Unit Conversion & Rounding in Optometry

Convert 12 degrees (°) to arcminutes (').

• 1 degree = 60 minutes of arc

• 12 × 60 = 720 arcminutes (‘)

• Final answer = 720 arcminutes (‘)

Convert an angle of 450 arcminutes (‘) to degrees (°).

• 1 degree = 60 minutes of arc

• 450 ÷ 60 = 7.5 degrees (°)

• Final answer = 7.5 degrees (°)

Round +2.12 D to the next quarter of an dioptre. 

=+2.0D

What is the focusing power of a lens with a focal length of +150 cm?

• F = 1/f’

• +150cm → 1.5m

  • 1cm = 0.01m

• F = 1 / 1.5m

• F = 0.67

• Final answer = F (focal length) = +0.67D

Your camera has a focal length of +200 millimetre (mm). What is it's focal power?

• F = 1/ f’

• +200mm → 0.200m

  • 1 mm = 0.001m

• F = 1/ 0.200m

• F= 5.0 D

• Final Answer = +5.0 dioptres (D)

Convert 500 micrometer (μm) tp meters (m).

• 1 μm = 1e^-6 m

• 500 μm = 500 x 10^-6 m

• Final answer = 0.0005 m

Convert 2.54 metres (m) to millimeters (mm).

• 1 m = 1000 mm

• 2.54 m = 2.54 x 1000 mm

• Final answer = 2540 mm

Rounded +1.86D to the closest quarter of a dioptre.

+1.75D

Round +1.62D to the closest quarter of a dioptre.

+1.50D

What is the focal lengths in mm if the lens (Volk lens) has a focal power of +90D (dioptre)?

• F = 1/ f’

• +90D = 1 / f’

• f’ = 1/90 = 0.0111 m

• 0.0111m → 0.0111 × 1000 = 11.1 mm

• Final answer = 11.1 mm

What is the focal length in mm when the lens has a power of +3.50D.

• F = 1 / f’

• +3.50D = 1 / f’

• f’ = 1 / 3.50D

• f’ = 0.2857 m

• 0.2857 m → 0.2857 × 1000 = 285.7 mm

• Final answer = 285.7 mm

Round 234.29837456 to three decimal places.

234.298

What is the focal length in centimetre (cm) of a BIO lens of +30 D (dioptre)? 

• F = 1 / f’

• +30D = 1 / f’

• f’ = 1 / 30 = 0.0333 m

• 0.0333 m → 0.0333 × 100 = 3.33 cm

  • 1cm = 0.01m

  • 1m = 100dm

• Final answer = 3.33 cm

Round +1.09 D to the closest quarter of an dioptre.

+1.00D

Convert 17 millimetres (mm) into metres (m).

• 17 mm to m

• 1 mm = 0.001m

• Final answer = 0.017 m

Convert 410x10⁹nanometres (nm) into meters (m).

• 1nm = 1e^-9

• 1m = 10⁹nm

• 410x10⁹nm = 410nm

You measured an angle of resolution of an telescope, which refers to the minimum distance two stars have to be apart from each other to be seen by this instrument. Your result is 0.4 degrees (°). Convert the result into arcseconds ('').

• 1 degree = 3600 arcseconds

• 0.4° = 0.4 x 3600 = 1440''

• Final answer = 1440''

You measured the stereoscopic angle of a patient. You found it to be 360 arcseconds (''). Convert this angle into degrees (°).

• 1 degree = 3600 arcseconds

• 360'' = 360 / 3600 = 0.1°

• Final answer = 0.1°

Round £3478.33 to the nearest hundred.

£3500

Round -5.12D to the closest quarter of dioptre.

-5.00D

Round -1.21D to the closest quarter of an dioptre.

-1.25D

Round 8.736 to 2 decimal places.

8.74

You determine the angle of resolution, which is the smallest distance two objects can be away from each other observed at a certain distance. You find an angle of 450 arcseconds (''). Convert this angle into degrees (°).

1 degree = 3600 arcseconds

450/ 3600 arcseconds

= 0.125 degrees

Round -1.57D to the closest quarter of an dioptre.

-1.50D

Convert 0.078 meters (m) into centimeter (cm).

• 1m = 100 cm

• 1 cm = 0.01 m

• 0.078 m = 7.8 cm