Rectifying calibration error of Goldmann applanation tonometer is easy!
Nikhil S Choudhari1, Krishna P Moorthy2, Vinod B Tungikar3, Mohan Kumar4, Ronnie George5, Harsha L Rao1, Sirisha Senthil1, Lingam Vijaya5, Chandra Sekhar Garudadri1
1 V S T Glaucoma Centre, Dr. Kallam Anji Reddy Campus, L V Prasad Eye Institute, Hyderabad, Andhra Pradesh, India
2 Department of Bio-engineering, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
3 Department of Production Engineering, SGGS Institute of Engineering and Technology, Nanded, Maharashtra, India
4 Department of Bio-engineering, Dr. Kallam Anji Reddy Campus, L V Prasad Eye Institute, Hyderabad, Andhra Pradesh, India
5 Department of Glaucoma, Jadhavbhai Nathamal Singhvi, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
Source of Support: None, Conflict of Interest: None
Purpose: Goldmann applanation tonometer (GAT) is the current Gold standard tonometer. However, its calibration error is common and can go unnoticed in clinics. Its company repair has limitations. The purpose of this report is to describe a self-taught technique of rectifying calibration error of GAT. Materials and Methods: Twenty-nine slit-lamp-mounted Haag-Streit Goldmann tonometers (Model AT 900 C/M; Haag-Streit, Switzerland) were included in this cross-sectional interventional pilot study. The technique of rectification of calibration error of the tonometer involved cleaning and lubrication of the instrument followed by alignment of weights when lubrication alone didn't suffice. We followed the South East Asia Glaucoma Interest Group's definition of calibration error tolerance (acceptable GAT calibration error within ±2, ±3 and ±4 mm Hg at the 0, 20 and 60-mm Hg testing levels, respectively). Results: Twelve out of 29 (41.3%) GATs were out of calibration. The range of positive and negative calibration error at the clinically most important 20-mm Hg testing level was 0.5 to 20 mm Hg and -0.5 to -18 mm Hg, respectively. Cleaning and lubrication alone sufficed to rectify calibration error of 11 (91.6%) faulty instruments. Only one (8.3%) faulty GAT required alignment of the counter-weight. Conclusions: Rectification of calibration error of GAT is possible in-house. Cleaning and lubrication of GAT can be carried out even by eye care professionals and may suffice to rectify calibration error in the majority of faulty instruments. Such an exercise may drastically reduce the downtime of the Gold standard tonometer.