How bad is my eyesight?

• 20/20 vision is the most commonly-known reference point for visual acuity – the measure of how clearly our eyes can see.
• Refractive errors are the leading cause of blurred vision worldwide and are straightforward to correct with glasses or contact lenses.
• Glaucoma, macular degeneration, and other serious eye conditions can also lead to poor vision without obvious symptoms – making regular eye examinations essential.

During an eye examination, your optometrist may describe your vision in numerical terms, such as ‘20/20 vision’ or ‘6/6 vision’. These numbers specifically refer to a measurement known as ‘visual acuity’, the most commonly used measure of vision function. Visual acuity measures the ability of the visual system (the eyes and the brain) to recognise fine details in the environment, or in other words – how clearly a person can see an object.

Visual acuity is often expressed as a fraction, where the first number indicates the distance that a person is standing away from the chart, and the second number indicates the distance a normal eye can read that particular line. The standard distance for reporting visual acuity in this format is 20 feet (6 meters).

Below are some examples of what this means for normal vision, vision that is above normal, and vision below normal.

• 20/20 (6/6) means the eye can see at 20 feet (6 metres) what a person with normal vision can also see from the same distance. This is considered normal distance vision.
• 20/40 (6/12) means the eye can see at 20 feet (6 metres) what a person with normal vision can see from 40 feet (12 metres) away. Because the eye can only recognise the same level of detail from a closer distance compared to ‘normal’, this suggests reduced visual acuity.
• 20/15 (6/4.5) means the eye can see at 20 feet (6 metres) what a person with normal vision can see from 15 feet (4.5 metres) away. Because the eye can recognise the same level of detail from farther away compared to ‘normal’, this suggests visual acuity above normal.

Good eyesight plays a critical role in every facet and stage of our lives, from assisting with everyday activities, to helping us function at our best at school or at work. Most of the time, minor reductions in vision are straightforward to correct with glasses or contact lenses. Poor eyesight becomes a potential concern when the eye’s visual acuity remains significantly reduced even with corrective lenses (‘best corrected visual acuity’).

The International Classification of Diseases (11th edition)1  is used by the World Health Organization to classify vision impairment and blindness based on visual acuity.

• No vision impairment: visual acuity equal to or better than 20/40 (6/12)
• Mild vision impairment: visual acuity between 20/40 (6/12) to 20/70 (6/18)
• Moderate vision impairment: visual acuity between 20/70 (6/18) to 20/200 (6/60)
• Severe vision impairment: visual acuity between 20/200 (6/60) to 20/400 (3/60)
• Blindness: visual acuity worse than 20/400 (3/60).

Adults can easily recognise when their eyesight is not clear enough for everyday activities, including reading, recognising faces and text, and driving at night. Children might show more subtle changes in behaviour, like holding books or tablets very close to their face, sitting very close to the television, squinting to see distant objects, or frequently rubbing their eyes.

Uncorrected refractive errors – including myopia (near-sightedness), hyperopia (far-sightedness), and astigmatism, are among the leading causes of reduced vision in people of all ages worldwide. Myopia, hyperopia, and astigmatism affect approximately 12%, 5%, and 15% of children globally, rising to 27%, 31%, and 40% respectively in adults.2  For most people, clear 20/20 vision is achievable with the right prescription.

Blurred vision is not always caused by a refractive error. Several eye conditions are leading causes of vision loss3 , including:

• Cataract
• Age-related macular degeneration (AMD)
• Glaucoma
• Diabetic retinopathy

Some of these, such as diabetic retinopathy, are closely linked to general health conditions. Others, such as age-related macular degeneration (AMD), glaucoma, and cataract, are largely age-related and cannot always be prevented, but can often be managed effectively when detected early.

Not necessarily. Poorer unaided vision is usually expected in eyes with higher prescriptions, as the prescription describes the optical power needed to correct the eye’s focusing errors.

The prescription does not indicate the best possible vision the eyes can achieve, nor does it accurately reflect the health of the eye. Once the correct prescription lenses are worn, poor vision often improves back to normal levels, provided that the eye and the rest of the visual system is healthy.

For example, someone with a -8.00 D prescription may achieve 20/20 vision while wearing glasses, while another person with only a -1.00 D prescription wearing the right prescription glasses may only have 20/40 vision due to an eye problem.

Our eyes must deal with a variety of lighting conditions in everyday life. Poor lighting conditions can negatively affect our ability to perceive details, especially at night time, during overcast weather conditions, or while indoors with dimly-lit environments. These can have serious impacts, as a disproportionate number of road traffic casualties occur at night.6 

Dim conditions can decrease vision in a number of ways, from the ability to detect fine detail and movement, light and dark contrast, and even colour vision.6  In low lighting, your pupils naturally dilate which allows more light into the eyes, at the cost of seeing glare and halos around lights, especially when driving at night. The back of the eye contains light-sensing cells (rod photoreceptors) that are specialised for low lighting, but are not very sensitive to detailed vision. Altogether, low lighting creates an unfavourable environment for clear vision.

While blurry vision at night is most commonly caused by uncorrected refractive errors, it can occasionally be a symptom of night blindness (nyctalopia). People with night blindness may have difficulty seeing in dim lighting or take longer to adjust when moving from a bright environment into the dark. It may be associated with conditions such as cataracts, retinal diseases, or vitamin A deficiency.

Low vision is different from having a high prescription. It refers to permanent vision impairment that cannot be fully corrected with glasses, contact lenses, medication, or surgery.

People with low vision still have some usable vision and are not completely blind, but their remaining vision is significantly reduced and can make everyday activities, such as reading, recognising faces, or moving around safely, much more difficult.

Many people with low vision can improve their independence by using low vision aids, special lighting, magnifiers, or other visual rehabilitation devices to make the most of their remaining vision.7