A diagnostic tool used to assess binocular vision, retinal correspondence, and suppression. The lenses have fine, parallel striations that cause a point light source to appear as a line perpendicular to the striations. When placed with the striations at 135° before the right eye and 45° before the left eye, a patient with normal binocular vision will perceive two lines crossing to form an “X.” Variations in the perceived image can help diagnose conditions such as suppression and anomalous retinal correspondence.

Bifixation, or bifoveal fixation refers to sensory fusion in which only the foveal images from each eye are combined into a single percept. It allows for clear, single binocular vision by uniting the high-resolution foveal images onto corresponding points in the visual cortex and enables fine stereopsis.

A type of strabismus where the angle of inward eye deviation is approximately 15 degrees, causing the image of the fixation point to fall on the physiological blind spot of the deviating eye. This eliminates the need for a suppression scotoma to prevent diplopia, as the blind spot naturally obscures the second image. The condition is relatively rare and typically occurs in older children and adults with a later onset of esotropia.

An optical device that uses two converging lenses and a septum to present a separate image to each eye, creating a three-dimensional effect when viewing stereoscopic photographs. Invented by Sir David Brewster in 1849, it improved upon Charles Wheatstone’s earlier mirror-based stereoscope. Brewster’s lenticular design was more compact and portable, contributing to its commercial success in the mid-19th century.

An ocular motility disorder characterized by a limitation of elevation in adduction, causing a divergence in straight upgaze. The restriction is typically of the same degree on version and duction testing, differentiating it from inferior oblique palsy. It can be congenital or acquired, with the congenital form being more common. Etiologies include a tight or inelastic superior oblique tendon-trochlea complex, inferior oblique adhesions, or a displaced lateral rectus pulley. Treatment depends on the severity of the limitation and includes surgery to weaken or lengthen the superior oblique tendon.