The document provides an overview of spectacle and electronic magnifiers. It defines spectacle magnifiers as high-powered lenses that provide relative distance magnification. Electronic magnifiers use a camera and display screen to digitally magnify printed materials. Different types of spectacle and electronic magnifiers are described, including their advantages and disadvantages. Methods for calculating the equivalent power of each type of magnifier are also outlined.

1. University of Gondar
College of medicine and Health sciences
Department of optometry
Presentation on spectacle & electronic magnifiers
Getachew kassahun ( B optom)
March,2023
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2. Objectives
At the end of this presntation learners are expected to
• Define spectacle and electronic magnifiers
• List different types of both magnifiers
• Determine calculaion of quivalent power
• List advantages and disadvantages of spectacle and electronic magnifiers
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3. Outline
 Definition
 Types of spectacle mag.
 Strong adds and binocularity
 Equivalent power of spectacle mag. when used with acc. or
add
 Advantages and disadvantages
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4. Definition
• Spectacle magnifier is high power plus lens to magnify retinal
images by providing a form of relative distance magnification.
• Have front vertex power greater than that used as a
conventional reading addition.
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5. Cont...
• The object is held within the focal length of a lens in order to
obtain a magnified & erected image.
• Increases the front vertex power , enabling a close working
distance without placing extra demands on accommodation.
• The magnifier acts as a converging system to neutralize the
rays created by the close WD.
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7. Types of spectacle magnifiers
Spherical
Aspheric
Aplantic
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8. 1.Spherical
Have the same power in all meridians.
As these lenses increase in power, oblique astigmatism and
curvature of field begin to distort image.
Available as High-powered single vision and bifocals
Bifocals are available
• Up to +16D with a 25-mm round segment
• Flat-top bifocal designs are available up to +8D.
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9. • Bifocals can be prescribe binocularly upto 4x
• more than 4x monocular is better
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10. 2. Aspheric
• Lens design used to minimize peripheral distortion( have
ellipsoidal surfaces).
• The convexity of the lens is progressively reduced toward the
periphery.
• Fulldiameter and lenticular designs.
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11. Aspheric cont...
1. Full-diameter aspheric designs are used in powers from +10 D to
+20 D.
2. The aspheric lenticular design is an aspheric lens on a plano base.
• This design has the advantages of less weight and decreased
thickness, with the disadvantage of smaller field of view.
• Has an optical zone diameter of 20 to 40 mm surrounded by the
plano carrier lens. This lens is used in powers from +10 D to +48 D.
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12. 3.Aplanatic or doublet spectacle magnifiers
• Designed with two convex lenses separated by an air space.
• The lenses may be glass or plastic and aspheric or spherical in
design.
• Can provide high amounts of magnification with minimal
spherical aberration, coma, oblique astigmatism, and curvature of
field in the peripheral area of the lens.
• Can be found in magnifications ranging from +8 D to +80 D.
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13. Common types of Spectacle magnifiers
1. Clip ons
2. Hyperoculars
3. High reading adds
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14. 1. Clip on magnifiers
lightweight Loupes attached to glass for viewing text
Available in
binocular (1.7x to 3x) and
monocular (4× to 7×) forms
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15. 2. Hyperoculars
• Bi-convex injection moulded lenses with an aspheric front
surface and a spherical back surface.
• Available in ready made hyperoculars
• Are biconvex lenticulars
• Can range; 4x to 12x( monocular) binocular upto 3x
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16. Hyperoculars...
Merit: have a good range of power
Give a high image quality,
Are light and cosmetically acceptable.
Quite versatile as they can be glazed to almost any frame.
Demerit: cannot be obtained with any prismatic or astigmatic
correction, and are too powerful to enable binocular alignment.
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17. 3.High reading adds
• Normally near add is prescribed upto +3.50 D
• Add > +3.50 D is called high reading add
• Are used to magnify retinal image.
• Given as an add over the best distance refraction.
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18. Amount of add
 Depends on the accommodation and the reading distance.
Can be Predicted by
1. Kestenbaum’s rule: Reciprocal of Snellen’s visual acuity
e.g 6/60 add= 60/6= +10D
2. Reciprocal of distance:(For Near) 100/reading distance
Example: If the near acuity tested at 40cm is 2M
Then in order to read 1M print, the patient must hold it at 20cm
The add required is 100/20= +5D
3. Lovie-Kitchin and Bowman formula
Required near addition (D)=
print size read
print size required
x present near add(D)
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19. Strong adds and binocularity
 High plus reading bifocals or spectacles make difficult to
achieve binocular vision.
Usually binocularity is easy upto +6.00D
Over +10.00DS the person is unlikely to be binocular
Challeng to binocularity is due to
1. Closer WD brings high convergence demands
2. Base out prism is induced if near pd is too big.
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20.  We can achieve binocularity with spectacle enlargement by decentration
or by adding base-in prism.
As a rule of thumb to allow calculation of decentration and/or prism
Fonda suggested 1Δ per dioptre of object-to-lens distance.
Bailey: after having distance PD
decentration = Add × 1.5 (1.5mm for each 1D add)
or= Add × 1.5 (+1 mm if PD >65 mm)
eg DP of 62 requires +6D
decentration=6x1.5= 9mm so NPD= 62-9=53mm
Strong adds and binocularity
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21. Indications for monocular magnifier
21
• Asymmetry loss of vision
• VA more than two line difference
• High add power >+10.00D.
• prescribe for better seeing eye
Monocular magnifier need occlusion of poor vision eye to
eliminate any possible retina rivalry between two eyes.
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22. Equivalent power of mag.
• Depends on the dioptric power of the spectacle correction
for magnification (addition )(F1) along with any
accommodation (F2) supplied by the patient.
• applied when use at distance shorter than focal length of
magnifier.
• The patient's refractive error is not included in F1 or Feq.
Feq = F1+F2.
Magnification= Feq/4
22
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23. Advantages of Spectacle magnifiers
 Cosmetically and psychologically acceptable
Greater comfort for prolonged reading
 Binocular viewing possible for low power
 Can be implemented with other aids
 Hands are free to perform tasks
 Larger field of view
 May incorporate correction for patient’s ametropia including Cylinder
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24. Disadvantages of Spectacle magnifiers
 May be heavy and physically constricting
 Shorter working distance than other low vision aids of the same
equivalent power
Lighting become more critical at closer (Need additional illumination)
Possibility of binocularity decrease
Lens distortion and aberration increase
Often not tolerated by elderly people
Convergence problems: need base in prism
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25. ELECTRONIC MAGNIFIERS
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26. Outline
 Definition
Types of CCTV
 Equivalent power of electronic magnifiers when used with
add
 Advantages and disadvantages
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27. ELECTRONIC MAGNIFIERS
Definition:
• Electronic devices that use a camera and a display screen to perform digital
magnification of printed materials.
• CCTV stands for Closed Circuit TeleVision and comprises a stand-mounted
or hand-held video camera connected to a monitor as to project the image
of an object onto the monitor or TV with magnifications ranging from 3X
to over 70X.
• The size of the new, electronically altered image can be considered to be a
RSM or an enlargement ratio (ER).
• The actual magnification depends on ER and the patient's WD from the
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28. Types of CCTV
• Electronic Desktop Magnifiers
• Flex arm
• Head mounted
• Portable (hand-held)
• Television readers
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29. Electronic Desktop Magnifiers
• Most desktop models have a movable table called an XY table, which is
mounted under the camera and monitor.
• Consists of 3 major components:
1. Camera- for capturing images
2. Monitor- to display the captured images
3. Movable reading platform- to place the reading text
• Provides adjustable magnification , focus, zoom, contrast, reverse
contrast
• Magnification varies from 3x to 70x
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31. Applied uses of CCTV:
• Educational
• Vocational
• Recreational
• Best for patient Having constricted VF, decreased VA and
decreased contrast sensitivity.
• Limitations include: portability, locating beginning and end of a
line(margin stop). difficulty searching, scanning and writing with
high magnification
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32. Flex arm video magnifier
• Are similar to desktop video magnifier, but the video camera
is housed in a flexible(movable) arm.
• Do not have the X-Y table so they can be more difficult to
use and not portable.
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33. Head mounted
• Head-mounted video magnification devices allow greater
portability and usage for a wider variety of tasks like distance ,
intermediate and near vision.
• Can improve both visual acuity and contrast sensitivity.
Limitations
large and heavy, poor appearance, low resolution
Problematic for people with physical limitation
Motion sickness and claustrophobia
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35. Portable (hand-held)
• A portable digital magnifier is a device with a camera on the
underside that captures the image of text, pictures, or other
items, and a monitor on the top side that displays the image.
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36. Television readers
• ‘Mouse’-style, more portable, first described in the 1970s.
• Consist of a camera usually mounted on rollers in a small hand-
held case that can be moved over the object of interest.
• They need to be connected to a television
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37. Equivalent power for electronic magnifiers
• Equivalent power depends on the magnification ratio of the
image size to the object size, and accommodation or addition
power used (F2).
• Fe = (F2) x image size/ object size
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38. Advantages
 Adjustable magnification
 Wide range of magnification up to 70x
 Flexible working distance
 Adjustable color, brightness and contrast
 Contrast reversal
 Binocularity possible
 Adjustable field of view
 Psychologically acceptable
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39. Disadvantages
o Bulky
o Not portable
o Requires more training and practice
o Difficulty of maintenance
o Not available
o More expensive
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40. References
• Low vision manual, edited by A. Jonathan et al. foreword by lan L Bailey.
• Optometric clinical practice guideline for low vision patients. AOA
• Basic and clinical science course: clinical optics
• Prescribing and use of pocket and electronic low vision aids
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