Vision Defects and which lenses are needed to correct them
There are three common eye defects:
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1. Myopia (SHORTSIGHTEDNESS)
2. Hyperopia (LONGSIGHTEDNESS
3. The Astigmatic (EYE-DISTORTED VISION)
Myopia (SHORTSIGHTEDNESS)
Myopia or nearsightedness is a condition where the eye is too long in relation to its refractive power.
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The light rays therefore intersect in front of the retina instead of on it. Blurred vision results. The further away the object observed, the more blurred it appears. Clear vision is limited to nearby objects. Shortsighted therefore means having a good near vision but poor distance vision. With an appropriate eyeglass lens, a myopic eye can once again enjoy clear vision at all distances. As you see here, the light rays are slightly diverged in front of the eye, shifting their point of intersection to the surface of the retina. This creates the same conditions as those enjoyed by emmetropic eyes, providing the wearer with excellent vision.
- A lens for myopia is a diverging or minus lens. Minus lenses are always thinner at the center than at
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the edge. The front surface is relatively flat, while the back surface has a more pronounced curvature. The higher the power required, the thicker the edge becomes and the heavier the lens.
Hyperopia (LONGSIGHTEDNESS)
- Hyperopia or long sightedness means the closer an object is, the more blurred it appears
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uncorrected, hyperopia bring on fatigue, sore eyes, headaches and eyestrain. The eye is too short in relation to its refractive power. The light rays intersect behind the retina, resulting in a blurred vision. An attempt is sometimes made to compensate for this defect by accommodation, but in the long term this leads to problems. With an appropriate lens, a hyperopic eye can see clearly again at all distances without strain. As you see, the light rays are converged in front of the eye, shifting their point of intersection to the surface of the retina. Accommodation can once again be used solely for adjusting to different distances.
- A lens for hyperopia is a converging or plus lens. Plus lenses are always thicker at the center than at
Screen_shot_2012-02-12_at_6.43.06_PM.png
the edge. The back surface is relatively flat, while the front surface has a more pronounced curvature. The higher the power required, the thicker the center becomes and the heavier the lens.
The Astigmatism (EYE-DISTORTED VISION)
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- Astigmatism is a condition where there is a variation in the shape of the cornea. Rays of light pass through the cornea on two planes - vertical and horizontal. In the astigmatic eye one corneal plane is steeper than the other, so that the rays of light do not come together at the same point. One point can be in front of the retina, the other behind. Both can be in front of the retina, etc.
The more unequal the curvature of the cornea, the more blurred your vision will be.
With an appropriate lens, an astigmatic eye can once again enjoy clear, undistorted vision. The rays of light are deflected in such a way they fall exactly on the retina.
- A lens for astigmatism is a cylindrical lens, i.e. it is not spherical in shape but has a different curvature in two directions. It can be more easily imagined as the section of a ring.
There are three common eye defects:
1. Myopia (SHORTSIGHTEDNESS)
2. Hyperopia (LONGSIGHTEDNESS
3. The Astigmatic (EYE-DISTORTED VISION)
Myopia (SHORTSIGHTEDNESS)
Myopia or nearsightedness is a condition where the eye is too long in relation to its refractive power.
Screen_shot_2012-02-12_at_6.42.46_PM.png
The light rays therefore intersect in front of the retina instead of on it. Blurred vision results. The further away the object observed, the more blurred it appears. Clear vision is limited to nearby objects. Shortsighted therefore means having a good near vision but poor distance vision. With an appropriate eyeglass lens, a myopic eye can once again enjoy clear vision at all distances. As you see here, the light rays are slightly diverged in front of the eye, shifting their point of intersection to the surface of the retina. This creates the same conditions as those enjoyed by emmetropic eyes, providing the wearer with excellent vision.
- A lens for myopia is a diverging or minus lens. Minus lenses are always thinner at the center than at
Screen_shot_2012-02-12_at_6.42.52_PM.png
the edge. The front surface is relatively flat, while the back surface has a more pronounced curvature. The higher the power required, the thicker the edge becomes and the heavier the lens.
Hyperopia (LONGSIGHTEDNESS)
- Hyperopia or long sightedness means the closer an object is, the more blurred it appears
Screen_shot_2012-02-12_at_6.42.57_PM.png
uncorrected, hyperopia bring on fatigue, sore eyes, headaches and eyestrain. The eye is too short in relation to its refractive power. The light rays intersect behind the retina, resulting in a blurred vision. An attempt is sometimes made to compensate for this defect by accommodation, but in the long term this leads to problems. With an appropriate lens, a hyperopic eye can see clearly again at all distances without strain. As you see, the light rays are converged in front of the eye, shifting their point of intersection to the surface of the retina. Accommodation can once again be used solely for adjusting to different distances.
- A lens for hyperopia is a converging or plus lens. Plus lenses are always thicker at the center than at
Screen_shot_2012-02-12_at_6.43.06_PM.png
the edge. The back surface is relatively flat, while the front surface has a more pronounced curvature. The higher the power required, the thicker the center becomes and the heavier the lens.
The Astigmatism (EYE-DISTORTED VISION)
- Astigmatism is a condition where there is a variation in the shape of the cornea. Rays of light pass through the cornea on two planes - vertical and horizontal. In the astigmatic eye one corneal plane is steeper than the other, so that the rays of light do not come together at the same point. One point can be in front of the retina, the other behind. Both can be in front of the retina, etc.
The more unequal the curvature of the cornea, the more blurred your vision will be.
With an appropriate lens, an astigmatic eye can once again enjoy clear, undistorted vision. The rays of light are deflected in such a way they fall exactly on the retina.
- A lens for astigmatism is a cylindrical lens, i.e. it is not spherical in shape but has a different curvature in two directions. It can be more easily imagined as the section of a ring.