Minus Power Glasses: Everything You Need to Know
What Does Minus Power Mean in Glasses?
Minus power in glasses is used to correct nearsightedness, also known as myopia. If you are nearsighted, objects close to you may appear clear while objects farther away become blurred.
Myopia is shown as a negative number in the sphere or SPH field. Examples include -1.50 or -4.00. Higher negative numbers mean stronger correction is needed to focus distant objects.
Myopia occurs because the eye is longer than average. Or, the cornea focuses light in front of the retina.
How Does Minus Power Correct Myopia?
Minus lenses are also known as concave lenses. They alter light before it enters the eye to focus images correctly on the retina.
The lens power required depends on the degree of myopia. Someone with a prescription of -1.00 D needs less correction than someone with a prescription of -6.00 D.
A stronger minus prescription does not in itself describe the health of the eye. It simply indicates the amount of optical correction needed for clear vision.
How Is Minus Power Measured?
Lens power is measured in diopters (D). Myopic prescriptions are written with a minus sign, such as:
- -0.75 D
- -2.50 D
- -5.00 D
Your right and left eye can have different prescriptions, so it is common to see different values for each eye.
An eyeglass prescription may also contain other values. For example, if you have astigmatism, the prescription can include CYL and AXIS in addition to the sphere value.
Your prescription can change over time, particularly during childhood and adolescence, but changes can also occur later in life. Regular eye examinations help ensure that your glasses or contact lenses continue to provide the correction you need.
Does a Higher Minus Number Mean Stronger Glasses?
Yes. A more negative number means that a stronger lens power is required to correct the myopia.
A -5.00 D prescription is stronger than -2.00 D. This does not mean the eyes are unhealthy. It means more power is needed to focus distant objects.
With stronger prescriptions, eyeglass lenses can become thicker around the edges. Different lens materials and designs can sometimes be used to make high-prescription glasses thinner and lighter.
Can You Use Contact Lenses Instead of Minus Power Glasses?
Yes. Many people with myopia use both glasses and contact lenses, switching between them depending on the situation.
Contact lenses provide a wide field of vision. They move with the eye and have no frame. They are convenient for sports and other active tasks.
People with myopia can use several types of contact lenses, including daily contact lenses and reusable monthly contact lenses.
If you want to compare the options available, you can also browse our complete range of contact lenses.
Is a Contact Lens Prescription the Same as a Glasses Prescription?
Not necessarily. Both may use minus power for myopia. However, glasses and contact lenses sit at different distances from the eye.
This difference is relevant with stronger prescriptions. Contact lens power may not be identical to eyeglass prescription power.
A contact lens prescription also contains information related to the lens itself, such as base curve and diameter. Toric and multifocal lenses can include additional parameters.
If you want to understand these values, see our guide to contact lens parameters.
Do not order contact lenses using an eyeglass prescription. You need a valid contact lens prescription for that specific lens.
Choosing Between Glasses and Contact Lenses
Glasses and contact lenses can both provide effective correction for myopia, and many people use a combination of the two.
Glasses require little daily maintenance. Contact lenses provide more freedom during sports. The best option depends on your prescription, health, and lifestyle.
An optometrist can assess your eyes and fit the right lens. They will show you how to use lenses safely.
When Should You Have Your Prescription Checked?
Distant objects may become harder to see. You might squint more often. It may be time to check your prescription.
Regular eye exams are important even if vision seems stable. Professionals can assess your prescription and overall eye health.
Understanding Minus Power
A minus sign on your glasses prescription means that the lens is correcting myopia. The more negative the number, the stronger the optical correction required.
Myopia can usually be corrected with contact lenses. However, a contact lens prescription is not always identical to an eyeglass prescription.
Explore our range of contact lenses, including daily lenses and monthly lenses, at Netlens.