Which tool is used to assess phorias and consists of a series of red cylinders?

The Maddox rod is specifically designed to assess phorias, which are deviations in the alignment of the eyes that occur when the eyes are not focused on an object. This tool consists of a series of red cylinders or rods that create a visual stimulus, allowing the examiner to determine the presence and magnitude of a phoria.

When the patient is tested using the Maddox rod, one eye views the red line created by the rod while the other eye looks at a point of light. This setup facilitates the observation of any misalignment that may arise due to the phoria. The ability to detect and measure phorias is crucial for understanding an individual's binocular vision and alignment, making the Maddox rod a vital tool in the field of ophthalmology.

Other tools listed, such as the slit lamp, phoropter, and visual field tester, serve different functions. The slit lamp is primarily used for detailed examination of the anterior segment of the eye, the phoropter is utilized for refraction to determine prescription, and the visual field tester assesses peripheral vision. Therefore, the Maddox rod stands out as the appropriate choice for evaluating phorias.