The Cardiff Acuity Test, designed by Dr J Margaret Woodhouse, is a selection of preferential looking pictures designed to measure acuity in toddlers aged 1-3 years and in individuals with intellectual impairment.
​
The test combines the principles of preferential looking and vanishing optotypes. It is based on the premise that a child, when presented with two different patterns, will fixate on the picture rather than on a plain stimulus. The test uses pictures that will interest a child (house, car, duck etc) positioned either at the top or at the bottom of an otherwise grey card. There are eleven visual acuity levels, with three cards at each level.
​
The examiner presents the cards, beginning with the largest picture, at a distance of either 1m or 50cm. The first card is presented at the patient's eye level and the examiner watches the child's eye movement, whether up or down, to estimate the direction of gaze. A mental note is made of this direction and then the second card is presented. Again the eye movement is observed. The examiner then checks the cards to see if both estimations are correct. If so, the next set of cards is presented in the same manner. If a wrong estimation of picture position is made or no definite fixation is observed, then the previous set of cards is again presented, using all three cards. The end point is found when two of the three cards are consistently seen correctly.
​
The Cardiff Acuity Test is sold worldwide, and royalties help support research in Cardiff into vision and visual development in children.