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Axial length measurement

Eye Care estimated about CNY 200-400

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Description

A non-invasive ophthalmic biometry procedure using optical coherence interferometry (e.g., IOLMaster or Lenstar) to precisely quantify the distance from the cornea to the retinal pigment epithelium for IOL power calculation.

Main Uses

1. Intraocular lens (IOL) power calculation prior to cataract or refractive lens exchange surgery; 2. Myopia progression monitoring in children and adolescents; 3. Diagnosis and staging of pathologic myopia; 4. Preoperative assessment for corneal refractive surgery (e.g., to exclude contraindications like nanophthalmos or excessive axial length); 5. Research and clinical trials evaluating anti-myopia interventions (e.g., atropine, ortho-K).

Normal Range

Typical adult axial length ranges from 22.0 mm to 24.5 mm; mean ~23.5 mm. Children show age-dependent norms: newborns ~16–19 mm, 1-year-olds ~19–21 mm, 6-year-olds ~21–22.5 mm, reaching adult values by adolescence. Values <22.0 mm suggest relative hyperopia; >24.5 mm indicate myopia risk. Measurement precision: ±0.02 mm (IOLMaster 500/700) or ±0.01 mm (Lenstar LS 900).

Low Values - Possible Causes

1. Hyperopia (farsightedness) due to shorter-than-average globe development; 2. Microphthalmos (congenital small eye); 3. Nanophthalmos (rare, extreme shortening with thick sclera and high IOP risk); 4. Post-cataract surgery anterior chamber depth artifact (rare, if misalignment occurs); 5. Corneal opacity or dense cataract causing signal failure and underestimation (though more commonly leads to measurement failure than low value).

High Values - Possible Causes

1. Axial myopia (most common cause — elongated posterior segment); 2. Pathologic myopia (progressive elongation with staphyloma, chorioretinal atrophy); 3. Scleral ectasia (e.g., in Marfan syndrome or Ehlers-Danlos); 4. Post-traumatic globe distortion (rare, asymmetric elongation); 5. Misalignment or off-axis measurement in highly myopic eyes leading to overestimation (less common with modern swept-source OCT-based devices like Lenstar LS 900).

axial length measurement IOLMaster Lenstar

estimated about CNY 200-400