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Metric and Other Conversions

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The following are some metric and other conversions that you may encounter on the job and on the exams:

Visual acuity is sometimes expressed in terms of meters instead of feet.  The 20/20 visual acuity expression is equivalent to 6/6 in meters.  Therefore, 20/40 would be equivalent to 6/12 and 20/400 would be equivalent to 6/120.  To convert from one to the other, divide the denominator by the numerator and then multiply the numerator of the other system by the result.

Examples:

Convert 20/80 to metric notation:

1. Divide 80 by 20 to get 4. 

2. Multiply 6 by 4 to get 24. 

3. Express the metric equivalent as 6/24.

 

Convert 6/18 to English notation:

1. Divide 18 by 6 to get 3.

2. Multiply 20 by 3 to get 60.

3. Express the English equivalent as 20/60.

 

Comment:  The visual acuity conversion is the one you are most likely to see on a certifying exam.

 

You may need to know how to convert pounds to kilograms.  The eye pressure reducing medications glycerin and  isosorbide is are administered per kilogram of body weight.  One pound equals .45 kilograms.

 

Example:

 

Convert 160 lbs. to kilograms:

1. Multiply 160 by .45 to get 72 kilograms. 

 

You may need to know how to convert fluid measurements:

  • 1 fluid oz. = 29.57 milliliters (round it off to 30)

  • 1 fluid oz. = 2 tablespoons

  • 1 fluid oz. = 6 teaspoons

  • 1 tablespoon = .5 fluid oz.

  • 1 tablespoon = 14.78 milliliters (round off to 15)

  • 1 tablespoon = 3 teaspoons

  • 1 teaspoon =  .33 tablespoons

  • 1 teaspoon = 0.17 fluid oz.

  • 1 teaspoon = 4.93 milliliters (round off to 5)

  • 1 milliliter = .034 fluid oz.

  • 1 milliliter = .068 tablespoons

  • 1 milliliter = .2 teaspoons

Comments:  I don't know about you, but I don't have the above listed conversions memorized.  If you need them in your clinic, you could just print this page for reference, or you could go to onlineconversion.com if you have web access.  You are most likely to need the fluid conversions at home.  You know how it goes.  You need to give little Collette some liquid cold medicine in milliliters, you have lost that little measuring thingy, but you have found a little measuring thingy that is in teaspoons.

 

If you get an exam question about such conversions, you will most likely be given the conversion factor.  An exam question might go something like this:

 

You must give your patient a medication with a dosage of 1 fluid oz. per 20 kilograms of body weight.  You patient weighs 180 pounds.  The conversion factor is: 1 pound = .45 kilograms.  How many fluid oz. of the medication will you give your patient?

 

A. 40

B. 4

C. 8

D. 80

 

Answer: 4

 

Solution: 

1. 180 x .45 = 81 kg (weight of patient in kilograms).

2. 81 / 20 = 4.05 fluid oz. (round off to 4 oz.)