In normal vision, light enters the eye and the image is focused clearly at a single point on the retina (the light-sensitive area similar to the film of a camera) at the back of the eye.  Refractive errors result from an abnormality of either the length of the eyeball or curvature of the front of the eye called the cornea.

When a refractive error exists, this image is NOT IN FOCUS and 3 situations can arise;

1. Myopia (short-sightedness)

The image is focused in front of the retina because either the eyeball is too long or the cornea too curved.  The person can see near objects but distant objects appear blurred.

This is the commonest refractive error is Asians and usually manifests between the ages of 6 to 16 years of age.  There is a correlation between short-sightedness and excessive reading, excessive playing of computer or handheld games and not spending enough time outdoors to see distant objects.

2. Hyperopia (long-sightedness)

The image is focused behind the retina because the eyeball is too short.  Near objects appear more blurred compared to distant objects.

3. Astigmatism

The image is focused at 2 points on the retina and objects at all distances appear blurred and distorted. Astigmatism is due to unevenness of the cornea.

Presbyopia

After the age of around 40 years old, regardless whether you have a refractive error or not, your focusing muscle starts to weaken and you will find reading near objects or books become more difficult.  This condition is called Presbyopia and you will need to wear Reading Glasses or Multi-Focal glasses to help you read.

Click to view OrlandoEyeInstitute video on Refractive Errors

How often should you have your eyes checked?

Disease-free adults should have the eyes checked every year while those with other illness such as Diabetes or Glaucoma need to have their eye checks more frequently (see Table below)

Normal Disease-Free Person	Yearly
Family History of Glaucoma	Yearly with Visual Field Test
Person with Glaucoma	4-6 monthly
Person with well-controlled Diabetes	Yearly
Person with poorly-controlled Diabetes	4-6 monthly
Person with ARMD	6 monthly with Retina OCT Scan

The eye tests should include:

• Measurement of any refractive errors (shortsighted, longsighted or astigmatism)
• Checking eye pressures (for glaucoma)
• Checking for cataracts
• Visual Field Test for people with glaucoma
• Retina OCT scan for people with Age-Related Macula Degeneration (ARMD) or Diabetes
• Assessment using Visual Acuity and Amsler Chart (see below)

Self Assessment Vision Chart to test for cataracts & ARMD

Self Assessment Amsler Chart to test for ARMD

Contact your Eye Doctor if you see distorted lines in this chart

All the lines here are straight.

---

Disclaimer. TELEME blog posts contains general information about health conditions and treatments. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. The information is not advice and should not be treated as such. 

If you think you may be suffering from any medical condition, you should seek immediate medical attention from your doctor or other professional healthcare providers. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information on this website.