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Z YEAR 2 BRS NEURO > Visual System Optics > Flashcards

Visual System Optics Flashcards

1
Q

What happens in refraction?

A

As light goes from one medium to another, the velocity changes

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2
Q

Do all substances have an index of refraction?

A

Yes

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3
Q

How do you figure out index of refraction?

A

speed of light in vacuum / speed of light in medium (must be less than 1 or equal to)

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4
Q

What happens as light goes from one medium into another?

A

the path changes, some of light reflects of the boundary and some light refracts through the boundary

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5
Q

What is the angle of incidence equal to?

A

angle of reflection

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6
Q

What changes depending on direction fo light?

A

Angle of Incidence > or < the Angle of refraction depending on the direction of the light

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7
Q

What are the two types of lenses?

A
  1. Convex

2. Concave

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8
Q

What is a convex lens?

A

Converging lens (convex) takes light rays and brings them to a point

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9
Q

What is a concave lens?

A

A diverging lens (concave) takes light rays and spreads them outward

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10
Q

What is an application of a converging lens?

A

A camera uses a lens to focus an image on photographic film

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11
Q

What happens in emmetropia?

A
  • Adequate correlation between axial length and refractive power
  • Parallel light rays fall on the retina (no accommodation)
  • perfect eye
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12
Q

What is ametropia (refractive error)?

A
  • Mismatch between axial length and refractive power

- Parallel light rays don’t fall on the retina (no accommodation)

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13
Q

What are types of ametropia?

A
  1. Near-sightedness (Myopia)
  2. Farsightedness (Hyperopia)
  3. Astigmatism
  4. Presbyopia
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14
Q

What is myopia? What are the different types?

A
  • Parallel rays converge at a focal point anterior to the retina
  • Etiology : not clear , genetic factor
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15
Q

What are the symptoms of myopia?

A
  1. Blurred distance vision
  2. Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
  3. Headache
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16
Q

What is hyperopia?

A

-Parallel rays converge at a focal point posterior to the retina
Etiology : not clear, inherited

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17
Q

What are the symptoms of hyperopia?

A
  1. visual acuity at near tends to blur relatively early
  2. asthenopic symptoms
    - eyepain
    - headache in frontal region
    - burning sensation in the eyes
    - blepharoconjunctivitis
  3. Amblyopia – uncorrected hyperopia > 5D
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18
Q

What is the blurriness like in hyperopia?

A
  1. nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur
  2. blurred vision is more noticeable if person is tired , printing is weak or light inadequate
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19
Q

What is astigmatism?

A

Parallel rays come to focus in 2 focal lines rather than a single focal point

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20
Q

Where does astigmatism come from?

A

Hereditary

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21
Q

What is the cause of astigmatism?

A

refractive media is not spherical–>refract differently along one meridian than along meridian perpendicular to it–>2 focal points (punctiform object is represent as 2 sharply defined lines)

22
Q

What is happening in astigmatism?

A
  • The two meridians (I and II) are perpendicular to each other
  • A punctiform object (o) is represented as a line segment Y0 And Y1 at the focal points of the two meridians
  • Midway between these two focal points is the “circle of least confusion” (Kr), the location with the least loss of image definition
23
Q

What are the symptoms of astigmatism?

A
  1. Asthenopic symptoms (headache , eyepain)
  2. blurred vision
  3. distortion of vision
  4. head tilting and turning
24
Q

What is the treatment of regular astigmatism?

A

cylinder lenses with or without spherical lenses (convex or concave), Sx

25
Q

What is the treatment of regular astigmatism?

A

igid cylinder lenses, surgery

26
Q

What is the near response trio?

A
  1. Pupillary Miosis (Sphincter Pupillae) to increase depth of field
  2. Convergence (medial recti from both eyes) to align both eyes towards a near object
  3. Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision
27
Q

What is presbyopia? How is it treated?

A
  1. Naturally occurring loss of accommodation (focus for near objects)
  2. Onset from age 40 years
  3. Distant vision intact
  4. Corrected by reading glasses (convex lenses) to increase refractive power of the eye
28
Q

What is the treatment of presbyopia?

A
  • convex lenses in near vision
  • Reading glasses
  • Bifocal glasses
  • Trifocal glasses
  • Progressive power glasses
29
Q

What are different types of spectacle lenses of presbyopia correction?

A
  1. Monofocal lenses : spherical lenses , cylindrical lenses

2. Multifocal lenses

30
Q

What are contact lens in presbyopia correction?

A

-higher quality of optical image and less influence on the size of retinal image than spectacle lenses
indication
-cosmetic , athletic activities , occupational , irregular corneal astigmatism , high anisometropia , corneal disease

31
Q

What are the disadvantages of contact lenses?

A
  1. careful daily cleaning
  2. disinfection
  3. expense
32
Q

What are the complications of contact lenses?

A
  1. infectious keratitis
  2. giant papillary conjunctivitis
    3, corneal vascularization
  3. severe chronic conjunctivitis
33
Q

What are intraocular lenses?

A
  • replacement of cataract crystalline lens

* give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses

34
Q

What is Keratorefractive surgery

A

RK, AK, PRK, LASIK, ICR, thermokeratoplasty

35
Q

What is intraocular surgery?

A

clear lens extraction (with or without IOL), phakic IOL

36
Q

What is the process of surgical correction?

A
  1. Pre operative eye
  2. Initial cutting of corneal flap
  3. Cutting of corneal flap
  4. Flipping of corneal flap
  5. Photorefractive treatment (laser)
  6. Corneal stroma reshaped post laser
  7. Corneal flap back in position
  8. Treatment completed
37
Q

When is Staar intra-collamer lens (ICL) inserted?

A

for the correction of myopia and astigmatism, lens on top of normal lens, but sooner or later the natural lens becomes more opaque so will have to remove both lenses before cataract operation

38
Q

What is clear lens extraction and intraocular lens?

A
  • IOL: Intra ocular lens.
  • Same as cataract extraction
  • Implantation of artificial lens
  • Lose accommodation (patient will need reading glasses)
  • Lens softer, coo expectation higher than regular cataract surgery
39
Q

What are the causes of myopia?

A
  • excessive long globe (axial myopia) : more common

* excessive refractive power (refractive myopia)

40
Q

What is the treatment of myopia?

A
  1. Correction with diverging lenses (negative lenses)
  2. Correction with contact lens
  3. Correction by removing the lens to reduce refractive power of eye
41
Q

What are the causes of hyperopia?

A

•excessive short globe (axial hyperopia) : more common
•insufficient refractive power (refractive hyperopia)
-With high hyperopia, hard to see objects near, and myopia always be always be able to see near and read so important in children

42
Q

What is the treatment with hyperopia?

A
  1. Correction with converging (positive lenses)
  2. Correction with positive lens + cataract extraction
  3. Correction with contact lens
  4. Correction with intraocular lens
43
Q

How is pupil constriction mediated in near response triad?

A

contraction of the circular Sphincter Pupillae Muscle within the Iris

44
Q

Why is a larger depth of field better in near response triad?

A

-the eye optical system is able to maintain clear focus over a certain range of viewing distances, even without relying on accommodation
-Eyes with shallow depth of field loose focus easily, even with the slightest object movement,
when viewing a near object

45
Q

What happens in convergence in the near response triad?

A

both eyes adduct medially at the same time,

to align both eyes towards a near object

46
Q

How is convergence in the near response triad mediated?

A

mediated by the simultaneous contraction of medial rectus extra-ocular muscles from both eyes

47
Q

Why is accommodation important in the near response triad?

A

the lens accommodates,

thus increasing the refractive power required to focus on a near object

48
Q

What happens to our lens over time?

A

natural lens looses its elasticity

49
Q

What is the problem with intraocular lenses?

A

monofocal lenses, so patient loses possibility to accommodate so help long distance but reading need help/spectacles

50
Q

What is in a cataract surgery?

A
  1. Remove natural lens by ultrasound tip which breaks and sucks up natural lens
  2. Then place artificial lens same position as natural lens

Z YEAR 2 BRS NEURO (21 decks)

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