The Maddox Rod test is used for measuring the size of horizontal and vertical phorias. This test normally involves looking at a spotlight in a darkened room with the Maddox rod in front of one eye. The Maddox rod distorts the image of the spotlight into a thin streak. The images received by the two eyes are so different that the eyes will dissociate. The patient is asked if the streak passes through the spotlight. If it does not, prisms are used to centre the streak. The prismatic power required to achieve this provides a measure of the phoria.


Target for measuring horizontal phorias


Target for measuring vertical phorias


To implement this test on a computer screen it is necessary to use a bar instead of a spot in order to achieve adequate brightness. The colour of the bar can be changed from the Settings screen.  Best results are obtained if the bar is matched in colour to the Maddox rod – i.e. a red bar for a red Maddox rod.


The bar on the screen should be oriented at 90 degrees to the axis of the Maddox rod – vertical bar for horizontal grooves and vice versa.


The orientation of the bar is changed by selecting the 1 or 2 icons on the Secondary Toolbar or by pressing 1 or 2 on the keyboard or remote.



The patient is asked to report if the streak seen with one eye passes through the bar on the screen. Prisms are used to centre the streak in the normal way. The bar can be made to flash by selecting the R icon on the Secondary Toolbar or by pressing R on the keyboard or remote. This can be useful if other lights in the room are producing secondary streaks. The patient can then be told to concentrate on the streak that is flashing.