Intraocular pressure was determined manometrically in owl monkey eyes with normal and edematous corneas. The pressure was measured with Perkins hand-held, Goldmann, and MacKay-Marg tonometers to compare relative accuracy. At manometric levels of 20, 30, and 40 mm Hg, a statistically significant difference in readings was found between normal and edematous corneas with use of the Perkins and Goldmann applanators, whereas no such difference was found with the MacKay-Marg tonometer. The MacKay-Marg tonometer most closely approximated the true intraocular pressure in edematous corneas.
McMillan F, Forster RK. Comparison of MacKay-Marg, Goldmann, and Perkins Tonometers in Abnormal Corneas. Arch Ophthalmol. 1975;93(6):420-424. doi:10.1001/archopht.1975.01010020434007