Marco Prism Exophthalmometer The Marco PRISM EXOPHTHALMOMETER is designed for accuracy and simplicity in the measurement of the exophthalmos. Prisms are made of clear plastic with easy-to-read millimeter lines on both sides. The eye is seen through the lower half and the scale through the upper, eliminating the difficulty of parallax and facilitating a rapid determination of protrusion. The Marco Prism Exophthalmometer has a silver hammer-tone finish and comes complete with a storage case with red velvet liner.