Mesoamerican ballgame many Caribbean islands including Cuba, Puerto Rico, and the West Indies, has been proposed as a descendent of the Mesoamerican ballgame, perhaps through the Maya. Mesoamerican ballgame The Mesoamerican ballgame was a sport with ritual associations played since 1400 BC by the pre-Columbian people of Ancient Mesoamerica. The sport had different versions in different places during the millennia, and a newer more modern version of the game, "ulama", is still played in a few places by the indigenous population. The rules of the game are not known, but judging from its descendant, ulama, they were probably similar to racquetball, where
Fixation disparity A patient's associated phoria is the amount of prism needed to reduce their fixation disparity to zero minutes of arc. The Mallett Fixation Disparity Unit Instrument used to measure the associated heterophoria (or compensating prism). It consists of a small central fixation letter X surrounded by two letters O, one on each side of X, the three letters being seen binocularly, and two coloured polarized vertical bars in line with the centre of the X which are seen by each eye separately. The instrument can be swung through 90° to measure any vertical fixation disparity. The associated phoria is indicated