Echelette optical low-pass filter as a Bangerter filter for diagnosis and treatment of amblyopia and diplopia.

This paper presents a new echelette optical low-pass filter that serves as a Bangerter filter (BF) for diagnosis and treatment of amblyopia and diplopia. Theoretical analysis and experimental measurements showed that echelette BFs have several advantages over the modern BFs used in medicine. Four echelette BFs with different grating periods and one BF were manufactured, and image blurring in an optical visual system with an echelette BF was experimentally investigated. The experimentally measured modulation transfer function and line spread function demonstrated definite image blurring (line expansion) that is inversely proportional to the width of the grating period. The results of measurements of the angular resolution of the optical system with an echelette BF coincide well with the results obtained by theory.