Description

The ETDRS Chart, or Early Treatment Diabetic Retinopathy Study Chart, is a highly specialized tool designed for precise visual acuity measurement. Widely recognized in clinical trials and research settings, it plays a crucial role in assessing visual acuity, particularly in patients with diabetic retinopathy and other ocular diseases.

Design and Layout

• Sloan Letters: Each chart line features five Sloan letters, carefully selected for equal difficulty. The arrangement ensures no formation of words or acronyms, maintaining the integrity of the test.
• LogMAR Scale: The letter size progresses geometrically, adhering to the logMAR scale. Each line is separated by 0.1 log unit, with each letter valued at 0.02 log unit.
• Visual Acuity Range: Comprising 14 lines with a total of 70 letters, the chart covers a visual acuity range from 20/200 to 20/10.

Physical Characteristics

• Dimensions: The chart measures 64.8 cm by 62.2 cm (25.5 x 24.5 inches).
• Material: High-contrast optotypes are printed on non-reflective, white polystyrene.
• Illumination: Designed for use with trans-illuminated or retro-illuminated cabinets, ensuring uniform lighting. Recommended luminance is 85 cd/m².

Testing Protocol

• Distance: Standard testing is conducted at 4 meters (13 feet), with protocols for reduced vision testing at 1 meter (3.28 feet).
• Multiple Versions: Charts R, 1, and 2 are available to prevent memorization, allowing comprehensive testing for each eye and both eyes together.
• Lighting: Utilizes a standardized light box, typically with 40-watt frosted cool white bulbs, replaced annually.

Scoring Methods

• Visual Acuity Score: Each correctly identified letter scores one point.
• LogMAR Method: Scoring adjustments are made based on the last row where all letters are read correctly.
• Conversion: Results can be converted to Snellen fractions or LogMAR values. A change of 15 letters is deemed clinically significant.

Clinical and Research Applications

• Gold Standard: Serves as the gold standard for best-corrected visual acuity (BCVA) testing in clinical trials.
• FDA Requirement: Required by the US FDA for trials measuring visual outcomes.
• Reproducibility: Known for high reproducibility and standardization, suitable for individuals aged 5 and older.

Maintenance

• Cleaning: The chart can be cleaned with mild soap and water.
• Lighting: Ensure standardized lighting and room illumination for accurate results.
• Training: Examiner certification may be necessary for clinical trial settings.

The ETDRS Chart's robust design and rigorous standardization make it an indispensable tool in the field of ophthalmology, providing reliable and consistent visual acuity assessments across various clinical and research environments.