Introduction
B-scan ultrasonography is an eye test that produces a two-dimensional, black and white cross-sectional view of the orbit (eye socket) and the eye. It is done on the outside or behind the patient’s closed eyelid and enables the doctor to get an accurate picture of internal eye structures, such as the choroid, vitreous, sclera, lens, and retina. The test uses high-frequency sound waves to measure and spotlight the structures around and in the eye. B-scan is a non-invasive and painless eye exam that only takes a few minutes.
It is particularly helpful in cases where it is challenging for the doctor to examine the patient’s eyes using routine eye tests. For example, in a situation where the patient has eye conditions that make a routine exam difficult like significant corneal opacities, tarsorrhaphy, edema, severe cataracts, keratoprosthesis, or vitreous hemorrhage.
Purpose
B-scan can be done at the doctor’s office, eye clinic, or hospital by:
- A technician
- An optometrist
- An ophthalmologist
The scan is an essential accessory for the clinical evaluation of many ocular and orbital conditions and diseases. Therefore, it is often done in addition to other eye examinations to assess the structures in the interior of the patient’s eyes when it is not possible to use fundoscopy. The doctor may order a B-scan if the patient is experiencing unexplained issues with their eyes or where the patient recently sustained trauma or injury to the eye area.
B-scan is particularly useful in the diagnosis and treatment of several eye abnormalities, including:
Retinal detachment:
An eye anomaly in which the retina is separated from the underlying layer. The signs and symptoms of the disorder include worsening of the patient’s outer area of the visual field and the patient reporting an increase in the number of flashes of light and floater in their eyes. Retinal detachment may be likened to a curtain over a part of the patient’s field of vision. The disorder can affect both eyes, and without treatment, may lead to irreversible loss of sight. A tear in the retina can be caused by injury to the patient’s eye, swelling of the eye, or posterior vitreous detachment. Other risk factors include previous cataract surgery and being short-sighted.
Glaucoma:
B-scan helps in the study, treatment and monitoring of patients with glaucoma. It is an eye disease that can lead to optic nerve damage and cause loss of sight. Open-angle glaucoma is the most common type of the disease. It develops gradually and the patient doesn’t experience any pain. If it goes untreated, the patient can become blind.
Tumor:
Uveal melanoma or cancer of the eye involves the iris and choroid or ciliary body. The tumors grow from pigment cells called melanocytes. They give color to the eye and are located within the uvea. The cells are different from the retinal pigment epithelium cells located beneath the retina which are not cancerous, i.e., don’t form melanomas. The doctor can assess the thickness and spread of a malignant tumor and decide on the treatment options.
B-scan can also be used to help detect or monitor:
- Lens implants
- Optic nerve anomalies
- Intraocular inflammations
- Foreign bodies or dislocated lenses
- Extraocular muscles and orbital tissue abnormalities
Preparation & Expectation
The patient doesn’t need to make special preparations for the ultrasound scan. The doctor will numb the patient’s eye using anesthetic drops before conducting the exam. The patient’s pupils will not dilate, but they may have blurred vision during the test. The patient should not experience any pain or discomfort.
The doctor will advise the patient not to rub their eyes until the medication has completely worn off. This is to prevent the patient from unknowingly scratching their cornea.
The patient may be able to drive 30 minutes after the test. However, s/he should be accompanied to the test or arrange to be taken home after the test.
Procedure
The patient will be seated with their eyes closed and the doctor will apply a gel on their eyelids. The gel may run down the patient’s cheek, but they will not feel any pain or discomfort. The doctor will place the B-scan probe gently on the surface of the patient’s eyelid and begin the test.
The B-scan machine generates ultrasound through the small probe. The patient will only feel the gel applied on the spot where the probe is in contact with the surface of their eyelid. The patient may be asked to turn their closed eyes in different directions so that the device can capture different areas of their eye and improve the ultrasound image.
Outcome
The B-scan will provide the doctor with structural information about the patient’s eye. Where the results are abnormal, the doctor will need to establish the cause and determine the best course of treatment for the patient.
An abnormal B-scan may show:
- Foreign bodies in the eye
- Inflammation or swelling in the eye
- Injury to the eye orbit that encloses and protects the eye or damaged tissue
- Retinal detachment, the pulling away of the retina from the back of the eye
- Cysts in the eye – vesicles with fluid, air or other material. Some can be cancerous and early treatment is critical
- Retinoblastoma (cancer of the retina), or in other areas of the eye, e.g., melanoma
- Vitreous hemorrhage which is the bleeding into the vitreous humor, the clear gel that occupies the space between the eye lens and the retina
Risks & Complications
B-scan is safe and has no risks or complications. However, to avoid accidental scratching of the cornea, the patient should desist from rubbing the numbed eye until the anesthetic wears off. This takes about 15 minutes.
