Introduction

The intraocular pressure is the fluid pressure inside the eye. It is the result of a dynamic balance between aqueous humour formation and outflow, which are nearly equal under normal conditions. Normal intraocular pressure varies between 10.5 to 20.5 mmHg with a mean pressure of 15.5 ±2.57mmhg (leydecker 1958). Intraocular pressure has an important role in case of detection of glaucoma, one of the most important cause of blindness worldwide. Ocular hypertension is associated with an increased risk of developing glaucoma and reducing intraocular pressure has shown to lessen progressive loss of visual field.

Accurate and precise measurement of intraocular pressure is, therefore, fundamental to the management of glaucoma. Three types of tonometer are used clinically viz. Indentation, Applanation and Non Contact Tonometer. Schiotz, in 1905 developed prototype of indentation tonometer. The concept of applanation tonometry is based on Imbert Ficks law which states that pressure inside a sphere (P) is equal to the force (F) required to flatten its surface divided by the area of flattening (A) . P=W/A.

Goldmann in 1954 modernised this tonometer and currently it is the most popular and accurate tonometer. This device is mounted on a slit lamp bio microscope. The standard Goldmann tonometer falls somewhat short in the regard due to its requirement for a slit lamp (non portability), topical anaesthesia, fluorescein and an ophthalmologist.

Bernard Grolman (1950) invented Non Contact Tonometer based on principle of applanation tonometer. Routine screening for glaucoma began with NCT.

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Dr Sakshi Sahni

Department of Ophthalmology, GMC Jammu, India