How do you communicate numbers to your glaucoma patient?

Shared decision making can reduce overtreatment, which places an unnecessary burden on the healthcare system and places the patient at risk of an adverse event.

Communicating statistics intelligibly is essential for shared decision making. Presenting outcomes in absolute measures is often easier to understand than relative numbers, which can both over- and underestimate the outcome ^1-4. Number needed to treat (absolute risk reduction ^-1) is another way to assess the clinical impact of an intervention in an intuitive way and communicate this to the patient ^1-3.

The Ocular Hypertension Treatment Study (OHTS) ⁵ analysed the risk of glaucoma after thirteen years in three equally sized groups based on the baseline risk of developing glaucoma. In the cohort as a whole, the risk of developing glaucoma was 22% in the observation arm and 16% in the treatment arm, corresponding to a 27% relative risk reduction or a 6% absolute risk reduction with treatment.

When the cohort was divided into three equally sized groups based on baseline risk, the protective effect (relative risk reduction) of medical treatment was 12.5%, 26% and 30% in the low, medium and high-risk group respectively. The absolute risk reduction in the three groups differed more: 1% (from 8% to 7%), 5% (from 19% to 14%) and 12% (from 40 to 28%). This corresponds to a number needed to treat of 98, 16 and 7 for the low, medium and high-risk group respectively.

If one focuses on absolute numbers and numbers needed to treat, it thus becomes obvious that the benefit of treatment is not equal for all and increases with baseline risk ⁶. Understanding and communicating benefits and risks clearly for shared decision making is important not only in ocular hypertension, but in all aspects of glaucoma care.

References

1. Freeman, A. L. J. How to communicate evidence to patients. DTB 57, 119–124 (2019).
2. Malhotra, A. et al. Choosing Wisely in the UK: the Academy of Medical Royal Colleges’ initiative to reduce the harms of too much medicine. BMJ 350, h2308 (2015).
3. Gigerenzer, G. Making sense of health statistics. Bull World Health Organ 87, 567 (2009).
4. J, C. A meta-analysis of the effects of presenting treatment benefits in different formats. Medical decision making : an international journal of the Society for Medical Decision Making 27, (2007).
5. Kass, D. M. A. et al. Delaying Treatment of Ocular Hypertension: The Ocular Hypertension Treatment Study. Archives of ophthalmology 128, 276 (2010).
6. Gordon, M. O. & Kass, M. A. What we have learned from the Ocular Hypertension Treatment Study. Am J Ophthalmol 189, xxiv–xxvii (2018).

Contributor: Niklas Telinius, MD, PhD, DMSc, Aarhus University Hospital, Denmark

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