FOR OPTOMETRIC OPTICS

1. Spectacle Magnification
PART 2

2. Magnification in Low vision
• Relative Distance Magnification (RDM)
• Relative Size Magnification (RSM)
• Projection Magnification
• Angular Magnification

3. Relative Distance Magnification (RDM)
• RDM=initial object to present distance / the same object
to new distance
• If an object is moved from the reference distance of
40cm to 10cm RDM=40/10=4
• Bring the object closer => increases the angular
subtends of the object=> appears larger
• Trees near the road side appears larger than that of the
far-distance
• Use of plus lens for accommodation

4. Relative Size Magnification (RSM)
• Magnification obtained by increasing the size of
the object at its original position.
• E.g. large print books, magazines, large display
screen
• RSM= angular size of enlarged object /angular
size of initial object
E.g. if at 40cm an object is 0.5mm high but is increased
to 2.0 mm high
RSM= 2/0.5=4

5. Projection magnification
• The magnification produced from the
formation of an enlarged image on a screen ,
of an opaque or transparent object e.g.
overhead projector, CCTV

6. Use of magnification in some
optical systems

7. THE MICROSCOPE
1)SIMPLE MICROSCOPE and 2) COMPOUND MICROSCOPE
1)SIMPLE MICROSCOPE- A single convex lens of
short focal length can be used to see magnified image
•
•
of a small object and is called a magnifying glass or simple
microscope
principle -when a small object is placed betn optical centre
& focus of a convex lens, its virtual erect & magnified
image is formed on the same side of the lens
The lens is so held that the image is formed
at the LDDV

8. • Magnifying power = angle subtended at eye by
image produced by lens/ angle subtended at unaided eye
by object at LDDV
• M= 1+D/fe,
D=LDDV, fe=eye piece lens
Uses-
• Jewelers & watch makers
• To see slides

9. • COMPOUND MICROSCOPE
– Objective piece - Short aperture and short focal
length
– Eye piece - short focal length and large aperture
– Principle -
• When a small object is placed just outside the
focus of the object lens its real , inverted and
magnified image is produced in the other side of
the lens between its f and 2f .

10. • The image produced by objective piece acts as
object for eye piece .
• The position of the eye lens is so adjusted that
the final image is formed at LDDV
• Me = 1+D/fe & Mo = v/ u
• M = Mo x Me = v/u (1+D/ fe)
• M= fo/fe= -Doc/D obj
At LDDV-
• M=fo/fe(1+fe/D)

11. TELESCOPE:
1. ASTRONOMICAL TELESCOPE :
– It produces virtual and inverted image
– Used to see heavenly bodies
•Principle -
– The objective forms the real and inverted image of the
distant object at its focal plane
– The position of eye piece is adjusted till the final image is
formed at LDDV.
– Normal adjustment - final image is formed at infinity
• M=fo / fe
– When final image is formed at LDDV -
• M= fo/fe(1+fe/D)

12. 2. TERRESTRIAL TELESCOPE:
– Produces an erect image
– Erecting lens is placed in between objective and eye piece
– Normal adjustment -
• M=fo/fe
– At LDDV-
• M= fo/fe(1+fe/D)

13. 3. GALLILEO’S TELESCOPE :
– It provides an erect image of the distant object by use of two
lenses
– The objective piece ( convex lens )form the real and inverted
image of the distant object on the other side of lens at the focal
plane of objective.
– This image acts as a virtual object for the eye piece(concave
lens) . Final erect image formed at infinity
– The difference between two lens equals to fo-fe
• M= fo/fe

14. OCULAR SYSTEMS
&
CLINICAL
SIGNIFICANCE

15. • Introduction :
• The ratio of size of image to the size of object
• M = image size / object size
= object vergence / image vergence
= image distance / object distance
• Human eye as the optical system the size of the image on
the retina is being compared with the size of the object of
regard
• Retinal image magnification (RIM) =
• Magnified retinal image size / original retinal size

16. – RIM has three components :
• Relative size magnification (RSM)
• Relative distance magnification (RDM)
• Lens vertex magnification (LVM)
– RSM and RDM can be achieved without the use of lens
where as LVM depends on the kind of lens placed before
the eye and its location
– It allows the use of magnifiers in such a way that image on
the retina are usable and functional although not in perfect
focus

17. • Clinical Significance :
• Direct ophthalmoscopy-
• Image is erect, virtual and
(about 15 times ) magnified in emmetrope ( more in
myopes less in hypermetropes).
• Indirect ophthalmoscopy -
• Image is real ,inverted
and magnified , which depends upon the dioptric
power of the convex lens , position of the lens in
relation to eye ball and refractive status of eye ball.

18. • Slit lamp Bio-microscope - Image is erect ,virtual and
magnification can be adjusted according to need as 10 X , 16 X
and 20
•Low magnification:
–
–
–
–
–
–
7X - 10X : General eye
Lids.
Bulbar conjunctiva/sclera.
Cornea/limbus.
Tears.
Anterior chamber/iris/crystalline lens.
•Medium magnification:
– 20X - 25X : Structure of individual
layers
– Epithelium/epithelial breakdown.
– Stroma.
– Endothelium.
– Contact lens fit/lens condition.
•
•
•
•
X.
High magnification:
– 30X - 40X : Details
Epithelium
– vacuoles
– microcysts
– dystrophies.
Stroma
– striae
– folds.
Endothelium
– Polymegathism
– guttata
– blebs
– cell density.

19. In low vision aids –
• Spectacle Magnifier: RDM
• Hand magnifier :
• Useful in short term visual task
• Magnification depends upon equivalent power and how the
magnifier is used (RDM and Angular Magnification)
• Stand magnifier :
• The fixed focused eye having a fixed distance from object of
regard
• Magnification depends on the power of the magnifier (RDM
and Angular Magnification)

20. •Paper wet magnifier :
• Reading aid in which thick plano- convex lens is held
in contact with the reading material.
• Magnification is relatively low
•In Aniseometropia -
• Contact lens produces low magnification than spectacle
thus removes the aniseokonia .
•In Closed circuit television (CCTV) -
• Projection and relative distance magnification are
used .
•In Telescope -
• Angular magnification is used.

21. THANK YOU