Certified Ophthalmic Assistant Practice Exam

How is an A-scan display described?

1. Multiple linear images

2. Single linear image

3. Two-dimensional image

4. Three-dimensional image

The correct answer is: Single linear image

An A-scan display is characterized as a single linear image that represents the amplitude of the echo signals received from the eye's internal structures. This type of ultrasound measurement provides a graphical representation where the x-axis indicates the distance to the interfaces in the eye (such as the lens and retina), while the y-axis shows the amplitude or strength of the returning echoes. Each peak on the graph corresponds to a different structure, allowing for precise measurements of distances inside the eye, such as axial length. This method is crucial for calculating parameters like lens power for cataract surgery and understanding other ocular conditions. The other choices describe different imaging modalities. Multiple linear images suggest a series of images that would indicate a different imaging technique such as B-scan ultrasonography, which provides two-dimensional cross-sectional images. Two-dimensional and three-dimensional images imply more complex data representations that capture breadth and depth, not suitable for the linear representation of A-scan. Therefore, the correct choice aligns with the fundamental characteristics of A-scan ultrasound technology in ophthalmology.