Transcript Intraocular pressure and CCT - Canadian Ophthalmological Society

Canadian Ophthalmological
Society
Evidence-based Clinical Practice
Guidelines for the Management of
Glaucoma in the Adult Eye
Intraocular Pressure and
its Measurement
General factors that affect
measured IOP
General
• Diurnal variation — IOP generally higher in the morning
vs afternoon; normal fluctuation 2–5 mm Hg
• Posture — higher in supine vs sitting position. Highest in
head down position
• Exercise — aerobic exercise generally lowers IOP, while
isometric exercise can increase IOP
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Systemic factors that affect
measured IOP
Systemic
• Valsalva (e.g. with breath holding or in some obese
patients) — generally increases IOP, although can
decrease
• Foods/drugs:
 Lower IOP — alcohol, fat-free diet, heroin, marijuana,
some systemic vasodilators (e.g., nitroglycerin, beta
blockers)
 Raise IOP — excessive water drinking, caffeine,
tobacco, corticosteroids
• General anesthesia — generally decreases (important
exceptions: ketamine, succinylcholine [which may raise
IOP])
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Tonometry — Goldmann
tonometry for reproducibility
Recommendation
As Goldmann applanation tonometry is the most
reproducible, it is recommended for IOP
measurement in patients with healthy corneas
[Level 31].
1. Phelps CD, et al. Albrecht Von Graefes Arch
Klin Exp Ophthalmol 1976;16;198:39–43.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix E: How to test calibration
of a Goldmann Tonometer
•
•
1.
2.
3.
Standard method for measuring IOP1
Periodic calibration check recommended: at least twice yearly
Set the tonometer in position on the slit-lamp stand, with the perspex
biprism head in place and the tension on the circular dial on the right side
(from the examiner’s side of the slit lamp) set at 5 mm Hg. The head
should lean slightly forwards (away from the examiner).
Slowly twirl the circular dial counter-clockwise until the head rocks back
towards you. The tension should read 0 to 2 mm Hg below zero (Figure 1).
Slowly twirl the dial clockwise until the head rocks forwards again. The
tension should read 0 to 2 mm Hg (Figure 2).
Figure 1
1. Garway-Heath DF. In: World Glaucoma Association:
Intraocular Pressure. Consensus series 4. The Hague:
Kugler Publications Copyright © 2008 SEAGIG, Sydney. Reproduced with
Figure 2
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
permission from Asia Pacific Glaucoma Guidelines, 2nd ed.
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Hong Kong: Scientific Communications, 208:1-117.
Appendix E: How to test calibration
of a Goldmann Tonometer
4.
5.
6.
Remove the calibration rod from its box. Firmly screw into position the
holding bracket that slides along the rod so that the closest mark in
front of the centre one (on the other side of the centre from you) is
aligned as exactly as you can (Figure 3).
Slip the rod and its holder into the receptacle on the right side of the
tonometer. The head will rock backwards towards you.
Slowly twirl the circular dial clockwise until the head rocks forwards.
Note the tension reading on the dial: it should be 20 to 23 mm Hg.
Figure 3
Copyright © 2008 SEAGIG, Sydney. Reproduced with
permission from Asia Pacific Glaucoma Guidelines, 2nd ed.
Hong Kong: Scientific Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix E: How to test calibration
of a Goldmann Tonometer
7.
8.
9.
Slowly twirl the circular dial counter-clockwise until the head rocks
backwards. The tension on the dial should read 17 to 20 mm Hg.
Remove the rod and holding bracket from the tonometer and
reposition the bracket so that it is aligned exactly with the most forward
mark on the rod—furthest away from you (Figure 4).
Replace the rod in its bracket in the tonometer receptacle. The
tonometer head should rock backwards, towards you.
Figure 4
Copyright © 2008 SEAGIG, Sydney. Reproduced with
permission from Asia Pacific Glaucoma Guidelines, 2nd
ed. Hong Kong: Scientific Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix E: How to test calibration
of a Goldmann Tonometer
10. Slowly twirl the dial clockwise until the head rocks forwards. The
tension should read 60 to 64 mm Hg.
11. Slowly twirl the dial counter-clockwise until the head rocks
backwards—the tension should read 56 to 60 mm Hg.
• The three threshold tension levels being used to test the
tonometer’s calibration are 0, 20, and 60 mm Hg.
• At each of these thresholds, you can gently twirl the dial backwards
and forwards, reading the tension as the head responds.
• These points should bracket the threshold level evenly—the higher
the level being tested, the greater the interval is likely to be.
Copyright © 2008 SEAGIG, Sydney. Reproduced
with permission from Asia Pacific Glaucoma
Guidelines, 2nd ed. Hong Kong: Scientific
Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Tonometry — role for finger
tonometry for special circumstances
Recommendation
Consideration can be given to finger tonometry to
estimate IOP as very low, normal, or very high in
certain situations (e.g., eyes with flat anterior
chambers [lens-cornea touch], eyes with
keratoprosthesis) [Consensus].
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Tonometer tips — disinfection
Recommendation
Applanation tonometer tips should be disinfected
between each patient [Consensus].
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Factors Influencing Accuracy
of IOP Measurement
Clinical features associated
with measurement errors using
applanation tonometers
Clinical feature
• Physiologically thin central cornea*
•
•
•
•
•
•
•
•
•
Insufficient or no fluorescein in tear film
Corneal edema (stromal and epithelial)
Physiologically thick central cornea*
Excessive fluorescein in tear film
Pressure on globe from examiner’s fingers
and/or from eye lid spasm
Obese patient
Hair lying across cornea distorting mires
Restrictive myopathy/muscle entrapment
Breath holding or Valsalva manoeuvre
*Assuming a structurally normal cornea;
i.e., no change in rigidity/biomechanics such
as with excessive hydration, scarring, or
refractive surgery.
Resulting error
Underestimation of IOP (true
IOP higher than what is
measured)
Overestimation of IOP (true
IOP lower than what is
measured)
True IOP could be higher or
lower than what is measured
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Clinical features associated
with measurement errors using
applanation tonometers (cont’d)
Clinical feature
Resulting error
• Lens-cornea apposition
• Tonometer not well calibrated
• Corneal abnormalities (scars, refractive
surgery, corneal graft, edema, Keratoconus)
• Marked corneal astigmatism
• Small palpebral aperture
• Nystagmus
• Tremor
Technical difficulties
(interpret
results with caution)
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix F: Tonometry mires
Figure 1—Excess corneal applanation
(IOP lower than tonometer reading)
Copyright © 2008 SEAGIG, Sydney. Reproduced with
permission from Asia Pacific Glaucoma Guidelines, 2nd ed.
Hong Kong: Scientific Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix F: Tonometry mires
Figures 2 and 3—Insufficient corneal applanation
(IOP higher than tonometer reading)
Copyright © 2008 SEAGIG, Sydney. Reproduced with
permission from Asia Pacific Glaucoma Guidelines, 2nd
ed. Hong Kong: Scientific Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Appendix F: Tonometry mires
Figure 4—Correct endpoint corneal applanation
(IOP equals tonometer reading)
Copyright © 2008 SEAGIG, Sydney. Reproduced with
permission from Asia Pacific Glaucoma Guidelines, 2nd
ed. Hong Kong: Scientific Communications, 208:1-117.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Tonometry — applanation
with difficult positioning
Recommendation
Hand-held devices such as Perkins/Kowa, TonoPen, and hand-held noncontact tonometers are
useful in children, and in those unable to come
easily to the slit lamp (e.g., obese, bedridden, with
postural difficulties) [Consensus].
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Central Corneal Thickness
and its Measurement
Documentation of IOP and
influence of CCT
Recommendation
Correction nomograms that adjust GAT IOP based
solely on CCT are neither valid nor useful in individual
patients. IOP should always be communicated as
measured IOP rather than “corrected” IOP, due to the
lack of a universal correction nomogram. When
recording and communicating IOP values, measured
IOP should be recorded with CCT in a manner that is
easily identifiable in the chart [Consensus].
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.
Central corneal thickness
measurement
Recommendation
Measurement of CCT, preferably with ultrasonic
means, should be performed on all patients with
glaucoma and ocular hypertension. The variance
from the mean in a given population may under- or
overestimate the true value of IOP in a given
individual, and may influence the risk of an
individual with ocular hypertension converting to
glaucoma [Level 11].
1. Brandt JD, et al. Am J Ophthalmol
2004;138:717–22.
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the
adult eye. Can J Ophthalmol 2009;44(Suppl 1):S1S93.