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The Four Prism Dioptre Reflex Test (also known as the 4 PRT, or 4 Prism Dioptre Base-out Test) is an objective, non-dissociative test used to prove the alignment of both eyes (i.e. the presence of binocular single vision) by assessing motor fusion. [1]
The Maddox rod test is a subjective method to measure horizontal and vertical deviations of the eyes, using a red line and a white light. The double Maddox rod test can also assess torsion and cyclotropias, by comparing the angles of two red lines.
From left to right: an accommodative fixation stick, a vertical prism bar, and a horizontal prism bar. The PFR involves placing a prism bar in front of an eye. In a patient with BSV, a natural shift of the eye occurs. When measuring horizontal fusion ranges, base in prisms assess fusional divergence while base out prisms assess fusional ...
A fixation disparity is not constant within a certain observer, but can vary depending on the viewing conditions. If test prisms with increasing amount are placed in front of the observer’s eyes, the fixation disparity changes in the eso direction with base-in prisms and in the exo direction with base-out prisms (Fig. 3).
Prentice's rule is a formula to calculate the amount of prism correction in a lens based on decentration and lens power. It can be used for prescribing, tolerance control, or determining unprescribed prism in eyeglasses.
Fundus photography is the process of taking pictures of the back of the eye, also known as the fundus. Learn about the history, optical principles and modes of fundus photography, as well as the different types of fundus cameras and their features.
Vision therapy is a term for various eye exercises that claim to cure learning disabilities and other problems, but lack scientific support. Learn about the different types of vision therapy, their conceptual basis, and their lack of efficacy and credibility.
Esotropia is a condition in which one or both eyes deviate inward, causing a cross-eyed appearance. It can be constant or intermittent, and has different types and causes, such as hyperopia, congenital, or accommodative factors.