NHMRC Glaucoma Guidelines - ANZGIG

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NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA Chapter 8 – Monitoring: long-term care baseline, tested and confirmed on three occasions, is required to identify an ‘event’. The definition of significant sensitivity reduction varies, for instance: • using Glaucoma Change Probability Maps with average variability measures from age-matched patients, using either the age-corrected threshold values; or pattern deviation values, where global effects on VF from corneal or cataract changes have been minimised (Heijl et al 2002; Leske et al 2004). These forms of software analysis are available commercially with some VF equipment • using set threshold reductions, which is a cruder, although still useful technique. For example, three points with ≥ 10dB loss, or with three times the short term fluctuation is proposed (Spry & Johnson 2002). A cluster of three points each 15dB removed from baseline provides another definition of event (Optometrists Registration Board of Victoria 2008). Trend analysis is regression analysis which quantifies the rate of loss in a VF index and/or the rate of loss in individual sectors or points of VF. It requires additional computer software and analysis of the regression. Linear regression is used, and slopes of change calculated as those slopes which are significantly different from zero (Spry & Johnson 2002). This allows easier prediction of time to severe visual loss (to reach approximately -20dB mean deviation for example) or blindness (-30dB). The accuracy of the trend, similar to event analysis, depends partly upon the variability of the VF tests. Regressions are notoriously subject to outlier effects and particularly to the final datum. Methods for managing these problems have been described, such as using only three tests per year, and a 3-omitting logic (Gardiner & Crab 2002). A number of guidelines have made recommendations for the frequency of VF monitoring. However it has been noted by the AOA (2002) that for any recommended interval, factors that determine frequency of evaluations should include the severity of damage (mild, moderate, severe), proximity of damage to fixation (more frequent evaluations for more severe disease), the rate of progression, the extent to which the IOP exceeds the target pressure, and the number and significance of other risk factors for damage to the optic nerve. Currently no single recommendation appears to take all these factors into account. Therefore the available recommendations have been combined to provide the most comprehensive level of recommendation currently available. These recommendations are based on guidelines and expert opinion, and are outline in Table 8.1. It is important that health care providers employ sound clinical reasoning, for in certain cases, follow-up VF testing may be required more, or less, frequently than the recommended intervals. For instance, a second test may be required to establish a baseline for future comparisons, to clarify a suspicious test result, or to overcome an apparent testing artefact (AAO 2005c). National Health and Medical Research Council 97
NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA Chapter 8 – Monitoring: long-term care Table 8.1: Time period (years) required to detect various rates of mean deviation (MD) change with 80% power in visual fields with low, moderate and high degrees of variability with 1(a), 2(b) and 3(c) examinations per year (Chauhan, Garway-Heath, Goñi et al 2008) One examination/year Variability Progression rate (dB/yr) Low Moderate High 0.25 13 19 30 0.5 9 13 19 1.0 6 9 13 2.0 5 6 9 Two examinations/year 0.25 6.5 9.5 15 0.5 4.5 6.5 9.5 1.0 3 4.5 6.5 2.0 2.5 3 4.5 Three examinations/year 0.25 4.3 6.3 10 0.5 3 4.3 6.3 1.0 2 3 4.3 2.0 1.7 2 3 Evidence Statement • Evidence supports undertaking visual field testing with automated perimetry on multiple occasions at diagnosis, in order to set a reliable baseline. An assessment of likely rate of progression will require two to three field tests per year in the first two years. Indications to change regimen The indications for adjusting a glaucoma management plan are: • target IOP is not achieved • the patient has progressive optic nerve or VF damage despite achieving the target IOP. The validity of the diagnosis and target pressure should be reassessed. Additional evaluation may identify conditions that are contributing to the progression of damage, and serve as a justification to escalate treatment. These evaluations include obtaining diurnal IOP measurements, repeating the central corneal thickness (CCT) measurement to verify a thin cornea or a change in corneal thickness after refractive surgery, or seeking evidence of unrecognised low ocular perfusion pressure. A neurologic evaluation also may be considered 98 National Health and Medical Research Council
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