excessively long globe

Refractive myopia= excessive refractive power

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14
Q

What type of myopia is more common?

A

Axial myopia

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15
Q

What are symptoms of myopia?

A

Blurred distance vision
Squinting to help overcome this
Headache as a result

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16
Q

How is myopia corrected?

A

A) Diverging lens (negative power)
B) Contact lens
C) Removal of lens to reduce refractive power

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17
Q

What happens to light rays in those with hyperopia?

A

Light rays converge at a focal point posterior to the retina

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18
Q

What are the types of hyperopia? Describe them

A

Axial hyperopia= excessively short globe

Refractive hyperopia= insufficient refractive power

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19
Q

What type of hyperopia is more common?

A

Axial

20
Q

Do those with near sightedness struggle to see near or far objects?

A

Far

21
Q

Do those with far sightedness struggle to see near or far objects?

A

Near

22
Q

Do those with myopia struggle to see near or far objects?

A

Far

23
Q

Do those with hyperopia struggle to see near or far objects?

A

Near

24
Q

What are symptoms of hyperopia?

A

Blurred vision when looking at things up close eg reading,
- worse if there is reduced light, print is weak or if person is tired
Asthenopic symptoms: eye pain, headache in frontal region, burning in eyes, blepharoconjunctivitis

25
Q

What do we call uncorrected hyperopia? And what refraction do they have?

A

Amblyopia

Refraction above 5D

26
Q

How is hyperopia corrected?

A

A) converging lens (positive power)
B) contact lens
C) correction with intraocular lens
D) correction with positive lens and cataract extraction

27
Q

What happens to light rays in astigmatism?

A

Parallel rays focus in 2 focal lines instead of at a singular focal point because the refractive media is not spherical

28
Q

What are symptoms of astigmatism?

A

Asthenopic symptoms: Headache, eye pain
blurred vision
distorted vision
head tilting/turning

29
Q

How is astigmatism treated?

A

Regular astigmatism: Cylinder lens with or without spherical lens (convex/concave)
Irregular astigmatism: rigid cylinder lens, surgery

30
Q

What is the near response triad? Describe it

A

Its how the eye adapts to look at close objects

1) pupillary miosis (by sphincter pupillae) to increase depth of field
2) convergence (by medial recti of both eyes) to align both eyes towards a near object
3) accomodation (by circular ciliary muscle) to increase the refractive power of the lens

31
Q

What is presbyopia?

A

Naturally occuring loss of accommodation

Distant vision intact

32
Q

What is accomodation?

A

Focus on near objects

33
Q

At what age is there usually onset of presbyopia?

A

40 years

34
Q

How is presbyopia corrected?

A 
Convect lenses:
-Reading glasses
-Bifocal glasses
-Trifocal glasses
-Progressive power glasses
Contact lenses:
Given for cosmetic, athletes, occupational, irregular corneal astigmatism, high anisometropia, corneal disease
35
Q

What are the 3 main types of optical correction?

A

Contact lens
Intraocular lens
Surgical correction

36
Q

What are some advantages of contact lens?

A

Higher quality of optical image, influences the size of the image less than spectacles

37
Q

What are some disadvantages of contact lens?

A

They need careful daily cleaning and disinfection, they’re expensive

38
Q

What is the best use of intraocular lens?

A

The replace the cataract crystalline lens
Optical correction of aphakia (no crystalline lens) as they avoid significant magnification and distortion via spectacles

39
Q

What happens when the lens is cleared surgically?

A

Patients loose the ability to accomodate and require reading glasses

40
Q

What happens to the zonules and lens in accomodation?

A

Zonules relax

Lens thickens and increases in their refractive power

41
Q

What is emmetropia?

A

Adequate correlation between axial length and refractive power
Parallel light rays fall on the retina

42
Q

What are complications of contact lenses?

A

Infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis

43
Q

What are types of surgical corrections?

A

Keratorefractive surgery: RK,AK, PRK, LASIK, ICR, thermokeratoplasty

Intraocular surgery: clear lens extraction (with or without IOL). phakic IOL

44
Q

What kind of lens is inserted for the correction of myopia or astigmatism?

A

Intra-collamer lens (ICL)

45
Q

What is IOL?

A

Intra ocular lens

Its the implantation of an artificial lens

BRS Year 2 (110 decks)

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