I often use the Jackson cross-cyl in my community eye care practice to help me determine the magnitude and axis of any astigmatic element the patient may have in their prescription. I find it difficult to give the patient clear instructions and they get confused. Do you have any tips?

It is important to speak clearly and slowly and to give instructions using simple language.

This is how I instruct the patients that I examine when using the Jackson cross-cyl:

‘If you look at the black and white circles in the mirror I’m going to show you two lenses and ask you with which lens the circles look roundest and sharpest. Neither lens will make the circles perfect but choose the one that makes them look best. The circles may look better without either lens but do your best to choose the best one.

This is how the circles with lens 1 and this is with lens 2.’

When determining the axis it is my experience that patients will respond quickly with a lens choice when there is an obvious difference in the appearance of the circles between the two lenses. When the difference is less obvious there is often a delay in responding while the patient takes time to think about the different views. This means the end point is near. Consider repeating the lens choice again. When the patient responds that there is no difference in appearance the endpoint has been reached.

Some patients may not say the appearances are the same but simply not be able to verbalise a choice. The endpoint has been reached.

Practice using these instructions during the Jackson cross-cyl and your patients will help you provide the optimum prescription.