Ocular Ultrasound

What is Ocular Ultrasound?

• A-scan and B-scan are two types of ultrasound examination used to evaluate the eye.

• A detailed eye examination reveals not only the structures of the eye but also signs of underlying health conditions such as high blood pressure and diabetes. 

• Several techniques have evolved for routine examination of the eyes and for planning eye surgery (such as cataract operations). Ultrasonography is an important tool both in evaluating eye disease and in performing eye surgery. 

• Although A-scan and B-scan are both based on the same ultrasound principle, they differ in certain respects.

A-scan

• A-scan is short for amplitude scan. This eye ultrasound provides detail about the length of the eye. 

• It is a one-dimensional scan of the eye. 

• Measuring the axial length of the eye with an A-scan is essential when an intraocular lens (IOL, an artificial lens) is to be implanted during cataract surgery. 

• It may also be used to assess visual abnormalities and other diseases of the eye, such as tumours. 

B-scan

• B-scan stands for brightness scan. It produces a two-dimensional cross-section of the eye.

• A B-scan is generally used to evaluate diseases of the posterior segment (the back two-thirds of the eye) and the orbit, typically when the ocular media (the fluids within the eye) are cloudy and direct visualisation is not possible. 

  • It can help diagnose eye conditions such as: 

    • Vitreous haemorrhage 

    • Retinal detachment  

    • Foreign bodies in the eye

    • Differentiating iris and ciliary body lesions

    • Differentiating vitreous opacities and membrane formations

    • Differentiating and measuring intraocular tumours

    • Identifying serous versus haemorrhagic choroidal detachments 

    • Identifying rhegmatogenous versus tractional or exudative retinal detachment

    • Ruling out scleritis

    • Identifying optic disc drusen versus papilloedema

How do A-scan and B-scan work?

• A-scan and B-scan are based on the principles of ultrasonography. Sound travels as waves, and for a sound to be audible to the human ear its frequency must be between 20 and 20,000 Hz (20 kHz). 

• Ultrasound uses sound at frequencies above 20 kHz. When sound of this frequency meets an object it bounces back, and these “echoes” return to the ultrasound probe. 

• The probe converts the sound energy into an electrical signal, which is then displayed as an image on a monitor. 

• The doctor uses different ultrasound frequencies to control the depth of the image, depending on the structures being examined. 

• For A-scan and B-scan eye examinations, a frequency of around 10 MHz is used.

What happens during A-scan and B-scan?

A-scan and B-scan are safe and painless procedures.

• During an A-scan, the doctor will put anaesthetic drops in your eyes to numb them. You will be asked to sit in a chair with your chin on a rest and to look straight ahead. The doctor will then place an ultrasound wand (a device that produces ultrasound waves, which bounce off the eye tissues to create echoes) gently on the front surface of the eye.

• During a B-scan, you will be asked to close your eyes, and a gel will be applied to your eyelids before the probe is used. The doctor may ask you to move your eyes in different directions.

Both tests are quick and cause minimal discomfort.

Athens EyeCare is equipped with the most advanced ocular ultrasound on the market, offering high-resolution images: the ABSolu ultrasound from Quantel Medical.