Understanding Your Prescription
Updated: Aug 5, 2021
You may not realise it, but optometrists use a wide variety of tests and procedures to examine your eyes. These tests range from reading an eye chart to complex tests using high-powered lenses to visualize the tiny structures inside of your eyes.
Before you even enter the testing room, you will usually be taken to a pre-testing area to use two pieces of equipment.
One is an Optomap image which is fast, painless and comfortable. Nothing touches your eye at any time and it is suitable for the whole family. To have the exam, you simply look into the device one eye at a time (like looking through a keyhole) and you will see a comfortable flash of light to let you know the image of your retina has been taken.
Under normal circumstances, dilation drops might not be necessary, but your eye care practitioner will decide if your pupils need to be dilated depending on your conditions. The capture takes less than a second. Images are available immediately for review AND you can see your own retina. You see exactly what your eye care practitioner sees - even in a 3D animation.
The visual field test is a subjective measure of central and peripheral vision, or “side vision,” and is used by your doctor to diagnose, determine the severity of, and monitor your glaucoma. The most common visual field test uses a light spot that is repeatedly presented in different areas of your peripheral vision.
In some opticians, you may find the Optometrist using a different Glaucoma test in their room. More commonly though this is done as part of the pre-test before the main eye examination. This test is important as typically you have no warning signs of glaucoma until you already have significant vision loss. For this reason, routine eye exams test for this to rule out early signs of glaucoma to protect your eyesight.
The Eye Examination
Once in the test, the optometrist will ask various questions, even if you have been seeing the same Optometrist for years, to understand your any progressive symptoms from previous history you may have. Your optometrist will ask why you are having your eyes examined, whether it is a routine check-up, or if you have come for a specific reason.
If you are experiencing problems with your eyes or vision, your optometrist will need to know what symptoms you have, how long you have had them and whether any changes have happened suddenly or slowly over a period of time. They will also need to know about your general health including any medication you are taking, whether you suffer from headaches, or have any close relatives with a history of eye problems that they may not already be aware of.
You will also be asked about your previous glasses or contact lenses. In addition, your occupation and hobbies such as sport can influence the type of lenses that are beneficial to your suited lifestyle.
A comprehensive eye exam evaluates your vision and the health of your eyes. There are various eye and vision tests that you are likely to encounter during your eye exam. You will be asked to look at the Snellen eye chart. This is the most known part of the test that everyone associates with an eye examination, looking at the letters ranging from very large at the top, to the tiny letters right at the bottom. Further tests determine your visual acuity, measuring the sharpness of your vision to get pin point accuracy in your final prescription. Sometimes a small hand held acuity chart is used to measure near vision also.
When your optician covers one eye at a time they are checking to see how your eyes work together in focusing on objects across the room, then on objects close to you. The optometrist can the examine how well your eye moves to pick up and focus on a fixed object.
Retinoscopy is where your optometrist obtains an approximation of your eyeglass prescription. In retinoscopy, the room lights will be dimmed and you will be asked to focus on a large target (usually the big “E” on the eye chart). As you stare at the “E,” your eye doctor will shine a light at your eye and flip according lenses in front of your eyes, which will determine your exact prescription.
The optometrists will also observe your eyes under a slit lamp to look at the general health of your eyes under high magnification. They will be looking at your eyelids, cornea, conjunctiva, iris and lens. Your optometrist will also use a hand held devise to look at the back of the eye to observe the retina and optic nerves.
A lot of people put off going to the Opticians because they are not having any problems with their vision, in the same way one puts off going to the dentist until you break a tooth! However it is good to get into the habit of getting your eyes checked once every 2 years, to ensure your eyes are healthy. Consider it an MOT on your eyes!
A copy of the prescription will provide dispensers with what refraction is required to provide you with clear vision again. The dispenser will go through the best options in frame choice and type of lenses that best suit your needs.
If you wish to try contact lenses, additional tests are required as ordinary sight tests are not sufficient to determine your prescription. Other tests also need to be conducted to determine the water content of your eyes, and the curvature and diameter of the contact lens. These tests are not conducted in a regular eye test. Even if you’re wishing to wear contact lenses full time because you hate wearing glasses, it’s not good practice not to at least own 1onepair of specs, or you are likely to over use your contact which ultimately causes problems with the eyes. What if your eyes are tired and you don’t wish to wear them from time to time. Contact lenses are not an excuse to ditch those glasses completely!
With glasses now being a fashion statement it’s easy to find something lovely you will be happy and proud to wear out of the house deterring you from not wearing your contact lenses 24-7!
Understanding your prescription
You will see your prescription for your right and left eye. The first column will say SPH which is an abbreviation for Sphere. It is the measurement of the correction on focusing power of the lens, measured in dioptres. It can read a – sign or a + sign. A negative sphere indicates not being able to see in the distance; the + not being able to see close objects. The higher the sphere, the great the amount of correction required to see correctly and thicker the lenses will be unless you have a thinner lens made, what we call a higher ‘index’.
The second column will say CYL which stands for cylinder. It’s the measurement of any degree of astigmatism. Basically what this means is, naturally a person’s eye is shaped like a football, however a person with an astigmatism will have an eye shaped a bit more like a rugby ball. The higher the number, the greater the degree of astigmatism (this is can be written in + or – depending on where you get tested).
Lastly, the third column reading Axis, just tell you what orientation/ direction the astigmatism is sitting at. It is measured in degrees from 1 to 180. You will only have a number written in that column if you have an astigmatism.
This sounds like a bit of a minefield, however it’s worth noting that most people with a prescription do have some degree of astigmatism even if very slight. It’s nothing to worry about.
Always feel free to ask the Optometrist or dispenser about your prescription to get a better understanding if you are unsure about anything. We are always there to help and would rather you left our practice without any unanswered questions or concerns.