| Refractive Errors |
| How do we see things? / Principle of image formation |
| The retina, the innermost structure of the eye, behaves like a projection screen which receives the inverse images and the cerebral centre of the brain redresses (form an erect) the image. |
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| Types of refractive errors: |
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Emmetropia |
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Hyperopia or Farsightedness |
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Myopia or Nearsightedness |
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Astigmatism |
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Presbyopia |
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| Emmetropia(Normal vision): |
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Emmetropia |
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A condition where no refractive error is presents |
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| Hyperopia or Farsightesness: |
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Eyeball is too short |
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Clear distance vision but suffer with eyestrain for near work |
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Correction by means of spherical plus lenses. |
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| Myopia or Nearsightedness |
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Eyeball is too long |
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Clear near vision and blurred distant vision, people generally squeeze their eyes to see the distant object |
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Correction by means of spherical minus lenses. |
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| Astigmatism |
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A point object will not have a point image. |
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Blurred vision for distance and near. |
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Generally have eyestrain and headache. |
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| Presbyopia |
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Lens begin to lost its elasticity/accommodating capacity. |
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Difficulty in focusing near object and clear distant vision. |
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Symptoms begins at the age of forty . |
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Corrected by means of bifocal/progressive lenses for near and intermediate vision. |
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