Clinical notes on Axial Length in Long Eyes
The surgeon must take extra caution in measuring axial length in long eyes.
• Eyes with axial lengths 26 mm or longer usually have a myopic staphyloma
• Traditional ultrasonic measurements measuring axial length to the deepest point where the ultrasound wave is perpendicular to the retina, usually measure to the deepest part of the staphyloma (the anatomic axial length).
• For IOL calculations, we need the optical axial length, which is from the anterior corneal vertex to the fovea.
• In highly myopic patients with staphyloma, the fovea can be midway up the staphyloma or on the rim.
• As a result, the anatomic axial length (from the anterior pole to the posterior pole of the eye) can be up to 3 mm longer than the optical axial length (from the anterior pole to the fovea).
• For every 1 mm of difference between the optical axial length and the anatomic axial length, a 2.5 to 3 D error in power prediction is made.
• patients with axial length greater than 26.5 mm (up to 35 mm) had anatomic and optical axial lengths that differed by up to 3 mm, which could cause an error of up to 9 D in IOL power.
To avoid this problem, surgeons should measure patients with long eyes (26 mm or more in length) with optical coherence tomography (OCT) instead of ultrasound.
• A partial interferometry device such as the Carl Zeiss Meditec IOLMaster (Jena, Germany) measures axial length accurately to the fovea because the patient must fixate on a target.
• The IOLMaster is the only technology currently available to measure axial length that uses light and not ultrasound.
• It is crucial that we measure long, highly myopic eyes using IOL master . However, it cannot measure eyes with dense cataract because opacification prevents the coherent light from forming a measurable interference pattern. In patients with dense cataract, ultrasound is the only option.
Axial Length in Long Eyes powerpoint presentation :
Biometry (axial length)
- 1. Axial Length Measurement ( Biometry ) Mohammad Reza ZARRIN (optometrist- MsC) Tehran University of Medical Sciences
- IOL Power Calculation 1. Keratometry 2. A-Scan Biometry 3. IOL Formula
- A-Scan Biometry Measurement of Axial Eye Length by Ultrasound
- Average Axial Length of Normal Eye 23.06 mm Majority 22.0 to 24.5 mm
- Accuracy of AL measurement using A-scan ultrasound is + 0.1 mm
- Difference in AL measurement Between both eyes + 0.3 mm
- Instrumentation
- Examination Procedure 1. History Taking 2. Patient Preparation 3. Biometry Technique
- Biometry Technique Contact – Applanation Method – Hand-Held Method Immersion
- Values are 0.14 to 0.36 mm longer with immersion technique than with contact method
- Potential Sources of Error with Contact Method 1.Corneal Compression 2. Fluid Excess 3. Misalignment of Sound Beam 4. Inappropriate Eye type
Axial Length in Long Eyes videos:
Axial length measurement (SCRS 3) – YouTube
Axial Length in Long Eyes
