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OV2004 clinical skills > indirect ophthalmoscopy > Flashcards

indirect ophthalmoscopy Flashcards

1
Q

what are the advantages of direct ophthalmoscopy?

A
  • high magnification (x15)
  • easy to find microscopic changes that might be missed
  • relatively good image with small pupil
  • portable
  • what you see where it is
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2
Q

what are the disadvantages of direct ophthalmoscopy ?

A
  • small field of view (10 deg of fundus at one go )
  • magnification affected by refractive error
  • short working distance - implications for PPE
  • image degrades with lens opacities
  • no stereopsis
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3
Q

why do we use indirect ?(VOLK)

A
  • to get a better field of view
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4
Q

what are the two main methods of binocular indirect ophthalmoscopy ?

A
  1. slit lamp BIO
    - using either a condensing (VOLK) lens ( high +ve power )
  2. headset BIO
    - also using a +ve powered lens, but the power of the lens used is less than that required with the SL technique
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5
Q

what is the image produced with a slit lamp BIO using a (VOLK)?

A 
. aerial image - in real space
. real image
. inverted image 
. stereo (3D) image 
. with a magnification of x2-x5- with headset
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6
Q

explain the optics behind direct ophthalmoscopy ?

A

1- initial object is the patients fundus
2- the light that is shone onto the fundus reflects through the condensing lens and forms an image
3- image formed is between condensing lens and the examiners eye
4- the examiner is not looking directly at the patient retina ( as with the direct ophthalmoscope) , but the intermediate image - hence the name indirect ophthalmosocpy

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7
Q

explain the optics of direct ophthalmoscopy ?

A
  1. our object is the patient’s retina
  2. light rays emerge from px eye ( it is well illuminated from the slit lamp/headset)
  3. the +ve lens refracts the light rays to a point, forming an image which we view through the SL/headset
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8
Q

what to record when viewing the fundus ?

A
  • CD ratio
  • colour of neural retinal rim
  • appearance of the margins
  • any deviation that isn’t real
  • abnormalities in the disc margin
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9
Q

what is the actual view of direct ophthalmoscope ?

A
  • laterally reversed and inverted
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10
Q

what is the position of condensing lens ?

A
  • the light rays cross at the px pupil plane and examiners pupil plane, they are copies of each other or ‘conjugate point’
  • conjugate points are ‘ corresponding pairs of object and image points and planes’
  • patient pupil size affects the field of illumination
  • size of lens and examiners pupil size affect field of view
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11
Q

what happens when using a larger diameter lens ?

A
  • larger diameter lens = larger field of view (FOV)

- larger field of view = greater optical aberrations

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12
Q

what is the property of volk lenses ?

A
  • VOLK lenses are aspheric to try and make the lens as large as possible while trying to minimise the optical aberrations
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13
Q

what happens when moving the lens closer to the eye ?

A
  • keeping the lens diameter the same, but moving lens closer to the eye would in theory lead to a larger FoV, but pupils would no longer be conjugate
  • the only way to move the lens closer and still see an image is to change the lens power
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14
Q

what is the lens position ?

A

about 1 cm from px eye

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15
Q

what is the working distance of superfield ?

A

7mm

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16
Q

what is the field of view of superfield ?

A
  • FoV is 95 degrees , however the magnification is slightly low at 0.76x
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17
Q

what is the slit lamp BIO-method 1?

A
  1. check the vision
  2. document the dilating the drug details ( drug, dosage, date )
  3. room light off
  4. set - up slit lamp
  5. keep lamp intensity to a minimum
  6. begin with low magnification
  7. slit beam height usually same height as pupil and width approx 2mm
  8. illumination system in line with viewing system
18
Q

how do we carry out the slit lamp BIO-method ?

A
  • px fixates at a distant target straight ahead
  • focus on the surface of the cornea
  • present the Volk lens in front of pupil - 5mm away
  • now move the SL joystick straight back towards you
  • at first, the surface of the volk lens surface will come into focus - scratches
  • then blurred red reflex of the retina
  • then the image of the fundus will come into focus
  • don’t move volk lens back at same time as slit lamp
  • rest fingers on forehead rest and use volk case to rest your elbow
19
Q

what are common mistakes with slit lamp BIO ?

A
  • students often mistake the iris for a blurred fundus image. The fundus image will be orange, not blue, brown or green
  • not aligning the observation and illumination systems- make sure they are straight and in line with the pupil
20
Q

what happens if image is out of focus ?

A
  • using the SL joystick, move slit lamp in and out, in a straight line, to bring image into focus
21
Q

what happens if you can’t see image ?

A
  • ensure the lights passing from the SL, through the volk lens, then through the centre of the pupil
  • ensure observation and illumination systems are aligned
  • try moving volk lens
  • tilt lens
  • check px fixation
22
Q

what to do if there are too many reflections ?

A
  • ensure volk lens is clean

- tilt lens inwards and outwards

23
Q

what is the full fundus examination ?

A
  • start with optic nerve head
  • move slit beam left, right, up and down to examine posterior pole
  • ask the patient to look into each of the 8 postions of gaze
  • when patient looks superiorly, you are viewing the superior fundus, but the image is still laterally reversed and inverted
  • assess the macula last
24
Q

how to view peripheral retina ?

A
  • tilt lens slightly to view peripheral retina
25
Q

how to position lens when px looks up ?

A
  • tilt upward when the patient looks up
26
Q

when to lift the lid ?

A
  • lift the lid when patient looks down
27
Q

what are the advantages of lenses with yellow filters?

A
  • sharp cut off at 490nm
  • better px comfort
  • less photophobia
  • maybe better protection of retina - less phototoxicity- blue light removed
28
Q

what are the disadvantages of lenses with yellow filter ?

A
  • yellow filters make it difficult to assess the colour of the retina/ONH
29
Q

what do we use volk lens scales for ?

A
  • retinal scales available
  • allow comparison of retinal lesions structures
  • quantitative assessment can be made
  • can monitor conditions for change in size over a period of time
  • difficult to use accurately ?
30
Q

what is the slit lamp BIO-method key steps ?

A
  1. align illumination and viewing system
  2. px fixates distant at a target straight ahead
  3. focus on the surface of the cornea
  4. present the volk lens
  5. move joystick straight back towards you
  6. surface of the volk lens surface will come into focus
  7. then blurred red reflex of the retina
  8. then the image of the fundus will come into focus
31
Q

what are the advantages of slit lamp BIO?

A

. binocular, stereoscopic, 3D view
. large field of view (FoV)
. wide range of lenses to choose from
. easy measurement of fundus lesions
. greater control over magnification with SL
. can use a range of filters on SL
. longer working distance
. no magnification effects with ametropia
. better view ( than direct) in presence of media opacities
e.g. cataract

32
Q

what are the disadvantages of slit lamp BIO?

A

. small pupils require dilation
. patient discomfort / photophobic patients
. difficulties reaching slit lamp chin rest - wheelchair access
. not portable ? use of portable slit lamp
. expense - slit lamp required
. image is laterally reversed and inverted
. takes time to become proficient

33
Q

which Volk lens has the greater magnification?

A

60D - lower power gives the greatest mag

34
Q

what is the headset BIO?

A

. headset unit with light source
. primarily used to screen for peripheral retinal tears/breaks
. good for paediatric examination-large area to be viewed at once
. +20D lens is the most commonly used
3.13x magnification FOV 46 deg ( static) and 60 deg ( dynamic )
. +40D ( magnification x15, FOV 65 deg ) for children
. indentation allows view of ora serrata

35
Q

how to adjust the head set ?

A

. set the inter-pupillary distance
. adjust the tilt of the observation system so that it is perpendicular to your line of sight
. adjust the straps for comfort
. adjust the illumination
. look through eye pieces at object 40 cms away
e.g. your thumb
. adjust PD and illumination mirror so that the illumination field is central to the observation holes

36
Q

what is the head set bio method?

A

. illuminate the patient’s pupil area by pointing the head/light towards the patient’s eye

. introduce BIO lens a few cm away from eye, then gradually move lens away from patients eye
-5cm working distance for 20D lens

. fundus should come into view

. as with SL BIO, tilt the lens to reduce reflections

37
Q

what are the advantages of head set bio?

A

. allows view of anterior retina to ora serrata - with indentation

. portable - useful for domiciliary work

. long working distance

. good view through media opacities

. more control over magnification and FoV due to lens choice

. useful for those unable to sit at a slit lamp e.g. children

. stereo view

38
Q

what are the disadvantages of head set bio ?

A

. requires mydriasis ( pupil dilation )
. less magnification than slit lamp BIO
. bright light

39
Q

what is hruby lens ?

A

. negative lens used to assess the fundus
. -58.6D lens
. non-contact
. produces a virtual, upright image
. image is not laterally reversed
. FoV typically 20-30 deg in an emmetropic eye
. high magnification

40
Q

what is fundus contact lens?

A

. allows view of central and peripheral retina

. e.g. Goldmann 3 mirror lens

41
Q

What does a lower power give ?

A

higher mag view

42
Q

What gives a big field of view /

A

higher power

OV2004 clinical skills (12 decks)

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