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Contact or immersion technique for axial length measurement?
1Department of Ophthalmology, Royal Newcastle Hospital, Australia.
Australian and New Zealand Journal of Ophthalmology
|March 18, 1999
Summary
Immersion and contact A-scan techniques yield consistent eye axial length measurements. However, immersion measurements average 0.1 mm longer, impacting intra-ocular lens power selection for cataract surgery.
Area of Science:
- Ophthalmology
- Biomedical Engineering
- Optometry
Background:
- Accurate axial length measurement is crucial for intraocular lens (IOL) power calculation in cataract surgery.
- A-scan ultrasonography is a common method for determining axial length.
- Both contact and immersion A-scan techniques are utilized, but their comparability requires investigation.
Purpose of the Study:
- To compare the axial length measurements obtained from contact and immersion A-scan techniques.
- To assess the consistency and differences between these two measurement methods.
Main Methods:
- A prospective study involving 225 patients undergoing cataract surgery.
- Axial lengths were measured using an Alcon Ocuscan machine with both contact and immersion techniques.
- Repeat measurements were performed on 12 patients to assess consistency.
Main Results:
- Immersion technique measurements averaged 0.1 mm longer than contact technique measurements.
- A statistically significant difference in axial length was observed between the two techniques.
- Repeat measurements confirmed the consistency of differences within each technique.
Conclusions:
- Both contact and immersion A-scan techniques provide reliable and consistent axial length data.
- A systematic difference exists between the two methods, with immersion yielding longer lengths.
- This difference has clinical implications for selecting the appropriate intraocular lens power, necessitating careful consideration of the chosen technique.