Hi to everybody and welcome to OptoTubeChannel, the first Italian YouTubeChannel dedicated to Optometry Today let’s talk about Howell test, a phoria evaluation test from a quantitative and qualitative point of view invented by the australian optometrist Edwin Howell. To break binocular vision is used a 6 base up diopters prism placed on the right eye for convention. Target is an oval shape, and from near it is smaller ( A4 format) than from far. It is an oval shape because it doesn’t recall attention in some point in particular way In the target center there’s a graduated scale which has the zero in the middle of the rectangular shape On the right is yellow and there are unpair numbers, on the left is light blue and there are pair number only On the zero there’s an arrow down directed. When we have placed the 6 diopters base us prism on the right patient’s eye, of this target he/she will see two, so he/she will have a double perception because the prism break vertically. The upper figure will be seen by the rleft eye, and the downer figure will be from the left eye cause the prism effect. So the black arrow position of the upper figure, compared to the downer, in the particular way to the graduated scale, will indicate phoria value. Better, during dissociation the upper arrow moves and touches/indicates a number of the graduate scale and this number is the phoria value. So how we can understand if it is an eso or exo phoria? For example, if the arrow is on the right and indicates a yellow number of the downer figure, we have an exo, conversely if it indicates a light blue number we have an eso. So this about quantitative aspect, but we also know something about qualitative aspect for example knowing if the arrow moves progressively or between an interval or if the movement is stable and constant. So we could indagate about phoria in each fixation position so also this is an interesting data to check eventual adaptation which the patient have embrace to do visual activities and be efficient. So this is all for the howell test, if you liked leave a like and subscribe this channel! Let’s see at the next opto-video! OPTO-STYLE!!!