b2boptic → items → item → pair → lens → rxData → glassesArrangement → prism

values	description
POSTERIOR	the slope of prism is towards the eye
ANTERIOR	the slope of prism is away from the eye:

<xs:simpleType name="PrismSlope">
  <xs:restriction base="xs:string">
    <xs:enumeration value="POSTERIOR"/>
    <xs:enumeration value="ANTERIOR"/>
  </xs:restriction>
</xs:simpleType>