Friendly UNcorporate Optometry

Aug 25 - 16

5 Factors For Minimizing Your Glasses' Lens Thickness

This is our most popular post!

So you are thinking about getting new glasses... but you are worried that the lenses will end up looking thick and heavy.  What are the factors that influence optical lens thickness in glasses? Read on...

1] Prescription: The higher your degree of nearsightedness or farsightedness will influence your lens thickness.  A lens to correct nearsightedness (myopia) will be thicker at the perimeter of the lens and a lens to correct farsightedness (hyperopia) will be thicker in the middle of the lens.  There is not much that you can do about your prescription - it is what it is - so use the other 4 factors to help minimize lens thickness.

2] Diameter: The larger a lens is across, the thicker it will be.  This consideration is often trumped by fashion or function (e.g. progressive bifocal) but try and minimize diameter to limit lens thickness.

3] Material: There are basically six difference plastics that are used to make lenses (glass rarely used these days).  These plastics are rated for their ability to bend light and there ability to sharply focus light.  They are identified with numbers (index) and/or names such as 1.6 or 1.53 or Polycarbonate.  Some retailers try an brand a particular plastic with a fancy name but they are all essentially the same six.  If you are offered a "Thinner-Lighter Lens" - find out what the index actually is to properly compare...in order or thickest to thinnest:  1.5 (CR39) > 1.53 (Trivex) > 1.59 (Polycarbonate) > 1.6 > 1.67 >  1.74.   The worst optical quality (sharpness) plastic is polycarbonate but it is also one of the most break resistant.  Optical quality also is influenced by the design of the lens (e.g. aspheric) but this would not significantly impact the thickness.  As a rule-of-thumb, you do not need to consider a mid or hi-index lens for prescriptions from -2.50 to +1.50.  Note that a 1.74 lens (thinnest) can reduce lens thickness by approximately 33% over a 1.5 (CR39) lens.

4] Mount:  The three most common frame mounts are: grooved, semi-rimless and drilled.  A grooved mount has the metal or plastic frame completely around then lens.  The lens has a raised lip at the edge that sits snugly into a groove in the frame.  This mount will allow your lenses to be thinnest.  If you are nearsighted, a semi-rimless or drilled mount will have little impact on the thickness when compared to a groove mount.  However, If you are farsighted these latter to mounts will cause your lenses to be thicker.  This is because the edges of your lenses have to me made thicker to carry a groove set into the lens edge.  Or in the case of drill-mount, the lens have to be make strong enough as not to break with stress

5] Surfaced or stock:  This factor is probably the most confusing and misunderstood - even for people in the industry.  If you are farsighted (i.e. a '+' prescription like +3.00), a surfaced (custom made) lens will deliver the thinnest end product (any material).  The selection of which to use gets messy because is a balance between wholesale cost and value to consumer plus all of the above factors.  Even when it is the best choice, a surfaced lens is not always selected by many optical retailers because it is far more costly to fabricate which negatively effects profit.  If you are nearsighted (i.e. a '-' prescription like -5.50), it does not matter if the lens is surfaced or stock.  The decision will be made on availability and cost as the thickness is the same.

Questions?   We will help you navigate!   Dr.j

Nov 23, 2016

I used to tint the lenses in my old glasses?

There was a great question from a patient this week "I used to tint the lenses in my old glasses to be my prescription sunglasses... can I still do that?

I have been practicing for over 20 years and tinting old lenses was a very common thing... so what changed as tinting is rarely done these days!?   The answer is two parts: lens materials and coatings.   #1 spectacle lenses are more-and-more being made from materials that just do not tint well e.g. poly-carbonate or hi-index plastics  #2 the increased prevalence of anti-reflective coatings and tough anti-scratch coatings.  These coatings harden the lens surface and make it impenetrable to tints.  

To tint a lens these days, the tints are applied prior to these coatings being applied.   Dr.j

Feb 27, 2017

Why do I see spots after a bright light?

Great question from a young patient last week... "Why do I see spots after a bright light?"   To understand why, lets first talk about how the eye works.   When any light hits the back of the eye (retina) a chemical reaction occurs that converts the light energy into electrical/nerve energy that goes to the brain.  This reaction takes fuel that is constantly being produced by the eye and then used up - over and over again.

Under normal circumstances the fuel's speed-of-creation can keep up with the fuel's speed-of-use.  However, when the eye is presented with intense brightness like a camera flash (or eye exam!), the fuel is used up much faster than production.   Because there is no/low fuel after the flash, this flashed zone of the retina appears dark because there is no creation of the electrical/nervous energy until the fuel regenerates.    dr.j

Oct 31st, 2016

Can I use up my vision?

"Do eyes have a limited amount of vision that you can use up over a lifetime?"  "Will using my eyes for detailed work like crafts cause damage in the future?" 

These related questions come up often in eye doctors' offices... here is my answer to this common concern:   You do not have a finite amount of vision.  Using your eyes for high visual demand tasks can cause temporary strain and tiredness... but this is not harmful to the eyes.  If you enjoy a craft, reading or something else visually challenging..do it!   It will not cause future damage.   Dr.j

Jan 12 - 17

New Glasses Distortion?

Why might glasses with the same prescription feel very different?

This week a new patient brought in two pairs of reading glasses made from the same 2015 prescription.  Pair #1 was made by a local Optician and pair #2 was ordered online.   The patient loved pair #1 and hated pair #2... she was convinced that the online folks had messed up the prescription because pair #2's lenses were thicker and she found that their distortion was intolerable.

When I checked the prescription of both pairs, they were identical.... So why would the 'feel' of the glasses be so different?    The answer is in the curves of the lenses.   A lens is like a math equation e.g.  If a lens prescription is +5.00...  there are different ways to fabricate that prescription just like there are different math equations that can add to +5.00...  1+4=5  and 2+3=5 and 5+0=5.    Our patient's problem was that pair#1 was fabricated with one lens equation and pair#2 was created with a completely different curve.

Now - This is generally something that a patient will get used to if he/she has one pair of glasses.  However in this case, because she wanted to wear both pairs part-time... every time the glasses are switched there will be seom adaption required. 

Questions about glasses?   We can help!  Dr.j

May 2017

Sunscreen for our eyes

As Summer fast approaches it has me thinking about new sunglasses.  Everyone knows that protecting eyes from the harmful rays of the sun with good sunglasses is just as important as protecting your skin with good sunscreen.  However, did you know that sunglasses also protect  delicate eyelid tissue from UV?    Our eye lids are a common place for skin cancer because we never put sunscreen close to our eyes.

Wear sunglasses this summer to protect both your eye and lids!  Dr.j

When works for you?

If you are looking for UNbiased UNcorporate Eye Care, see your future here with us

All Content Dr. Jason Morris Studio Eye Care and Cataract Club