Prospective, open-labeled, randomized, controlled, multicenter study at two clinical investigative sites in Tucson, Arizona. The subjects will undergo intraocular pressure measurement with the CATS tonometer prism and the Goldmann applanation tonometer prism (GAT). Seventy-five (75) Subjects 18 and older and will be enrolled. Subjects will be screened based on standard of care vision examination at the clinical investigation sites. All subjects will undergo a standard ophthalmic exam and informed consent. IOP will be measured using a Goldmann tonometer armature with both the standard flat GAT prism and the modified curved CATS prism alternately inserted. The only additional measurement is central corneal thickness (CCT) which is used to correct for one of the corneal biomechanical errors seen in the GAT prism and is currently standard of care.

Inclusion Criteria:

• Written informed consent (and assent when applicable) obtained from subject or subject's legal representative and ability for subject to comply with the requirements of the study.
• Male and female patients, at least 18 years of age

Exclusion Criteria:

• Subject has undergone ocular surgery within the last 3 months
• Uncontrolled systemic disease that in the opinion of the Investigator would put the subject's heath at risk
• Pregnant or nursing women
• Subjects with only one functional eye
• Those with one eye having poor or eccentric fixation
• Eyes displaying an oval contact image
• Those with corneal scarring or who have had corneal surgery including corneal laser surgery
• Microphthalmos
• Buphthalmos
• Contact lens wearers
• Severe Dry eyes
• Lid squeezers - blepharospasm
• Nystagmus
• Keratoconus
• Any other corneal or conjunctival pathology or infection.
• Central corneal thickness between 0.600 mm and 0.500 mm (more than 2 standard deviations about the human mean)