What Does Sphere, Cylinder and Axis Mean?

What Is Sphere in Eye Prescription?

Sphere in an eye prescription indicates the person’s required lens power to be able to see clearly. Sphere on your prescription may be written as SPH and is measured using the unit diopters to correct either farsightedness or nearsightedness.

How are Nearsightedness and Farsightedness Represented in Diopters?

Nearsightedness and farsightedness are represented in diopters through the numbers that are displayed on your prescription. In front of these numbers, there will either be a minus (-) sign if you are nearsighted or a plus (+) sign if you are farsighted.

How is Astigmatism Measured?

Astigmatism is measured in diopters on your prescription. The range that most people with astigmatism have is between 0.5 and 0.75 diopters according to the American Academy of Ophthalmology. If your astigmatism strength is 1.0 or more, you may likely require glasses and patients who do not have any astigmatism have 0 diopters.

Why is the "Axis" Important in Treating Astigmatism?

The axis is important in treating astigmatism as it indicates the location of astigmatism in the eyes according to the Vision Centre. The axis is measured in degrees and ranges from 0 to 180. Similarly to a map, the 180-degree line runs across the eye from east to west and the 90-degree line goes up and down, according to the American Academy of Ophthalmology. For normal eyesight, your prescription would not have an axis number as having an axis number is only an indication of astigmatism present in the eye.

What do "OD" and "OS" Mean on an Eyeglasses Prescription?

OD and OS on an eyeglass prescription refer to the right and left eye respectively. OD is short for the Latin term oculus dexter which means ‘right eye’. OS is a short for the Latin oculus sinister which means ‘left eye’. This differentiation between left and right eye is crucial in determining the prescription of various lens types such as progressive lenses as vision strength can and often does vary in both eyes.

How Do Optometrists Determine the Axis Value for Astigmatism?

Optometrists determine the axis value for astigmatism by using special tools during a complete eye test. Optometrists can identify astigmatism through a refraction test, which helps to identify how the eyes bend light. The optometrist may likely point a bright light towards your eyes and get you to look through different lenses.

What Happens if Astigmatism is Not Corrected with Eyewear?

Astigmatism that is not corrected with eyewear may lead to the development of amblyopia mainly in children. Refractive amblyopia is a type of amblyopia that can develop when there is an imbalance in the focusing ability in the eyes as a result of astigmatism and other conditions. Uncorrected astigmatism may also lead to other complications such as eye strain and headaches. However, it is also important to note that not all eyewear prescriptions require astigmatism correction.

How do Optometrists Test for Refractive Errors During an Eye Test?

Optometrists test for refractive errors during an eye test using tools such as autorefractors and phoropters. Autorefractors measure the refractive error of a patient's eye, by presenting the patient with a distant image to focus on and using computerized equipment to calculate the power. This allows for an assessment of the eye’s focusing abilities, as well as an initial prescription estimate. The phoropter allows for further prescription accuracy. You will be asked by the optometrist to look at an eye chart, as various lenses are cycled in front of each eye. You will be asked which lens offers better vision.

How does Pupillary Distance (PD) Affect Lens Accuracy?

Pupillary distance affects lens accuracy as if it is measured incorrectly, the optical centre will be incorrectly placed within the prescription frames. The optical centre refers to the part of the lens where the wearer experiences the clearest vision according to the Community Eye Health Journey.

What is an Example of a Glasses Prescription?

An example of a glasses prescription is if you have -1.00 under the term SPH (sphere), this indicates that you require 1 diopter of strength to correct nearsightedness. If there is a +2.50 on your prescription, this indicates that 2.5 diopters are needed to assist with farsightedness. The higher the number in this section, the more correction needed. Next to SPH, there is a column for cylinder which is where a number with a minus or plus may appear to indicate the extent of astigmatism in each eye. This column is then followed by more columns for Axis, Int ADD, ADD, H Prism and V Prism. An axis will have a number between 0 and 180 degrees to specify the right angle to correct astigmatism. ADD, which stands for addition, will signify how much magnification is required for near vision which is accompanied by a plus symbol. This indicates if you require reading glasses, or multifocal or bifocal lenses. Int ADD stands for intermediate addition and indicates the magnification needed for intermediate vision such as for computer use. Prism may be added to your prescription if you are experiencing double vision or have difficulty focusing. A possible example of a glasses prescription for astigmatism will include a number in the cylinder column of your prescription. According to the Vision Centre, astigmatism that measures from 1.00-2.00 diopters is considered mild, severe astigmatism is 2.00-3.00 and extreme astigmatism is 3.00 diopters and above.

How Often Should Eyeglasses Prescriptions Be Updated?

Eyeglass prescriptions are generally recommended to be updated every 2 years. For seniors, it is recommended this be done annually as eye sight tends to weaken in old age. Ultimately, it is important to be aware of signs of eye weakness such as squinting, headaches and blurry vision. An eye test should be done as soon as you experience symptoms such as these as you may be in need of a new prescription.

What are the Risks of Wearing Glasses with the Wrong Prescription?

The risks of wearing glasses with the wrong prescription include eye strain and fatigue, blurred vision and dizziness. Read more about these high risks of wearing glasses with the wrong prescription in detail below.

• Eye strain and fatigue: Eye strain and fatigue can occur as your eyes will be forced to focus harder on what is in front of them, leading to strained vision. This can cause achy and tired eyes when wearing incorrect prescription glasses.
• Blurred vision: Blurred vision will likely occur when wearing the wrong prescription, as well as altered depth perception. This can make a variety of tasks, such as reading and driving more difficult and unsafe respectively.
• Dizziness: Dizziness can occur as a result of wearing the wrong prescription. The lack of alignment between your prescription and your eyes true vision needs can cause vertigo particularly when doing sudden eye movements.

How does Age Affect Changes in Eyeglass Prescription?

Age can affect change in eyeglass prescriptions particularly in the early to mid-40s according to the Americans Optometric Association. During this time, adults and even seniors may start to have problems seeing clearly at close distances, which is referred to as presbyopia. If you find yourself holding books farther away to see clearer or removing your glasses to see better up close, you may have presbyopia. It is important to consult an optometrist when eye problems such as this arise, alongside other vision changes that occur as you age.