Learning How to Read an Eyeglass Prescription then Order Glasses Online

…..at Zenni Optical.


I had new progressive glasses prescribed in February 2022.

This prescription was MUCH stronger than previous prescriptions prompting the technician to question the Optometrist, just to make sure he did not mess up.

He did not, but, the technician told me to let her know if I experienced any issues……and to expect at least 2 weeks to get used to the glasses. (It takes time for the brain and eyes to coordinate what they are seeing…..I did not know that!)

Everything was fine…..for 8 months.

Then……I experienced a “wobble” when getting up to walk, similar to getting used to new glasses, so I went back to my old, 2020, progressive glasses to see if the wobble stopped.

It mostly did, but not completely.

I waited a little over two weeks to see if the wobble stopped, and it was pretty much gone, at which time I embarked on a quick STUDY of optometry, focusing on how to read the prescription, and understanding the differences between PROGRESSIVES and LINED BIFOCALS.

Reading the Prescription

Let’s look at the prescriptions first, as a basic understanding of the rest of this blog kinda requires it…..

My prescription looks as follows (I only show the fields that had numbers in them):

OD (Right Eye)+1.25-1.5097+2.50
OS (Left Eye)+4.00-4.75138+2.50


I am farsighted (the plus values in the Sphere). A minus value shows nearsighted.

I have an astigmatism in both eyes depicted by the numbers in the Cylinder (the severity of astigmatism) and Axis (which shows the angle of the astigmatism). The left eye is much worse than the right. And…..to make matters worse…..I have age related cataracts in the left eye. Arrrghhh….

The magnification for the reading part of the bifocal is the number under the Add column: +2.50.

That number (+2.50) determines, not only the magnification for reading but also the distance from your eyes where reading is in focus: The focal point.

The focal point is based on the following formula:

f = 1/D (are you now sorry you blew off Algebra? haha)

Where f = focal point in meters (the distance from your eyes where the image is clear) and D = the Add number in diopters (in my case both eyes = +2.50).

Doing the calculation….my focal distance according to the prescription should be = .4 meters which is 40 cm (move the dot over 2 spaces) and at 2.54 cm / inch = 15.74 inches.

Great for a book, but, my Pixelbook Go screen is further away than that. In fact, using the bifocals based on the prescription…..I have to get abnormally close to the screen to see it clearly.

Thus the need for computer glasses. 🙂

If I ordered “computer” glasses and used a D value of 2.00 (rather than 2.50), I calculate that my new computer glasses will allow me to see my chromebook screen clearly as long as it is about 20 inches away. That extra 4.25 inches of focus length will help a lot.

In theory. 🙂

Oh……why OD is the right eye and OS is the left eye remains a mystery. 😉

Progressives vs Lined Bifocals

Progressive bifocals have the two main focus modes, near and distance, but it also has a whole bunch of focus points in-between.

Although that comes in handy for focusing on just about anything at any distance……it makes it hard to find (at least for me) the focus I need, and when I do, for example for reading, it is a VERY narrow field of focus not even covering a few words in a paperback book (I read A LOT and the focus width is VERY important). As it is (with the progressives)……I have to move my head….constantly….as I read.

I made a preliminary decision that I may benefit from simple LINED bifocals where I would have only two focus modes…..distance or near. And for reading, I will (in theory) have a wider field of view so I could see the whole page in a book clearly by just moving my eyes. (NOTE: it turned out to be true…..the whole damn book, both open pages, is now in focus!!!!)

To complete testing of my theory (that lined bifocals may be better for me)……I went online to order simple BIFOCALS (with a line) to test in place of the progressives:


Ordering the Frames and Lined Bifocals

Going to the Zenni Optical web site (mainly because of 49er George Kittle’s endorsement), I picked out a cool frame (for me!), and then set out to order the lenses….

The first thing I had to do was enter the distance between my pupils known as the PD measurement! And, as luck may have it, that number was NOT on my prescription! I suspect I know why……but, Arrrghhh…..just the same. 😉

Long story short, after watching a video, I think it was on Zenni, I made a business card with dots every 1/8th inch on it, held it up to my forehead, and took a picture with my Pixelbook Go.

I then put the picture of me and the business card in Google Drawings and drew two vertical lines from my pupils to the 1/8th inch dots. Figuring out the millimeters between them, I came out with a PD of 60.

The rest of the form was easy since I had all the numbers I needed from the prescription. The only question I had was the ADD of +2.50 but it turns out that that number shows the eyeglass maker that the glasses will be a bifocal (aka old person) with a near view magnification of +2.50 diopters!

My new Zenni +2.50 lined bifocals

In the picture above, the sections of glass below the horizontal lines are the +2.50 near view sections. So I look down (with only my eyes) to read and everything is CRYSTAL clear…..and enlarged!


Oh, as an added benefit, the glasses from Zenni (yes, I was surprised) are as close to PERFECT as you can get. Far better quality than the glasses I got from my Optometrist…..

……AND……$98.00 vs $201.00 !!!

Sooooooooo, I bought the computer glasses, for $102.00 from Zenni too!

For single vision, I added the +2.00 ADD into the SPHERE value (so I can be 20 inches or so from my Pixelbook) on my prescription above: Now my single vision, computer glasses, Sphere is: +3.25 OD, and +6.00 OS while the Cylinder and Axis stay the same.

As for cost…..TWO Zenni glasses $102.00 + $98 = $200……which is still cheaper than ONE pair of glasses from the Optometrist.

My new, really cool, Zenni computer glasses….and Grogu. 🙂

I now have 2 glasses for the price of one…..and…..MUCH better quality!

UPDATE Dec 24, 2022: To complete my testing (and since the glasses are so cheap)…..I also ordered premium progressives from Zenni ($150.00) to see how they work. Supposedly these will have wider field of focus ranges than ordinary progressives…..I’ll let you know how they are in a couple of weeks. 🙂

Update May 4, 2023: Shocking results on progressives! More to follow….

Living With My New +2.50 Lined Bifocals

First of all….no wobble.

Secondly……super crystal clear vision for far (driving, walking, watching TV) AND near for reading. The Optometrist (my first time seeing him) nailed the prescription! 🙂

Third…..super wide field of focus. For reading….the whole damn book is in focus! And for watching TV they are perfect! Hanging out with Blaze at night….the stars are now crystal clear.

On the not so bright side…..with a +2.50 diopter…..I have to get really close to my phone or Pixelbook Go to see clearly. For example, in the grocery cart I set my phone down (it has the grocery list in Google Keep) on the ForCarol.com tote bags and I have to scrunch down now to read the list. Ditto at checkout entering info into the machine. BUT…..I read, work on my Pixelbook Go, and watch movies and sports on TV A LOT more than I grocery shop….soooo, what I have is good! 🙂

That said…..I am still going to fully test my computer glasses for reading, looking at my phone in the grocery store, and looking at the dashboard stuff (speedometer, clock, etc) while I drive (not driving with them, just sitting and looking!)

Depending on the results of that further testing…..

I may change my 2024 Bifocal near to +2.00 diopters. And I also think I may extend the computer glasses a few more inches, but, I have over a year to think about all that.

We will see….. 😉


Progressive glasses are great for some people, but, for others they may not be.

I wonder if age is a factor?

Stay tuned: Shocking and surprising progressives results to follow……

Using Zenni.com, I can buy TWO glasses: Bifocals AND Computer (I am using my new computer glasses as I type this…..AWESOME) for the price of one pair at the Optometrist…..while getting a major UPGRADE in quality to boot!

And, this has been fun as I learned a bit about optometry in the process……

Geek on!

Update April 24, 2023:

Lined +2.50 bifocals are my day-to-day glasses (including reading very small print). I use the +2.00 computer glasses for computer work AND for the occasional intermediate focus needs while doing projects, etc.

May 4, 2023: Stay tuned: Shocking and surprising progressives results to follow……

More GEEK stuff…..



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