The CATS Tonometer Prism (CATS) is a modified Goldmann applanation tonometer (GAT) prism that is optimized to work with the GAT's operating system to reduce errors in the measurement due to patient anatomical variation. This is used to measure intraocular pressure by applying a known force on the globe of the eye and measuring intraocular tension by applanation. Tonometer prisms are assembled onto a GAT as a patient contacting component that is then utilized by the GAT to assess intraocular pressure.
An ophthalmic, manually-operated, measuring instrument designed for determining the intraocular pressure (IOP) by exerting an external force in direct contact with the eye which provides a reading of the resistance of the tunica of the eye to deformation (the extent of corneal indentation) which is expressed in millimetre(s) of mercury (mmHg). This device (known as a contact type, e.g., a Schioetz or Perkins tonometer) is used in the diagnosis of glaucoma and may be hand-held or used in conjunction with a slit lamp.