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Sample MCQs > Chua Optics Corrections > Flashcards

Chua Optics Corrections Flashcards

1
Q

What is eclipse burn caused by

A

Infrared radiation

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2
Q

When is blue/yellow defect found

A

Retinal dystrophies

Glaucoma
Autosomal dominant optic neuropathy

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3
Q

What does the farsowrth munsell hue 100 contain?

A

84 colour discs that differ only in hue to be arranged in order

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4
Q

Relation of scattering and wavelength of light

A

Inversely proportional - the shorter the wavelenght, the more scattering

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5
Q

How much light does the cornea scattter

A

10%

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6
Q

What can pinhole improve

A

Ametropia of up to 4D

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7
Q

Birefringent materials have

A

2 different refractive indicesW

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8
Q

What is normal stereoacuity

A

60 seconds of arc or better

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9
Q

What are the range of stereoacuity tested by titmus test?

A

3000 to 40 seconds of arc

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10
Q

Frisby test

A

600-15 seconds of arc

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11
Q

TNO test

A

480-15 seconds of arc

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12
Q

Lang

A

1200-550 seconds of arc

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13
Q

Where is the image located in reflection at place surface

A

Erect, virtual, laterally inverted, along a line perpendicular to the reflecting surface
As far behind the surface as the object infront of it

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14
Q

What is the relationship between radius of curvature and focal point of a spherical mirror

A

Focal point is half the radius of curvature

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15
Q

When does total internal reflection occur?

A

When light travels from a medium with a higher refractive index to one with lower index

Thus to visualise the anterior chamber angle, a contact lens with higher refractive index than the cornea needs to be used to overcome the total internal reflection

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16
Q

What wavelength is devaited more by refraction?

A

Shorter wavelenght (blue light)

17
Q

Where are fresnel prisms applied? How do they reduce VA

A

To the back of glasses lenses

Reduce VA by chromatic aberration

18
Q

Which direction does base of prims face to correct a strabismus

A

Opposite direction of the deviation in the deviated eye in vertical strabismus

OR

Opposite direction of the deviation in either eye in horizontal strabismus

19
Q

What happens when decentring a myope lens nasally? inferiorly?

A

NAsal - base out prism induced

Infeiror - base up prims induced

20
Q

What happens when decentring a hyperope lens nasally? inferiorly?

A

Nasal - base in prism induced

Inferior - base down prism induced

21
Q

8PD right esotropia correction split R and L

A

R 4PD base out, L 4PD base out

22
Q

When does f1 = f2

A

When the media on each sid eof lens are the same

23
Q

What is axial magnification?

A

Magnification of depth of image along the optical axis

24
Q

What is angular magnification of a loupe

A

Angle subtended by the image divided by the angle subtended by the same object placed 25cm away from eye

25
Q

What magnification/minification does cyl lens cause?

A

In meridian 90 degrees to axis

26
Q

What is maddox rod used for

A

Distance phoria measurement

Double maddox rod for cyclotorsion

27
Q

Against the rule astigmatism

A

Steeper meridian (more converging power) is at 180 so more plus required at 180 to correct (or weaker plus)
Note: this will be axis 90 on the prescription to act in meridian of 180

28
Q

With the rule astigmatism

A

Steeper meridian at 90 degrees vertical (Axis 180)
So more plus required to correct at 90 (axis 180)

More plus cylinder is at 90 (axis 180) and minus cylinder is at 180 (axis 90)

29
Q

What does the Geneva lens measure do?

A

Calibrated for crown glass
Measures base curve
Can measure lens diameter and thickness

30
Q

What can a focimeter measure

A

Back vertex power
Prism
Axis of cylinder
Optical centre of lens

31
Q

What does light absorption in a tinted lens depend on ?

A

Thickenss of lens - absorption higher in area where lens is thicker

32
Q

What is thickness of anti-reflective coating?

A

Quarter of the wavelength of incident light

Made from metal oxides

33
Q

What do photochromic compounds made of glass vs plastic use

A

Glass - silver halide
Plastic - organic compounds

34
Q

What temporature do photochromic lenses darken more rapidly?

A

Low temperature as heat reduces the effect of light on photochromic lenses

Sample MCQs (20 decks)

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