Hand-held applanation tonometer.

FOR glaucoma screening programmes it is important to have an accurate tonometer which causes the minimum of disturbance to the patient.The Goldmann applanation tonometer has all the necessary qualities for this purpose but it is not easily portable.The instrument to be described employs the same principles as the Goldmann tonometer but can be held in the hand and does not require a slit-lamp microscope.It can be used with the patient upright or supine.The prism is clipped on a counterbalanced arm mounted on a pivot to which is attached a coiled spring.A knurled wheel engages with a gear wheel on the pivot and can be turned to increase or decrease the force applied to the prism.Calibration marks show the force applied in grammes (Fig. 1 a, b).Illumination of the prism is obtained from four miniature bulbs set at the base of a cone of perspex which surrounds the prism.The outside of the cone is painted black to minimize light scatter and the whole cone can be easily removed to give access o the prism.A ring of blue perspex at the base of the cone gives the light the necessary colour for viewing the fluorescein; another bulb illuminates the scale.Magnification is obtained with a +2000 D lens (Fig. 2).