Indian Journal of Ophthalmology

: 1984  |  Volume : 32  |  Issue : 5  |  Page : 432--434

Clinical evaluation of the non-contact tonometer and comparison with goldmann applanation tonometer

B Sridhar Rao 
 SankaraNethralaya A unit ofMedical Research Foundation, Madras, India

Correspondence Address:
B Sridhar Rao
Sankara Nethralaya, A unit of Medical Research Foundation, 18 College Road, Madras-600 006.

How to cite this article:
Rao B S. Clinical evaluation of the non-contact tonometer and comparison with goldmann applanation tonometer.Indian J Ophthalmol 1984;32:432-434

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Rao B S. Clinical evaluation of the non-contact tonometer and comparison with goldmann applanation tonometer. Indian J Ophthalmol [serial online] 1984 [cited 2021 Sep 25 ];32:432-434
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Full Text

The Non contact Tonometer is a pneumatic applanation tonometer which measures the intraocular pressure without touching the eye. This study was designed to evaluate the American Optical Non-contact tonometer in glaucomatous and non­glaucomatous patients and to compare these intraocular pressure readings with that of Goldmann Applantion tonometer which is considered to be the clinical standard of reference.


The Intraocular pressure was measured in 187 eyes of 100 patients attending the out Patient Department with normal corneas. All the measurements were made at one visit in a standardized sequence. The intraocular pre­ssure was first measured with the Non-contact tonometer. After the power switch is turned to the `ON' position, the eye piece reticule ring is adjusted to good focus. The patient is explained that a puff of air is used to measure the pressure in his eye and the effect is demonstrated in the finger. The instrument is triggered after 30 seconds warm up.

Multiple measurements, usually 3 per eye are made. Between each measurement 8 to 10 seconds gap is given as readings taken in rapid succession will be inaccurate. These measurements were done without using any topical anaesthesia and were repeated after instillation of4% Xylacaine drops. After Non­contact tonometer measurements were made by an Ophthalmic assistant, applanation tonometry was performed by the Ophthal­mologist. This' was done to eliminate any bias in the readings, when both the measurements were performed by the same person. We used Goldmann applanation tonometer attached to Haag-Streit slit lamp.


The Intraocular pressure readings obtained with Non-contact tonometer were compared with Applanation tonometry readings. Three readings were obtained without the topical anaesthetic and three reading with topical anaesthesia [Table 1][Table 2][Table 3][Table 4][Table 5][Table 6].

In the eyes with poor correlation between the two readings the Non contact reading was falsely high in 86% and falsely low in 14% of eyes [Table 6].

The Non-contact tonometer readings were more accurate in the pressure range less than 20 mm Hg. The readings obtained with the use of topical anaesthesia tend to be lower com­pared to readings obtained without the use of topical anaesthetic.


The patients acceptance of Non-contact tonometer was good and only a few patients experienced a scare during the procedure by the impact of air puff. The Non-contact tonometer was easily performed by a trained Ophthalmic assistant. When the Non-contact tonometry was done after topical anaesthetic corneal haziness resulted in 16 patients, necessitating use of the override switch; this was also resorted to in 15 eyes with astigmatic corneas. The lowest Non-contact tonometer .reading obtained without the use of topical anaesthetic appears to correlate best with Applanation tonometry, compared to other readings. The highest Non-contact tonometer reading tend to be falsely high. It is unlikely that Glaucoma will be undetected with Non­contact tonometer because multiple readings are taken and if any of the three readings are high the intraocular pressure can be rechec­ked with an applanation tonometer. Non­contact tonometer can be considered as a valuable screening derice and can be used routinely for measuring intraocular pressure in all patients. Further it has a special place in a patient who has undergone recent surgery or in infected eyes where intraocular pressure can be measured without any risk of mic­robial contamination. However in a patient with gross surface irregularity of the cornea, the intraocular pressure cannot be measured. In patients with minimal surface irregularity reliable readings are obtained with the use of override switch. Non-contact tonometer was easily performed in children who would not co-operate for Schiotz tonometer.


The correlation between the non-contact tonometer and applanation tonometer was done.[2]


1Non-Contact tonomete, Service and Operator mannual.
2Moses R.A., 1958. Amer. J. Ophthalmol 46: 865. 3. 'Johnson C.C.. 1967. Arch. Ophthalmol 78: 416.