Letter charts are not only used to measure visual acuity, they are also used as targets for subjective refraction. This is the main reason distance acuity is measured more often than near acuity. At a long distance, accommodation is relaxed, so that the refraction can be more accurate.
Popliteal artery. The popliteal artery branches off from the femoral artery. It is located in the knee and the back of the leg. Its courses near the adductor canal and the adductor hiatus, distinctive open areas inside the thigh. At its far end, it splits into the anterior and posterior tibial arteries. During its course, the popliteal artery branches into other significant blood vessels.
A popliteal cyst, also known as a Baker's cyst, is a fluid-filled swelling that causes a lump at the back of the knee.