The horizontal coincidence test, also known as the cover-uncover test or Hirschberg’s test, assesses binocular alignment and detects strabismus (misaligned eyes).

How it’s done:

1. Patient fixates: The patient looks at a target, usually a light or object.
2. Covering one eye: One eye is covered, and the movement of the uncovered eye is observed.
3. Uncovering the eye: The covered eye is uncovered, and the movement of both eyes is observed.

Purpose:

The test helps detect:

1. Strabismus: Misalignment of the eyes (esotropia, exotropia, hypertropia, etc.).
2. Binocular vision problems: Issues with how the eyes work together.

The test provides valuable information about binocular alignment and helps diagnose and manage strabismus and other binocular vision problems.