When you describe your glasses prescription as low or high, people are generally talking about their sphere value. The sphere (SPH) power indicates the level of visual correction required to address nearsightedness (myopia) or farsightedness (hyperopia).
How Sphere Values Work
- They’re measured in diopters
- An SPH value of 0.00 indicates 20/20 vision
- Diopters increase or decrease in increments of 0.25
- A lower SPH value signifies a milder refractive error
For nearsighted individuals, the lowest SPH value possible is -0.25. However, such a minor refractive error typically doesn’t necessitate eyeglasses.
Generally, corrective lenses aren’t needed for those with SPH values under -1.00, unless they struggle to see clearly in specific situations, like reading a board in class or viewing a presentation at work.
According to All About Vision, you have a low prescription strength if your SPH value falls within the following ranges:
- Nearsightedness: between -0.25 and -2.00 diopters
- Farsightedness: between +0.25 and +2.00 diopters
If I Have a Low Sphere Value, Does That Mean My Vision Is Pretty Good?
It’s easy to assume that having a low sphere value means that your vision is in good shape. However, this isn’t always the case.
Other vision problems like astigmatism or presbyopia can still impact your overall vision quality.
Even with a low sphere value, symptoms like eye strain, headaches, or night vision difficulties can occur and interfere with everyday tasks.
Determining Your Sphere Value
During a comprehensive eye exam, an eye doctor uses a phoropter to measure the exact level of nearsightedness or farsightedness you have.
The process involves reading an eye chart and testing a series of lenses to find the clearest vision.
If you have nearsightedness (difficulty seeing objects in the distance clearly), your sphere value will be a negative number.
If you have farsightedness (difficulty seeing objects up close clearly), your sphere value will be a positive number.
Remember to have regular eye exams to keep your prescription up-to-date, as vision changes can happen gradually. Ensuring that your prescription is accurate will help you see clearly and comfortably.