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Update Your Consensus Knowledge

Intraocular Pressure

From time to time IGR will publish some of the consensus statements as part of the WGA promulgation strategy.

Central Corneal Thickness

1. On average, greater central corneal thickness (CCT) results in overestimation of intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT).

Comment: The extent to which CCT contributes to the measurement error (in relation to other factors) in individual patients under various conditions has yet to be established.

Calibration of Goldman Applanation Tonometry

1. Currently there are no data to support a specific frequency of calibration verification for GAT.

Comment: The frequency for verification of GAT calibration of at least twice yearly is suggested. For clinical research, a verification error > ± 1 mmHg should be the threshold to send the tonometer for recalibration; the threshold for clinical practice may be higher and requires a cost-benefit analysis.

Goldman Applanation Tonometry

1. To obtain a GAT measurement, which is relatively unaffected by daytime changes in CCT, the patient should desirably have been awake with his/her eyes open for at least two hours prior to the measurement being made.
2. The wearing of contact lenses on the day when tonometry is performed may lead to an artifactually raised IOP as measured by GAT.

Comment: Contact lens wearing patients should have tonometry performed after having been awake, without contact lenses, for at least two hours for contact lens-induced and diurnal corneal edema to resolve.

Intraocular Pressure

1. There is strong evidence to support higher mean IOP as a significant factor for the development of glaucoma.
2. There is strong evidence to support higher mean IOP as a significant risk factor for glaucoma progression.
3. IOP is more variable in glaucomatous than in healthy eyes, but both 24-hour IOP fluctuation and IOP variation over periods longer than 24 hours tends to be correlated with mean IOP.
4. There is currently insuffi cient evidence to support 24-hour IOP fl uctuation as a risk factor for glaucoma development or progression.

Comment: 24-hour IOP measurements are comprised of day-time (diurnal) and night-time (nocturnal) periods.

Comment: Diurnal IOP is generally highest after awakening and decreases during the day-time period.

Comment: Posture is an important variable in the measurement of IOP; IOP in the sitting position is generally lower than in the supine position.

5. There is currently insuffi cient evidence to support IOP varia-tion over periods longer than 24 hours as a risk factor for glaucoma development and progression.
   
   

Target IOP

1. The determination of a target IOP is based upon consideration of the amount of glaucoma damage, the IOP at which the damage has occurred, and the life expectancy of the patient, and other factors including status of the fellow eye and family history of severe glaucoma.

Comment: At present, the target IOP is estimated and cannot be determined with any certainty in a particular patient.

Comment: There is no validated algorithm for the determination of a target IOP. This does not, however, negate its use in clinical practice.

2. It is recommended that the target IOP be recorded so that it is accessible on subsequent patient visits.
3. The use of a target IOP in glaucoma requires periodic re-evaluation.

Comment: This entails examination of the optic nerve and assessment of visual function to detect glaucomatous progression, the effect of the therapy upon the patients quality of life, and whether the patient has developed any new systemic or ocular conditions that might affect the risk/benefit ratio of therapy.

Comment: During the re-evaluation, it is essential to determine whether the IOP target is appropriate and should not be changed.