Correlation Of The Non Contact Tonometer With The Perkins Applanation Tonometer

Abstract

Glaucoma is now the second leading cause of blindness globally, after cataracts, according to World Health Organization. Approximately 11.2 million Indians above 40 years suffer from glaucoma. Raised intra ocular pressure is an important risk factor for development and progression of glaucoma. Therefore, intra ocular pressure measurement is essential in ophthalmological assessment. Perkins tonometer is portable, simple and also considered gold standard because it is based on the same principles as the Goldmann applanation tonometer. But it needs topical anaesthesia, fluorescence staining, needs a specialist to do procedure .Corneal factors, like astigmatism, corneal curvature, and central corneal thickness, affect the accuracy of applanation tonometer. In measuring intra ocular pressure by Non-contact tonometer there is no need of anaesthetic, staining, no effect of corneal factors and can be done by a non medical or paramedical personnel. The need of this study is to correlate intraocular pressure measured using Noncontact tonometers with Perkins applanation tonometer and to study reliability of the Non-Contact Tonometer as screening tool, considering its advantages over Perkins in Indian context where large numbers of patients have to be screened and risk of transmission of infection is high. Aims and Objectives of this study were • To correlate the intraocular pressure by the Non contact tonometer with the Perkins applanation tonometer. x Methods: It is a comparative study on Patients attending outpatient Department of Ophthalmology BLDEU’s Shri B M Patil Medical College, Hospital and Research Centre, Bijapur, Karnataka from December 1st 2014 to 31st March 2016. With a minimum sample size of 128, we had included 260 participants in our study. Data was collected using a proforma, with the informed consent of the patient, followed by obtaining history and routine ophthalmological examination. Patients were subjected to two methods of tonometry – Non Contact Tonometry and Perkins Applanation Tonometry (Perkins under topical anaesthesia with 0.5% Proparacaine eye drops). Non Contact Tonometer readings were recorded first, then Perkins tonometer. Three readings were taken for each method and mean calculated. The data was statistically analyzed using Paired T test and Correlation co efficient. Sensitivity and Specificity were also calculated for the Non contact tonometer. Results: The non contact tonometer showed excellent agreement with the Perkins tonometer. The correlation coefficient of intraocular pressure measured by Non contact tonometer and Perkins applanation tonometer is 0.879 and 0.894 for right and left eye respectively with p value of <0.05 in our study participants (both male and female), showed strong positive correlation between the intraocular pressure measured by Non contact tonometer and Perkins applanation tonometer. The non contact tonometer also scored high as an effective screening tool. The non contact tonometer showed high sensitivity 95.5 and 94.3 for right eye and left eye respectively (right eye more than left xi eye) i.e. very few false negative results as well as high specificity 94.5 and 99.1 for right eye and left eye respectively (left eye more than right eye) i.e. few false positive results; thus coming across an excellent agreement with Perkins applanation tonometer, using an intraocular pressure of more than or equal to 21 mm Hg with the Perkins applanation tonometer as the standard criterion. Interpretation & Conclusion: The current study shows that the Non contact tonometer compares well with the Perkins applanation tonometer (hand held version of gold standard Goldmann applanation tonometer) and showing excellent agreement with it. The non contact tonometer can be used as a reliable screening tool.