Part II: Lenses: How To Get The Best

Times are tough. Which means buying an inexpensive pair of prescription glasses online may seem like a good idea. But is saving a few dollars worth it in the long run, especially when you may be harming one of the greatest senses you’re lucky to have? In the second part of our blog series, we explore the potential hazards of incorrect lenses when buying online.

The Prescription

When you go get your eyes checked, the Optometrist puts a large instrument called a phoropter on your eyes. We all know the 1, 2, 3, 4 dance, as the Optometrist figures out which lenses help make the letters in front of you clearer, but what’s actually going on there? The doctor is doing a refraction test, in essence working out the best way to bend the light to help you see better. They’re also helping to correct where an image lies on your retina, so that your brain can perceive it correctly. This test will help the Optometrist identify your prescription. The doctor will eventually hand you a piece of paper with numbers on it, some plus or minus symbols and, for some, degrees for axis.

The Problem: When you go online to buy your glasses, you’re asked to input your prescription. But there are so many things that can go wrong when you’re entering these numbers. Even the tiniest typo can cause severe headaches, eyestrain, poor vision, nausea, and even loss of colours, causing your eyesight to get worse! Because the average person doesn’t understand what their prescription means, they’ll often enter +5.00, for example, instead of +0.50, or put in a plus symbol instead of a minus. And believing their Optometrist gave them a prescription that’s too weak or too strong, some people will even add or subtract numbers on the fly. This is a disaster waiting to happen.

The Measurements

A hugely important measurement when you’re buying prescription eyewear is your pupillary distance. Your PD informs the person making your glasses as to where your eyes will sit in the lenses. It’s the distance, in millimeters, between the centres of the pupils in each eye. Another key measurement is the height of your ocular centre, which ensures that you look through the middle of the lens. Positioning the lenses correctly in relation to the centre of your pupils and the height of the ocular centre are key to optimum vision.

The Problem: When you’re buying a pair of glasses online, the site will tell you how to take your own PD. But measuring your PD is simply not a do-it-yourself kind of thing. Imagine trying to look in a mirror while holding a ruler against your nose to measure from the centre of one pupil to the other. It’s virtually impossible to get an accurate measurement this way. If your PD is not accurate, you will experience a prismatic effect, an effect that occurs when light bends in the wrong direction. This causes poor vision, headaches, and eyestrain, potentially making your eyesight worse. 

The Lenses

Production for lenses and coatings have greatly improved in the last five years, focusing on new technologies that provide you with crisper and clearer vision. Getting the right lenses has never been more crucial, both in terms of getting the proper vision correction as well as getting a cosmetically appealing piece of eyewear. There are six basic types of materials that are used in making prescription lenses: Regular Plastic (1.49 index), Polycarbonate (1.59 index), Mid-Index Plastic (1.6 index), High-Index (1.67 index), Ultra High-Index (1.74 index) and Glass. All of these options have pros and cons, benefitting each individual differently depending on their prescription and use. And cosmetically speaking, your lenses can affect the way your eyes look in your glasses, making them appear larger or smaller. And since the current style is to wear bigger frames with minus prescriptions, you have to look out for what we call “peanut head syndrome.”

The Problem: You’re not in the optical field, so when it comes to buying your lenses online, you don’t even know where to start. The websites will all offer you single vision lenses, and then make you pay for additional scratch-resistant coating, UV protective coating and anti-reflective coating. How about we let you in on a little secret: The single vision lenses you’re buying automatically come with those coatings! And the “free” lenses you’ll get are made from impact-resistant polycarbonate, a material that’s bulletproof but expands and contracts in certain environments. This means that your lenses won’t recognize certain wavelengths of light, distorting your vision and allowing for loss of colour. The ironic part is you’ll be using technology to order something that is lacking technology in every sense.

The Bottom Line

All Optometrists, Ophthalmologists and Opticians in Canada are governed by very specific standards of practice. Rules are put in place for the safety of the patient. Once a prescription lens is put into a pair of eyeglasses, it becomes a medical device. Your local Optometrist and Optician have standards that they abide by, and a continuing education is a large part of that. We are all up to date with the latest technologies in lenses and contact lenses, and we pass that knowledge on to you. So when it comes to your vision, leave it to the experts.