When you receive your eye test results, you’ll likely notice various terms and strange-looking abbreviations.
One of the first key values you’ll see is SPH, which stands for 'Sphere.' This value plays an important role in determining the strength of the lenses you need to correct your vision.
In this article, I’ll break down what SPH means, how it affects your vision, and why it matters when choosing your prescription glasses.
Let’s dive in.
What is SPH?
SPH is an abbreviation for sphere; a measurement that indicates the focal strength of a lens, measured in dioptres (D), needed to correct either short-sightedness (myopia) or long-sightedness (hyperopia). This measurement is what helps your optician create lenses to correct your vision.
Positive SPH (+): If the number has a plus sign, it means you are long-sighted. You may find it harder to focus on close objects for tasks such as close-reading.
Negative SPH (-): If the number has a minus sign, it means you are short-sighted. You may struggle to see distant objects clearly such as the television or reading road signs.
For example, an SPH of +2.00 would help someone who is long-sighted, while an SPH of -1.50 would help someone who is short-sighted.
How SPH affects your lenses
The stronger your SPH value, the more focal power is required to correct your vision. This is achieved through stronger lens curvature which can be either convex (for + prescriptions) or concave (for – prescriptions).
Your strength of sphere power can affect the weight, thickness and overall cost of your prescription lenses. Depending on your prescription, you may require thinner lenses, also known as high index lenses.
If you're buying prescription lenses online, check out the table below which illustrates the best refractive index based on your SPH and CYL powers.
|
SPH power |
CYL power |
Rec. index |
|
up to +/- 2.00 |
Up to +/- 1.50 |
1.50 (Standard) |
|
+/-4.00 to 6.75 |
Up to +/- 2.00 |
1.60 (Thinned) |
|
+/-7.00 to 9.00 |
Up to +/- 2.00 |
1.67 (Super thin) |
|
+/-7.00 to 9.00 |
+/-2.25 to 6.00 |
1.74 (Ultra thin) |
Are high index lenses necessary?
Nobody wants magnified “bug eyes” or ridiculously thick, heavy lenses. This is why high index lenses are a good option for thinner sleeker lenses if you have a high SPH or CYL value.
For example, a +5.00 SPH in a standard index lens will be much thicker compared to a +5.00 SPH in a 1.67 index lens.
How SPH affects your frame
Strong sphere powers can also influence the type of glasses frame you can wear. If you’re shortsighted and have a high minus (-) SPH power, your lenses will be thicker at the edges where they locate into the frame. Spectacles made from metal or thin acetate may expose the edges of your lenses which can look a little cumbersome.
If you have a strong minus sphere power, it’s a good idea to stick to thick acetate frames and choose high index lenses to avoid your lenses ‘spilling’ out the rims. Aspheric or double aspheric lenses will also help to reduce their weight and thickness – all whilst making them appear flatter and more visually appealing.
SPH in combination with other prescription values
Your SPH value is just one part of your overall eye prescription. You might also see values for CYL (Cylinder), AXIS, ADD and Prism. These work together to give you the most precise vision correction possible.
While SPH corrects either short-sightedness or long-sightedness, CYL and AXIS are used to correct astigmatism, a condition where the cornea isn’t symmetrically curved. Together, these values give the information needed to create prescription lenses that meet your unique vision needs.
How to read SPH on your prescription
Understanding your prescription can be straightforward once you know what to look for. You’ll always find the SPH as the first value under a heading marked “SPH” or “Sphere” on your prescription for your right (OD) and left (OS) eyes.
Here’s a typical example:
|
|
SPH |
CYL |
AXIS |
|
OD (R) |
-1.75 |
-0.50 |
090 |
|
OS (L) |
-2.00 |
-0.75 |
085 |
In this case, the person’s SPH for their right eye is -1.75 and -2.00 for their left eye, indicating they are short-sighted. Their lenses will help them see distant objects more clearly.
FAQs about SPH
What is a normal SPH?
There isn’t really a 'normal' SPH as it depends entirely on your vision. However, many people have prescriptions that fall between -3.00 and +2.50, which is considered mild to moderate in terms of vision correction.
Is SPH good or bad?
SPH isn’t inherently good or bad—it’s simply a dioptric measurement to correct near or farsightedness. The SPH value tells your optician how much correction your eyes need to help you see clearly.
Do I need glasses for SPH?
Whether or not you need glasses depends on your required SPH (sphere) power and how it impacts your day-to-day vision. Even a mild SPH of +/-1.25 may warrant glasses for tasks like driving, working on a computer, or reading.
Is 2.25 SPH good?
An SPH of 2.25 is neither 'good' nor 'bad'—it simply indicates the dioptric power your eye/s need to see. In this case, it would represent moderate correction for either long or short-sightedness.
Is 0.75 SPH eyesight bad?
An SPH of 0.75 is considered mild and typically means you only need slight correction for clear vision. A sphere of this strength is quite common and many people with this prescription only wear glasses part-time, such as when reading or driving.
What is the lowest eye prescription?
The lowest SPH value typically prescribed for glasses is around +/-0.25. While this is a very mild correction, it can still make a noticeable difference for people who need it.
There is, however, the possibility of a 'zero-strength' lens which is known as plano (Latin for plain). If you see PL, 0.00 or an infinity symbol (∞) it means you require no corrective SPH power in that eye.
Please note that you can have a plano sphere power, but may still require a cylinder correction for astigmatism.
I hope this guide has helped you get better understanding of SPH on your eye prescription and why it’s important when choosing your glasses.
If you want more information about your prescription or lenses, please check out our other eyecare blog posts.
Thanks for stopping by.