NHMRC Glaucoma Guidelines - ANZGIG

NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA
Chapter 6 – Identifying those at risk of developing glaucoma
Recommendation 7
Assess risk of progression of glaucomatous damage
Good Practice Points
• Calculate the rate of visual field loss regularly (for example review every four months) for the first two
years, and then less frequently (for example every six months) thereafter if stable. This will depend on
the health care setting and the individual patient’s risk of progression.
• Reduce IOP by 20-50% in patients with glaucomatous optic neuropathy depending on the level of risk
to preserve visual field and to reduce progression.
• Reduce IOP more aggressively in those patients with greater risk factors for progression.
• Patients diagnosed late, with more advanced glaucoma damage, suffer higher rates of progression of
visual loss. More aggressive IOP reduction is required.
Introduction
There is a strong body of research, developed over many years that has established the risk factors
for glaucoma development and progression. However, a standard approach is still required to
organise these risk factors into a hierarchy of risk, including the best ways of assessing them,
and identifying how they interact with disease incidence, prevalence and progression. There are
ongoing questions regarding which patients should be treated, how vigorously to treat them,
and when to initiate treatment. Overall, the literature presents general agreement regarding the
significant association between elevated intraocular pressure (IOP), advancing age, ethnicity and
family history concerning the risks for developing most types of glaucoma.
Risk calculators have been developed to facilitate the application of research findings into clinical
practice. Risk calculators work by applying risk-prediction coefficients from multivariate analysis
from clinical trials and epidemiological studies into risk-modelling formulae that can be applied
to individual patients. Risk calculators are based on an assumption that each patient comes from
a similar population as participated in the clinical trial. Health care providers enter the patient’s
clinical findings into the formulae to calculate the likelihood of that patient developing glaucoma,
or progressing to another stage of the disease. Risk calculators have also been useful for assisting
patients and their health care providers to make decisions about treatment (Mansberger & Cioffi
2006; Gordon, Torri, Miglor et al 2007).
However, risk calculators tend not to include confidence intervals (which are often quite large)
and thus can give a false impression of reliability in terms of prediction. The performance of
the predictive models derived from the Ocular Hypertension Treatment Study was assessed by
Meirdeiros, Zangwill, Bowd et al (2007). They concluded that the Ocular Hypertension Treatment
Study-derived predictive models performed appropriately in independent patient samples.
Their reduced model included age, IOP and central corneal thickness (CCT). The full model
included these and visual field (VF) pattern standard deviation and vertical cup:disc ratio. Both
models predicted conversion of ocular hypertension (OH) to glaucoma at five years in 70% of
cases. A prediction score of 50% indicates random chance, i.e. no additional predictive value
whereas 100% indicates perfect prediction. Whilst these models have some value, they are far from
perfect. Future refinement of optic nerve damage indices and indicators of nerve structure should
improve the accuracy of these models.
The majority of risk factors which are significantly associated with the development of glaucoma
can be identified and measured using a comprehensive patient history. However other important
48 National Health and Medical Research Council