Low Vision, What Does it Means? Causes, Treatment, & Prevention - Ario Watson

Normal Vision

Low Vision

What is Normal Vision?

A person is able to perform all close and distant visual tasks that are normally expected in his community. Refractive correction (e.g. glasses) may be needed to give ‘normal’ vision. A person with ‘normal’ vision is someone who has between 6/6 and 6/12 (20/20 and 20/40) vision.

What is Low Vision?

A person with low vision is one who has impairment of visual functioning even after: treatment, for example an operation and/or standard refractive correction (has been given glasses or lenses) and has a visual acuity of less than 6/18 to light perception, or a visual field of less than 10° from the point of fixation (i.e. 20° across) but who uses, or is potentially able to use, vision for the planning and/or execution (doing it!) of a task.

How do we define who’s legally blind?

You’re legally blind if your better eye — when using a corrective lens — has a central visual acuity of 20/200(6/60)or lower, or field of vision of no more than 20 degrees.

The complete lack of light perception and form perception, and is recorded as “NLP,” an abbreviation for “no light perception.”

What Are Low Vision Aids?

Low vision aids are devices which help people use their sight to better advantage. These aids may be optical lenses, such as magnifiers or telescopes, or non optical devices, such as visors, filters, reading slits, stands, lamps and large print.

What are the Symptoms of Low Vision?

They may have difficulty :-

  • Reading
  • Using a computer or tablet
  • Writing
  • Watching television
  • Recognizing faces
  • Seeing switches, dials or other mechanical controls
  • Seeing the board at front of a school classroom
  • Shopping
  • Driving a car

What Causes of low vision?

Eye diseases are a common cause of low vision. For example:-

  • Hazy, blurry vision can result from Cataract.
  • Blurred or partially obscured central vision is typical of macular degeneration.
  • Diabetic Retinopathy causes blind spots, blurriness and visual distortions.
  • Poor peripheral vision is a hallmark of glaucoma.
  • Retinitis Pigmentosa reduces peripheral vision and the ability to see in the dark.
  • Heredity and Eye Injuries can result in low vision.

Vision loss can be classified into 4 basic categories:-

  1. Overall blurred vision
  2. Central field loss
  3. Peripheral field loss
  4. Hemianopic defects.

OVERALL BLURRED VISION

Such patients will show following signs:-

  • Reduced visual acuity
  • Reduced contrast
  • Poor night vision
  • Glare and photophobia

These signs will manifest following complaints from these patients:-

  • Difficulty in recognizing far of objects and details
  • Difficulty in reading and writing
  • Unable to write in straight lines
  • Glare
  • Loss of confidence in going outdoors at night.

The following intervention is helpful in solving their complaints:-

  • Increase contrast—in the house by using high contrast color schemes in furniture, door, windows etc.
  • Enhance contrast in reading and writing—use bright light, fairly good contrast print and black bold tip pens to write
  • Advise to carry a flash light, and install strong intensity light sources (preferably bulbs to fluorescent tubes) in staircase, kitchen, rooms, or work areas
  • Absorptive lenses and filters will help outdoors to reduce glare.

This group refers to patients who have total or partial loss of central field of vision.

These field defects are likely in following diseases: –

  • Diabetic Maculopathy,
  • Hypertensive Retinopathy,
  • Macular Degeneration,
  • Degenerative Myopia,
  • Optic Atrophy (Congenital),
  • Retrobulbar Neuritis Etc.
Diabetic Maculopathy
Degenerative Myopia

Such patients will show following signs:-

  • Cannot recognise fine details for distance and near
  • Poor color vision
  • Further reduction of visual acuity in bright light.

 On taking their history the following complaints are often referred to: –

  • Inability to see faces and recognize people
  • Difficulty in reading and near tasks
  • Cannot discriminate colors of clothes
  • Lacks confidence in going outdoors.

Following are the possible intervention or devices which can help the patients who lose their central vision :-

  • Advise sitting close to the object like during watching TV.
  • Reading disability is a major problem to solve. Denser the central vision loss greater is the problem in correcting them by optical devices. Reading can be possible by bringing the object as close as possible. High plus add glasses with full field frame may help. Stand Magnifiers usually work in helping them read through the eccentric areas
  • Enhance Contrast of the room and furniture.
Cannot discriminate colors of clothes
CONTRAST OF THE ROOM AND FURNITURE
CENTRAL VISION LOSS

PERIPHERAL VISION LOSS

This group refers to the patients who have lost their peripheral field of vision, totally or partially.

Chorioretinitis
Retinitis pigmentosa

These defects are likely in the following pathologies :-

  • Chorioretinitis,
  • Colobomas,
  • Glaucoma,
  • Degenerative myopia,
  • Optic atrophy (neurological)
  • Retinitis pigmentosa,
  • Retrobulbar neuritis, etc.
Retinitis pigmentosa

The patients with peripheral loss of field will show following signs :-

  • Mobility problems both indoors and outdoors
  • Slow dark adaptation
  • Poor vision in dim light
  • Poor near reading vision depending upon the extent of the field defect
  • Glare and photophobia.

These patients will have following complaints :-

  • Knocking over objects, and uncertainty in moving around
  • Inability to find or locate objects
  • Difficulty in reading because the words get lost.

Field expanders may be help?

  • Give time to eyes from moving indoors to outdoors and vice versa to allow for slow dark adaptation
  • Use sunglasses or glare cutting devices outdoors
  • CCTV systems or electronic devices help more in such cases than those with other type of field defects
  • Patients should avoid traveling alone in dim light and as far as possible carry a flash light with them.

Hemianopsia

Hemianopsia is loss of half of the field of view on the same side in both eyes. People who have a stroke or traumatic brain injury, may lose one half of their side vision to the right or left.

Effects include :-

Half of the visual field is lost. Can’t to see to either the left or right from the centre of a person’s field of vision.

Optical Low Vision Aids

Optical aids use magnifying lenses to make objects look larger and easier to see.

Magnifying spectacles.

Magnifying spectacles are worn like eyeglasses to keep your hands free. They can be used for reading, threading a needle or doing other close-up tasks. Often objects need to be held much closer with these magnifying glasses than with regular reading glasses or bifocals.

Hand-held magnifiers.

These are magnifiers to hold over print material. Some models have built-in lights.

Stand magnifiers

These magnifiers rest above the object you are looking at. This helps to keep the magnifying lens at a proper distance. Being on a stand also is helpful to people who have a tremor or arthritis. Some stand magnifiers have built-in lights.

Telescopes

These are used to see objects or signs far away. Some telescopes can be attached to eyeglasses. Others are held like binoculars.

Non-Optical Devices

The following are some examples of nonoptical devices :-

  • Reading lamp 
  • Reading stand 
  • Writing guide 
  • Reading guide 
  • Signature guide
  • Bold line note books and paper
  • Black ink bold tip pens
  • Soft lead pencil — 2B, 4B, 6B etc.
  • Needle threader
  • Notex

Watches, timers and devices with audible announcements to measure blood pressure or blood glucose.

Large-print books, newspapers, magazines, playing cards and bank checks

Audible books

Telephones, thermostats, watches and remote controls with large-sized numbers and high-contrast colors

Needle threaders, magnifying mirrors and tactile (textured) labels

Electronic Devices

Video magnifiers  (CCTV’s, also called video magnifiers).

The primary electroptical device is a standard CCTV (Closed Circuit Television) System.

 These electronic devices are available in portable and desk formats. They combine a camera and a screen to magnify printed pages, pictures or other small objects. You can adjust them to meet your special vision needs.

Computers can usually read aloud or magnify what is on the screen.

JAWS screen reading software for the blind It is software which converts a normal PC into a talking computer so that the blind can learn to operate the computer independently.

Audio books and electronic books

The audio books, you can listen to text that is read aloud. With electronic books like Kindle, Nook and others, you can increase word size and contrast.

Smartphones and tablets 

let you change text size, adjust contrast and use voice commands. There also are many apps to choose from, such as programs that read material aloud, magnify or illuminate.

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