In the context of ocular health, what does "refraction" specifically measure?

Refraction specifically measures the eye's refractive error, which is how well the eye can focus light onto the retina. This process involves evaluating how light bends as it passes through different parts of the eye, particularly the cornea and lens. When a person has refractive errors, such as myopia (nearsightedness) or hyperopia (farsightedness), it means that light is not focusing correctly on the retina, leading to blurred vision. The assessment of refractive error is essential for determining the appropriate corrective lenses or treatments needed to achieve clear vision.

The other choices address aspects of the eye that contribute to overall ocular health but do not pertain to the concept of refraction. The curvature of the cornea is an important factor in determining refraction, but it is not the direct measurement of refractive error itself. The thickness of the lens and the health of the retina are also critical to overall eye function, but they relate to different assessments within ocular health rather than specifically measuring how well the eye focuses light.