Eye Health and Screening

Screening and Early Intervention

Screening, in medicine, is a strategy used in a population to identify the possible presence of an as-yet-undiagnosed disease in individuals without signs or symptoms. This can include individuals with pre-symptomatic or unrecognized symptomatic disease. As such, screening tests are somewhat unusual in that they are performed on persons apparently in good health.

Screening interventions are designed to identify disease in a population or a specified ‘at risk’ sub-population early, thus enabling earlier intervention and management with the aim to reduce morbidity, mortality and suffering from a disease. Several types of screening exist: universal screening involves screening of all individuals in a certain category (for example, all children of a certain age). Case finding involves screening a smaller group of people based on the presence of risk factors (for example, because a family member has been diagnosed with a hereditary disease).

Careful thought and consideration must be given to any efforts to introduce screening. Critical questions around the introduction of screening might include:

  • Group to be screened – those >50 years, those with a family history, etc.
  • What can be done if an issue is identified – availability of therapeutic interventions, accessing vision rehabilitation services, etc.
  • Cost to the healthcare system – how will the costs of screening be covered? What infrastructural investments will be required? etc.

Without screening, diagnosis of disease only occurs after symptoms develop. However, disease frequently begins long before symptoms occur. This is the case in AMD, where symptoms usually only appear in the later stages of the disease.

Screening for eye disease typically involves a dilated eye exam and enables Eye Care Professionals to uncover common abnormalities of the visual system and related structures, as well as less common but extremely serious problems, such as ocular tumours. This evaluation can also uncover evidence of many forms of systemic disease that affect the eyes, like hypertension and diabetes. With appropriate intervention, potentially blinding diseases such as glaucoma, cataract and diabetic retinopathy often have favourable outcomes. Screening creates greater opportunity for early treatment and preservation of vision and has the added very important benefit of enabling affected individuals to prepare for the potential of future visual impairment, giving them the time and opportunity to develop strategies and plans to maintain their independence and quality of life.

Importance of Early Diagnosis

The American Academy of Ophthalmology (AAO) recommends that everyone gets a baseline eye examination at age 40, the time when early signs of disease or changes in vision may occur. A baseline eye exam at 40 acts as a reminder to adults as they age to be aware of their eye health. It can help identify signs of eye disease at an early stage when many treatments can have the greatest impact on preserving vision. Follow-up eye examinations would be dependent upon overall health and results of the baseline examination. People 65 or older should have their eyes checked every year or two. (https://www.aao.org/eye-health/tips-prevention/screening).

While the introduction of population-based screening programmes such as that recommended by AAO would increase the number of patients diagnosed with AMD and other eye diseases, many of which may also be painless and otherwise asymptomatic in their early stages (e.g. glaucoma), implementation of such a screening program would inevitably be associated with increased health care costs.

A study in Japan26 assessed the clinical and cost effectiveness of screening for AMD once every 5 years beginning at the age of 50. The results showed screening to be clinically effective, showing a decrease of 41 % in the number of blind patients. However, the screening intervention was found to be not cost-effective as it exceeded the 3-times GDP per capita per quality adjusted life year (QALY) gained.

A study in Ireland27 looked at the cost effectiveness of a hypothetical program of public education campaign and eye screening for people over 70 years. The intervention would be for screening for all causes of vision loss not just AMD. From a societal perspective the intervention would be deemed cost-effective.

Checking Your Eye Health

There are a number of simple tests that can be performed in the comfort of your home to help you to identify potential vision problems that demand professional attention. However, care must be taken when interpreting self-test results, as these tests are not designed to pick up all problems, e.g. blind spots, peripheral vision issues, intra-ocular pressure, etc. Please remember that these tests are not a substitute for regular dilated eye exams conducted by your Eye Care Professional.

Eye Tests

The Amsler Grid

This is a test for macular degeneration. You may use it to monitor your vision between visits to your ECP. The test consists of a grid of squares. Wearing your normal corrective lenses you test each eye one at a time. With one eye covered and the grid at arm’s length from you, look at the centre of the grid. If your eye is functioning properly, you should be able to see the centre white dot and the four corners and sides of the grid. The lines should appear to be straight and continuous from top to bottom and side to side. Any or worsening distortion in the grid should be discussed with your ECP.

It is worth noting that reading glasses may interfere with the grid. If you wear glasses consult with your ECP to establish a baseline view of the Amsler Grid against which any changes and deterioration may be measured.

 

The Ishihara Test

This is a colour perception test for red-green colour deficiencies. The test consists of a number of coloured plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in colour and size. Within the pattern are dots which form a number or shape clearly visible to those with normal colour vision, and invisible or difficult to see to those with a red-green colour vision defect. Other plates are intentionally designed to reveal numbers or shapes only to those with a red/green colour vision deficiency, and to be invisible to those with normal red/green colour vision.

 

The Visual Acuity Test

Typically performed using a standardized Snellen chart, this is an eye exam that checks how well you see the details of a letter or symbol from a specific distance. Visual acuity refers to the ability to discern the shapes and details of the things you see. You may need an eye exam if you feel you’re experiencing a vision problem or your vision has changed. Children frequently take visual acuity tests. Early testing and detection of vision problems can prevent issues from getting worse. Optometrists, driver’s license bureaus, and many other organizations use this test to check your ability to see. Visual acuity is expressed as a fraction: having 20/20 vision means that your visual acuity at 20 feet away from an object is normal. A person with 20/40 vision must be 20 feet away to see an object that people can normally see from 40 feet away.

 

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