A. Applanation tonometer.
B. Indentation Tonometer
C. Pascal Dynamic Contour Tonometer
D. Rebound Tonometer
Ans:A. Applanation tonometer.
- It is the procedure eye care professionals perform to determine the intraocular pressure (IOP), the fluid pressure inside the eye.
- Applanation tonometry is based on the Imbert-Fick principle, which states that the pressure inside an ideal dry, thin-walled sphere equals the force necessary to flatten its surface divided by the area of flattening (P = F/A, where P = pressure, F = force and A = area). In applanation tonometry, the cornea is flattened and the IOP is determined by varying the applanating force or the area flattened.
- The Goldmann applanation tonometer measures the force necessary to flatten an area of the cornea of 3.06mm diameter.
- The Perkins tonometer is a type of portable applanation tonometer, which may be useful in children, anesthetised patients who need to lie flat, or patients unable to co-operate with a sitting slit lamp examination.
- Non-Contact Tonometry
- In air puff tonometry, the applanating force is a column of air which is emitted with gradually increasing intensity.
- Ocular Response Analyzer
- The principle of indentation tonometry is that a force or a weight will indent or sink into a soft eye further than into a hard eye.
- It consists of a curved footplate which is placed on the cornea of a supine subject. A weighted plunger attached to the footplate sinks into the cornea in an amount that is indirectly proportional to the pressure in the eye.
- It is an applanation tonometer with some aspects of indentation tonometry. It consists of a 5mm diameter, slightly convex, silicone tip on the end of a piston that rides on a stream of air. The cornea is indented by the silicone tip. When the cornea and the tip are flat, the pressure pushing forward on the tip is equal to the IOP.
- The Tono-Pen involves both applanation and indentation processes
- It determines intraocular pressure by bouncing a small plastic tipped metal probe against the cornea. The device uses an induction coil to magnetise the probe and fire it against the cornea. As the probe bounces against the cornea and back into the device, it creates an induction current from which the intraocular pressure is calculated.
PASCAL DYNAMIC CONTOUR TONOMETER
- The Pascal Dynamic Tonometer utilizes a piezoelectric sensor embedded in the tip of the tonometer to measure the dynamic pulsatile fluctuations in IOP.