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Neurology and Neuroscience > Visual System Optics > Flashcards

Visual System Optics Flashcards

1
Q

What is refraction?

A

light passing through one medium to another, the velocity changes

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2
Q

How can the ratio of the speed changes in refraction be written?

A

n = Speed of light in a vacuum / Speed of light in a medium

The denominator will ALWAYS be SMALLER and produce a unitless value greater or equal to 1

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3
Q

What is a mediums index of refraction??

A

The ratio of the speed of light changing from the vacuum to the medium

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4
Q

What happens when light reaches a new medium?

A

Some light reflects some light refracts

Creates an angle of Incidence = angle of reflection

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5
Q

What two types of lenses are there?

A

Convex : converging lens takes light and brings them to a point. positive lens

Concave : diverging leans take lights rays and spreads them outward, negative lens

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6
Q

What is Emmetropia?

A

Adequate correlation between axial length and refractive power

Parallel light fall on the retina with no accommodation

as it should be

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7
Q

What is Ametropia?

A

Refractive error

Mismatch between axial length and refractive power

SO parallel rays do not fall on retina - no accommodation

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8
Q

Give examples of Ametropia?

A
  • near sightedness = myopia
  • Farsightedness = Hyperopia
  • Astigmatism
  • Presbyopia
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9
Q

What is myopia?

A

parallel rays converge at the focal point anterior to the retina

caused by:

  • excessive long globe
  • excessive refractive myopia ( more common )
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10
Q

What are the symptoms of myopia?

A

Blurred distance vision

Squint to improve visual acuity when gazing into distance

Headache

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11
Q

What three methods can be used to correct myopia?

A

Correction with diverging lens

Correction with contact lens

Correction by removing the lens to reduce refractive power of the eye

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12
Q

What is hyperopia?

A

Parallel rays converge at focal point posterior to retina

Caused by:

  • excessive short globe (axial hyperopia, more common)
  • Insufficient refractive power (refractive hyperopia)
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13
Q

What are the symptoms of hyperopia?

A

Visual acuity at near tends to blur relatively early

  • blur could be inability to read to sometime blurring
  • more noticeable if person is tired, light inadquate

Asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis

Amblyopia – uncorrected hyperopia > 5D

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14
Q

How to treat hyperopia?

A

Correcting with converging lens
or correction with a positive lens. + cataract extraction

Correction with contact lens
Correction with intraocular lens ( can be in anterior or posterior chamber )

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15
Q

What is Astigatism?

A

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

Hereditary

Due to refractive media not spherical which changes refraction along one meridian than along the meridian perpendicular to it

  • 2 focal points (punctiform object is represented as 2 sharply defined lines)
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16
Q

What are the symptoms of astigmatism?

A

Asthenopic symptoms
Blurred vision
disrotrion of vision
head tilting and turning

17
Q

How to treat astigmatism?

A

to treat regular astigmatism : cylinder lenses or convex/concave

Irregular astigmatism : rigid cylinder lenses, surgery

18
Q

What are asthenopic symptoms?

A

headache

eyepain

19
Q

What is the near response triad?

A

The pathways that mediate near vision

These are three simultanoues pathways

–> pupillary miosis - pupil constricts increasing the depth of field of the optics of the eye

  • this is mediated by the contraction of the circular sphincter pupillae muscles in iris

–> Convergence - medial recti both align both eyes towards a near object

–> accommodation - lens increases refractive power to focus on near object through circular ciliary muscle

20
Q

What if eyes have a shallow depth of field?

A

Lose focus easily even with slight object movement

when viewing a near object

21
Q

What is Presbyopia?

A

Naturally occuring loss of accommodation

onset from 40+

corrected by reading glasses

convex

to increase refractive power of eye

22
Q

Why is the age of onset for presbyopia 40?

A

As we age natural lens looses its elasticity and so ability to accommodate is lost

Vision is not as clear when at near

23
Q

What types of convex glasses can be given for presbyopia?

A

reading
bifocal
trifocal
progressive power glasses

24
Q

What spectacle glasses can be given for presbyopia correction?

A

Monofocal
Spherical
Cylindrical
Multifocal lenses

25
Q

Why may contact lenses be given?

A

higher quality of optical image, less influence on size of retinal image than spectacle image,

can be a cosmetic decision, atheltic activities, occupations, irregular corneal astigmatism, high anisometropia, corneal disease

26
Q

What are the disadvantegs to contact lenses?

A

careful daily cleaning and disinfection

expense complication

infectious keratitis

giant papillary conjuctivitis

corneal vascularization

severe chronic conjuctivitis

27
Q

Why may intraocular lenses be considered?

A

replacement of catarect crystalline lens

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

28
Q

What types of surgeries are avaible for correction?

A

Keratorefractive

Intraocular surgery

29
Q

Give types of keratorefractive surgeries?

A 
RK
AK
PRK
LASIK
IC
thermokeratoplasty
30
Q

Give types of intraocular surgery?

A

clear lens extraction with or wihtout IOL

Phakic IOL

31
Q

What are the steps used in surgical correction for LASIK?

A
  • Initial cutting of corneal flap
  • Cutting of corneal flap
  • Flipping of corneal flap
  • Photorefractive treatment (laser)
  • Corneal stroma reshaped post laser
  • Corneal flap back in position
  • Treatment completed
32
Q

What is ICL surgery?

A

Intra - collamer lens

inserted for the correction of myopia and astigmatism

33
Q

Why will a px need reading glasses after clear lens extraction + IOL treatment?

A

same as cataract extraction but also implantation of intra ocular artificial lens

the px loses accommodation so will need glasses

34
Q

Which of the following is false for myopia?

A) May be associated with large globe
B) Light ray converges behind the retina
C) May be associated with increased corneal curvature
D) Unable to see objects clearly at distance without glasses or other optical correction

A

= false is B

35
Q

In accommodation which one of the following does not take place?:

A) Relaxation of Circular Ciliary Muscle
B) Relaxation of Zonules
C) Thickening of Lens
D) Increase of Lens Refractive Power

A

Relaxation of circular ciliary muscle does not happen

Neurology and Neuroscience (21 decks)

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