1.07 Hand neutralisation

General rule - positive power along a merdian will produce with/against movements

Against

General rule - negative power along a merdian will produce with/against movements

With

What kind of movement do cyls give

Scizzors movements when rotated

Moving the cyl along its axis gives no movement because cyl powers act 90 degrees from axis!!

Marking up the optical centre

Magnification effects

• Positive lens

• Negative l ens

+thicker

-thinner

Steps for neutralising a sphero cylindrical lens

1. Rotate lens so theres no scissors misalignment of the cross

2. Mark the principal meridians witha small dot

3. Move the lens perpendicular to each line of the cross in turn and observe the direction of movement

4. Neutralise each meridian separately using 2 spheres or one sphere and one cyl

   • the sphere chosed should be the one that leaves a with movement along the other principle meridian

   • The other meridian can then be corrected using a positive cylinder (with sphere still in place)

How to identify which is the most positive/negative meridian

Determining the axis of the neutralised lens

Measuring prism power

Tips