Week 1.12 Indirect Opthelmoscopy And Contact Tonometry Flashcards
With stronger lenses…
Less magnification and wider FOV
When to use volk
- poor direct view (opacity, high rx)
- stereoscopic view
- wider field required
- not for viewing whole fundus
Binocular indirect - headset
Stereoscopic view
Hand held condensing lens 20D
Image inverted
Lower power higher mag, smaller FOV greater WD
When to use binocular indirect - headset
- direct view poor
- stereoscopic view
- can’t get on SL - babies, wheelchair
- to see whole fundus
- diabetics
- RD symptoms
- children
Indentation
There’s a part of the retina (ora serrata) that is not able to be seen due to pupil margins getting in the way so we have to indent the eye and push that area into our field of view
What is a monocular indirect method
Welch Allyn panoptic
- monocular indirect with an incorporated errefcting prism - img in THE RIGHT WAY UP
25º FOV
26% increase in magnification
Greater working distance between practitioner and patient
Is binocular headset indirect or direct
Indirect
IMG IS INVERTED AND REVERSED same as volk
When doing bio headset which direction does the px look if wanted to view inferonasal of the right eye
Down and left
Px always looks in the bit you want to assess doesn’t matter about what method u have used. So basically ignore the first bit and focus on the second part of the question
Where does px look when viewing superotemporal peripheral fundus of the right eye with a headband bio is true?
Px looks up/right and you view the bottom part of the img
Again, forget the method used and break the question in 2 parts. Px look up and right as that superotempral and then the most superior part of that image is the bottom so that’s why second option.
Applanation tonometers
- flatten rather than indent cornea
- displace less aqueous
- scleral rigidity insignificant
- corneal rigidity approx same for all eyes
Imbert fick principle
Force applied to applanate a sphere = pressure inside x applanated area
Why 3.06
That’s the weight that is proportional to the IOP inside the eye pushing against us
If we increase the weight on the tonometer what happens to the area
Area gets bigger - semi circles start to get larger and they overlap more
If you decrease the weight the applanation area…
Gets smaller - semi circles shrink and gets smaller and overlap less
What weight on tonometer
~1.5g
When realigning which mire do you have to move rtowards
Towards the bigger mire
Advantages of Goldman tonometer
Easy to use
Accurate
Force on cornea small
Cheap
Patients like it
Can check calibration and amend readings if <3mmHg error
Disadvantages tonometer
Needs anaesthetic and Fluorescein
Disinfection
Can damage cornea
Acquired skill
Repeating readings reduce IOP
What is the Perkins tonometer
Hand held Goldman
Counterbalances to use at all angles
comparable accuracy
