Glaucoma: How can screening tests help?
Many eye doctors offer screening tests for glaucoma. But if you don't have any risk factors or your doctor doesn't have good reason to believe you may have this eye condition, statutory health insurers will not cover the test (in Germany). There has not yet been any good-quality research on whether or not screening programs for the general population are beneficial.
Glaucoma is an eye disease that causes vision to become progressively worse. This leads to the gradual loss of field of vision (what you can see without moving your eyes). One possible cause of glaucoma is too much pressure inside the eye (intraocular pressure), which damages the optic nerve over time. The most common form of glaucoma is primary open-angle glaucoma (POAG). It progresses slowly, and will not cause any immediate vision problems. By the time you notice that you have glaucoma, damage to the eye is usually already at an advanced stage and cannot be reversed. About 2 out of 100 people over the age of 40 have glaucoma. It is estimated that about 1,100 people go blind every year in Germany due to glaucoma.
Advantages and disadvantages of the screening tests
Certain treatments can prevent or delay vision loss, so it is critical to diagnose the disease as early as possible. But there is no general consensus on whether screening for the general population is the best way to do this. Some experts support the idea of offering glaucoma screening to everyone over the age of 40. Others think it would be better to only screen for glaucoma in people who have certain risk factors.
Screening will generally always have advantages and disadvantages, regardless of what is being tested for. A test may produce the wrong results – for example, if someone is diagnosed with glaucoma after the screening test, although their eyes are actually healthy. This is called a "false positive" result. If people are wrongly diagnosed with a disease, they may take medication they don't need and the diagnosis might cause unnecessary distress.
- In a test known as ophthalmoscopy, the eye doctor uses a special instrument called an ophthalmoscope to look into your eye. This makes it possible to detect optic nerve damage.
- Intraocular pressure is measured using a technique called tonometry.Here the eye is first numbed with a drop of liquid. The doctor then presses a small probe against the cornea to measure the pressure inside the eyeball.
A slit lamp is used to examine the front section of the eye. This is done to see whether the fluid (called aqueous humor) can flow out of the eye freely.
These tests don't take very long, and they carry little risk and aren't painful. If your doctor believes you have glaucoma, he or she can also measure your field of vision. This is done to see whether there are any gaps in your field of vision and whether blind spots have already developed.
The costs of these tests will only be covered by statutory health insurance funds in Germany for the following reasons:
- You regularly use steroids (such as corticosteroids) to treat another medical condition.
- Something in the front part of your eye is preventing aqueous humor from flowing out.
- You have typical glaucoma symptoms, such as gaps in your field of vision or trouble seeing.
- Diabetes has caused eye damage.
- You have eye injuries that make it necessary to rule out glaucoma.
- You have planned eye surgery, and need to rule out the possibility of glaucoma before or after the procedure.
- The back of your eye has changed and/or your intraocular pressure is too high.
If these special cases do not apply to your situation, glaucoma screening will usually be classified as an individual healthcare service in Germany (individuelle Gesundheitsleistung, or IGeL for short) and you will have to pay for it yourself. Eye doctors usually offer this screening for about 15 to 40 euros.
Benefits of screening
Over the last few years, different groups of researchers have looked into the question of whether offering screening to everyone over a certain age has any benefits. They did a search for studies looking into whether screening prevented loss of vision. They also wanted to find out how reliably the eye tests can tell whether someone has glaucoma or not. If the tests are unreliable, some cases of glaucoma might not be diagnosed (false negatives) or may be treated later. Another possible mistake can happen if people who do not actually have glaucoma are diagnosed with it, and then undergo further examinations or treatment (false positives).
But the searches for studies didn't turn up much: Hardly any research has been done on the benefits of general glaucoma screening. This means that it is not possible to say whether screening for glaucoma will have any advantages or disadvantages for people who do not have any symptoms or are not at greater risk of developing glaucoma. And many questions remain unanswered:
- Who benefits from screening? For what age groups does it make sense? Will people who do not actually have a high risk of developing glaucoma have unnecessary treatment due to misdiagnosis?
- Which tests are best suited for screening purposes?
- How often should screening be done?
Testing intraocular pressure is not enough on its own to diagnose glaucoma or determine whether you have a higher risk of developing glaucoma. Some people have glaucoma even though they don't have high intraocular pressure. Whereas others may have high intraocular pressure, but don't develop glaucoma. So it is important to know that further tests are needed in order to see whether
- you have an increased risk of developing glaucoma or,
- glaucoma can currently be diagnosed or ruled out.
These tests involve examining the optic nerve and the nerve fibers of the retina, as well as testing your field of vision. You may need more tests if your doctor thinks you might have glaucoma. A thorough examination will also include your doctor asking about your medical history, your life circumstances and symptoms.
- Older people: The risk of glaucoma increases with age. Only about 0.4% of all 40-year-olds are affected, but around 4% of 75-year-olds have it.
- People whose parents or siblings have glaucoma
- People with black skin
- People who are extremely short-sighted
- People who have diabetes
Not clear whether the advantages outweigh the disadvantages
Why is screening not covered by statutory health insurers in Germany if glaucoma can be treated when caught in time? Just because a disease can be treated, it does not automatically mean that it is a good idea to have everyone tested. To decide whether screening makes sense, you need to know whether its supposed advantages can actually be proven. And you have to know about possible disadvantages.
Experiences with other screening programs have shown that misdiagnosis is inevitable. This can make patients out of people who do not actually have the disease. They are then given further examinations that may be unnecessary or unpleasant. Or they may be treated even though they will not benefit from the treatment and could experience side effects. So there is a risk of too many people being wrongly diagnosed and too many people having unnecessary treatment.
These fundamental concerns might not apply to glaucoma screening. But that is precisely the problem: The actual advantages and disadvantages of glaucoma screening cannot be assessed with any certainty right now, simply because no good-quality research is available.
Ervin AM, Boland MV, Myrowitz EH, Prince J, Hawkins B, Vollenweider D et al. AHRQ Comparative Effectiveness Reviews: Screening for Glaucoma. Agency for Healthcare Research and Quality (AHRQ); 2012.
Hatt S, Wormald R, Burr J. Screening for prevention of optic nerve damage due to chronic open angle glaucoma. Cochrane Database Syst Rev 2009; (2): CD006129.
Kapetanakis VV, Chan MP, Foster PJ, Cook DG, Owen CG, Rudnicka AR. Global variations and time trends in the prevalence of primary open angle glaucoma (POAG): a systematic review and meta-analysis. Br J Ophthalmol 2016; 100(1): 86-93.
Schnell-Inderst P, Hunger T, Hintringer K, Schwarzer R et al. Individuelle Gesundheitsleitungen. Deutsches Institut für Medizinische Dokumentation und Information (DIMDI). Schriftenreihe HTA, Bd 113.
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