Abstract: A vision testing apparatus and a method for testing vision in terms of contrast sensitivity and spatial frequency response are provided. The apparatus and method utilize a plurality light-polarizing optotypes which are provided on sheets of an oriented polymeric material. The optotypes are presented one at a time to a patient in conjunction with a polarizing filter such that rotation of the filter relative to the optotype will cause the contrast of the optotype to vary from a first condition wherein the pattern of the optotype is indistinguishable from its background to a second condition wherein the optotype is seen at a maximum level of contrast. The patient will indicate the point at which he or she first sees the optotype. The sequential presentation of a series of optotypes having patterns which vary in their spatial frequencies will provide a measure of both contrast sensitivity and spatial frequency response for each patient tested.

Abstract: A color-corrected vision testing apparatus and method are provided, such having a blue filtered incandescent illuminating source in a light-occluding housing for high contrast translumination of test patterns also in said housing to obtain improved testing of acuity levels.

Abstract: A system for dispensing a cryogen such as liquid nitrogen. The system employs two vessels containing the liquid cryogen. One serves as a pressure vessel and the other as a storage vessel. Liquid from the pressure vessel is vaporized in a ballast chamber exposed to ambient temperature, resulting in pressurized refrigerant gas. A valve selectively admits the pressurized gas into the liquid storage vessel, causing the stored liquid to be dispensed at a selected site.