Visual acuity scored by the letter-by-letter or probit methods has lower retest variability than the line assignment...

Area of Science:

• Ophthalmology
• Clinical Measurement Science

Background:

• Accurate visual acuity measurement is essential for diagnosing and monitoring eye conditions.
• The optimal method for scoring visual acuity remains unclear, impacting clinical reliability.

Purpose of the Study:

• To identify the visual acuity scoring method with the lowest test-retest variability in a clinical setting.
• To compare the variability of line assignment, ETDRS (Early Treatment Diabetic Retinopathy Study), and probit scoring methods.

Main Methods:

• Investigated three scoring methods (line assignment, ETDRS, probit) using the ETDRS visual acuity chart.
• Compared 32 patients with macular disease and 38 age-matched normal subjects.
• Analyzed test-retest variability after six chart repetitions, converting results to log MAR values.

Main Results:

• Significant differences in variability were found among the scoring methods (p < 0.0001).
• The line assignment method exhibited the highest variability; ETDRS and probit methods showed similar, lower variabilities.
• ETDRS and probit methods yielded a within-test standard deviation of approximately 0.04 log MAR units (two letters).

Conclusions:

• The ETDRS and probit methods offer lower test-retest variability for visual acuity measurements than the traditional line assignment method.
• These findings support the use of ETDRS or probit scoring for enhanced reliability in clinical visual acuity assessments.