What does a phoropter measure during an eye examination?

A phoropter is an essential instrument used in eye examinations primarily to measure a person's refractive error and determine their visual acuity. When a patient looks through the phoropter, the optometrist or ophthalmologist can present various lenses and determine the best combination for clear vision. This process allows for the assessment of nearsightedness, farsightedness, and astigmatism, which are all aspects of refractive error.

In addition to measuring refractive error, the phoropter helps assess visual acuity. By presenting different lenses to the patient, the eye care professional can evaluate how well they can see at different distances. The results collected from the phoropter are crucial in formulating a precise prescription for corrective lenses.

While other choices mention important aspects of vision care – such as eye pressure and color vision – they do not pertain to the primary functions of a phoropter. Eye pressure is typically measured with a tonometer, and color vision tests are conducted separately, often using tools like Ishihara plates. Therefore, the correct answer encompasses both refractive error and visual acuity, highlighting the phoropter's significant role in comprehensive eye examinations.