Description

The ETDRS Chart, or Early Treatment Diabetic Retinopathy Study Chart, is a specialized tool designed for precise and standardized measurement of visual acuity. Widely used in clinical trials and ophthalmic examinations, it offers unparalleled accuracy and consistency, making it a gold standard in the field.

Design and Layout

• Sloan Letters: Each chart features ten Sloan letters (C, D, H, K, N, O, R, S, V, Z) arranged to maintain equal recognition difficulty and avoid forming words.
• LogMAR Scale: The letters are organized on a logarithmic scale, with each line separated by 0.1 log unit, ensuring a consistent and challenging visual assessment.
• 14 Lines: Each chart contains 14 lines, with five letters per line, providing a comprehensive evaluation range.

Material and Dimensions

• Size: Approximately 64.8 cm wide by 62.2 cm high (25.5 x 24.5 inches).
• Material: Constructed from non-reflective, white polystyrene for high contrast.
• Illumination: Designed for use with trans-illuminated or retro-illuminated cabinets to ensure uniform lighting.

Testing Protocol

• Distance: Standard testing distance is 4 meters (13 feet), with protocols for reduced distances for low vision patients.
• Age Suitability: Suitable for both adults and children typically aged 5 and older.

Scoring Methods

• Visual Acuity Score (VAS): Based on the count of correctly identified letters.
• LogMAR Method: Provides a logarithmic scoring system, easily convertible to Snellen notation.
• Sensitivity: Capable of detecting clinically significant changes in visual acuity.

Standardization and Use

The ETDRS Chart is recognized for its superior accuracy compared to traditional Snellen charts. It is extensively used worldwide to monitor conditions such as diabetic retinopathy and age-related macular degeneration.

Versions and Compatibility

• Versions: Available in three versions (R, 1, and 2) with varying letter sequences.
• Compatibility: Works with traditional and LED ETDRS Illuminator Cabinets, offering back-lit options with recommended illumination levels.

Maintenance

• Cleaning: Charts can be cleaned with mild soap and water.
• Illumination Devices: Should be maintained according to guidelines to ensure optimal performance.

Clinical Relevance

The ETDRS Chart addresses limitations of the Snellen chart and is often referenced in clinical protocols and regulatory standards. Its results are highly reproducible, providing reliable visual acuity assessments across different examiners and locations.