Description

The ETDRS Chart, or Early Treatment Diabetic Retinopathy Study Chart, is a highly specialized tool designed for precise measurement of visual acuity. Widely recognized in clinical trials and ophthalmic examinations, it serves as a gold standard, particularly beneficial for patients with diabetic retinopathy and other eye conditions.

Design and Layout

• Sloan Letters: Each line of the chart comprises five Sloan letters, chosen for their consistent difficulty. These letters are arranged to prevent the formation of words or acronyms, ensuring unbiased results.
• Geometric Progression: The chart features a geometric progression in letter size, known as logMAR, from line to line. This design includes standardized spacing between letters and rows, typically across 14 lines.

Material and Dimensions

• Size: Approximately 64.8 cm wide by 62.2 cm high.
• Material: Constructed from non-reflective, white polystyrene, providing high-contrast optotypes.
• Illumination Compatibility: Designed for use with trans-illuminated or retro-illuminated cabinets, offering uniform background luminance.

Testing Protocol

• Distance: Standard testing is conducted at 4 meters, with protocols for reduced distances for low vision patients.
• Letter Sizes: Ranges from 58.18 mm to 2.92 mm in height, corresponding to Snellen visual acuity fractions from 20/200 to 20/10.

Scoring System

• Visual Acuity Score (VAS): Scoring is based on letter count or logMAR, with each letter contributing 0.02 log units.
• Reproducibility: Allows for consistent, quantitative results across different sites and subjects, easily convertible to Snellen notation.

Versions and Formats

• Multiple Versions: Includes variations like Chart R, Chart 1, and Chart 2 to prevent memorization and accommodate different testing needs.
• Formats: Available in printed, backlit, and computerized formats.

Clinical Relevance

The ETDRS Chart is essential for best-corrected visual acuity (BCVA) measurement, required by regulatory bodies such as the FDA for clinical trial assessments. Its design, based on the Bailey-Lovie principles, enables detection of clinically significant changes in visual acuity, making it invaluable for vision studies worldwide.