Day 5.2 - Lensometer How-to

Lensometer How-to

How to use the Lensometer:  

1. To adjust the height and angle of the lensometer, use the turning knob located on the right side of the base.

2. Turn the knob on the eyepiece, which is closest to the eye, counterclockwise until it stops. Look through the eyepiece while slowly turning it to the right, gradually bringing the numbers into focus.  When the numbers become sharp and defined, stop. It is important to ensure the lensometer is in focus each time you use it. If you pass the point of clarity, to where it is blurry, start over by turning it all the way counterclockwise.

3. Place the glasses on the lensometer so that the top-middle (about ¼ of the way down from the top) of the right lens is directly in front of the light source.
4. Pull the gripping lever, located on the right of the arm towards you then back, allowing it to pinch the glasses into place, holding them still while you are measuring. While looking through the lensometer, re-position the glasses so that you can see where the narrow and wide lines cross. In general, you should read the glasses with these lines crossed in the center of the smallest circle.
5. Turn the large black knob (power drum) on the right towards and away from you with your right hand and at the same time move the large black wheel at the end of the lensometer with your left hand until the narrow green lines come into focus and are solid (no breaks, splinters, etc.).                                                       
6. After the narrow lines come into focus, turn the black knob away from you (the top goes away). If the wide lines come into focus then you have found the correct axis. Turn the black knob back toward you until the narrow lines come back into focus. Write down the numbers seen on the big black knob and the dial at the end of the lensometer. 
7. Turn the wide black knob away from you again, until the wide green lines come back into focus. Write down the difference from the first number to the current number. It will always be a negative number. (Ex: if you got +3.25 for your first number and you got +2.25 for your second number. You take the difference so you would write it out as +3.25 -1.00 and you look at the far knob and get your axis number. (Ex: if your axis was 080 then you would have the right lens read and written down as +3.25 -1.00 x080)
8. Sometimes you may need to dot a lens in order to get the PD and to make sure the axis is correct.  If you need to dot the lens, simply push down on the dotting lever.
9. After reading the right lens, pull the release lever towards you and switch the glasses to the left lens. Then pull the lever towards you, then back, allowing it to pinch the glasses into place.
10. Repeat steps 5-7 for the left lens.

Prism:

1. If when switching from the right lens to the left lens, you need to adjust the platform so that the narrow and wide lines are crossed at the same height, make note of the change in height. This shows that the glasses are correcting for a prism. You would write this above the current RX section (ex: OD BU 1). Prism is written using the following descriptions: BU – Base Up, BD – Base Down, BO – Base Out, BI – Base In.

Bifocals:

1. After finishing both lenses, look carefully at the glasses to see if they are bifocals. If they have bifocals, turn the lever on the right side to raise the glasses' platform so that the light will shine through the bifocal part of the glasses. To measure a no-line bi-focal, you should ‘lay out’ the lens, using the lens mapping chart.
2. By looking through the lensometer, turn the large black knob on the right towards you until the large lines come into focus. The difference from the second reading to this third reading is the power of the bifocal. (Ex: +2.00) This would be written to the lower right. Ex: Small lines clear at -3.00 (axis x090), Big lines clear at -3.50, Big lines clear in the bi-focal at -1.00 = -3.00 -0.50 x090  +2.50  The Bi-focal is always a positive number.
3. To check if the lens is a no-line lens or no-line bifocal, hold the lens up to the light and find a straight vertical line somewhere in the room. While moving the glasses left and right, you will see the line as straight at the top, but bends left and right on the bottom half of the glasses, this tells you there is a no-line or no-line bifocal. You can also ask the patient if the glasses have a bifocal in them.
4. After determining that the glasses are no-line bifocals, hold them up to a light source and find the add power. This number is found furthest away from the nosepiece in each lens. The number is written as a 2-digit number: 15 = +1.50, 17 = +1.75, 20 = +2.00, etc. Also, make note of the shape that you see near the number, it will most likely be a circle, diamond, or other symbol.
5. Find a sheet of paper explaining the shapes of the no-line bifocal lenses. Take the dry-erase marker and make a dot on each of the symbols you found earlier when holding the glasses up to the light. Line the glasses up with the printed chart for the specific symbol and trace the semi-circle, cross or T, and channel of near vision onto the glasses.
6. After drawing these, repeat steps 5-7 by adjusting the light source on the lensometer to go through the semi-circle. This will ensure accurate readings on the first two numbers. Adjust the glasses so the bifocal is read at the bottom of the near channel.