Why the correct answer is right
Spectral Domain Optical Coherence Tomography (SD-OCT) utilizes light waves to capture high-resolution, cross-sectional images of the eye. Its advanced technology allows for an axial resolution of approximately 5 to 10 microns, which is roughly 1/10th the thickness of a human hair. This incredible level of detail is necessary for clinicians to clearly distinguish the individual layers of the retina and the cornea.
Why the other options are incorrect
Options like 100-200 microns or 500 microns represent a much coarser resolution, similar to what you might see in standard ultrasound imaging, which cannot show microscopic retinal structures. A resolution of 1-2 millimeters is far too large, as the entire thickness of the retina is usually less than half a millimeter. If the resolution were that low, the instrument would only see a single blurry shape instead of distinct cellular layers.
Memory aid
Think of the S in SD-OCT as standing for Sharp and Small. Just as a Sharp pencil can draw tiny details that a thick marker cannot, the SD-OCT uses light to "draw" a picture of the eye with a precision of 5 microns—the same number of fingers on a hand used to hold that sharp pencil.
Real-world application
In a clinical setting, this 5-10 micron resolution allows opticians and doctors to detect the earliest signs of diseases like glaucoma or macular degeneration. By measuring the specific thickness of the retinal nerve fiber layer, they can identify microscopic thinning before the patient even notices a change in their vision. This precision is the gold standard for monitoring eye health over time.
