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Optical and non optical devices used in low vision
- 1. Optical and Nonoptical low vision devices Asra Warees Bachelors of Optometry Paramedical College Faculty of Medicine Aligarh Muslim University
- 2. Low Vision Devices •LVDs are devices that enhance the residual visual function by increasing the visual information available to the person with low vision. •Optical devices, Low Vision Devices (LVD), consist of one or more lenses placed between the eye and the object to be viewed, which increase the size of the object on the retina. • Non-optical devices are supplementary devices that do not use optical lenses, while optical LVDs incorporate lenses, resulting in optical magnification.
- 3. Two types ofoptical devices DISTANCE •Telescopic devices (sometimes intermediate distances) •Intraocular LVAs (IO-LVAs) NEAR •Spectacle magnifiers •Hand-held magnifiers •Stand magnifiers •Telescope system for near (telemicroscope)
- 4. 7 categories Optical Distance Non-optical Near LVD • Spectacle magnifiers •Hand-held magnifiers • Stand magnifiers • Telescope system for near (telemicroscope) • Galilean telescope • Keplerian telescope • Relative size and larger assistive device • Glare, contrast and lighting control device • Posture and comfort maintenance devices • Handwriting and written communication devices • Orientation and mobility techniques and devices • Sensory substitution devices • Medical management and life skill devices
- 5. Hand held magnifier •Enlargedvirtual image behind the magnifier •Material held at focal point of lens USE: •Reading or any near activity •One hand is in use •Can be used with distance and near glasses for providing extra magnification
- 6. Advantages and Disadvantages Advantage •Convenientfor short-term tasks •Fairly inexpensive • Devices have their light source, thereby improving contrast •Portable Disadvantage •Decrease the field of view •One hand is occupied •Tricky handling is required •The lens is always held at the correct focal distance in order to obtain the maximum power.
- 7. Stand magnifiers •The standmagnifier produces an enlarged virtual image in front of the eye (Fig. 5.3) and therefore patients require their near prescription to view the resultant image. •The material is placed within the focal length of the lens.
- 8. Use •For near •For schoolaged children •Used in high magnification •Image is always in sharp focus Advantages •Device of choice for tremors, arthritis ,constricted field •Have your own light source •Portable Disadvantages •Image distortion •Reduce the field of view •Requires flat surface to place reading material
- 9. Spectacle magnifier •An erect, virtual , and magnified image is produced •Magnification by a convex lens is obtained by bringing the object within its focal distance. •Full field •Half eye (use for prolong reading)
- 10. Advantages and Disadvantage Advantages •cosmeticallyacceptable •Easy to use •Both hands are free •Large field of vision •Near and distance Disadvantage •Spherical abberation •Short working distance •Reduce illumination
- 11. Telescopic devices 1.Galilean telescope 2.Kepleriantelescope (Astronomical) •Distance- telescopic lens system •Two elements- objective lens(+ve lens) and eye piece(+-ve) 1.Galilean Telescope •Convergent objective lens and divergent eyepiece •Virtual and erect image formed •Parallel rays of light strike the convergent objective lens and image formed at second focal point of the lens. •Eyepiece (position)— primary focal point is coincident with the image formed by the objective lens.
- 12. Advantages and disadvantage Advantages •Smallcompact light unit •Easy to produce •Upright image Disadvantage •Low magnification 2x – 3x •Restricted field of view
- 13. 2. Kaplerian telescope •Comprisesof convergent objective and eyepiece lenses. •Parallel rays of light strike the convergent objective lens and image formed at second focal point of the lens . •Eyepiece (position)— primary focal point is coincident with the image formed by the objective lens. •Inverted and real image.
- 14. Advantages and Disadvantages Advantages •Largefield of vision •High magnification 6x to 8x Disadvantage •Inverted image •Heavy •Complicated •Difficult to use
- 15. Circuit television (CCTV) •Electronicdevice used for near work •Camera— focus reading material and project on TV screen •40 times enlarge •Reasonable field of view •Good for near task (patient has severe visual impairment) •Can be found as portable device Disadvantages Typically not portable Expensive Takes time to learn
- 16. Non – opticaldevice #Commonly used non-optical devices can be classified under 7 categories as follows •Relative size and larger assistive device •Glare, contrast and lighting control device •Posture and comfort maintenance devices •Hand writing and written communication devices •Orientation and mobility techniques and devices •Sensory substitution devices •Medical management and life skill devices.
- 17. Relative size/Larger assistivedevices •Large print material( enlarged photocopy, computer printouts of large font size) •18 font size recommended Advantages •Cosmesis— the individual is able to read looking like a person with normal vision Disadvantages •Books are too heavy •Less availability
- 18. Glare, contrast andlighting control devices •RP patient — requires high illumination—recommended flash light •Glaucoma and cataract— glare —use different tinted lenses •Albinism—indirect lighting— proper seating arrangements against direct sun or use of curtains Control devices are 1. Adjustable table lamp 2. Adjustable wall lamp 3. Adjustable clip lamp 4. Halogen lamps
- 19. Posture and comfortmaintenance devices •Adjustable reading stands encourage a comfortable body posture to the patient
- 20. Hand writing andwritten communication devices Writing guides •Piece of black cardboard which has slit cut into it. •Black colour— enhance contrast— reading writing material •Eg: letter writer, cheque guides and signature guides helpful in written communication. Bold line notebook •Notebook with black bold line •Makes reading easier
- 21. Cont.. Felt tip penand 3B pencil •Bold pen and pencil (Eg: 3B, 4B) •Increase contrast —reading easy Devices for reading •Typoscope reading guide •Fixed reading stand •A talking calculator •Tape recorder •Flash card •Talking book •Talking dictionary
- 22. Orientation and mobilitydevices •Orientation—use remaining sense to establish one’s local in one’s environment •Mobility—art of moving from one place to another independently, safely •Cost effective •Easily available •Folding and unfolding models •Training is needed
- 23. Sensory substitution devices •Hearing, olfactory and tactual clue •Hearing and tactual— academic purpose • Olfactory sense—skill and mini Medical management and life skill device 1. Needle threader —has a tiny iron string help in threading a needle 2. Colour identifier —Tactual identifier—different shape of button and embroidery pattern. 3. Talking clock and watch —Raised button for no with speech output option.
- 24. Devices for Domesticactivity •High contrast stove •High contrast vegetable cutting board •Bright colour rack •Whistling kettle •Kitchen tool—bright colour and high contrast handle Devices for recreation •Large ludo •A large chess set •A TV with large screen •Large and colourful football •High contrast playing card
- 25. Devices for selfcare activities •A magnifying mirror with extra illumination Device for healthcare •Digital thermometer •A talking body thermometer •Insulin units measuring device Devices for computer tasks •Talking appliances, enlarged and high contrast screens, and enlarged or tactile keyboard •A zoom text ( special low vision software)