Which tool uses a series of red cylinders to assess phoria?

The Maddox rod is a tool specifically designed to assess phoria, which is a type of strabismus characterized by a misalignment of the eyes that may not be apparent under normal circumstances but can be induced under specific conditions. The Maddox rod consists of a series of red cylinders or rods that are positioned in front of one eye while the other eye sees a light source. This setup helps to measure the extent of the phoria by creating a perceptual disparity between the two eyes. The patient will typically report how the red light is perceived in relation to its location against a white light. This allows the clinician to determine the degree and direction of the misalignment, providing vital information regarding the patient’s ocular alignment.

In contrast, other options serve different purposes. The Worth four-dot test evaluates binocular vision and quantifies the ability to fuse two images from two different light sources, while the Ishihara plates are specifically used for assessing color vision deficiencies. The Marcus Gunn reflex assesses the integrity of the afferent pathway of vision rather than eye alignment.