Indirect ophthalmoscopy allows examination of the retina using an inverted magnified image. A strong convex lens is placed near the eye to make the eye highly myopic. This brings light from the retina to a focused real image between the lens and observer. The image size and position depends on the eye's refractive error - it is at the lens focus for emmetropia, in front for myopia, and behind for hyperopia. Indirect ophthalmoscopy provides a large field of view useful for retinal pathology assessment and laser treatment. Though difficult to learn, it allows examination of peripheral retina and is useful in media opacity.

1. Indirect Ophthalmoscopy
• Invented by Nagel in 1864
• An inverted reverse real image
• Magnification:2 to 4 times
• Field of vision: 40 to 50 degrees
• Optical working distance 40 to 50cm
• Good illumination and stereopsis
• Ease of use with scleral inventor
• Lenses for 14 to 30 D range

2. Types
• Head Mounted
• Spectacle Mounted

3. Condensing lenses
Three types
• Biconvex
• Plano convex
• Aspheric
• Two different curved surfaces - to avoid spherical
aberration
• Steeper curvature faces the examiner
• + 20 ,+30 , +14 D

5. Parts of indirect ophthalmoscopy

6. Principle
The Principle of indirect ophthalmoscopy is
to make the eye highly myopic by placing a
strong convex lens in front of the patient's
eye so that emergent rays from an area of
fundus are brought to focus as a real,
inverted image between the lens and the
observer's eye.

8. Field of Illumination
• More in myopia and less in hypermetropia as
compared to emmetropia

9. Image Formation
• EMMETROPIA
• MYOPIA
• HYPERMETROPIA

10. Emmetropia
• Emmetropic eye, rays from fundus are parallel,
brought to a focus by the condensing lens
Image formed at the principal focus of the lens
Hence, size of image remains the same, no matter the
position of lens.

11. Myopia
• Rays are convergent
• Image formed in front of the eye
• Final image by condensing lens within its own focal
length
• Image is smaller when lens is nearer to anterior focus
of the eye and larger when away

12. Hypermetropia
• Rays divergent and appear to come from behind the
retina
• Image by condensing lens in front of its principle
focus
• Image is larger when lens is nearer to the anterior
focus of the eye and smaller when away.

13. Relative Position of Image
• In Emmetropia: - at the principal focus
• In Myopia: - Nearer to the lens than its
principal focus
• In Hypermetropia: - Farther away from the
principal focus

14. Factors affecting field of view
• Patient's pupil size
• Power of the condensing lens
• Over all size of the condensing lens
• Refractive error
• Distance the condensing lens is held from the
patient's eye

15. Image Characteristics
• Real, inverted and magnified
• Magnification depends on:
Dioptric power of the convex lens
Position of lens in relation to the eyeball
Refractive state of the eyeball

16. Prerequisites
• Dark room
• Source of light and a concave mirror or self
illuminated indirect ophthalmoscope
• Convex lens (commonly used +20D)
• Pupils of the patient's eye should be dilated

17. Procedures
• Patient is made to lie in the supine position, with one
pillow on a bed or couch and instructed to keep both
eyes are open.
• The examiner throws the light into the patient's eye
from an arm distance.
• Binocular ophthalmoscope with head band or that
mounted on the spectacle frame is employed most
frequently.
• Keeping his or her eyes on the reflex, the examiner
then interposes the condensing lens.

18. • In the path of beam of light ,close to patient's
eye,then slowly moves the lens away from the eye
until the image of the retina is cleared seen.
• The examiner moves around the head of the
patient to examine direct quadrants of the fundus.

19. •He or she has to stand opposite the clock hour position
to be examined ..eg.to examine inferior quadrant(around
6 o'clock meridian)the examiner stands towards the
patient's head (12 o'clock meridian)and so on.
•By asking the patient to look in extreme gaze, using
scleral indenter,the whole peripheral retina upto ora
serrata can be examined.

22. Applications
Indirect ophthalmoscopy is essential for the
assessment and management of the retinal
detachment and other peripheral retinal
lesions.

23. Advantages
• Larger field of view
• Lesser distortion of retinal image
• Useful in hazy media
• Useful eyes with nystagmus
• Delivery of LASER
• Better resolution.
• Binocular examination of fundus up periphery
• Useful in high spherical or astigmatism refractive
errors.

24. Disadvantage
• Difficult to learn
• Less magnification there for details of a small
lesion not visualized properly
• Impossible with very small pupil
• More uncomfortable to the patient

25. Thank you