Ultrasound Probe Selection for Ocular Ultrasound
For ocular ultrasound examination, a high-frequency linear array probe with frequencies between 7-20 MHz should be used for posterior segment imaging, while frequencies of 35-80 MHz are recommended for anterior segment imaging. 1, 2
Probe Selection Based on Ocular Structure
Posterior Segment Imaging
- Frequency range: 7-20 MHz
- Probe type: Linear array
- Applications:
- Whole globe imaging
- Vitreous assessment
- Retinal and choroidal evaluation
- Posterior ocular tumors
- Retinal detachment
Anterior Segment Imaging
- Frequency range: 35-80 MHz (ultrasound biomicroscopy - UBM)
- Probe type: High-frequency linear array
- Applications:
- Cornea examination
- Anterior chamber angle assessment
- Iris and ciliary body visualization
- Lens evaluation
- Detection of Descemet's membrane abnormalities
Technical Considerations for Probe Selection
Resolution vs. Penetration Trade-off
- Higher frequencies (35-80 MHz) provide superior spatial resolution but limited penetration depth 1
- Lower frequencies (7-20 MHz) offer greater penetration but somewhat reduced resolution 2
- 10 MHz probes are better for examining low-intensity reflectors such as the vitreous humor 3
- 20 MHz probes provide superior resolution for detecting details at the posterior pole 3
Specific Clinical Applications
- A-scan ultrasound: Uses 7-11 MHz transducers
- 7-8 MHz for determining echogenicity of ocular tumors
- 10-11 MHz for measuring axial length of the eye 2
- B-scan ultrasound: Operates at 10-20 MHz for measuring posterior ocular tumors 2
- Ultrasound biomicroscopy (UBM): Operates at 40-100 MHz to evaluate anterior ocular structures 2
Practical Considerations
Image Quality Optimization
- Ensure proper probe positioning at 90° angle for consistent measurements 4
- For patients with significant stromal edema, ultrasound biomicroscope with 50-70 MHz probes provides the most accurate measurements 4
- When examining vitreous abnormalities, a 10 MHz probe is preferable as it better visualizes vitreous particles 3
Documentation Requirements
- Document the indication for the procedure
- Record the views obtained
- Describe the structures studied
- Provide interpretation of findings
- Note any limitations or impediments to performing a complete exam 4
Safety Considerations
- Plane-wave modalities are well within FDA safety guidelines for ocular use 5
- Conventional Doppler modes may exceed FDA safety guidelines 5
Common Pitfalls to Avoid
- Using too high frequency for posterior segment evaluation, resulting in inadequate penetration
- Using too low frequency for anterior segment structures, resulting in insufficient resolution
- Improper probe positioning affecting measurement accuracy
- Failing to adjust frequency based on the specific ocular structure being examined
By selecting the appropriate ultrasound probe frequency based on the target ocular structure, clinicians can optimize image quality while ensuring adequate tissue penetration for comprehensive ocular assessment.