NHMRC Glaucoma Guidelines - ANZGIG

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NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA Chapter 5 – Prognosis: understanding the natural history ■ Chapter 5 Prognosis: Understanding the natural history Recommendation 2 Reduce intraocular pressure Recommendation 3 Monitor visual field and determine rate of any field loss Recommendation 4 Assess risk of conversion from ocular hypertension to glaucoma Good Practice Points • Patients at low risk of conversion should be considered for monitoring • Patients at high risk of conversion should be considered for treatment • Educate patients on the risks for consequences of conversion to glaucoma Introduction The natural history of glaucoma is poorly defined and heterogeneous. There is a subgroup of people with ocular hypertension (OH) or early primary open angle glaucoma (POAG) in whom there is either no disease progression or the progression is so slow that the condition will never exert a significant effect on vision. An individual’s risk of progressive and sight-threatening glaucoma cannot be predicted with precision, however there is improving evidence to specifically identify candidates for treatment. If treatment decisions wait until there are overt signs of disease, this generally results in irreversible optic damage and likely disease progression. Early treatment reduces the number of individuals who develop visual field (VF) defects. The progression of visual defects from acute or poorly controlled glaucoma may lead to rapid damage and permanent loss of vision. This can have devastating consequences. However, intervention is sometimes associated with significant side effects. Therefore, it is critical to appropriately target candidates for intervention. Normal tension glaucoma There is sound evidence that medical treatment is effective in preserving VF in people with normal tension glaucoma (NTG) (Sycha, Vass, Findal et al 2003). The Collaborative Normal Tension Glaucoma Study (CNTGS 1998) demonstrated that when subjects with cataracts are removed from analysis, there are progression rates of 12% for treated cases versus 35% for non-treated cases. This demonstrates the beneficial effects of treatment. However, treatments carry significant side effects (e.g. development of cataracts), and as such, the trade-off between risk and benefit should be carefully considered in each case (Sycha et al 2003). National Health and Medical Research Council 39
NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA Chapter 5 – Prognosis: understanding the natural history The Collaborative Normal Tension Glaucoma Study (1998) identified a 10-fold range in deterioration rates in VF from -0.2dB/year to -2.0 dB/year, illustrating the marked variability in natural rates of deterioration in NTG. This variability prevents prediction of individual rates of VF loss. These guidelines provide recommendations for a standard process for monitoring in Chapter 8. Evidence Statements • Evidence strongly supports reducing intraocular pressure in patients with normal tension glaucoma, in order to preserve the visual field and reduce glaucomatous progression rates. • Evidence strongly supports monitoring rates of visual field loss in patients with normal tension glaucoma. Communication with patients While lowering intraocular pressure slows or halts glaucoma progression, all interventions carry risk. Potential benefit and possible harm (the therapeutic index) need to be balanced carefully, with patient involvement where possible, in decision making. Ocular hypertension The majority of patients with OH will not progress to POAG in the short term (90% will not convert within five years) (Burr, Mowatt, Herandez et al 2007). Within five years however, 9.5% of untreated patients will progress to POAG, compared to 4.4% of medically treated patients (Burr et al 2007). Patients with an initial intraocular pressure (IOP) of 26mmHg or more are more at-risk of progressing to glaucoma. Conversion time to POAG from OH is significantly shorter for individuals not undergoing treatment (Fleming, Whitlock, Beil et al 2005). It is reported that 37% of optic nerve fibres need to be lost before a field defect can be identified on VF testing (Kerrigan, Zack, Quigley et al 1997; Quigley, Nickells, Kerrigan et al 1995). Therefore undetected progression may be occurring in untreated individuals because current standard automated perimetry is insufficiently sensitive to detect functional loss at this stage of disease. This highlights the need for using the most sensitive methods of VF testing and structural assessments for patients with OH. Risk factors for progression to glaucoma include elevated IOP, increased cup:disc ratio, older age, and thinner corneas (Friedman, Wilson, Liebmann et al 2004). There is also strong evidence that central corneal thickness (CCT) is a reliable indicator for the risk of conversion from OH to glaucoma. The strongest evidence links the likelihood of conversion to poorly controlled and high IOP. In the Ocular Hypertension Treatment Study (Gordon, Beiser, Brandt et al 2002; Gordon, Torri, Miglior et al 2007; Kass, Huerer, Higginbotham et al 2002), univariate and multivariate analyses identified that every 1mmHg increase in mean IOP level was associated with a 10% increased risk of conversion from OH to glaucoma. These guidelines provide recommendations for a standard format for assessing risk (see Chapter 6) and monitoring (see Chapter 8). 40 National Health and Medical Research Council
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