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Neurology and Neuroscience > Vision2 > Flashcards

Vision2 Flashcards

1
Q

What happens to light when it goes from 1 medium to another

A

Velocity changes
, the path changes!

Some of the light reflects off the boundary and some of the light refracts through the boundary.

Angle of incidence = Angle of Reflection

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

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2
Q

What is refractive index or index of refraction

A

The denominator in this case will ALWAYS be smaller and produce a unitless value greater or equal to 1. This value is called the new medium’s INDEX OF REFRACTION, n.

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3
Q

What are the two basic lens

A

Convex and concave

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4
Q

What is convex lens

A

A converging lens (convex) takes light rays and brings them to a point.
has a real focal point eg (magnifying glass)

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5
Q

What is a concave lens

A

A diverging lens (concave) takes light rays and spreads them outward.
Virtual focal point behind lens

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6
Q

What is Emmetropia

A

Adequate correlation between axial length and refractive power

Parallel light rays fall on the retina (without accommodation)

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7
Q

What is the name for refractive error

A

Ametropia (refractive error)
Mismatch between axial length and refractive power
Parallel light rays don’t fall on the retina without accomodation

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8
Q

What are the different types of Ametropia

A

Near-sightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia

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9
Q

What happens in Myopia

A

Parallel rays converge at a focal point anterior to the retina

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10
Q

What is the etiology of Myopia

A

not clear , genetic factor

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11
Q

What are the causes of myopia

A

excessive long globe (axial myopia) : more common
excessive refractive power (refractive myopia)

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12
Q

What are the symptoms of myopia

A

Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache

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13
Q

How do you correct myopia

A

. Correction with diverging lenses (negative lenses)
b. Correction with contact lens
c. Correction by removing the lens to reduce refractive power of the eye

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14
Q

What is hyperopia

A

Parallel rays converge at a focal point posterior to the retina

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15
Q

What is the etiology of hyperopia

A

not clear, inherited

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16
Q

What are the causes of hyperopia

A

excessive short globe (axial hyperopia) : more common
insufficient refractive power (refractive hyperopia)

17
Q

How do you correct hyperopia

A

a. Correction with converging (positive lenses)
b. Correction with positive lens + cataract extraction
c. Correction with contact lens
d. Correction with intraocular lens

18
Q

What is astigmatism

A

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

19
Q

What is the etiology of Atigmatism

A

Etiology : heredity

20
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)

21
Q

Physics behind astigmatism

A
22
Q

What is the circle of least confusion and where is it seen

A

the location with the least loss of image definition. Midway between these two focal points.
Seen in astigmatism

23
Q

What are the symptoms of stigmatism

A

Asthenopic symptoms (headache , eyepain)
blurred vision
distortion of vision
head tilting and turning (to compensate)

24
Q

What is the treatment of astigmatism

A

Regular astigmatism : cylinder lenses with or without spherical lenses (convex or concave), Sx
Irregular astigmatism : rigid cylinder lenses, surgery

25
Q

What is the near response triad

A

near vision is mediated by three separate,
but simultaneous pathways.
This is known as the Near Response Triad

26
Q

What happens in near response triad

A

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

27
Q

What happens in pupillary miosis in the near response triad

A

In Pupillary Miosis, the Pupil constricts,
increasing the depth of field of the optics of the eye.

This is mediated by the contraction of the circular Sphincter Pupillae Muscle within the Iris.

With larger depth of field,
the eye optical system is able to maintain clear focus over a certain range of viewing distances,
even without relying on accommodation.

28
Q

What happens in convergence in near response triad

A

In Convergence, both eyes adduct medially at the same time,
to align both eyes towards a near object.

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

29
Q

What happens in accomodation in near response triad

A

In accommodation, the lens accommodates,
thus increasing the refractive power required to focus on a near object.

30
Q

what is prebyopia

A

Naturally occurring loss of accommodation (focus for near objects)
Onset from age 40 years
Distant vision intact

31
Q

How is presbyopia corrected

A

Corrected by reading glasses (convex lenses) to increase refractive power of the eye
Reading glasses
Bifocal glasses
Trifocal glasses
Progressive power glasses

32
Q

What are the different types of Optical correction

A

Spectacle lenses
Monofocal lenses : spherical lenses , cylindrical lenses
Multifocal lenses

Contact lenses
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

Intraocular lenses
Replacement of cataract crystalline lens
Gives best optical correction for aphakia

33
Q

What are the disadvantages of contact lens

A

disadvantages : careful daily cleaning and disinfection , expense

34
Q

What are the complications of conjunctivites

A

infectious keratitis
giant papillary conjunctivitis ,
corneal vascularization
severe chronic conjunctivitis

35
Q

What are the advantage of intraocular lens

A

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

36
Q

What are the disadvantages of intraocular lenses

A
37
Q

What are the other types of surgical corrections

A

Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty
Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL

38
Q

Which statement 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

B) Light ray converges behind the retina

39
Q

In accommodation, which one of the following events 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

A) Relaxation of Circular Ciliary Muscle

Neurology and Neuroscience (6 decks)

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