low vision devices for distance and near

1. Low Vision Devices
Different types of telescopes
Magnifiers and other devices in low vision
Presented By:- Guided By:-
Mohammad Aamir Miss Sravani Reddy Mam
B.Optometry 5th sem Faculty- SLAS ITM
School of Life & Allied Science University Raipur
ITM University Raipur,
Chhattisgarh

2. Low vision:- A condition caused by eye disease, in which visual acuity is 20/70
or poorer in the better-seeing eye and cannot be corrected or improved with regular
eyeglasses.

3. Low vision device:- A device to help to improve visual ability of a person
with low vision. Low vision devices may be optical or non-optical. Optical devices
such as a magnifying glass involve the use of lenses to improve vision whereas non-
optical devices such as large print help bring images closer to the eyes.

4. Types of low vision devices
 Optical:-
1- Distance
2- Near
 Magnifiers
 Electronic devices
 Non Optical

5. Low vision optical devices for distance
Telescopes:-
 Work on the principle of angular magnification
 Telescopes with magnification from 2x to 10x are prescribed
 They can be prescribed for distance, intermediate and near tasks
 Field of view decreases with magnification
Types:-
 Hand held monocular
 Clip on design
 Bioptic design: mounted on a pair of eye glasses

6. Hand held monocular telescopes Clip on design
Bioptic design

7. Principal:-
 Telescopes consist of two lenses ( in practice two optical system) mounted such
the focal point of the objective coincides with the focal point of the ocular.
 Objective lens is converging lens
Galilean telescope
 The eye piece is a negative lens and the
objective is a positive lens
 Resultant image is a virtual and erect
 Loss of light reduces brightness of the image
 Field quality is poor
Keplerian telescope
 Both eye piece and objective are positive leens
 Resultant image is real and inverted. Prisms are
incorporated to erect the image
 Loss of light is more in this system
 Field quality is relatively good

8.  Magnification of a telescope is given by the formula M=fₒ/fₑ
 Telescopes can be used to focus near objects by
- changing the distance between objective and ocular lens
- increasing the power of the objective lens

9. Advantages:-
Only possible device to enhance distant vision
Disadvantages:-
 Restriction of the field of view
Appearance and apprehension
Expensive and costly
Depth perception is distorted

10. Low vision optical devices for near
Magnifying Spectacles
 High plus reading glasses to magnify the images
Given as an add to the best distance refraction
Reading distance is calculated by 100 divided by add
Magnification is 1/4th the power of lens
Used for near work
Amount of add needed depends on the accommodation and the reading distance

11. Advantages:-
 Hands are free
Field of view larger when compared to telescope
 Greater reading speed
 Can be given in both monocular and binocular forms
 More portable
 Cosmetically acceptable
Disadvantages:-
 Higher the power, closer the reading distance
 Close reading distance causes fatigue and unacceptable posture
 Patients with eccentric fixation are unable to fix through these glasses

12. Low vision optical devices for near
Magnifiers
 Useful for near work
 Designed to be held close to the reading material to enlarge the image
 The eye lens distance should be minimum to achieve larger magnification
Two types;
 Hand magnifier
 Stand magnifiers
Hand Magnifiers Stand Magnifiers

13. Hand Magnifiers
 Available from +4.0 to +68.0 D
 Available in three designs:-
• Aspheric – reduces thickness and peripheral distortion
• Aplantic - flat and wide distortion free field and good clarity
• Biaspheric – eliminating aberrations from both surfaces
 Most patients accept up to 6x magnification

14. Advantages:-
 The eye to lens distance can be varied
 Patient can maintain normal reading distance
 Work well with patients with eccentric viewing
 Some have light source which further enhance vision
 Easily available, over the counter
Disadvantages:-
 It occupies both hands
 Patients with tremors, arthritis etc have difficulty holding the magnifier
 Maintaining focus is a problem especially for elderly
 Field of vision is limited

15. Stand Magnifiers
 The magnifiers are stand mounted
 The patient needs to place the stand magnifier on the reading material and move
across the page to read
 Has a fixed focus
Advantages:-
 They are a choice for patients with tremors, arthritis and constricted visual
fields
Disadvantages:-
 Field of vision is reduced
 Too close reading posture is uncomfortable for the patient
 Blocks good lighting unless self illuminated

17. Low vision optical devices for near
Closed circuit television system
 Closed circuit television system (CCTV) consists of a monitor, a camera and a
platform to place the reading text
 It has control for brightness, contrast and change of polarity
 Magnification varies from 3X to 60X

18. Non Optical Devices
Illumination
Positioning:-
 Light source should be to the side of better eye
 Moving light closer will yield higher illumination
Higher levels of illumination is needed in patients with:-
 Lost cone function (macular degeneration)
 Glaucoma retinopathy
 Retinitis pigmentosa, Chorioretinitis
Reduced illumination:-
 Albinism
 Aniridia

19. Non Optical Devices
Reading stand:-
 Easy comfortable posture to the patient

20. Non Optical Devices
Writing Guide
 Black cards with rectangular cut outs horizontally along the card
 The patient can feel the empty cut out spaces and write

21. Non Optical Devices
Signature guide

22. Non Optical Devices
Typo scope / Reading guide
 Masking device with a line cut out from an opaque, non reflecting black plastic
or thick paper
 Reduces glare and controls contrast

23. Non Optical Devices
Notex
 It is a rectangular piece of cardboard with steps on top right corner which helps
in identifying the currency of the note
 1st cut indicates Rs. 100, 2nd cut indicates Rs. 50, and so on.

24. Non Optical Devices
Relative size devices
 Larger object subtends a larger visual angle at the eye and is thus easier to
resolve
 Large print material
 Large type playing cards, computer keyboards
 Enlarged clocks, telephones, calendars

25. Non Optical Devices
Computer software
 Jaws screen reading software
 Connect out loud internet and email software
 Magic 8.0 screen magnification software and speech

26. Non Optical Devices
Glare reducing devices
 Glare is described as unwanted light
 It is disabling in patients with cataracts, corneal opacities, albinism, retinitis
pigmentosa
 Devices to prevent glare:
 Sunglasses
 Caps
Umbrella
 Polaroid glasses
 NoIR filters
 Corning photochromic filters
(CPF glasses)

27. Non Optical Devices
CPF Glasses
 Attenuate 100% of UVB wavelengths.
 Block 99% of UVA wavelengths.
 Block 99% of UVA wavelengths. in the eye, causing discomfort and hazy
illusion.
 Attenuate 98% of high-energy blue light, with exception of CPF 450, which is
96% of high-energy blue light.
 The number of the CPF glasses correspond to wavelength in nanometers above
which light is transmitted

28. Non Optical Devices
Color and contrast enhancement
 Maximize contrast by using a light color against black or dark color
 Choose colors in the room or working area which have high contrast

29. Non Optical Devices
Pinhole Glasses
 Multiple holes of approximately 1mm size are made in the glasses
 The distance between the holes should be at least 3-3.5 mm or
approximately the size of the pupil
 Used in patients with corneal opacities or conditions with irregular
reflexes
 Not used in patients with central field defects as it reduces
illumination and visual acuity

30. Non Optical Devices
Mobility Assisting Devices
 Patients with low vision suffer a major problem of mobility
 Long canes
 Strong portable lights

32. Help when there is no cure

34. Reference
 Low Vision Aids – Monika Chaudhry
 https://www.slideshare.net/AsthaJain1/low-vision-aids?qid=1bf23c50-34dd-
43ee-a967-5af1a1eb1fc9&v=&b=&from_search=1
 Images from – google images
https://www.google.com/search?biw=1094&bih=494&tbm=isch&sxsrf=ACYBGN
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