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Optics > 14. Instruments > Flashcards

14. Instruments Flashcards

1
Q

Principles of direct ophthalmoscope

A

o Lenses which focus light form a bulb onto a mirror  real image formed (just below corneal reflection so it does not lie over the visual axis)
o Mirror reflects light in a diverging beam to illuminate the patients eye
o Light reflected back by the retina into observers eyeF

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2
Q

Field of view

A

o Governed by hole in mirror or the observer’s pupil
o Large when dilated (obviously)
o Becomes larger as the distance between patient and observer DECREASES

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3
Q

Image formed by a direct ophthalmoscope

A

ERECT

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4
Q

direct ophthalmoscope and astigmatism

A
  • Unable to correct for astigmatism (only spherical lenses incorporated)
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5
Q

Direct ophthalmoscope and myopic eyes

A

Field of view: small
Size of image: large
Emmetropic observer: converging light –> concave lens

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6
Q

Direct ophthalmoscope and hypermetropic eyes

A

Field of view: large
Size of image: small
Emmetropic observer: diverging light –> convex lens

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7
Q
A
  • Observer’s retina = L
  • Patients retina = I
  • Image formed in observer’s eye = A
  • Principal plane = J
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8
Q
A
  • Observer’s retina = E
  • Patients retina = B
  • Image formed in observer’s eye = AF
  • Principal plane = C
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9
Q
A
  • Observer’s retina = D
  • Patients retina = A
  • Image formed in observer’s eye = IL
  • Principal plane = A
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10
Q

indirect ophthalmoscope

A
  • Used with powerful CONVEX lens – must be aspheric to minimise aberrations
  • Condensing lens held at arms length, image viewed at 40-50cm distance
  • Binocular indirect has +2.0D in prismatic eye piece-viewer does not need to accommodate
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11
Q

indirect ophthalmoscope image formed

A

real, vertically and horizontally inverted, situated around 2nd principle focus

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12
Q

indirect ophthalmoscope field of illumination

A

is limited by: size of subjects pupil (dilated = larger), refractive status

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13
Q

indirect ophthalmoscope field of view

A

size of observer’s pupil, apparatus of condensing lens

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14
Q
A

indirect ophthalmoscope
* D: 2nd principle focus
* G: 1st principle focus

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15
Q

Indirect ophthalmoscope: myopia

A

field of illumination: largest
position of image: inside second prinipal focus
image size as lens moved away: increases

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16
Q

Indirect ophthalmoscope: normal

A

field of illumination: normal
position of image: at second principal focus

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17
Q

Indirect ophthalmoscope: hypermetropia

A

field of illumination: smallest
position of image: outside second principal focus
image size as lens moved away: decreasesl

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18
Q

linear magnification

A

= focal length of the condensing lens / distance between nodal point and the retina of subjects eye

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19
Q

linear magnification example 13D at 15mm

A

o if the distance is 15mm, the linear magnification is the focal length x15 mm
o For a 13D (f = 75mm) = x5 linear magnification (75/15=5)

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20
Q

angular magnification

A

o = power of subjects eye in D / power of condensing lens in D

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21
Q

direct vs indirect ophahloscope

A
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22
Q

retinoscopy

A

accurate objective measurements of the refractive state of an eye

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23
Q

3 stages of retinoscopy

A

o Illumination stage: light directed into the patients eye to illuminate the retina
o Reflex stage: image of the illuminated retina is formed at the patient’s far point
o Projection stage: noting the behaviour of the luminous reflex by the observer in the patients pupil

24
Q

illumination stage

A

Light is reflected onto the patients fundus using a plane or concave lens
Plane = with movement
Concave = against movement

25
Q

reflex stage

A

An image of the illuminated retina is formed at the patient’s far point

26
Q

projection stage

A

Observers views the image of the illuminated retina as a reflex in the patients pupil at a convenient distance
Point of reversal or neutral point of retinoscopy is reached when the patients far point coincides with the observers nodal point  no movement is observed

27
Q

Placido’s disc

A
  • Used to check the general shape of the cornea
  • Examiner looks through the disc with a convex lens  can see the regularity or distortion of the cornea
  • Shorter the radius of curvature  steeper meridian  smaller the reflected image
28
Q

keratometer

A
  • Measure the radius of curvature of a central zone of the cornea approximately 3 to 4mm in diameter
  • Radius of curvature of the axial zone of the emmetropic eye is 7.8mm
29
Q

what is constant in all keratometers

A

u (distance of object from mirror) is fixed in all

30
Q

what moves in keratometers

A

o Von Helmholtz: fixed = object, adjusted = image size
o Javal Schiotz: fixed = image, adjusted = object size

31
Q

corneal topography indications

A

o Corneal astigmatism
o Contact lens fitting
o Refractive surgery
o Keratoconus

32
Q

most commonly used corneal topography

A
  • Computerised videokeratorapghy (CVK)
    produces a colour coded map
33
Q

compound microscope

A
  • Produces a magnified view of a near object
  • Consists of two convex lenses – objective and eyepiece lens
34
Q

image from a compound mircoscope

A

: virtual, inverted (horizontally and vertically), magnified

35
Q

how are porro prisms used

A

incorporated into microscope so that the imaged are erect and non-inverted

36
Q

slit lamp

A

low powered binocular compound mircoscope with bank of galilean telescopes to change magnification

37
Q

diffuse ilimunation

A

directing full beam
for anterior capsule

38
Q

direct focal illumination

A

obliquely

39
Q

specular reflection

A

gaze in the middle, beams bisecting
for corneal endothelium

40
Q

slceoritc scatter

A

off axis illumination
scattered around the cornea

41
Q

retro-oillumiantion

A

co-axial
ir

42
Q

lateral

A

cornea opacities

43
Q

without lenses can only examine

A

anterior third of the vitreous

44
Q

hruby lens

A

plano-concave lens
vitrual, erect and diminshed image

45
Q

90D and 78D

A

inverted image

46
Q

20D angular mag, field of view and laser spot

A

Mag: 2.97
Field: 46
Laser: 0.34

47
Q

28D angular mag, field of view and laser spot

A

Mag: 2.16
Field: 55
Laser:0.46

48
Q

78D angular mag, field of view and laser spot

A

Mag: 0.87
Field: 73
Laser: 1.15

49
Q

90D angular mag, field of view and laser spot

A

Mag: 0.72
Field: 69
Laser: 1.39

50
Q

SF angular mag, field of view and laser spot

A

Mag: 0.72
Field: 12
Laser: 1.39

51
Q

standard area for goldman

A

3.06mm

52
Q

overestimates

A

Excessive fluorescein
Thick cornea
ATR astigmatism
Cornea scar

53
Q

underestimates

A

Inadequate fluorescein
Thin cornea
WTR astigmatism
Corneal oedema

54
Q

pachymeter

A

uses iamge I and II

55
Q

OCT

A

uses IR 843 and the time delay produces iamges

Optics (18 decks)

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