الفهرس 
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Abstract
Biometry is a technique used to calculate the intraocular lens implant power prior to cataract surgery. An accurate biometry enables the patient to achieve the best possible unaided vision post-operatively.
The Ultrasound is used to measure the axial length of the eye,corneal thickness, anterior chamber depth, lens thickness and vitreous humour depth.There are two distinct types of ultrasound A-scan biometry . The first type, contact applanation biometry, relies on the ophthalmologist pressing the probe on the central cornea and pointing towards the macula. The second technique, immersion biometry which requires placement of a scleral shell between the patient’s lids, filling it with saline, and immersing the probe into the fluid, avoiding contact with the cornea. In general, immersion biometry is more accurate than contact applanation biometry because it avoids corneal compression, thereby leading to measurements that are slightly longer than with contact applanation.