Tonometry in ophthalmology

WINTERTemplateIntraocular pressure

and tonometry

01

Intraocular pressure

• What is intraocular pressure?• What unit?• Normal range• Causes of abnormal measurement

Anatomy and physiology

Diurnal variation

Factors that may increase IOP

FEVER

DRUGS

Factors that may decrease IOP

ACIDOSIS

Tonometry • Definition Tonometry is the measurement of

intraocular pressure by a tonometer

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

Parts of the instrument

1.Tonometer tip

2. Metal rod

3. Housing

4.Force adjustment knob

Performing goldmann applanation tonometry

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

Performing schiotz tonometry

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

Contraindications

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

Performing rebound tonometry

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.

Thank you