Intraocular pressure & tonometry 2011.4.22 녹내장 컨퍼런스 Intraocular pressure & tonometry 서울성모병원 안과 R4 정수경

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

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 5.5 7.5 10 15 로 증가

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

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

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.

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.

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.

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

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 439-642 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;45:3118–3121. Siganos, D. et al. J Cataract Refract Surg 2004;30(4):746–751.

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.

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 http://www.aao.org/publications/eyenet/200505/glaucoma.cfm

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. http://www.aa 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

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

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.

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

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

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)