Making Sense of Your Optical Prescription: Understanding Your Eye Condition

January 30, 2023

If you wear glasses or contact lenses, you may have received an optical prescription from your Optometrist. While the numbers and symbols on your prescription may look confusing, they are actually providing important information about your eye health. In this blog post, we will break down the four most common eye conditions and what they mean for your vision.

Myopia (Nearsightedness or Short-sightedness)

Myopia, also known as nearsightedness, is a condition in which objects up close are clear, but distant objects appear blurry. This is caused by the eye being too long or the cornea being too curved, which causes light to focus in front of the retina instead of directly on it. Myopia is indicated on a prescription as a negative number, such as -2.00.

Myopia often onsets in childhood and can progress quickly during the years we are growing fastest. Often, patients with myopia have at least one myopic parent. In recent years, new technologies in glasses and contact lenses have been shown to reduce the rate of progression of Myopia. Ask your Optometrist how we can help.

Hyperopia (Farsightedness or Long-sightedness)

Hyperopia, also known as farsightedness, is a condition in which objects at a distance are clear, but objects up close appear blurry. This is caused by the eye being too short or the cornea being too flat, which causes light to focus behind the retina. Hyperopia is indicated on a prescription as a positive number, such as +2.00.

Patients with uncorrected hyperopia tend to mention symptoms such as tired eyes, eyestrain and difficulty in lower light levels. These occur when the muscular ability of the eye (and flexibility of the crystalline lens) is unable to mask the condition.

Children with large amounts of hyperopia can present with 'a squint' (strabismus) and can develop a condition called Amblyopia (commonly called a 'lazy eye') which can also run in families. For this reason, in Scotland, children are screened at nursery age for eye movement disorders and visual dysfunction. Correction is available in the form of glasses, patching (occlusion therapy) and sometimes surgery.


Astigmatism is a condition in which the cornea is more 'rugby ball shaped', causing light to focus unevenly on the retina. This results in blurred vision at all distances. Astigmatism is indicated on a prescription as a number followed by a cylinder (CYL) and axis (AXIS) measurement. For example, -1.00/+1.25 x 90 indicates a prescription for a person with astigmatism who needs a -1.00 lens for nearsightedness and a +1.25 correction for astigmatism, with the axis of the astigmatism at 90 degrees.

Astigmatism usually presents as difficulty with concentrated tasks such as reading, screen work, TV, cinema and going to live events. Patients with astigmatism can have difficulty with lights in high contrast situations - typically streaks emanating from headlights, streetlights and floodlights. This makes difficulty with driving at night a good reason to have a chat with your local, friendly Optician.


Presbyopia is a condition that occurs over the age of 40 years old, causing the lens of the eye to become less flexible and making it harder to focus on objects up close. This results in the need for reading glasses or bifocal lenses. Presbyopia is indicated on a prescription as a “add” power, such as +1.50.


Your optical prescription is a valuable tool that helps your Optometrist determine the best correction for your vision. By understanding the measurements on your prescription, you can better understand your eye condition and make informed decisions about your vision correction. Regular eye exams are important for maintaining good eye health and keeping your prescription up to date. If you have questions about your prescription or any concerns about your vision, don’t hesitate to ask us for clarification.

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