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Sample MCQs > Chua 3 > Flashcards

Chua 3 Flashcards

1
Q

What is field of view in direct vs indirect ophthalmoscope?

Magnification?

A

Direct 6 degrees
Indirect 25 degrees

Direct 15x
Indirect 13D - 5x, 20D - 3x (60D/power of lens)

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2
Q

What affects field of view in indirect ophthalmoscopy?

A

Size of observer’s pupil
Diameter of condensing lens - larger = larger field of view
Power of condensing lens - stronger lens = larger field of view

Size of patient’s pupil affects field of illumination

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3
Q

What lenses are used to reduce aberration in indirect?

A

Aspheric lenses

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4
Q

Where is the image formed in indirect?

A

AT/near second principal focus of condensing lens

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5
Q

How does laser spot magnification change with strength of lens?

A

Laser spot magnification increases with stronger lenses

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6
Q

What happens to image size in emmetrope / myope / hypermetrope when lens moved towards patient eye

A

Emmetrope - no change in image size

Myope - larger image size as lens moved away from patient eye

Hypermetrope - smaller image size as lens is moved away from patients eye

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7
Q

Where is image located in indirect of myopic eye? Hypermetropic?

A

Myopic - within second principal focus of condensing lens

Hypermetropic - outside of second principal focus of condensing lens

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8
Q

What can with movement on retinoscopy indicate? Against movement?

A

Against is always myopia

With can be myopia if myopia is less than dioptric value of working distance (working distance needs to be subtracted)

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9
Q

When is the neutral point reached?

A

When paitent’s far point conincides with the observer’s nodal pointW

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10
Q

What mirror systems are used for retinoscopty?

A

Plane and CONCAVE mirror

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11
Q

What does the keratometer do to negate ocular movement?

A

Double central image

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12
Q

What are magnification / field of view / laser spot magnification of 20D, 28D, 78D, 90D

A

Magnification, decreases with stronger lens
20D - 2,97
28D - 2.16
78D - 0.87
90D - 0.72
Superfield - 0.72

Field of view
20D - 46
28D - 55
78D - 73 (larger diameter than 90D)
90D - 69
Superfield 120

Laser spot increases with increasing power

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13
Q

How do con helmholz keratometer and javal schiotz keratometer differ

A

vOn-helmhOltz - fixed Object size, image size adjusted to measure the corneal curvature

Uses parallel glass plates X and Y to double the image to overcome eye movmeents
Angle of inclination varied by observer until edges of two images touch

javal schIotz - fixed image size - object size varied to measure corneal cruvatre
Consists of pair of mires (small latterns with coloured windo a and B mounted on curved side arms
Doubling of image through Wollaston prism in viewing telescope
Space between mires is object size
Each step of mire is equivalent to 1D

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14
Q

What is a slit lamp made up of?

A

Low powered binocular compound microscope with lighting systema nd microscope on common focal plant

Prisms to invert image and shorten

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15
Q

How does the slit lamp adjust magnification

A

Galilean telescopes of different powers incorportated into slit lamp

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16
Q

What is diffuse illumination

A

Full height, broad, low brightness, slightly out of focus beam onto ocular surface from side
TO inspect anterior capsule

17
Q

What is direct focal illumination

A

Direct oblique medial beam accurately focussed on part under inspection

18
Q

Specular reflection? What is it good for?

A

Gaze directed to bisect angle between axis of illumination and observation

Corneal endothelium and anterior lens capsule can be examined this way

19
Q

Sclerotic scatter

A

Slit beam is directed onto the limbus from side, whole limbal area glows
Decentration of slit lamp
Light scattered all around cornea

20
Q

Retro illumination

A

Iris atrophy
Light reflected from choroid seen

21
Q

Lateral illumination

A

LIght directed to the side of lesion - some of light enters the lesion causing it to glow internally

22
Q

What filter for examining vitreous

A

Blue/green
Low wavelength light scattered more
Less light reflected from fundus

23
Q

What is the Hruby lens? Power? Image?

A

Plano concave lens -58.6 power
Held with concave surface towards eye

Virtual erect diminished image

Image formed within the eye

24
Q

Power of eye, cornea, lens

A

Power of eye +58.6

Cornea 43.1
LEns 19.1 (15 in situ)

25
Q

What is panfunduscope lens? Field of view?

A

High power convex contact lens

Acts as condensing lens
Forms real, diminished, inverted image of fundus withing spherical glass element
This flatens the image and redirects light towards the observer

Very wide field of view 120 degrees
Whole fundus as far as equator may be seen in one view

26
Q

What does specular microscopy depend on?

A

Structures with different refractive indices relfex light at different angles

Angle between axes of illumination and observation is critical

27
Q

What is the correction for astimatism in goldmann tonometer?
Only for large astigmatism

A

MEasurement is made at 43 degrees to the flatter meridian

WTR astigmatis lower IOP 1mmHg/4D
Agaisnt the rule higher IOP 1mmHg/4D

28
Q

What pachymeter is more precise?

A

Ultrasound

Only works when perpendicular to posterior surface of cornea

29
Q

How does OCT work? REsolution?

A

Cross sectional 2D image of retina
Resolution 10uM
Infrared light 643nm - split into reference beam reflected off mirror, sample beam reflected off retina - temporal differences between two reflections result in interference signal

30
Q

What is the scheiner double pinhole principle

A

Parallel rays of light from distant object reduced to two pencils of light - form single focus on retina if emmetropic
Two spots if ametropic

Adjusting position of object until one focus is seen determines far point and refractive error can be determined

31
Q

What is used for photoscreening of children?

A

Polaroid camera with flash
Alteration of red reflex which occurs in presence of refractive error, strab, or media opacity is captured on film
Can screen for refractive amblyopia

Sample MCQs (20 decks)

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