Is Minus 4.5 Legally Blind? What a High Minus Power Really Means

It is a worrying thing to type into a search box. Here is the short, calm answer: the number on your prescription is not how legal blindness is decided.

Lens power versus legal blindness

Your prescription number tells the optician what lens will bring your eyes into focus. Legal blindness is a different thing. It is judged from how well you can see with the best correction, together with your field of view, and the exact thresholds are set by each country's rules. A person who sees clearly in glasses is not described that way because of their power. Only an eye-care professional can assess your own eyes and give any certificate.

What -4.5 means

The minus sign means short-sightedness (myopia): near things are clear and distant things are blurry without your glasses. The 4.5 is the strength of the lens in dioptres. See how to read your prescription.

Is -4.5 high?

It is commonly described as moderate. Powers beyond roughly -6 are often called high myopia, though clinics use slightly different labels. Higher powers are usually checked more closely over time because they are linked with other eye conditions that an optometrist or ophthalmologist looks for.

What to expect from the lenses

• Thicker edges. Minus lenses are thicker at the rim, and a smaller frame keeps the edge thinner.
• High-index lenses are thinner and lighter. See high-index lenses explained.
• An anti-reflective coat reduces glare, which thicker lenses can show more. See lens prices.

What to do next

• Keep up regular eye tests. See how often to get your eyes tested.
• Report sudden flashes, new floaters, a curtain over your vision or sudden blur to a doctor straight away.
• For a child whose power keeps rising, speak to an eye-care professional about options.

This article is general information, not medical advice. For persistent symptoms or any sudden change in your vision, see an eye-care professional.