What Is a Sector Prism?
A triangular prism used in ophthalmic testing where the power is confined to a specific section or "sector" of the lens, often by truncating the apex or base.
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Clinical Use
Most commonly seen in Rotary Prisms (found in phoropters) and certain diagnostic tools where the practitioner needs to quickly introduce or remove a specific amount of prism power in the visual field.
Testing Alignment
The sector design allows for the prism power to be applied temporarily, quickly assessing the amount of misalignment (phoria or tropia) that needs correction.
Prism in Phoropters
The Risley Rotary Prism found in a phoropter uses two counter-rotating sector prisms to provide any amount of horizontal or vertical prism up to the instrument's limit.
What is the difference from a full prism?
A full prism covers the entire aperture of the lens. A sector prism only covers a partial area, making it suitable for rotary mechanisms.
What are prism bars?
Prism bars are non-sectorized, step-wise series of full-aperture prisms used to measure large degrees of strabismus.
Why is prism used in vision therapy?
Prism is used to train the eyes to align properly by shifting the light image, thereby forcing the visual system to compensate and improve eye teaming skills.