What Does My Eyeglass Prescription Mean? An Easy Explanation by an Optometrist
Reading your eyeglass prescription can initially seem confusing due to the abbreviations and numbers. Here's an easy guide to help you understand the key elements of your prescription:
OD and OS: These are abbreviations derived from Latin terms. OD (oculus dexter) refers to the right eye, and OS (oculus sinister) refers to the left eye. Sometimes, you might also see OU, which means both eyes.
Sphere (SPH): This number indicates the power of the lens needed to correct your vision. A negative value (-) signifies nearsightedness (myopia), and a positive value (+) indicates farsightedness (hyperopia). The number is measured in diopters, the unit used to denote the power of the lens. The higher the absolute value of the diopter, the stronger the lens's power and the more significant the vision correction it provides.
Cylinder (CYL): This value is present if you have astigmatism, which means your cornea is irregularly shaped. Astigmatism is a common condition that can cause blurred or distorted vision. Like the sphere, the cylinder is measured in diopters. A negative cylinder number suggests the lens must correct for nearsighted astigmatism, while a positive number is for farsighted astigmatism. If your prescription has no astigmatism, your optometrist may denote this by writing D.S., which stands for diopter sphere. Most lenses are manufactured in negative cylinder, so your optometrist or Licensed Optician will need to transpose your prescription if it’s written in positive cylinder form.
Axis: This number appears if your prescription has a cylinder value and ranges from 1 to 180 degrees. It indicates the orientation of the astigmatism in your eye. The axis number should always be written as 3 numbers to ensure accuracy. So we would never write axis 47, we would instead write axis 047.
Add: This number is used for multifocal lenses like bifocals, trifocals, or progressives. It represents the additional magnifying power applied to the bottom part of the lens to assist with reading. It's also measured in diopters.
Prism: This is less common and is used to help correct eye alignment problems. It's measured in prism diopters, and it helps align the vision in both eyes, preventing double vision or improving binocular vision function for near-point or distance activities.
Pupillary Distance (PD): This is the distance between the centers of your pupils, measured in millimetres. Monocular Pupillary Distance (PD) measurements, detailing the distance from the bridge of the nose to the center of each pupil, are generally superior to binocular PD measurements, which only record the total distance between the pupils. Accurate monocular PD ensures that the optical centers of the lenses align exactly with the line of sight for each eye. This precise alignment prevents discomfort, eye strain, and blurred vision, making monocular PD measurements essential for optimal eyeglass performance.
When you receive your eyeglass prescription, it might look something like this:
OD: -2.00 -1.25 x 90
OS: -1.50 -1.00 x 85
Add: +2.00 (if needed for reading)
The first number (-2.00 and -1.50) represents the sphere, the second number (-1.25 and -1.00) is the cylinder, and the third number (90 and 85) is the axis. The Add value is usually a uniform number that applies to both lenses if required. However, in some cases, this power may differ between the eyes. This might be because a person had an eye surgery on only one eye, or because of a large difference in power between their two eyes.
Does My Prescription Specify The Lens Design?
While your eyeglass prescription provides detailed information about the power needed to correct your vision, it typically doesn't specify the lens design or materials. This aspect of your eyewear is crucial and can greatly influence how comfortable and effective your glasses are in daily use.
It's best to consult with a Licensed Optician to navigate your lens choices. They have the expertise to recommend the best lens types, materials, and coatings that complement your lifestyle, prescription needs, and aesthetic preferences. This is especially important for progressive, office, and higher index lenses. By having this conversation, you ensure that your eyeglasses are not only functional but also tailored to provide the best vision and comfort possible.
When Does My Eyeglass Prescription Expire?
Eyeglass prescriptions generally have an expiry date determined by the prescribing optometrist, but they usually remain valid for one to two years. The exact duration can vary depending on factors such as the patient's age, eye health, and how stable their vision is.
Due to rapid vision changes, children and older adults might need more frequent prescription updates. Similarly, individuals with certain medical conditions like diabetes or those experiencing noticeable vision changes might require more frequent examinations and prescription updates. The expiration of your eyeglass prescription is determined by medical guidelines and individual eye health, not by the type of insurance you carry.
That said, the most common expiration date for eyeglass prescriptions is one year. However, many opticals may extend this timeline to two years without written consent from your optometrist. It's important to note that if you're purchasing new eyeglasses because your vision doesn't seem that clear, it's always recommended to see your optometrist for an eye health examination and updated prescription. This regular check-up is crucial for maintaining your eye health.
It's never recommended to refill an eyeglass prescription that's more than two years old. Vision can change significantly over time due to factors like aging, health conditions, or even lifestyle changes. An outdated prescription can lead to inadequate vision correction and may contribute to headaches or other visual symptoms.
You Never Need To Ask For A Copy of Your Prescription
Under regulations, your optometrist must provide you with a copy of your eyeglass prescription after your eye exam; you do not need to request it. Providing patients with their prescriptions immediately after their exams promotes transparency and empowers individuals to make informed decisions about their eyewear, enhancing consumer rights and encouraging competitive pricing among providers. It’s important to be cautious of eye care clinics that direct you to speak with a sales associate to receive your prescription.
In addition, you should be wary of eye clinics offering free eye exams in exchange for purchasing eyewear, as this could indicate a compromise in the quality and impartiality of the eye care services provided.
Fill Your Eyeglass Prescription with The Latest in Eyewear and Lenses at Helio Optometry in Edmonton
If your glasses no longer seem to be doing the trick, or if it's just been a while since your last check-up, it's probably time for an update. Don't let blurry vision make your days harder. Book an appointment at Helio Optometry, where expert care meets precision in every prescription. Our comprehensive eye exams are tailored to meet the unique needs of each patient. Take a step towards clearer vision today because seeing well should never be out of sight! Contact us today for more information.
