Transpose Calculator Glasses

Optical Transposition Calculator

Transposed Prescription

New SPH

New CYL

New Axis

function calculateTransposition() { var s = parseFloat(document.getElementById('inputSph').value) || 0; var c = parseFloat(document.getElementById('inputCyl').value) || 0; var a = parseInt(document.getElementById('inputAxis').value) || 0; if (a 180) a = 180; // 1. New Sphere = Old SPH + Old CYL var newSph = s + c; // 2. New Cylinder = Opposite sign of Old CYL var newCyl = c * -1; // 3. New Axis = Old Axis +/- 90 var newAxis = a + 90; if (newAxis > 180) { newAxis -= 180; } function formatVal(num) { var sign = num >= 0 ? "+" : ""; return sign + num.toFixed(2); } var fSph = formatVal(newSph); var fCyl = formatVal(newCyl); var fAxis = newAxis.toString().padStart(3, '0'); document.getElementById('resSph').innerText = fSph; document.getElementById('resCyl').innerText = fCyl; document.getElementById('resAxis').innerText = fAxis; document.getElementById('outputString').innerText = fSph + " / " + fCyl + " x " + fAxis; document.getElementById('resultArea').style.display = 'block'; }

Understanding Glasses Prescription Transposition

In the world of optics, eyeglass prescriptions can be written in two different formats: plus-cylinder form and minus-cylinder form. While both forms describe the exact same corrective lens, ophthalmologists usually use plus-cylinder, while optometrists and lab technicians typically use minus-cylinder.

How to Transpose Your Prescription Manually

If you want to convert your prescription manually, there are three specific steps to follow:

1. Combine SPH and CYL: Add the sphere power and the cylinder power together. This becomes your new Sphere power. Be careful with signs (e.g., -2.00 + +0.50 = -1.50).
2. Reverse the Cylinder Sign: Change the sign of the cylinder. If it was a plus (+), change it to a minus (-). If it was a minus (-), change it to a plus (+). The numerical value remains the same.
3. Rotate the Axis: Change the axis by 90 degrees. If the original axis is between 1 and 90, add 90. If the original axis is between 91 and 180, subtract 90. The result must always be between 1 and 180.

Real-World Example

Original Prescription: -3.00 +1.50 x 045

• New SPH: -3.00 + (+1.50) = -1.50
• New CYL: Reverse +1.50 to -1.50
• New Axis: 45 + 90 = 135
• Result: -1.50 -1.50 x 135

Why is Transposition Necessary?

Transposition is essential for communication between eye care professionals and lens manufacturers. Most optical labs manufacture lenses in minus-cylinder form because it offers better peripheral vision and aesthetic qualities in modern lens designs. Our transpose calculator glasses tool ensures that whether you are a student or a patient, you can quickly verify the alternative format of your script without error.

Note: This tool is for educational purposes only. Always consult with a licensed optician or optometrist before ordering lenses based on transposed figures.