3 tonometry and ocular
TRANSCRIPT
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r mon arnarr mon arnar
With acknowled ements toWith acknowled ements to
Dr RobertDr Robert HarperHarper
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B k r n h n in r i n I PB k r n h n in r i n I P
Glaucoma is characterized by raised IOP, opticneuro a y an amage caus ng v sua e
loss traditional view
progressive optic neuropathy, with a typicallycupped, pale optic disc and a characteristic loss of
sensitivity to light Sponsel in 1980s
a variable combination of raised IOP, optic discchanges and visual field loss Quigley in 1990s
Randomised controlled trial evidence 2000+
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Theories of optic nerve damage
Reduced blood flow/vascular dysregulation
laminar plates
Current view: RGC death is causes b a o tosisand remodelling of the optic nerve head, mediatedby mechanical forces, ischaemia and reperfusion
injury (IOP and OBF implicated in these issues)
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Age
IOP
Race
Diabetes Mellitus
Hypertension
M o ia Corneal thickness
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Background: IOP at presentation:Background: IOP at presentation:
epidemiologyepidemiology
Study No POAG % with
normal IOP
Des Moines, USA 189 68
Ferndale, Wales 20 35Framingham, USA 40 52
Baltimore, USA 194 59
Beaver Dam, USA 104 32Roscommon, Ireland 41 37
Blue Mountains, Aus 108 75
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.
IOP 16-21mmHg ~ 2.5x
IOP 22-29mmHg ~ 13x
Baltimore Eye Study 1991
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ac groun : str ut on oac groun : str ut on o
Av=15.7 mmH
SD=2.7 mmHg
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str ut on s ewe
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Background: IOP and clinical trialsBackground: IOP and clinical trials
Key randomised glaucoma trialsOHTS, EMGT, CNTGS, CIGTS, AGIS, EGPS
Lowering IOP exerts a favourable influence on the
development and progression of glaucoma Lower IOP means better rotection
Lowering IOP does not always stop progression
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reduction/progression relationship
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summarysummary
Multi-centre study, 1636 patients with OHT- mm g - yrs, compar ng convers on
rate to glaucoma in Rx versus No Rx
Conversion 4.4% in Rx group and ~9% incontrol rou i.e. no Rx
>90% of OHT pts did not convert after 5 years
, ,predictors for conversion to POAG
CCT was a risk factor for POAG conversion
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stu y summarystu y summary
First treatment versus no treatment RCT in
Population screening 44K 255 pts recruited
Randomised to IOP or no Rx~
IOP reduction reduced progression risk by
~
Lower risk patients and no treatment option
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Typical tonometry referral criteriaTypical tonometry referral criteria
Contact applanation tonometry
IOP >22mmHg with disc changes
IOP >35mmHg (urgent)
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e ear est tonometer
a pat on
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n entat on tonometers
If a plunger of known weight is rested
indentation should (?) be proportional to
Note: ocular rigidity/facility of aqueousoutflow (see separate lecture on
tonometr
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Plunger may be connected to lever arm and
scale (e.g. Schitz) or to electronic recordingsystem (e.g. Mueller)
From Henson (1983)
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c otz
The footplate is rested on the cornea and the
plunger is free to indent the cornea. A varietyof weights may be used to minimise errorsdue to corneal rigidity (use with tables)
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Normal weight (knurled knob above
footplate) = 5.5grams giving total of 16.5grams to be supported by cornea. Additionalweights are 7.5, 10, 15 g
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n entat on
Shiotz o
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sa vantages
50g)
Difficult to disinfect note also CJD risk ?
Displacement of aqueous
Effect of corneal ri idit on readin
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vantages
Cheap Portable
Can measure ocular tension of eye
w scarre cornea
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pp anat on tonometrypp anat on tonometry
Imbert-Fick law IOP = tonometer weight (g) / area (mm2)
Method of choice for tonometry (currently)
Constant area, variable force
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Gambs Cone just touching cornea
3.06 mm black square
3.06 mm diameter
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Difficulty with Gambs
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o mann tonometero mann tonometer
Applanation diameter 3.06 mm
very e u sp ace .
bending force = surface tension
1 gm equiv to 10 mmHg-
- SD of differences
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o mann Doubling prism to separate images by 3.06
mm
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, .comparing calibrate new
instruments.
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Ad
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Advantages
cheap
comfortable (apart from anaesthetic)
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sa vantages
cannot be delegated
contact w t cornea s g t c ance oabrasion)
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rrorsrrors
Lids touching the probe ( IOP)
ur ace ens on orce a ere m n ma
Prolon ed contact IOP
Corneal astigmatism (>3DC)
Incorrect vert cal al gnment ( IOP)
Calibration s stematic or random or Observer errors ( or IOP)
Meniscus width (usually IOP)
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en scus w ten scus w t
Thickness of flourescein ring Ideal ~ 1/10th diameter cone (0.3mm*)
~2mmHg
.
~0.35 mmHg
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er ns
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Hand held
A l h r Portable
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NonNon--contact applanation tonometrycontact applanation tonometry First NCT designed by Grolman and introduced by
American Optical in 1972 r nc p e was cons ere as ear y as y r c
Zeiss
Reichert (formerly American Optical) NCT II and
Keeler Pulsair EasyEye
Nidek NT-2000/4000
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Canon TX-10
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pr nc p epr nc p e r g na rects an a r-pu towar s t e cornea -
point of applanation detected by optical system, time
electronically (time relates to the IOP)
Later enerations measure air- ulse ressure at
applanation Keeler Pulsair is hand-held and can be used in any
pos t on - creates rampe a r pu se w c automat ca yapplanates cornea at alignment. Optical system detects
.generation instrument is Pulsair EasyEye
Modern NCTs use lower ulse ressure than theoriginal Reichert instrument
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m tat onsm tat ons Some NCT advantages could become limitations
if the user is unaware of the errors that can beintroduced in estimating IOP
See variations in IOP in slides below
Essential to take at least 3-4 readings per eye inorder to balance out the effect of the ocular pulse
NCTs can provide clinically meaningful measuresof IOP which equate to those obtained by theGoldmann instrument
NCT has not replaced GAT as the technique ofchoice in the hospital setting
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actors a ect ngactors a ect ng s ort terms ort term
Time of Day (diurnal range) Normal ~3-6 mmHg
Glaucoma avera e ~13 mmH
Diurnal variation in plasma cortisol (?)
- ,
Repeat tonometry and phasing
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Typical IOP Diurnal Variation in Normals,
showing nocturnal dip.
25
15
10IO
5
0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12
Time of Day (Hours)
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actors a ect ngactors a ect ng s ort terms ort termArterial pulse
-
Drinking/Fluid intake
Water and coffee +3 mmHg in 20 min alcohol -3mmHg in 5 min
Contraction of extra/intraocular muscle IOP
Accommodation
Blinking and lid squeezing
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actors a ect ngactors a ect ng s ort terms ort termBlood pressure, exertion, posture
sitting to supine 1-6 mmHg increase
nvers on ncreases++ o - mm g
aerobic exercise can lower IOP
straining can increase IOP
ti ht collar or neck tie 4mmH holding breath
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ystem c an ocu ar seaseystem c an ocu ar seaseSystemic disease
association between raised IOP/Glaucoma andsystemic hypertension and DM
the secondary glaucomas!
anterior uveitis and retinal detachments
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Lee at al. The corneal thickness and intraocular pressure story: where are we
now? Clin ExpOphthalmol 2002; 30: 334-337
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ornea t c ness anornea t c ness anPost PRK
7
5
6
Hg)
3
4
tion(m
1
2
O
Predu
0
0 25 50 75 100 125 150 175
I
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ar y correct on actorar y correct on actorCCT
(mm)
10mm
Hg
15mm
Hg
20mm
Hg
25mm
Hg
30mm
Hg
. + . + . + . + . + .
0.48 +2.2 +2.6 +2.9 +3.3 +3.6
. . . . . .
0.52 -0.4 -0.2 +0.0 +0.1 +0.30.54 -1.6 -1.5 -1.4 -1.3 -1.2
0.56 -2.8 -2.8 -2.8 -2.8 -2.7
0.58 -3.9 -4.0 -4.1 -4.1 -4.2
Additive correction (in mmHg) to be added to IOPrea ngs a eren s or eve s o a er
Ehlers et al, 1975).
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ornea t c nessornea t c ness
Knowledge of CCT provides information on
an n v ua s r s an a ows correc on o
IOP (OHTS, Brandt 2004)
No single correction factor is agreed upon. - .
difference from an average CCT is suggested
European Glaucoma Society (2003)
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Choose based on
Validity/Precision
issues
Ease of use
Value for money
ppearance
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eve opments n tonometryeve opments n tonometry
Ocular Res onse AnalyserTonopen
neumatonometry
Pascal D namic Contour tonometer
Integrated tonometer/pachymeter unit
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cu ar esponse na ysercu ar esponse na yser
Reichert ORA
Bi-directional dynamic
Corneal hysteresis:
corneal rigidity,
Clinical trials awaited
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Pascal Dynamic Contour TonometryPascal Dynamic Contour Tonometry
Based on principle of contour
Contour tip concave, with
with contact surface
va ues c a me to e c oserto true manometric levelscompared to GAT
1Kniestedt et al, Archives of Ophthalmology 2004
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onopenonopen
Applanation device with small footprint-
abnormalities
A sterile cover must be over the tip
button until CAL appears in the window
Ensure atient has anaesthetic, entl taTonopen against cornea. Final averagedreading (of usually 4 6) displayed
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neumatonometerneumatonometerResistance to air flow
varies with IOP
3mm diameter area
Back pressure in air
resistance to air flow
Force applied adjusts to maintain
constant area of applanation
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Overcomes some of the problems
Measures
IOP (mmHg) ulse am litude
(mmHg)
ulse volume (l) pulse rate (/min)
ocular blood flow
(l/min)OBF tonometerOBF tonometer
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cont nuous recor ngcont nuous recor ng
14
Hg
13
IOPm
12
11
10
Time (sec)
1 2 3 4 5 6
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cu ar oo ow onometercu ar oo ow onometer
Earl studies su estedhelpful in vascularaetiolo of POAG/NTG
Benefit of OBF now
Still affected by cornel
c ness more anGAT?)
--
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--
Distribution of IOP
Normal and Glaucoma
Distribution of POBF
Normal and Glaucoma
16
18
20
20
25
10
12
14
15
4
6
8
5
10
0
2
8 12 16 20 24 28 32 36 400
100 400 700 1000 1300 1600 More
IOPPOBF
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natomy ys o ogy onatomy ys o ogy o The eye receives its blood supply from 2 sources of
the ophthalmic artery: Ciliary arteries
Central retinal artery
Ciliary supply accounts for 95% of total OBF
Intraorbital (pial arteries and CRA)
Pre-laminar (posterior ciliary arteries)
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pt c nerve oo supp ypt c nerve oo supp y
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et o s o assess nget o s o assess ng
Angiography
Laser doppler velocimetry
Laser doppler flowmetry
Heidelberg Retina Flowmetry (HRF)
Laser speckle phenomenonue e en op cs
Retinal vessel analyser
ornea empera ure Colour Doppler imaging
er p era oo ow
See Flammer et al, Prog Ret Eye Res 2002, 21:359-93.
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n g aucoman g aucomaeren ec n ques measure eren aspec s o
ocular blood circulation and numerous studies have
-groups (see Flammer et al review, 2002)
.
There is reduced OBF in glaucoma that involves differentarts of the e e includin the o tic nerve head retinal
circulation, the retrobulbar and peripheral blood flow
The reduced OBF appears more pronounced in patients
w t The effect of reduced OBF is more pronounced under
. .
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oss e causes o re uct onoss e causes o re uct on
Increased resistance to OBF
Anatomical variations
Vascular dysregulation
ecrease per us on pressure
Due to increased IOP
Due to decreased BP
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an per us on pressurean per us on pressureOcular perfusion pressure (OPP) cannot be
Estimate:
OPP=2/3 mean arterial BP minus IOP
Medical thera directed towards
increasing OPP
qu va en re uc ons may no g ve esame increase in OPP
Perfusion ressure and POAGPerfusion ressure and POAG
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Tielsch et al (1995) Arch Ophthalmol 113:216-221