Evaluation of three applanation tonometers in dogs

Abstract

SUMMARY The Mackay-Marg, Tono-Pen, and Challenger applanation tonometers were evaluated in vivo in 12 clinically normal eyes of 6 dogs. Tonometric measures of intraocular pressure (iop) were compared with closed manometric iop measurements from the anterior chamber of anesthetized dogs. The tonometers were evaluated at iop that ranged from 5 to 100 mm of Hg. The Mackay-Marg tonometer was the most reliable instrument when evaluated at iop from 5 to 100 mm of Hg (r2 = 0.996) and from 10 to 30 mm of Hg (r2 = 0.962). The Tono-Pen tonometer was also reliable (r2 = 0.967) over the range of iop, but consistently overestimated iop at lower pressures and underestimated iop at higher pressures. The Mackay-Marg and Tono-Pen measurements were essentially linear. When evaluated from 10 to 30 mm of Hg, r2 was 0.828 for the Tono-Pen tonometer. The Challenger tonometer, although reliable over the full range of iop (r2 = 0.965), proved to be less accurate, as indicated by lack of a good linear equation.