Bilaal Optics · Manual focimetry simulator
Focimetry result sheet
Correct prescription · minus-cylinder notation
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Bilaal Optics
Developed by Bilaal
Clinical learning tool
Manual Focimetry Simulator
Practise finding both principal powers and measuring sphere, cylinder, axis and prism from a randomly generated or user-entered prescription.
Program overview
This interactive simulator recreates the controls and target behaviour of a manual focimeter. Work through a hidden random prescription or enter a known prescription, including prism and base direction, while learning the controls.
Before you begin
- Find the first focus. Begin in plus and reduce power. Rotate the axis until the first mire group is at its sharpest.
- Find the second focus. Record the first reading, then reduce power until the perpendicular mire group is sharp.
- Write the prescription. Sphere = most positive power. Cylinder = difference between the two powers. Axis = axis at the most negative power.
- Measure prism. Use the displaced centre of the mires against the concentric 1Δ rings. The displacement direction gives the prism base direction.
Manual focimetry simulator
Eyepiece view · Single / triple-line mires · 1Δ per ring ·
Power drum
Axis dial
Choose a practice prescription
Choose one of the two options below: generate a random prescription OR enter your own prescription.
OR
Select a lens type, choose whether to include prism, then generate your practice prescription.
Enter your prescription below, then click the button to practise with it.
Choose + or − for the sphere, then enter its value. Leave cylinder or prism blank for 0.00. Plus-cylinder prescriptions are automatically transposed into minus-cylinder form. Lens selection determines the screen direction for BI and BO prism.
Current lens: randomly generated prescription
Focus the single line first, then the triple lines.
0.25 D steps
Measurement notebook
First power · sphere—
Second power · sphere + cylinder—
Axis at first reading—
Axis at second reading—
Power readings are recorded as set, even if the target is not in focus. The second-reading axis is 90° from the recorded first-reading axis.
What is the prescription?
Enter minus-cylinder notation. Choose + or − for the sphere, then enter its value. Sphere and cylinder are checked using BS EN ISO 21987:2017 mounted-lens power tolerances. For spherical lenses, cylinder and axis may be left blank. A blank cylinder is treated as 0.00 D. Prism may be left blank when the target is centred.
For BI or BO prism, use the right or left lens shown beside the practice lens.
Check / reveal your answer to unlock the result sheet.
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