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Low Vision Devices

Low Vision Devices

April 30, 2019

Low vision is not defined by specific acuity limits. It is a condition that involves a minimal ability to see , which is unresolved or uncorrected by traditional eye glasses, contact lenses or corrective surgery. However, “persons with low vision may be helped to use their residual vision with special visual devices”.

Low vision is a continuum. Untreatable eye diseases causing low vision have always been overlooked. We present a few practical pearls on low vision devices, for everyday practice, for general ophthalmologists.

General Principles

There are certain general principles that need to be followed when assessing, training and prescribing low vision devices. The foremost prerequisite is proper lighting. One needs to assess whether visual skills have been mastered e.g. scanning, tracking and reading. The material used during assessment should be interesting, especially for children. Proper posture and reading distance should be maintained.

Low Vision Devices

Low vision devices helps the low vision client to use the residual sight more effectively, thereby enabling them to continue reading and participating in hobbies, activities and profession. These low vision devices range from simple to complex, depending on individual needs.

The low vision devices are categorized as:-

  • Non Optical Devices
  • Optical Devices
  • Electronic Devices
 

Non Optical Devices

 Example: Lamp, Cap, Writing guide, signature guide, Reading stand etc.

Optical Devices

 Microscopic glasses

Uses:

  • Reading any material.
  • For writing.
  •  Looking at objects from close range.
 

 Advantages

  • Psychologically Acceptable.
  • Easily Available.
  • Hands are free for tasks requiring manual manipulation.
  • Easy to carry.
  • Can be used for long periods.
  • Wider field of view.

But exact reading distance is important with microscopic glasses for proper magnification and clarity.

Practical tips for the clients with microscopic glasses:

When microscopic glasses are prescribed as low vision aids, it is necessary to inform the client of the optical principles and all the disadvantages. Low vision assistants should instruct clients in several areas. The most important is reading distance. The best way to teach adaptation to short focal lengths is to have the clients touch his nose with the reading material, then slowly take it back, until it focuses.

Hand Magnifiers

Uses

  • For reading signs, labels, price books.
  • Identifying money.
 

Advantages

  • Inexpensive and easily available.
  • Cheap to make
  • Easy to carry.
  • Available from low to high power.
 

Note: the patient has to hold the hand magnifier, thus not suitable for work involving use of hands.

Practical tips for the clients with Hand Magnifier:

When clients begin to use hand magnifiers, the tendency is to hold the lens up to the eye and look through it. They do not seem to grasp the idea of holding the magnifier near the page and maintaining the longer reading distance. To make it clear, have your client start with the magnifier on the page. They should then raise it slowly until the magnification is maximum.

Stand Magnifiers

Uses:

  • Reading from a book, or newspaper
  • Looking at a picture or diagram
 

Advantages:

  • Eye to lens distance can be varied.
  • Easy to use
  • Available from low to high power
  • Allows light onto print because of the thin legs
  • Useful for patient with constricted field of vision and macular degeneration.
  • Light weighted because of the plastic material

But may result in poor posture after prolonged use of stand magnifier.

Practical tips for the clients with Stand Magnifier:

The eye-to-lens distance causes some difficulty and requires explanation. It is usual for the patients to involuntarily pull on the stand magnifiers, as if viewing through a telescope. This will improve the field of view only minimally, and blur the image if accommodation is inadequate. Instruct your client to maintain an appropriate reading distance.

Telescopes

 Uses:

  • Reading from a black board or at a distance
  • Spot reading and viewing such as reading bus numbers and street signs.

Advantages:

  • Very small in size & compatible
  • Cosmetically easily acceptable
  • Can be used in a class room for black board reading
  • Very light weight
  • Available in spectacle mounted and clip on designs.

Other designs of telescope are also available

The disadvantage is the difficulty in reading & writing/ copying simultaneously.

Practical tips for the clients with Telescopes:

Client should be taught to use a telescope in several steps. First, the instructor should focus the telescope for infinity and teach the user the correct way to hold it. Using two hands to hold the telescope provides more stability than one, and one arm or hand should be supported against a stationary object or the body. The client should first view the distant object with the naked eye, & only then raise the telescope to view it more clearly.

Newer low vision devices available in India

Fresnel Prisms: These forms of prisms can be used to correct several visual disorders. These are more comfortable and cosmetically appealing than conventional prisms, & it can be stuck onto spectacles.

Useful as a field expander in case of hemianopias.

  • Useful in the cases of diabetic retinopathy, macular degeneration, to shift the scotoma
  • It can also be used in cases of nystagmus and strabismus
  • Electronic Devices CCTV (closed circuit television) is simply a video camera that projects an image on to a monitor or television screens. It is also called a video magnifier. It enhances the image up to 10 times to its original size, & can sharpen the contrast too.

Models available: Head mounted, Hand Held Camera’s, Separate Monitors, Stand- Alone, Television Screen.

The magnification is adjustable, according to user need & preference.

Uses:
Visually impaired people can use the same low vision aids for regular reading activity. Children can use the CCTV to enlarge the pictures, graphics and very small objects (such as coins, plants, insects etc.)

CCTV was not easily acceptable earlier due to high cost, but cost-effective versions are now available.

Guidelines For Prescribing

Optical LVDs

  • Determine the best distance correction
  • Measure the best corrected acuity
  • Determine the target acuity
  • Demonstrate the appropriate device
 

Low Vision and its management still remains a grey area for most health care providers in the field of ophthalmology. To meet these demands, all clients with low vision should receive an early and appropriate referral, preferably to an integrated programme.  Low cost high quality devices as made available to meet the requirements.

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Ojas Eye Hospital A Center of Excellence for Contoura Vision, Femto Bladefree Lasik in Mumbai, India.