When you go in for a routine two-yearly eye test with your optometrist, it is always helpful to bring your glasses prescription, especially if this is the first time you are visiting our practice in Canberra. Along with your current glasses and any contact lenses you might be wearing, bringing in all these would help our optometrist determine your most up-to-date prescription accurately.
Determining Your Spectacle Prescription
Our vision fluctuates throughout the day for various reasons. It can sometimes fluctuate as much as 10% of your prescription. That means if you have an optical prescription of -2.50D, it could fluctuate by as much as 0.25D.
Bringing in your previous optical prescription allows our optometrist to determine what results were finalised based on your comfort of vision. In most cases, if you were over or underprescribed by 0.25D of your optical prescription, it won’t impact hugely on your visual acuity. Still, it sometimes can interfere with the comfort of vision.
I have my glasses with me. Do I still need to bring in the written optical prescription?
Having your glasses is better than not bringing them to the appointment at all. Prescription in the glasses sometimes can be different to what is being prescribed on paper, especially if you have a high prescription.
Depending on the frame, if it has a significant wrap like a pair of sunglasses, any decent optical lens laboratory will compensate and tailor your prescription to your frames. This may involve adjusting the lens power of the optical prescription slightly depending on how the frame sits on your face.
Occasionally, your prescription may have prisms incorporated into your optical prescription. Prisms are used to correct ocular misalignment. Sometimes they are used to help with eye fatigue, especially with near work and computer usage. If that’s the case, often, the amount of prism incorporated in your prescription may not manifest itself when we check the power of the lenses of your glasses. Depending on the lens laboratory that makes your glasses, the prism can often be incorporated by adjusting your interpupillary distance (PD). This may not be apparent when we initially check the prescription of your glasses but would be mentioned in your prescription.
If your optical prescription has very high cylindrical power (astigmatism) and a significant difference between your right and left eye, then sometimes the prescription is adjusted and compensated for your comfort. Your optometrist could achieve this by modifying the script, either increasing or decreasing the power of the right or left lens to create more “balance” when you use your glasses. A more balanced prescription doesn’t necessarily mean you’ll see perfectly out of each eye individually but instead achieving the best comfort and clarity whilst using both of your eyes together. Again, this type of adjustment would be mentioned in your written optical prescription.
The Bottom Line
Having prior information regarding your lenses and your previous prescription is beneficial in updating your optical prescription. It will provide your optometrist with a clearer idea of your glasses prescription and what to prescribe to ensure your vision is clear and comfortable. Without having a previous prescription, a simple prescription update appointment could be needlessly drawn out and tiresome and risk becoming inaccurate. Your prior prescription gives us an idea of what answers you provided during your previous eye examination. It allows your optometrist to check for consistency and accuracy, ensuring your new pair of glasses are trouble-free.