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Visual Impairment

Understanding Visual Impairment  

Understanding Visual Impairment

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The term ‘visual impairment’ refers to limitation of or absence of sight, which includes partial sight or blindness.  It does not refer to someone who is short-sighted (myopia) or long-sighted (hyperopia).

Partial sightedness
Someone who is partially-sighted has a serious loss of sight but they are not blind.
The World Health Organization (WHO) defines partial sightedness as where a person cannot clearly see how many fingers are being held up at a distance of 6m (19 feet) or less, even when they are wearing glasses or contact lenses.

WHO defines blindness as severe sight loss, where a person is unable to see clearly how many fingers are being held up at a distance of 3m (9.8 feet) or less, even when they are wearing glasses or contact lens. However, someone who is blind may still have some degree of vision.


Sight loss can be sudden and severe, or it can be a gradual deterioration over a long period of time. In most cases, sight loss occurs gradually with distant objects slowly becoming more difficult to distinguish.
Other than reduction of vision, you may experience other symptoms such as:

  • eye pain
  • a burning or gritty sensation in your eyes
  • a blurring or distortion of your vision

However, symptoms such as these are usually caused by specific eye-related problems, such as:

  • glaucoma (a group of eye conditions that affect your vision)
  • dry eye syndrome (keratoconjunctivitis)
  • cataracts (where a cloudy area forms in the lens of the eye)
  • macular degeneration (where your vision gradually begins to deteriorate over a long period of time)


The leading causes of chronic blindness include:

  • Cataracts - where a cloudy area forms in the lens of the eye
  • Glaucoma - a group of eye conditions that affect your vision
  • age-related macular degeneration (AMD) - where the vision gradually deteriorates with age
  • corneal opacities - where continual scratching of the cornea (the transparent window at the front of the eye) causes it to become inflamed and then opaque (cloudy)
  • diabetic retinopathy - where the tiny blood vessels that nourish the retina become damaged
  • trachoma - a bacterial eye infection
  • childhood eye conditions such as those caused by vitamin A deficiencies, for example corneal scarring and visual loss

Sometimes, blindness can also be caused by injury or trauma to the eyes. 75% of all visual impairment conditions can be prevented or treated.


During the testing of your eyes, your optometrist will carry out a number of different tests to check your vision and the overall health of your eyes. He will then determine whether you need glasses and, if so, what type of lenses you need. Some of these tests include:

  • Snellen testthis test is used to determine how good your vision is. During the test, you will be asked to read from a letter chart that has an illuminated background and rows of black letters that get progressively smaller on each line. This is the conventional type of Snellen chart, but some optometrists may use slightly different versions of it.
  • If you do not currently wear glasses or contact lenses and your optometrist decides that you need to wear them, you will need to have further tests to determine what kind of glasses (or lenses) you need. During these tests, you will be asked to wear a number of special lenses and to look at various charts displaying different letters and colours.
  • If you have a high risk of developing eye conditions such as glaucoma or diabetic retinopathy, or if your optometrist has found signs of these conditions, you may need to have some more vision tests. Some of the vision tests are as below:
    • Visual field test
    • Tonometry
    • Ophthalmoscopy


If you have an eye disease that causes visual impairment, it is important that you go to your eye doctor on a regular basis. Depending on the cause, there may be different options for treatment. These include surgery, laser treatment, medications and eye drops.


To stop your eyes becoming damaged by undiagnosed conditions, it is very important to have regular eye examinations. Most people should have their eyes tested at least once every two years. But if you have a medical condition, such as diabetes, glaucoma or high blood pressure, you will probably need to have your eyes tested more regularly. Your eye doctor can advise you on how often you should have your eyes tested.


Find out more information from:

Singapore National Eye Centre
NHS Choices
The AGS Foundation for Health in Ageing
Medline Plus


1. How often should I go for an eye examination?

As one gets older, age-related eye conditions are more likely to crop up. Look out for common eye symptoms like vision changes or pain, flashes or floaters, distorted lines, dry eyes that itch and burn. To keep track on vision changes, you should go for a baseline eye screening when you are 40. Your doctor will assess how often you need to return for follow-up screenings.

If you have a risk factor for eye disease (you have diabetes, high blood pressure, a family history of eye disease like glaucoma, or are taking prescription medications which affect the eyes), you should see your ophthalmologist more frequently. Ask your eye doctor on the ideal check-ups interval.

2. What should I do after my cataract surgery?

You will be entitled to medical leave after your cataract surgery, so try to take a rest. You may read,  watch TV or do light exercises. You can go out, but try to avoid crowded and dusty places. Wearing sunglasses when you are outdoors may help to keep your eyes comfortable and less sensitive to light. Follow your doctor's instructions carefully to instill eye drops for about a month to prevent infection and reduce inflammation. When you sleep, please put on the eye shield given to you for at least 1 week so that you don’t press on the operated eye. 

3. What should I avoid doing after my cataract surgery?

For the first few days, your vision may be blurred. You should be careful to avoid falling over or hurting your head or eye. It is common to experience some eye irritation and discharge after surgery. However, for the first month, refrain from rubbing or touching your eye and avoid getting dust or soap water in your eye.

Do not swim; do not use a hot tub, visit a sauna or spa. This is because there is a small wound in your eye, and you need to prevent it from getting contaminated. You may find that your pre-existing spectacles are not right anymore after the cataract operation. This is because the power of your operated eye has changed due to the surgery. Usually the power of the operated eye would stabilize at 1 month after the operation, at which time you can be measured for a new power for your glasses.

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