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Clinical Reference

Eye Care Calculators

Back Vertex Power Calculator

Exact Power
RGP / Custom (0.25 Steps)
Soft Toric (Commercial)

This calculator converts eyeglass prescriptions to contact lens powers using the back vertex power equation. It accepts minus and plus cylinder formats (auto-transposing plus cylinder). Default vertex distance is 12mm.

Back Vertex Power Equation:
BVPcontacts =
BVPglasses 1 − (vertex × BVPglasses)
Related Links:

Diopter-Radius Converter

Result (mm)

To convert between radius of curvature (mm) and diopters (D), use the formula:

D = (n − 1) × (1000 / R)

Where D is the dioptric power, R is the radius of curvature in millimeters, and n is the refractive index (typically 1.3375).

Related Links:
Safe Daily Dose Calculator

The safe daily dosage is calculated based on 5.0 mg per kilogram of actual body weight, per the 2016 AAO Guidelines.

Cumulative Dose & Toxicity

🧠 The 1000 Gram Threshold

Retinal toxicity risk increases significantly after a cumulative dose of 1000 grams. Annual screening is recommended, with increased vigilance as this threshold is approached.

Rx Transposition Calculator

Convert between Plus and Minus cylinder formats.