The Howard-Dolman Test

Test Components

- Two vertical rods (black or white)

- One fixed rod (stationary reference)

- One movable rod

- Viewing apparatus with rectangular aperture

- Pulley system or manual control mechanism

- Standard viewing distance: 6 meters

Test Specifications

- Illumination: Standard room lighting

- Rod dimensions: Typically 15cm height, 1.5cm width

- Viewing window: Approximately 7.5cm x 3cm

- Background: Usually black or neutral gray

Testing Procedure

Setup

1. Position patient at exactly 6 meters from apparatus

2. Ensure proper illumination

3. Verify patient wearing appropriate correction

4. Confirm binocular vision status

Administration

1. Patient views both rods through aperture

2. Movable rod positioned randomly in front or behind fixed rod

3. Patient adjusts movable rod position

4. Goal: Align both rods at same apparent distance

5. Multiple trials performed (typically 8-10)

Measurement and Recording

Data Collection

- Record distance deviation from fixed rod in millimeters

- Note direction of error (anterior or posterior)

- Calculate average deviation

- Document standard deviation

Calculations

1. Stereoscopic threshold = (Mean deviation × 2)

2. Stereoacuity in seconds of arc = tan⁻¹(threshold/viewing distance)

Result Interpretation

Normal Values

- Adults: 2-7 seconds of arc

- Children: May be slightly higher

- Threshold increases with age

Clinical Significance

Normal Results

- Good stereopsis

- Functional binocular vision

- Adequate depth perception

Abnormal Results

- Reduced stereoacuity

- Potential binocular vision dysfunction

- Possible ocular misalignment

Clinical Applications

Primary Uses

1. Quantifying stereoacuity

2. Monitoring binocular vision disorders

3. Occupational screening

4. Post-treatment evaluation

Advantages

- Quantitative measurement

- Objective assessment

- Good reliability

- Real-space testing

Limitations

- Requires dedicated apparatus

- Fixed testing distance

- Time-consuming

- Space requirements

Special Considerations

Testing Conditions

- Proper room illumination

- Accurate viewing distance

- Patient alertness

- Clear instructions

Common Sources of Error

1. Incorrect viewing distance

2. Poor illumination

3. Patient fatigue

4. Monocular cues

Professional Applications

Occupational Assessment

- Aviation industry

- Military personnel

- Industrial workers

- Professional drivers

Clinical Monitoring

- Strabismus treatment

- Vision therapy progress

- Surgical outcomes

- Amblyopia management

Conclusion

The Howard-Dolman Test remains a valuable tool in orthoptic practice for quantitative assessment of stereopsis. While more modern alternatives exist, its real-space testing environment and quantitative nature make it particularly useful for specific clinical and occupational applications.

Note : This document serves educational purposes exclusively and does not constitute medical advice or treatment guidelines