Effects of Fresnel Prism Power on Contrast Sensitivity and Visual Acuity

Abstract

Purpose: To investigate the effect of a Fresnel prism on contrast sensitivity and visual acuity values.

Methods: We measured contrast sensitivity and visual acuity in 19 healthy subjects after they had worn Fresnel prisms ranging from 5 to 40⊿, in 5⊿ steps. Contrast sensitivity and visual acuity values were converted to log contrast sensitivity values and logMAR values, respectively.

Results: The log contrast sensitivity values in each spatial frequency area (1.5, 3, 6, 12 and 18 c/d) and the logMAR of visual acuity both gradually decreased when prisms of 5 to 40⊿ were worn. Log contrast sensitivity decreased with increasing power of the prism; significant changes were obtained at each spatial frequency area: 0.66 at 35⊿, 0.69 at 20⊿, 0.49 at 15⊿, 0.34 at 15⊿ and 0.17 at 10⊿. Furthermore, the logMAR value at 10⊿, at which a significant decrease was seen, was 0.1.

Conclusions: These optical factors of low resolution are complex and controversial issues. However, the Fresnel prism proved to be more useful in orthoptics and low vision as these optical factors came to be understood.