Comparison of different tonometers.

INTRODUCTION: Glaucoma is chronic optic neuropathy characterized by structural and functional damage to the optic nerve head (as evidenced by thinning of the neuro retinal rim and by progressive visual field loss) caused by many factors among which intraocular pressure is an important and critical factor. While IOP is not the only causative factor, it still remains the only risk factor amenable to and modifiable by treatment and the only indicator which can be constantly monitored at every visit or assessment as a measure of success of treatment. This study compares the intraocular pressure values obtained by different tonometers and compares the correlation between the values obtained. AIM OF THE STUDY: To compare the IOP values obtained from Schiotz tonometer, Non-contact tonometer, Pascal’s dynamic contour tonometer and Perkins hand held applanation tonometer and to evaluate their relationship with central corneal thickness if any. DESIGN: Random cross sectional analytical study. INCLUSION CRITERIA: 1) Patients between the ages of 20 – 80 years 2) IOP between 7.0 – 50 mm of Hg by Perkins hand held applanation tonometer EXCLUSION CRITERIA: Patients with corneal edema. Patients with corneal ulcer. Patients with corneal opacity IOP 50 mm of Hg by Perkins hand held applanation Tonometer. Patients with nystagmus MATERIALS AND METHODS: Four hundred patients attending out patients department of Regional Institute of Ophthalmology, Government Ophthalmic Hospital, Chennai were screened and their intraocular pressure and central corneal thickness were measured. RESULTS: Perkin’s hand held applanation tonometer was taken as the gold standard technique and the other methods were compared to it. All the three techniques showed good agreement between the readings, with Pascal’s DCT agreeing at 0.75 intra class correlation (ICC), NCT at 0.72 ICC and Schiotz indentation tonometer at 0.66 ICC. CONCLUSION: All the tonometers showed significant correlation with the gold standard technique (Perkin’s applanation tonometer), over a range of intra ocular pressures, between 20 to 80 years, in diabetics and hypertensives and also in patients with different CCT values. But Pascal’s DCT showed higher correlation with the gold standard as compared to NCT or Schiotz indentation tonometer