Tonometry

1
Tonometry
qumber Defination

• Objective measurement of IOP
• based, most commonly, on the forces required to
  flatten the cornea,or the degree of corneal
  indention produced by a fixed force.

2
Applanation Tonometry
qumber Principle

• Imbert-Fick principle
• For an ideal dry thin walled sphere pressure
  inside sphere(P) equals the forces(F) required
  to flatten its surface divided by the area(A) of
  flattening
• PF/A

3
Goldmann tonometer

• IOP is proportional to
• Pressure applied to the globe(cornea)
• Thikness of the walls of Globe(cornea Which is
  variable)

Very accurate variable-force tonometer consisting
of double prism
4
Why pressure does not rise with tonometer pressure

• The cornea being rigid resists
  flattening.
• Capillary attraction of the tear film
  meniscus pulls the tonometer towards the cornea
• Capillary attraction and corneal
  rigidity cancel each other

Flattened area has diameter of 3.06mm
5
Procedure

• Topical anesthetics and fluorescein
• Goldmann tonometer mounted on slit lamp
• Two semicircles
• The dial on tonometer rotated to align inner
  margins
• Reading on dial noted

6
Potential errors

• Inappropriate fluorescein
• Pressure on the globe
• Incorrect calibration
• Corneal pathology

7
Other tonometer

1. The schiotz(cheep,easy,no slitlamp)
2. The perkins(hand held,goldmann prism)
3. The air-puff(non-contact,air jet,no
   anaesthesia,accurate only from low-to-middle
   range,startle patient with noise apparent force
4. The pulsair 2000 keeler(handheld,noncontact,no
   noise,accurate as goldmann
5. The tonopen(compares goldmann,distorted,edematous
   cornea,bandage contact lens)