Maddox rod

A tool used in ophthalmology to assess ocular alignment

Maddox Rod

The Maddox rod is an ophthalmic device used primarily to evaluate ocular alignment and diagnose heterophoria and strabismus. It consists of a series of parallel cylindrical lenses or rods, typically made of glass or plastic, which are mounted in a frame. When a light source is viewed through the Maddox rod, it appears as a line perpendicular to the orientation of the rods. This optical property is utilized in various clinical tests to assess the alignment of the eyes.

Maddox rod and pen torch

History

The Maddox rod was invented by Ernest Edmund Maddox, an English ophthalmologist, in the late 19th century. Maddox developed this tool to provide a simple and effective method for detecting and measuring ocular deviations. Since its invention, the Maddox rod has become a staple in the field of ophthalmology and optometry.

Principle of Operation

The Maddox rod works on the principle of cylindrical lens refraction. When a point light source is viewed through the rod, the cylindrical lenses refract the light into a line. The orientation of this line is perpendicular to the axis of the cylindrical lenses. By observing the position and orientation of the line relative to the light source, clinicians can determine the presence and type of ocular misalignment.

Clinical Use

The Maddox rod is primarily used in the Maddox rod test, which is a subjective test for assessing binocular vision and ocular alignment. During the test, the patient is asked to look at a point light source through the Maddox rod. Depending on the alignment of the eyes, the patient will perceive the light as a line that may be displaced from the light source. The direction and amount of displacement help in diagnosing conditions such as esophoria, exophoria, hyperphoria, and hypophoria.

Maddox rod tools

Procedure

1. The patient is seated at a comfortable distance from a point light source. 2. The Maddox rod is placed in front of one eye, with the rods oriented either horizontally or vertically. 3. The patient is asked to describe the position of the line relative to the light source. 4. The test is repeated with the rods oriented in the opposite direction and with the other eye. 5. The clinician interprets the results to determine the type and degree of ocular misalignment.

Advantages and Limitations

The Maddox rod test is a quick and non-invasive method for assessing ocular alignment. It is particularly useful in differentiating between phoria and tropia. However, the test is subjective and relies on the patient's ability to accurately describe their visual perception. It may not be suitable for young children or individuals with communication difficulties.

Maddox rod test results

Related Tests

The Maddox rod is often used in conjunction with other tests such as the cover test, prism cover test, and Worth 4 dot test to provide a comprehensive assessment of binocular vision and ocular alignment.

Related Pages

• Ophthalmology
• Optometry
• Binocular vision
• Strabismus
• Heterophoria

Double Maddox Rod with and without trial frames