1. Intraocular pressure & tonometry
녹내장 컨퍼런스
Intraocular pressure & tonometry
서울성모병원 안과 R4 정수경

2. Classification of tonometer
1) Indentation tonometer
2) Applanation tonometer
3) Noncontact tonometer
4) Miscellaneous tonometer

3. Indentation tonometry
Schiotz indentation tonometry
Potential source of error
“Average” coefficient of ocular rigidity (K)
Expulsion of intraocular blood
Relatively steep or thick cornea -> falsely high IOP reading
로 증가

4. Applanation tonometer
Goldmann applannation tonometer
Maklakoff applanation tonometer
Perkins applanation tonometer
Mackay-Marg tonometer (Tono pen)
Pneumotonometer
PASCAL tonometer

5. Applanation tonometer
Maklakoff applanation tonometer
Consisted of a dumbbell shaped metal cylinder
The resultant circular white imprint on the endplate corresponded to the area of flattened cornea.
IOP read from a conversion table
Perkins applanation tonometer
Use the same biprism as the Goldmann applanation tonometer
Dumbbell: 아령

6. Applanation tonometer
Mackay-Marg tonometer (Tono pen)
A plate of 1.5 mm surrounded by a rubber sleeve.
The force required to keep the plate flush with the sleeve was electronically monitored.
Tono pen - a handheld instrument with a strain gauge that creates an electrical signal as the footplate flatten the cornea
A built-in single-chip microprocessor senses the proper force curves and averages 4 to 10 readings.

7. Applanation tonometer
Pneumotonometer
Similar to the Mackay-Marg tonometer in that a central sensing device measures the IOP
The force required to bend the cornea is transferred to a surrounding structure.
The sensor is air pressure.

8. Applanation tonometer
PASCAL tonometer
FDA clearance in 2003, commercially in 2004
Portable slit lamp mounted device
Samples IOP 100 times /s
+ocular pulse amplitude +systemic pulse rate
Digital output of IOP + graphic output of the ocular pressure pulse
PASCAL has a concave tonometer tip that matches corneal curvature and measures pressure directly by means of a miniaturized, built-in sensor. When it touches the cornea it allows the cornea to assume its natural shape when pressure on both sides is equal and distortion of the cornea is minimal. DCT is different from applanation tonometry. “It’s a new principle, a new concept,” said Dr. Stamper, who has conducted two DCT studies. 
OPA : ocular pulse amplitude - the difference between diastolic IOP and systolic IOP
OPA is suggestive of choroidal blood flow
PASCAL repeatedly samples intraocular pressure at a rate of 100 times per second. The ocular pulse amplitude (OPA) and the systemic pulse rate are continuously measured and recorded by the instrument. In addition, the ocular pressure pulse is graphically represented on the patient report.

9. Applanation tonometer
PASCAL tonometer
The cornea is a spherical shell made of
a material that resists stretching and is
fairly flexible to bending deformations.
There is a container that is filled with
casting resin surrounding an entire globe.
A pressure (p) measured by a pressure sensor
could exactly correspond to the true IOP (P),
if a small part of the wall by a pressure
sensor with identical surface shape is replaced.
Dynamic contour tonometry: principle and use
Clinical and Experimental Ophthalmology2006;34: 837–840

10. Applanation tonometry
PASCAL tonometer – Intraocular pressure
More accurate than other tonometers. It provided the most accurate IOP readings within ± 0.7 mmHg, whereas Goldmann readings were consistently below true IOP by an average of 4 mmHg in the study performed on eye bank eyes.
A little higher in general than applanation tonometry in people with thin or average thickness corneas.
Healthy eye (CCT um) ; excellent concordance with Goldmann applanation tonometry value
LASIK eye; better suited to monitor IOP than other tonometry value
Concordance : 일치, 부합
DCT is a newly Food and Drug Administration (FDA) – approved device that is designed to measure IOP, independent of
corneal thickness, corneal curvature, and ocular rigidity.
Kaufmann, C. et al. Invest Ophthalmol Vis Sci 2004;45:3118– Siganos, D. et al. J Cataract Refract Surg 2004;30(4):746–751.

11. Applanation tonometry
PASCAL tonometer – Ocular pulse amplitude
Indirect measurement of the choroidal perfusion and reflects
the ocular blood flow
An independent risk factor for glaucoma and possibly for NTG
A decrease in OPA of patients suffering from NTG is detected.
Br J Ophthalmol 2002;86:981–984
The OPA was correlated with GAT and DCT IOP measurement, and correlated neither with blood pressure nor with age in normal healthy eyes.
Physiological diurnal variability and characteristics of the ocular pulse amplitude (OPA)
with the dynamic contour tonometer (DCT-Pascal1)
Int Ophthalmol (2007) 27:357–360
Concordance : 일치, 부합
DCT is a newly Food and Drug Administration (FDA) – approved device that is designed to measure IOP, independent of
corneal thickness, corneal curvature, and ocular rigidity.

12. Miscellaneous tonometers
Ocular response analyser (ORA)
A rapid air (20ms jet of air) impulse to apply force to the cornea ->
monitor the deformation of
cornea
2) records two applanation events
the first- inward moving
the other- returning
The difference between the
appplanation pressure ; CH
4) The average of these 2 pressures; Goldmann-equivalent intraocular pressure

13. Miscellaneous tonometers
Ocular response analyser (ORA)
Noncontact measurement of the biomechanical properties of the cornea
the corneal hysteresis (CH)
the corneal resistance factor (CRF)
the corneal-compensated intraocular pressure (IOPCC)
the Goldmann-equivalent intraocular pressure (IOPG)
the corneal hysteresis (CH) ; the viscosity as a measure of absorption and energy conversion of the cornea and the whole eye
the corneal resistance factor (CRF); to display the elastic properties
POAG patients have properties with lower CH.
Theoretically, CH improved buffering might result in reduced stress/strain on both the optic nerve and peripapillary scleral tissues; this, in turn, reduces the risk for glaucomatous structural damage.
Corneal-compensated IOP (IOPcc) is derived from both IOPand corneal biomechanical data.
Similar to DCT-IOP findings, several published clinical studies have reported that IOPcc is unrelated to
central corneal thickness

14. Miscellaneous tonometers
Rebound tonometers
Icare tonometer (Icare Finland, Helsinki)
Measure IOP without the use of topical anesthetics
Comfortable and highly reproducible in healthy school-aged children
Screen tool in children
The opportunity to monitor IOP at home.
1mm 직경의 24mm 길이의 일회용 probe 이용함

15. Miscellaneous tonometers
Rebound tonometers
Icare tonometer (Icare Finland, Helsinki)
Reproducibility and Tolerability of the ICare Rebound tonometer in School Children
J Glaucoma 2007;16:185–188
Impact or dynamic tonometry
An assembly of 2 coils coaxial to a probe shaft that bounce a magnetic probe off the cornea and detect the deceleration of the probe caused by the eye.
RBT : rebound tonometry
It contains an assembly of 2 coils coaxial to a probe shaft
that bounce a magnetic probe off the cornea and
detect the deceleration of the probe caused by the eye
(Figs. 1, 2).
The probe slows down faster as the
IOP increases and, consequently, the higher the IOP,
the shorter is the duration of impact.

16. Miscellaneous tonometers
IOP monitoring devices
Prototypes
Contact lens
Implantable device
Scleral band
SENSIMED Triggerfish sensor device
Shield 의 reference논문 참조 !!
Swiss 에서 만듬

17. Comparison of tonometers
Most precise method; manometric measurement of the cannulated anterior chamber
Most common used method; Goldmann & Tono - pen
Less common used method; noncontact tonometer, Perkins, pneumotonometry, Schiotz tonometer
Goldmann Vs Tono-pen
Normal range; good correlation
Higher IOP – tono-pen underestimate
Lower IOP- tono-pen overestimate
Manometric :압력계로 잰
Cannula: 금속관

18. Tonometry for special clinical circumstances
Irregular corneas ; Pneumatic tonometer is useful
(West CE et al, 1972 AJO)
Goldmann > tonopen (Geyer O et al, 1992 BJO)
Soft contact lens; Pneumatic tonometer = Tono- pen
(Rubenstein et al, 1985 Arch Oph)
(Khan et al, 1989 AJO)
Gas filled eye; Pneumatic tonometer < Goldmann = Tonopen
(Del Priore LV et al, 1989 Ophthalmology)