Using a lensometer (HD).

In this video, I wanted to show you how to use the lensometer.

The lensometer is a device used for checking prescription glasses

and can be a little confusing.

The first step is, of course, to put

the glasses in the frames here,

and you can see this platform moves up and down.

And you want to put the optical center of this lens

such that it aligns here,

and this little brace holds the glasses in place.

You want to make sure both glasses

are touching the bottom of this platform.

Turn it on, and then look through this eye piece,

and this is what you should see.

Now, the hard part with using this machine

is you have to use two dials at the same time.

There's an axis dial up here

and there is a focus dial down here.

And you spin both of these and the goal

is to get the three small lines--

the three little lines-- next to each other,

lined up and in focus.

So if we zoom in, we can see that there's three lines.

You want to get them lined up and in focus.

And then you can mark down what this is.

So if you look on our dial here and our focus,

we can see this is a 3.25 so that's the sphere.

The sphere is 3.25.

Now you move the focus in whatever direction it takes

in order to get the three fat lines in focus.

And the difference between those is your cylinder power.

So we went up +2.75 to get to 6.0.

So that's our cylinder +2.75.

Our axis looks like it's about 12 degrees.

So here is our prescription.

Now, to get the bifocal power,

I need to move the glasses up to the bifocal segment

and see how much you need to change it

to get the three fat lines in focus again.

So we went from +6.0 to +8.5,

so our add is +2.50.