Hypermetropia
Far-sighted: nearby objects look blurred.
Reading far away
Someone holds a newspaper at arm's length, much farther than 25 cm, to read it. They can see a bus far down the road clearly.
Where does the light from the newspaper come to a focus in their eye when it is close?
What this lesson covers
The idea
In hypermetropia (far-sightedness) nearby objects look blurred: the near point is farther than 25 cm and light from a close object focuses behind the retina, because the eye lens's focal length is too long or the eyeball too small.
Reading far away
Someone holds a newspaper at arm's length, much farther than 25 cm, to read it. They can see a bus far down the road clearly.
Where does the light from the newspaper come to a focus in their eye when it is close?
- Behind the retina
- In front of the retina
- Exactly on the retina
Compare the eyes
Open every tab. The rays come from a nearby object. The pictures are schematic, not to scale.
Far-sighted
A person with hypermetropia sees distant objects clearly, but nearby objects look blurred because their light is focussed behind the retina. The lens can be too weak (long focal length) or the eyeball too small.
In hypermetropia (far-sightedness) nearby objects look blurred: the near point is farther than 25 cm and light from a close object focuses behind the retina, because the eye lens's focal length is too long or the eyeball too small.
Notes
In hypermetropia nearby objects look blurred; the near point is farther than 25 cm and light from a close object focuses behind the retina (focal length too long or eyeball too small).
Check yourself
A person with hypermetropia can see…
In hypermetropia, light rays from a closeby object are focussed…
Hypermetropia arises because…
The near point of a person with hypermetropia is…
- nearby objects clearly, but not distant objects. That describes myopia. A person with hypermetropia sees distant objects clearly.
- distant objects clearly, but not nearby objects distinctly — correct. Yes!
- neither nearby nor distant objects. A person with hypermetropia can see distant objects clearly.
- at a point in front of the retina. In myopia the image of a distant object forms in front of the retina. In hypermetropia the rays from a close object focus behind the retina.
- exactly on the retina. That happens in a normal eye. In hypermetropia the rays are focussed behind the retina.
- at a point behind the retina — correct. Yes!
- the focal length of the eye lens is too long, or the eyeball has become too small — correct. Yes!
- the eye lens has excessive curvature. Excessive curvature of the eye lens is a cause of myopia.
- the eyeball is elongated. Elongation of the eyeball is a cause of myopia.
- nearer than 25 cm. The near point of a hypermetropic person is farther away than 25 cm.
- farther away than the normal near point of 25 cm — correct. Yes!
- the same as the normal near point of 25 cm. The near point is farther away from the normal near point, which is why reading material must be kept much beyond 25 cm.