Effect of defocus on visual field measurement.

Area of Science:

• Ophthalmology
• Visual Science
• Optometry

Background:

• Visual field testing is essential for diagnosing and monitoring various eye conditions.
• Refractive errors, such as ametropia and presbyopia, can potentially influence visual field test outcomes.
• Understanding the impact of uncorrected refractive error on perimetry is critical for accurate clinical interpretation.

Purpose of the Study:

• To investigate the effect of defocus on visual field contrast thresholds.
• To determine the specific visual field regions and target sizes most affected by defocus.
• To provide recommendations for optimizing clinical perimetry accuracy in the presence of refractive errors.

Main Methods:

• Evaluated contrast thresholds using Goldmann perimeter targets, focusing on target size III (26 min arc diameter).
• Assessed the impact of defocus on contrast sensitivity at various eccentricities from the visual field center.
• Compared the effects of defocus on different stimulus sizes and visual field locations.

Main Results:

• Defocus increased contrast thresholds for stimuli equal to or smaller than Goldmann target III within 30-40 degrees of the visual field center.
• Defocus had minimal effect on contrast thresholds for larger stimuli and beyond 30-40 degrees eccentricity.
• Significant impact of defocus on contrast sensitivity was observed primarily in the central visual field for smaller targets.

Conclusions:

• Accurate clinical perimetry for small targets within 30-40 degrees requires correction of ametropia and presbyopia using spectacle or contact lenses.
• Larger stimuli and peripheral visual field testing are less affected by defocus.
• Investigating potential refractive origins for unexplained scotomata is recommended.