A-Scan Biometry
A-Scan Biometry is a diagnostic technique used in ophthalmology to measure the length of the eye and assess the anterior chamber depth, corneal thickness, and lens thickness. The primary application of A-scan biometry is in the measurement of the axial length of the eye, which is crucial for the calculation of the intraocular lens (IOL) power required for cataract surgery. It is also useful for diagnosing and managing conditions that affect the size and shape of the eye, such as myopia (nearsightedness), hyperopia (farsightedness), and
A-scan biometry provides precise measurements that help ophthalmologists determine the best surgical approach, particularly in planning cataract surgery and refractive surgery like LASIK.
glaucoma.
How A-Scan Biometry Works
The A-scan uses ultrasound technology to measure the distance between the front and back of the eye. During the procedure, an ultrasonic probe is placed on the surface of the anesthetized eye, sending high-frequency sound waves into the eye. The sound waves are reflected by various internal structures of the eye, such as the cornea, lens, and retina, and the time it takes for the echoes to return is recorded. The device then calculates the axial length based on the speed of sound in tissue and the time it takes for the sound waves to return.
Preparation:
- The patient is usually given topical anesthetic drops to numb the eye and make the procedure comfortable.
Probe Placement:
- A small, handheld probe is gently placed against the eye, usually with a coupling gel to reduce any discomfort.
Sound Wave Emission:
- The probe sends out ultrasonic sound waves, which travel through the eye and bounce back upon hitting the various structures within the eye.
Measurement Calculation:
- The time it takes for the echoes to return is measured, and the system calculates the axial length and other necessary measurements like corneal thickness and anterior chamber depth.
Results:
- The results are displayed on a screen as numerical values for various eye measurements. These include axial length, anterior chamber depth, and lens thickness, which are used for IOL power calculation in cataract surgery.