9. Image of blub is formed
just below the hole,so the
reflection does not
interfere with viewing.
10. 1.Preliminary examination by a plane mirror at 1
meter give an idea about refrective error:
Emmetrope only red reflex.
Hypermetropia with movement.
Myopia against movement.
Routine way of using
Direct Ophthalmoscope
12. 2.Preliminary examination by a plane mirror at 22 cm
Diagnosis of opacity eg: cataract.
Recognition of RD or Tumour.
Level of the opacity can be identified by the
parallactic displacement.
Routine way of using
Direct Ophthalmoscope
13.
14. Movement of the opacity in
relation to the movement of the
observer.
Parallactic displacement
15. Parallactic
displacement
Behind the pupil
opacity moves with
examiner,s motion.
At the pupil
the opacity is stationary
with examiner,s motion.
In front of the pupil
opacity moves opposite to
examiner,s motion.
16. It is method by which an
Erect magnified image
of the fundus can be
seen.
Direct Ophthalmoscope
Definition
20. • We assume that anterior focal point of the subject (Fs)
coincide with the anterior focal point of the observer
(Fo).
• Image on the examiner,s retina is always inverted
seen as erect.
Optical principle
21. • Also, the image size varies with the refractive state of
the patient,s eye.
• The image being smaller in hypermetropia,and larger in
myopia than in emmetropia.
Optical principle
38. To focus this image on the observer,s
retina he should use a concave lens.
39.
40. The image formed on the observer,s
retina is
• Smaller when a hypermetropic eye is
viewed ,Larger when a myopic eye is
viewed when an emmetropic eye is
examined
• But the use of a correcting lens reduces
the discrepancy in size.
41.
42. The formula for Magnification achieved by a loupe
is
If ascribe dioptric power of 60+ D to the patient,s
emmetropic eye, the magnification of the direct
ophthalmoscope is 15x.
Magnification
Magnification
Dioptric power of the loupe
44. Size of the pupil of subject,s eye.
Size of the pupil of observer,s eye.
Error of refraction:
H----> greatest
M----> smallest
The distance between the observed eye and
observer eye (decrease distance----> increase field)
Ophthalmoscopic
Field of vision