PUBH 3100 Week 7 Chronic Condition Paper Example

A Disease With No Start Date: Primary Open-Angle Glaucoma Through Its Stages, and What an Undatable Onset Does to the Prevalence Figures Everyone Quotes

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Walden University

PUBH 3100: Human Disease and Prevention

Instructor Name

Month Day, Year

A Disease With No Start Date: Primary Open-Angle Glaucoma Through Its Stages, and What an Undatable Onset Does to the Prevalence Figures Everyone Quotes

The Problem of Onset

For many diseases, onset can be dated: the day a fever started or the week a lump appeared. Primary open-angle glaucoma, the most common form of glaucoma in the United States, offers no such day. It is a progressive disease of the optic nerve in which the cells that carry visual signals to the brain are gradually lost, and early loss produces no symptoms because the brain fills in gaps in peripheral vision (Weinreb et al., 2014). By the time a person notices a problem, much of the nerve may already be damaged. This paper follows the condition through its stages and asks what an undatable onset does to prevalence estimates that public health reports quote.

The Course of the Disease

Susceptibility

Older age, African ancestry, family history and higher pressure inside the eye raise the risk of open-angle glaucoma. Many people with high eye pressure never develop glaucoma, and some people with normal pressure do, so pressure is a risk factor rather than the disease itself.

Early Disease

Cells in the optic nerve begin to die, and the optic disc, the visible head of the nerve at the back of the eye, develops a deeper cup. Visual field tests may still be normal, because many cells can be lost before testing detects a defect. Nothing is felt.

Moderate Disease

Visual field tests show defects, often arcs of missing vision away from the center. The person usually still does not notice, especially if the other eye covers the gap.

Advanced Disease

Field loss reaches toward central vision, and reading, driving and moving safely become difficult. Loss of nerve cells cannot be reversed; treatment, mainly by lowering eye pressure, can slow further loss but not restore what is gone (Weinreb et al., 2014).

Staging Without a Start Date

Clinicians stage glaucoma by the condition of the optic nerve and the extent of visual field loss at the time of examination. Staging describes where a person is, not when they started. Two people at the same stage may have reached it over five years or twenty. This matters for public health because the usual measures of disease frequency assume that we can tell who has the disease at a given time and, for incidence, when it began.

What an Undatable Onset Does to Prevalence

Prevalence Depends on Detection

Prevalence counts the share of people living with a condition at one point in time. For a disease that produces no symptoms until late, prevalence counted from diagnoses measures diagnosis, not disease. When a national examination survey of Americans 40 and older photographed the optic disc and measured visual fields, 78% of people found to have glaucoma had not been diagnosed or treated, and the prevalence of undiagnosed glaucoma was 2.9%, rising to 6.6% among those over 70 (Shaikh et al., 2014). A prevalence figure based on people who report a glaucoma diagnosis would therefore count only about one person in five who has the disease.

Prevalence Depends on Definition

Because the disease has no clear starting point, studies must draw a line somewhere on a continuum of nerve damage and field loss. The survey above defined suspicious optic discs using a statistical cutoff, the 99.5th percentile of the cup-to-disc ratio in its own population. A different cutoff would produce a different prevalence. The global meta-analysis that estimated a prevalence of 3.54% among people aged 40 to 80 pooled studies that used varying definitions and examination methods (Tham et al., 2014), so its single figure combines several ways of deciding where disease begins.

Incidence Is Harder Still

Incidence, the rate of new cases, requires knowing when each case began. With no dateable onset, studies estimate incidence by examining people repeatedly and counting those who meet the definition at a later visit but not an earlier one. The estimated onset then depends on how often people were examined and how sensitive the tests were, not on any biological starting point.

Comparing the Figures

Table 1

How the Same Disease Produces Different Prevalence Figures

Note. Figures from Shaikh et al. (2014) and Tham et al. (2014); the first row is inferred from the survey's undiagnosed share.

Who Goes Uncounted

The undiagnosed share is not spread evenly. In the national survey, Black adults had about 4.4 times and Hispanic adults about 2.5 times the odds of having undiagnosed and untreated glaucoma compared with non-Hispanic White adults (Shaikh et al., 2014). Prevalence based on diagnoses will therefore understate glaucoma most in the groups already at higher risk of the disease and less likely to have regular eye examinations. A report that compares diagnosed prevalence across groups could even reverse the true pattern, showing less glaucoma where there is more. For public health planning, this means that diagnosis-based figures should not be used to decide where to direct screening or services without examination-based data to correct them.

What This Means for Prevention

Because early glaucoma is silent, waiting for symptoms means waiting for irreversible loss. Prevention therefore depends on finding disease in its early or moderate stage, which raises its own questions about who to examine and how often. Prevalence figures based on diagnoses will understate the problem in exactly the groups least likely to receive eye examinations.

Summary

Glaucoma's onset cannot be dated, so staging describes position rather than duration, prevalence depends on detection and definition, and incidence depends on how often people are examined. Any prevalence figure should be read with the questions: counted how, and defined where?

References

Shaikh, Y., Yu, F., & Coleman, A. L. (2014). Burden of undetected and untreated glaucoma in the United States. American Journal of Ophthalmology, 158(6), 1121-1129. https://doi.org/10.1016/j.ajo.2014.08.023

Tham, Y.-C., Li, X., Wong, T. Y., Quigley, H. A., Aung, T., & Cheng, C.-Y. (2014). Global prevalence of glaucoma and projections of glaucoma burden through 2040: A systematic review and meta-analysis. Ophthalmology, 121(11), 2081-2090. https://doi.org/10.1016/j.ophtha.2014.05.013

Weinreb, R. N., Aung, T., & Medeiros, F. A. (2014). The pathophysiology and treatment of glaucoma: A review. JAMA, 311(18), 1901-1911. https://doi.org/10.1001/jama.2014.3192