Vertex Distance Calculator

Vertex Distance Calculator

Your lens strength changes when your glasses sit closer or farther from your eyes. This calculator helps you adjust your lens power so your glasses stay accurate.

How It Works

What You Need to Enter:

• Lens Power (F): Your prescription strength in diopters.
  • Use a plus (+) number if you’re farsighted.
  • Use a minus (-) number if you’re nearsighted.
• Current Vertex Distance (d₁): How far your lenses currently sit from your eyes (in millimetres).
• Desired Vertex Distance (d₂): How far you want your lenses to sit from your eyes (in millimetres).
• Lens Type: Pick one:
  • Myopia (-): Nearsightedness.
  • Hyperopia (+): Farsightedness.

How the Calculator Finds Your New Lens Power:

The calculator uses this formula:

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Effective Power = F / (1 ± Δd × F)

Here’s what that means:

• Δd (Delta d): The difference between your current and new vertex distances, converted to meters.
  (To convert millimetres to meters, divide by 1000.)
• ± (Plus or Minus): Depends on your lens type:
  • Use a minus (-) for myopia.
  • Use plus (+) for hyperopia.

This calculation makes sure your lens strength stays correct at the new distance.

What You’ll See:

• Effective Lens Power: Your adjusted lens strength is rounded to two decimal places (in diopters).
• Summary of Inputs: A quick reminder of the numbers you entered.

If You Make a Mistake:

• The calculator will let you know if something is missing or incorrect.
• Results only appear when all fields are filled correctly.

Features:

• Calculate Button: Click to see your adjusted lens power.
• Reset Button: Clears all fields and results so you can start fresh.
• Dynamic Results: Results appear only after a correct calculation.

Who Should Use This?

This tool is helpful for opticians, technicians, or anyone adjusting lens prescriptions. This calculator keeps your prescription accurate if you’re changing frames or lens positions.