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Editors Selection IGR 15-2

Quality of Life: Impact of undiagnosed glaucoma on quality of life

Comment by George Spaeth on:

67442 Mental Health Status and Quality of Life in Undiagnosed Glaucoma Patients: A Nationwide Population-Based Study, Jung KI; Park CK, Medicine, 2016; 95: e3523

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Jung and Park deserve congratulations for trying to eliminate a knotty problem related to understanding the relationship between glaucoma and psychological characteristics, including self-perceived quality of life. They note that prior studies have demonstrated a poorer quality of life and more depression in those with glaucoma than those without glaucoma. But is the relationship causative? That is, does glaucoma cause the depression, or does depression cause the glaucoma?? One of the many confounding factors in such studies ‒ as pointed out by several, including Jampel et al.,¹ is the possible effect of knowing one has glaucoma. Because those who know they have glaucoma are more concerned about going blind than those without glaucoma it seems reasonable to assume that this, and other fears, could cause depression. Furthermore, one of the medications used to treat glaucoma, timolol, can cause depression. These and other complicating considerations have severely limit the ability of investigators to nail down a causal relationship between glaucoma and depression or quality of life; that is, having glaucoma may not CAUSE depression or decreased quality of life, and being depressed or having a poor quality of life many not CAUSE glaucoma. Association can be very close but unrelated to causation.

One of the medications used to treat glaucoma, timolol, can cause depression

Jung and Park had the great insight that one way this problem could be addressed was to compare those who knew they had glaucoma with those who actually had glaucoma, but did not know that they did. Brilliant. Their study, based on data from an extensive Public Health Data base in Korea, seems to show definitely that those who do actually have glaucoma but do not know they have glaucoma have more mental health problems and a poorer quality of life than those who know they have glaucoma. Therefore, they suggest, glaucoma can be considered to be responsible for causing those problems, or those problems can be considered responsible for causing glaucoma. They quote studies purporting to show that depression can cause heart disease by effecting inflammatory cytokines. Unfortunately, their study does not demonstrate a causative relationship between mental health problems and glaucoma, either direction.

The problem, that they did not address, is that the two populations being compared in their study ‒ (1) those who knew they had glaucoma; and (2) those who had glaucoma but did not know it ‒ were not comparable. Population 2, those who did not know they had glaucoma, were significantly older, thinner, sicker (with diabetes and systemic hypertension), poorer and less educated than those who knew they had glaucoma. Because there is evidence that those who are older are more likely to be depressed than those who are younger, it is reasonable to conclude that Jung and Park's population 2 would be expected to be more depressed and have a worse self-reported quality of life than their population 1. Depression is also believed by some to be related to general health, income and education. So it is not surprising that the older, sicker, poorer and worse educated were depressed. Did those attributes cause their glaucoma? Did the depression? Or vice versa? Who knows?

They also found that those who had been diagnosed by a doctor as having depression were not more likely to have glaucoma than those with a known diagnosis of depression.

It is not big data that will provide useful insights and facts. Big data may be revealing, but only when it is properly interpreted. Consider the generally accepted belief that those who exercise are healthier and live longer than those who do not exercise. But if one bases this conclusion on the health and longevity of a huge unselected population one could explain such an apparent causative relation by saying that those who are sick do not feel well and therefor do not exercise and die younger than those who are healthy and feel well and live longer.

Ah, "tis a puzzlement."

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