Lens Form & Analysis
Compound Lenses

Most prescriptions which require cylinder also require a spherical component. This would apply in cases of compound myopic astigmatism and compound hyperopic astigmatism. In these cases we combine a spherical lens with a cylinder to form a compound lens. The figure above shows a simple +1.00 D spherical lens and a +2.00 D cylinder. In the illustrations below, we have combined the two lenses into one. Figure A shows the cylinder axis oriented along the 90 degree meridian, in figure B the axis is at 180 degrees, and figure C shows the axis at 45 degrees. In each case the compound lens is superimposed upon an optical cross.

Remember, we started with a +1.00 sphere and then combined it with a +2.00 cylinder. The power of our new compound lens, therefore, will be a combination of the two. In example A above, the power of the compound lens in the 90� meridian is still equal to +1.00 D since the axis of the cylinder is oriented in that direction and there is no power along the axis of a cylinder. Along the 180� meridian, however, the power of the lens is +3.00D. This is because the full +2.00 D of cylinder power is in effect and we must add this power to the original +1.00 diopter of spherical power. So +2.00 + 1.00 = +3.00. This prescription would be written: +1.00 + 2.00 x 90, or +3.00 - 2.00 x 180. Study examples B and C above to see how the power in the various meridians of the compound lens changes as the axis of the cylinder changes.