Frisby Stereo Test

Test Components

- Three transparent acrylic plates of different thicknesses:

- 6mm plate

- 3mm plate

- 1.5mm plate

- Each plate contains four squares

- One square contains a circular pattern printed on rear surface

- Three squares have patterns on front surface

- Stand for plate presentation

Physical Properties

Plate Specifications

- Size: 20cm × 20cm

- Pattern elements: Random circular shapes

- Target: Circular area of 4-5cm diameter

- Background: Similar circular elements

Testing Procedure

Standard Setup

1. Well-lit environment (normal room lighting)

2. Patient wearing habitual correction

3. Initial testing distance: 40cm

4. Plates presented perpendicular to line of sight

Administration Steps

1. Begin with thickest plate (6mm)

2. Present at recommended starting distance

3. Patients identifies which square contains the "floating" circle

4. Rotate plate between presentations

5. Progress to thinner plates if successful

6. Adjust testing distance as needed

Measurement Parameters

Stereoacuity Calculation

- Based on plate thickness and viewing distance

- Measured in seconds of arc

- Values vary with testing distance:

- 6mm plate: 340" to 20"

- 3mm plate: 170" to 10"

- 1.5mm plate: 85" to 5"

Testing Distances

- Standard distances:

- 30cm

- 40cm

- 50cm

- 60cm

- 80cm

Clinical Applications

Primary Uses

1. Screening young children

2. Assessment of real-depth perception

3. Monitoring binocular vision disorders

4. Post-treatment evaluation

Advantages

- No special glasses required

- Uses natural depth cues

- Portable and durable

- Child-friendly

- Minimal learning effect

- Free from monocular cues

Limitations

- Limited range of stereoacuity testing

- Influenced by illumination conditions

- Position-dependent results

- Not suitable for severe suppression cases

Result Interpretation

Normal Values

- Adults: 20-30 seconds of arc

- Children: May vary based on age

- Consider age-appropriate norms

Clinical Significance

Normal Results

- Indicates functional stereopsis

- Suggests good binocular vision

- Normal sensory fusion

Abnormal Results

- Reduced/absent stereopsis

- Possible binocular dysfunction

- May indicate strabismus

- Potential amblyopia

Special Considerations

Testing Environment

- Adequate lighting essential

- Avoid reflections on plates

- Maintain proper viewing angle

- Clean plates before testing

Patient Factors

- Age appropriateness

- Attention span

- Understanding of instructions

- Visual acuity status

Clinical Usage

Diagnostic Applications

1. Screening procedures

2. Strabismus evaluation

3. Amblyopia monitoring

4. Vision therapy assessment

Treatment Monitoring

- Pre/post surgical evaluation

- Vision therapy progress

- Amblyopia treatment

- Binocular vision rehabilitation

Conclusion

The Frisby Stereo Test remains a valuable clinical tool in orthoptics, particularly for pediatric assessment and real-depth stereopsis evaluation. Its natural viewing conditions and absence of special viewers make it especially useful for initial screening and ongoing monitoring of binocular vision disorders.

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