Lens Transposition and Spherical Equivalents
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Questions and Answers

Transpose the following prescription: +1.00 +2.00 x 90

+3.00 -2.00 x 180

Transpose the following prescription: +100 +200 × 90

+3.00 -2.00 x 180

Transpose the following prescription: -0.75 +3.00 x 180

+2.25 -3.00 x 090

Transpose the following prescription: +2.25 +1.75 x 085

<p>+4.00 -1.75 x 175</p> Signup and view all the answers

Transpose the following lens prescriptions: +4.25 +1.50 x 135

<p>+5.75 -1.50 x 045</p> Signup and view all the answers

Transpose the following lens prescription: -4.00 +3.00 x 45

<p>-1.00 -3.00 x 135</p> Signup and view all the answers

Transpose the following lens prescription: -3.00 +0.75 x 180

<p>-2.25 -0.75 x 90</p> Signup and view all the answers

What is spherical equivalent of -1.00 +2.00 x 180?

<p>Plano</p> Signup and view all the answers

What is spherical equivalent of +2.00 +2.50 x 90?

<p>+3.25</p> Signup and view all the answers

What is spherical equivalent of -0.75 + 1.50 x 180?

<p>Plano</p> Signup and view all the answers

What is spherical equivalent of -2.50 +2.50 x 155?

<p>-1.25</p> Signup and view all the answers

What is spherical equivalent of +2.25 +0.50 x 150?

<p>+2.50</p> Signup and view all the answers

The spherical equivalent of +1.00 +2.50 x 90 is?

<p>+2.25</p> Signup and view all the answers

Transpose the following prescription: -3.00 +2.00 x 30

<p>-1.00 -2.00 x 120</p> Signup and view all the answers

Transpose the following prescription: -3.00 -2.00 x 30

<p>-5.00 +2.00 x 120</p> Signup and view all the answers

Transpose the following prescription: +3.00 -2.00 x 30

<p>+1.00 +2.00 x 120</p> Signup and view all the answers

Transpose the following prescription: +3.00 +2.00 x 30

<p>+5.00 -2.00 x 120</p> Signup and view all the answers

Convert DVA of 20/20 feet into meters.

<p>6/6</p> Signup and view all the answers

Convert DVA of 20/30 feet into meters.

<p>6/9</p> Signup and view all the answers

Convert DVA of 20/40 feet into meters.

<p>6/12</p> Signup and view all the answers

Convert DVA of 20/50 feet into meters.

<p>6/15</p> Signup and view all the answers

Convert DVA of 20/60 feet into meters.

<p>6/18</p> Signup and view all the answers

Convert DVA of 20/70 feet into meters.

<p>6/21</p> Signup and view all the answers

Convert DVA of 20/80 feet into meters.

<p>6/24</p> Signup and view all the answers

Convert DVA of 20/100 feet into meters.

<p>6/30</p> Signup and view all the answers

Flashcards

Transposing a Lens Prescription

Converting a lens prescription from one format to another, typically from a 'plus cylinder' format to a 'minus cylinder' format or vice versa.

Transposing: +1.00 +2.00 x 90

The transposed lens prescription is +3.00 -2.00 x 180. The sphere power increases by the cylinder power, the cylinder power becomes negative, and the axis rotates by 90 degrees.

Transposing: -0.75 +3.00 x 180

The transposed lens prescription is +2.25 -3.00 x 090. The sphere power becomes +2.25 ( -0.75 + 3.00), the cylinder power is now -3.00, and the axis is rotated to 90 degrees.

Transposing: +4.25 +1.50 x 135

The transposed lens prescription is +5.75 -1.50 x 045. The sphere power becomes +5.75 (+4.25 + 1.50), the cylinder power changes to -1.50, and the axis is rotated 90 degrees to 45 degrees.

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Transposing: -4.00 +3.00 x 45

The transposed lens prescription is -1.00 -3.00 x 135. The sphere power decreases to -1.00 (-4.00 + 3.00), the cylinder power becomes negative, and the axis increases to 135 degrees.

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Spherical Equivalent

A single value that represents the average refractive power of a lens, calculated by adding half of the cylinder power to the sphere power.

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Spherical Equivalent: -1.00 +2.00 x 180

The spherical equivalent is Plano, meaning the lens has no overall refractive power. Calculated as -1.00 + ( 2.00 / 2) = 0.

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Spherical Equivalent: +2.00 +2.50 x 90

The spherical equivalent is +3.25. Calculated as +2.00 + (2.50 / 2) = +3.25.

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Spherical Equivalent: -2.50 +2.50 x 155

The spherical equivalent is -1.25. Calculated as -2.50 + ( 2.50 / 2) = -1.25.

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Transposing: -3.00 +2.00 x 30

The transposed lens prescription is -1.00 -2.00 x 120. The sphere power is -3.00 + 2.00 = -1.00, the cylinder power becomes -2.00, and the axis is rotated by 90 degrees to 120 degrees.

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Transposing: +3.00 +2.00 x 30

The transposed lens prescription is +5.00 -2.00 x 120. The sphere power becomes +5.00 (+3.00 + 2.00), the cylinder power becomes -2.00, and the axis is rotated by 90 degrees.

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Converting DVA (Distance Visual Acuity) from Feet to Meters

Converting the distance visual acuity from feet to meters, maintaining the same ratio. For example, 20/20 feet is equivalent to 6/6 meters.

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DVA Conversion: 20/30 Feet to Meters

20/30 feet is equivalent to 6/9 meters. We divide both numerator and denominator by 3.33 to get this conversion.

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DVA Conversion: 20/40 Feet to Meters

20/40 feet is equivalent to 6/12 meters. We divide both numerator and denominator by 3.33 to get this conversion.

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DVA Conversion: 20/50 Feet to Meters

20/50 feet is equivalent to 6/15 meters. This is derived by dividing both the numerator and denominator by 3.33.

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DVA Conversion: 20/60 Feet to Meters

20/60 feet is equivalent to 6/18 meters. This conversion is achieved by dividing both numbers by 3.33.

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DVA Conversion: 20/70 Feet to Meters

20/70 feet is equivalent to 6/21 meters. This conversion is achieved by dividing both the numerator and denominator by 3.33.

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DVA Conversion: 20/80 Feet to Meters

20/80 feet is equivalent to 6/24 meters. This is achieved by dividing both numerator and denominator by 3.33.

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DVA Conversion: 20/100 Feet to Meters

20/100 feet is equivalent to 6/30 meters. This is achieved by dividing both numerator and denominator by 3.33.

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Study Notes

Lens Transposition

  • Transposing a prescription involves converting it from its original form to another, maintaining equivalent optical power.
  • The process adjusts the sphere and cylinder values while changing the axis measurement.

Example Transpositions

  • From +100 +200 × 90 to: +3.00 -2.00 × 180.
  • From -0.75 +3.00 × 180 to: +2.25 -3.00 × 090.
  • From +2.25 +1.75 × 085 to: +4.00 -1.75 × 175.
  • +4.25 +1.50 × 135 becomes: +5.75 -1.50 × 45.
  • From -4.00 +3.00 × 45 to: -1.00 -3.00 × 135.
  • From -3.00 +0.75 × 180 to: -2.25 -0.75 × 90.

Spherical Equivalent Calculations

  • The spherical equivalent simplifies a lens prescription into a single power.
  • Example conversions yield:
    • For -1.00 +2.00 × 180: Plano.
    • For +2.00 +2.50 × 90: +3.25.
    • For -0.75 +1.50 × 180: Plano.
    • For -2.50 +2.50 × 155: -1.25.
    • For +2.25 +0.50 × 150: +2.50.
    • For +1.00 +2.50 × 90: +2.25.

Additional Transpositions

  • Prescription of -3.00 +2.00 × 30 transposes to: -1.00 -2.00 × 120.
  • -3.00 -2.00 × 30 transposes to: -5.00 +2.00 × 120.
  • +3.00 -2.00 × 30 turns to: +1.00 +2.00 × 120.
  • +3.00 +2.00 × 30 results in: +5.00 -2.00 × 120.

Vision Acuity Conversions

  • Converting Distant Visual Acuity (DVA) measurements from feet to meters involves fractional notation.
  • DVA of 20/20 feet equates to: 6/6.
  • DVA of 20/30 feet equates to: 6/9.
  • DVA of 20/40 feet equates to: 6/12.
  • DVA of 20/50 feet equates to: 6/15.
  • DVA of 20/60 feet equates to: 6/18.
  • DVA of 20/70 feet equates to: 6/21.
  • DVA of 20/80 feet equates to: 6/24.
  • DVA of 20/100 feet equates to: 6/30.

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Description

This quiz covers the concepts of lens transposition and spherical equivalent calculations. It includes examples of converting prescriptions while maintaining equivalent optical power. Test your understanding of these essential optical math skills.

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