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This tool is currently in beta testing

Insight Optical Training · Professional Tools

Insight Prism Toolkit

Prism calculations for optical practice — fast, clear and clinically meaningful.

v0.5.1User testing

Binocular prescription

Enter the Rx once and reuse it across the toolkit. Prism is recorded separately as horizontal and vertical components.

Right eye (R)






Left eye (L)






Transposition changes only sphere, cylinder and axis notation. Prism values are preserved.

Calculator







Calculate induced prism from Rx power in the relevant meridian and optical-centre displacement.

Prism (Δ) = decentration (cm) × lens power (D)
Enter the values above and calculate.

Work backwards from desired prism to the required optical-centre displacement.

Decentration (cm) = prism (Δ) ÷ lens power (D)
Enter the values above and calculate.

Combine horizontal and vertical prism components while retaining the clinically useful component notation.

Resultant = √(horizontal² + vertical²)
Enter components above and calculate.

Split a binocular prism requirement between the two eyes. Horizontal prism keeps the same BI/BO base in each eye; vertical prism is split with opposite bases so the required vertical imbalance is preserved.



50%
Horizontal total = R + L. Vertical total = difference between opposite-base R and L components.
Enter the binocular prism requirement and calculate.

A 50/50 split is the usual starting point, but the balance can be shifted between eyes where dispensing or clinical considerations require it.

Calculate the vertical prism induced in each eye when viewing above or below the optical centres, then determine the net binocular vertical imbalance.


Induced vertical prism (Δ) = vertical displacement (cm) × power in the 90° meridian
Enter the viewing position above and calculate.

For a conventional near-vision imbalance check, leave “include prescribed vertical prism” unticked. The tool reports each eye separately and expresses the relative imbalance explicitly.

Calculate near vertical imbalance and show the two single-lens compensation options: conventional slab-off (BU) and reverse slab-off (BD).

Compensation required = difference between R and L vertical prism at the reading point
Enter the reading drop and calculate.

Conventional slab-off adds BU prism to the more-minus/less-plus lens in the 90° meridian. Reverse slab-off adds BD prism to the more-plus/less-minus lens. The tool reports both mathematically equivalent routes; final lens design and manufacturability remain a dispensing/laboratory decision.

Insight Optical Training · Running calculation checks…
Professional dispensing aid for user testing. Check the result against the full clinical prescription, lens design and laboratory requirements before ordering.