A novel high-frequency visual acuity chart

Area of Science:

• Ophthalmology
• Optometry
• Vision Science

Background:

• Standard eye charts present blurred letters when out of focus.
• The Snellen fraction is the traditional metric for visual acuity.

Purpose of the Study:

• To develop and evaluate a high-frequency eye test chart.
• To compare the performance of the new chart with standard charts.
• To assess the validity of the Snellen fraction.

Main Methods:

• Developed a high-frequency chart with striped letters on a grey background.
• Simulated refractive errors using defocusing lenses on a camera and human eyes.
• Calibrated the chart by comparing letter sizes for equal visibility.

Main Results:

• High-frequency chart letters become invisible, not blurred, when defocused.
• No constant ratio exists between Snellen letter size and high-frequency letter size for equal visibility.
• The new chart requires significantly smaller high-frequency letters for reduced acuity compared to Snellen letters.

Conclusions:

• The Snellen fraction's basis for visual acuity is arbitrary.
• Current visual acuity charts calibrated by Snellen's system may lack accuracy.
• A new high-frequency chart offers a potentially more accurate method for visual acuity testing.