Will My Prescription Glasses Be Thick?
It’s one of the first questions directed at optometrists when it comes time to settle on a pair of prescription lenses: “How thick will they be?”
How Thick Will My Prescription Glasses Be?
You, because “thick” is subjective. Some people consider any lenses that are not completely hidden within a frame to be thick. Others notice thickness only when it reaches the level of “Coke Bottle” glasses.
Your prescription, in that a stronger one will produce a thicker lens. Diopters are the units used to measure refractive errors and the lenses used to correct them. The higher your corrective diopter rating grows the more curve your lens will require to compensate…and more physical material will be required to house those longer, deeper curves. Any prescription with a diopter rating in excess of +/- 4.0 or so is generally considered to be entering the high end of the spectrum. The higher that diopter rating creeps, the thicker the lenses grow. Some people require prescriptions as high as +/- 20.00 diopters or more, producing lenses that are extremely thick, heavy, and distortive.
Additionally, the type of prescription you require plays a factor in thickness. A prescription for farsightedness, measured in “+” diopters, requires lens curves that are thinnest at the center and grow progressively thicker as they fan out. The edges of a farsighted prescription are the thickest part of the lens…so even a relatively mild prescription can result in lenses that jut out from the frames, distort the look of the eyes, or preclude you from selecting certain types of frames due to the thickness and weight of the lenses.
High index lenses, which are made of a plastic or glass material that is specially formulated and compressed to produce thinner lenses, is a common way to combat the effects of thick lenses. Standard-material lenses – such as CR39 plastic, Trivex, or polycarbonate plastic – fall within the 1.50-1.56 index. For a lower prescription, these materials produce relatively thin lenses, but as the prescription rises in strength a standard material lens can become prohibitively thick. Here’s a look at the higher index ratings and their ability to reduce lens thickness:
- 1.61-1.67 index – the first upgrade level considered “high index.” Lenses produced from material in this range can reduce thickness by up to 30% in comparison to 1.50 lenses.
- 1.74 index – the flattest and thinnest lens available in plastic. Lenses produced from 1.74 material can reduce thickness by up to 45% in comparison to 1.50 lenses.
- Above the 1.74 index rating, only glass lenses are available, up to an index rating of 1.9. Because of the changeover from glass to plastic, lens thickness is not comparable. However, high index glass lenses can be significantly thinner when compared to low index glass lenses.
If the diopter rating on your prescription is high enough to require lenses that are too thick for your wants or needs, consider making the switch to high index lenses. The higher your prescription is, the more benefit you will reap if you upgrade from standard material to high index.