direct ophthalmoscope
TRANSCRIPT
Direct Ophthalmoscope
Dr.Mohammad Khabbaz
Methods of Fundus Examination
Direct
ophthal
moscope
Direct Ophthalmoscope
System of Lens focusing light on a 45 dgree mirror with Hole.
Mirror reflect light in diverging beam then illuminate patient,s eye.
Light reflected from illuminated retina of the patient ,then passes back through the hole to observer,s eye.
Image of blub is formed just below the hole,so the reflection does not interfere with viewing.
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 usingDirect Ophthalmoscope
Red reflex1 meter
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 usingDirect Ophthalmoscope
22 cm
Movement of the opacity in relation to the movement of the observer.
Parallactic displacement
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 pupilopacity moves
opposite to examiner,s motion.
It is method by which an Erect magnified image of the fundus can be seen.
Direct OphthalmoscopeDefinition
Maculadisk
vessels
• 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
• 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
34mm
Emmetropia
Rays emerging from subject,s retina are parallel
Hypermetropia
Rays emerging from subject,s retina are divergent
Rays enter observer,s eye are divergent
Inverted smallest image Behind the observer,s retina
Inverted smallest image Behind the observer,s retina
The image will be blurred
An emmetropic obsrever has to:To accommodate or
To use a correcting convex lens
In order to bring the light to focus in his retina
When accommodate the rays enter his eye converging so focused on the retina
The anterior focal point of the observer,s eye Fo approaches his eye
Myopia
Rays emerging from subject,s retina are convergent
Invertedlargest image In front of the observer,s retina
The image will be blurred
To focus this image on the observer,s retina he should use a concave lens.
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.
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
Magnification
In E----M=60/4=15x.
In H----M= <15x (F<60D).
In M----M= >15x (F>60D).
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)
OphthalmoscopicField of vision
Thank you for your attention