Optic disc haemorrhage: the more we look the more we find

In 1970, Stephen Drance published a paper describing optic disc haemorrhage in open-angle glaucoma. In doing so he was re-evaluating an unusual glaucoma sign first described by Bjerrum 112 years ago. But at the time and for many years thereafter, disc haemorrhages were thought to be rare signs of a rare glaucoma subtype of little relevance to the disease generally. In 1998, we reported a disc haemorrhage population prevalence of 1.4% in the Blue Mountains Eye Study (BMES) on the basis of a single stereo-disc photograph examination. This was much higher than previously reported. We also found it to be the single strongest glaucoma risk factor, occurring in 13.8% of those with the disease. But optic disc haemorrhages are transient phenomena, usually lasting 6–12 weeks. Such a prevalence in a cross-sectional study suggested three possible explanations: that the BMES findings were a very unusual chance occurrence; that the period prevalence in the whole sample was much higher; or that the same optic discs have frequent recurrent haemorrhage which could be detected at almost any time point. Elucidating these possible explanations required frequent examination of a cohort over a reasonably long period of time. The Early Manifest Glaucoma Trial (EMGT) followed a population-based cohort of 255 participants over a median of 8 years. It reported disc haemorrhage prevalence by clinical examination every 3 months and optic disc photography every 6 months. At the baseline EMGT examination 13.7% of the sample had an optic disc haemorrhage, remarkably similar to the BMES estimate. When all study visits (usually 10) were included some 55% of participants in this trial had a disc haemorrhage at least once. This supports the idea that, far from being rare, disc haemorrhages occur in a large proportion of the most common forms of glaucoma. But because they are transient repeated examinations are needed to detect them. The EMGT data also showed that careful clinical examination of a glaucomatous optic disc is almost as good as photographic assessment performed half as often. This important finding is in contradistinction to the Ocular Hypertension Treatment Study which reported very poor rates of 6-monthly slit-lamp detection when compared to annual photographs. The EMGT report did not tell us whether disc haemorrhages continue to increase over time (so that eventually everyone will have one) or plateau after a period. In this issue of the journal, Drs Suh and Park answer this important question in a large clinic-based glaucoma cohort. The key methodological strength of this study was the large number of glaucoma patients studied and the high frequency of observation. Around 600 consecutive hospital outpatients with glaucoma were examined every 1–3 months for 3 years, then every 1–6 months for up to 15 years. Photographs were taken every 6–12 months. Like the EMGT, the authors reported good agreement between clinical and photographic detection. The overall probability of a disc haemorrhage was 45.5% in eyes with normal tension glaucoma and about half that rate in eyes with higher initial intraocular pressure (IOP). The cumulative incidence of disc haemorrhage rose over time; about half of all initial haemorrhages were detected in the first year, and about three-quarters by 3 years. But by 5 years the incidence started to plateau with very few initial haemorrhages found after this time. We know that disc haemorrhages have important prognostic significance. The EMGT found disc haemorrhages at follow up to be an independent predictor of glaucoma progression, the risk increasing with increasing haemorrhage frequency. Indeed, it was the only significant follow-up risk factor when post-treatment IOP was analysed. The Ocular Hypertension Treatment Study reported a fourfold increase in risk of glaucoma in eyes in which a disc haemorrhage occurred. A recent clinic-based cohort of 348 glaucoma patients followed for an average of 8.2 years reported twice the rate of visual field progression in eyes that had a disc haemorrhage at any time during follow up. Importantly, intervention to further lower the IOP after a disc haemorrhage reduced the rate of glaucoma progression. Rates of disc haemorrhage after IOP lowering are a little more complex. The EMGT found very similar rates of disc haemorrhage in treatment and control groups. Furthermore, no relationship could be found between the amount of IOP lowering and rate of haemorrhage in the treatment group. Although this could suggest IOP lowering does not affect disc haemorrhages, some care needs to be taken in interpreting these data. Like Suh and Park’s study, the EMGT found a strong association between disc haemorrhage and low baseline IOP. The complicating factor here is that eyes with disc haemorrhage may need more IOP lowering to reduce their frequency and slow glaucoma progression. Although the EMGT found IOP lowering slowed glaucoma progression overall, eyes with haemorrhages progressed faster despite a similar IOP fall.