18. A patient's visual acuity was tested using a Snellen chart. The results indicated that her vision was 20/50. What does this result mean?
19. Following eye surgery, a man was required to wear an eye patch over his right eye. What effect will this patch have on the man's vision?
20. During a test for near-point accommodation, Subject A had an accommodation distance of 15 cm in both eyes, and Subject B had an accommodation distance of 30 cm. Which one is likely the younger person? Explain.
21. Explain why many vertebrates, including cows and domestic dogs and cats, have much better night vision than humans.