Indirect ophthalmoscopy- introduction, biophysics, fundus drawing

1. INDIRECT
OPHTHALMOSCOPY
- Dr Shruti Laddha

2. Introduction:
1851 Direct Helmhotz
1852 Indirect Mono ocular Independent light source Ruete
1861 Indirect Binocular Independent light source Geraud –
Teulon
1951 Indirect Binocular
headmount
Integrated,clinically useful Charles
Schepens

3. MONOCULAR INDIRECT OPHTHALMOSCOPE :

4. MONOCULAR INDIRECT
OPHTHALMOSCOPY :
• It was introduced by Reute in 1960s.
• It was designed for its use in undilated pupil.
• The original monocular, hand-held indirect ophthalmoscope used
an external light source reflected by a mirror held in front of the
observer's eye.
• The monocular indirect method allows the use of low-power
lenses[13D] through which small details are seen larger.
• Since it is monocular, stereoscopic examination is not possible.

5. Binocular Ophthalmoscope :• It was first invented by Dr.Charles Schepens in 1951.
• It was for the first time when entire periphery of the retina
was seen in three dimensional view.

6. Evolution : Nothing escapes evolution.
THEN NOW

7. • Indirect ophthalmoscope is an indispensable tool
to diagnose and manage vitreoretinal disorders.
• Facilitate observation of peripheral retina, it laid
the basic foundation for the modern treatment
of vitreo retinal diseases.

8. PRINCIPLE O
F INDIRECT OPHTHALMOSCOPY• The technique is called Indirect because the fundus is seen through a
condensing lens.
• The principle of indirect ophthalmoscopy is to make the observer’s eye
myopic by placing a strong convex lens in front of it.
• When both the illuminating and reflected beam pass through the
pupil, that area of fundus is seen.

9. • A pencil of rays can be traced from the patient's fundus to the
observer's retina.
• An intermediate, inverted but real image of the patient's
fundus is formed in the focal plane of the ophthalmoscopy lens,
between the lens and the observer.
• The observer must accommodate on this image.

10. • Normal interpupillary distance is about 60 mm
• Reduced to 15 mm by use of prism in IDO

11. EXTENDING THE FIELD
Limited field of view
in the direct method.
Peripheral rays of
light do not reach
observer's pupil
The lens redirects peripheral rays
toward the observer’s pupil.
The field of view in indirect
ophthalmoscopy is determined by
the rays emerging from the
patient's eye that can be caught in
the lens.

12. FIELD OF VIEW
• The field of view is determined by the ratio of lens diameter and
focal length. This ratio can be written as:
Field of view = Lens diameter / Focal length
= Lens diameter × dioptric power
• Given lenses of equal power, a larger lens provides a wider field
of view.
• If lenses have equal diameters, a stronger lens provides a wider
field of view; however, after an optimum power, stronger lenses
[more convex] tend to have smaller diameter, hence a stronger
lens does not always provide a larger field.

13. • Total magnification depends on lens power [inversely
proportional] and observation distance.
• Hence, the stronger the lens, the less magnified is the image
but wider field of view.
MAGNIFICATION:

14. The power of the condensing lens determines:
• Field of view
• Magnification
• Working distance
Lens Power (D) Static Field of View Magnification
+30 40 1.97
+20 30 3.25
+14 22 4.17

15. COMPENSATION FOR REFRACTIVE ERROR
• With the indirect method, minor changes in the
observer's accommodation can compensate for major
changes in the patient's refractive error.
• In indirect ophthalmoscopy, compensation for
refractive error in patient’s eye can be made without
additional lenses.
• The presbyopic observer, who cannot change
accommodation, can compensate by changing
observation distance.

16. • Distance between observer ‘O’ and lens ‘L’ = 45 cm.
• Emmetropic eye: Aerial image at E’ and observer need to
accommodate upto 2.5D [40cm].
• Myopic eye [-5D]: Aerial image will be at M’ and accommodation
of 2.4D [41cm] is required to see it clearly.
• Hypermetropic eye [+5D]: Aerial image will be at H’ and observer
will have to accommodate upto 2.6D[38.4cm].
OLE

17. • Change of +/ - 0.1 D in observer’s accomodation accounts
for difference of +/ - 5 D in patients refractive error.
• Thus, minor changes in the examiner's accommodation
can easily compensate for major refractive errors that
patient may have.
• The presbyopic observer, who cannot alter
accommodation, can compensate for the patient's
refractive error by changing the observation distance or by
using a near-vision aid.

18. Technique of Indirect ophthalmoscopy
• Head set adjustment
• Eye piece adjustment
• Light beam adjustment
• Choosing ,positioning and technique to hold condensing lens.
• Positioning of the patient
• Scleral indentation
• The fundus drawing

20. Adjustment of Eye piece, Head band

21. IPD
IPD knob

22. Adequately adjusted IPD – at arms length
Adjusting IPD

23. Aperture setting

24. Filter knob

25. Condensing Lens :
Three types
• Biconvex
• Plano convex
• Aspheric

26. Technique
Ideal position of the ophthalmoscope.
• Axis perpendicular to the visual axis of examiner.
• The scope not resting on the nose of the examiner.
• The eyepiece as close to the examiners pupils as possible.
• Adequately adjusted IPD.

27. • Proprioception helps
patient to look in
cardinal gazes
• Patient should be urged
to keep the other eye
open
Examination Proper

28. Holding the lens
Pivot

29. • Tilt the BIO lens to remove undesirable reflections
• Moving closer towards the image will magnify the view
but decrease the field
• Moving away from the image will increase the field of
view but decrease the magnification.
Problems and solution

30. • They have two differently curved surfaces; the surface with
the steeper curvature should face the examiner to decrease
peripheral aberrations
• When the lens is perpendicular to the line of viewing, the
reflections from both front and back surfaces are in the
center and are most bothersome.
By tilting the lens a little, these reflections can be moved out
of the line of view without degrading the image.

31. Scleral Indentation:
-Thimble scleral
depressor
-Pencil type depressor
-Cotton tipped applicator
To examine periphery between equator and ora serrata by
creating a mound to view.
Start superonasal superior ,superotemporal,
Inferotemporal, inferior, inferonasal

32. Scleral Depression Technique
• Holding the depressor

33. • A – Patient looks down, depressor on margin of sup tarsal plate
• B – Depressor advanced into the orbit as patient looks up but no
depression applied as yet
• C – Scleral depression applied gently to area of interest

35. • For 3 or 9 o clock –
• Sometimes necessary to apply pressure over the bulbar
conjunctiva directly
• Topical anaesthesia
• Depressor should be introduced and removed from the
conjunctival sac very slowly
• Perform this examination last as proparacaine may cause
corneal epithelial edema
• Use a 70 percent isopropyl alcohol swab to clean the
depressor

36. Filters
• Green light – Nerve fibre layer, Blood vessels,
microaneurysms
• Red light – Subtle pigmentary abnormalities
• Blue light – Angioscopy
• Yellow filter – Reduces photophobia

37. FUNDUS DRAWING
Amsler Dubois Chart

39. Fundus drawing:
• Disregard Sup/Inf and Temp/Nasal while drawing
• What ever appears closer to the observer in the condensing
lens is peripheral (anterior)
• Observe the disc and follow a vessel to the periphery
• Observe the macula at the end for best patient co-operation

47. ADVANTAGES:
• Optimal working distance = 40 to 50 cms
• Good illumination & stereopsis : Better view in presence of
media opacities
• Ease of use with scleral indenter
• Lenses from 14 to 30 D range
• Image not affected by the patients refractive power
• In children, eyes with nystagmus
• Delivery of LASER, operating room for cryo/scleral buckling.

48. • Inverted and reversed image.
• Relative lack of magnification.
• Difficult to master.
• Small movements alter significantly the size and clarity.
DISADVANTAGES :

49. Comparison with Direct Ophthalmoscopy
Retinal Detachment: Principles and Practice, Third Edition Daniel A. Brinton and C. P. Wilkinson