tonometry in ophthalmology
TRANSCRIPT
Intraocular pressure
• What is intraocular pressure?• What unit?• Normal range• Causes of abnormal measurement
Types of tonometer
Applanation tonometer Indentation tonometer
• Goldmann applanation tonometer• Perkins tonometer• Pneumatic tonometer• Tonopen • Noncontact(air-puff) tonometer
• Schiotz tonometer
Goldmann applanation tonometer
• ‘GOLD STANDARD’• Based on Imbert-Fick principle Pressure=force/area of flattening• Mounted on a slit-lamp biomicroscope
Disinfecting the applanating tip• Remove the tonometer tip from the biprism
after each use• Disinfect by swabbing the tip with a cotton-
tipped applicator that has been soaked in isopropyl alcohol
• Rinse the tip with water and dry with gauze.
Contraindications • Active infections• Recurrent corneal erosions• Corneal abrasions that are not healed
Schiotz indentation tonometry
• Inexpensive, portable, easy to use instrument
Advantages Disadvantages
• Limited accuracy in conditions like high myopia, following surgery and corneal oedema
• Uses the fact that a plunger will indent a soft eyeball more than a hard one
Parts of instrument
Curved metal foot plate
Metal plunger
Frame with handles
Variety of weights
Numbered scale
Indicator needle
Hammer
Disinfecting schiotz tonometer• Remove the plunger from the cylinder• Wipe the footplate and the plunger with
the alcohol• Rinse the footplate and plunger with water
and wipe it with gauze
Rebound tonometry• bounce a magnetized probe off the cornea
and detect the deceleration of the probe caused by the eye.
• The deceleration is more rapid if the IOP is high and slower if the IOP is low.
• The probes are disposable between patients, so, disinfection is not necessary
Disadvantage of this tonometer is that it can only be used in an upright patient (the probe falls out if the instrument is facing downward)
Parts of rebound tonometer
Display
Selector button
Measurement button
Grip
Forehead support
Forehead supporting adjusting wheel
probe
Digital tonometry• Rough estimation of intraocular pressure
by finger tips especially in uncooperative patients or in absence of instruments.
Recap • Name one cause of ocular hypotony• IOP is highest in the morning. T/F• Name one drug which can cause increased IOP• What is the gold standard instrument to
measure IOP?• Name one contraindication for schiotz
tonometer.