Myopia
Near-sighted: the image falls in front of the retina.
Seeing the board
Some students can read a book easily but cannot read the writing on a far-away board.
Where does the image of the far board form in their eyes?
What this lesson covers
The idea
In myopia (near-sightedness) distant objects look blurred: the far point is nearer than infinity and a distant object's image forms in front of the retina, owing to excessive curvature of the eye lens or elongation of the eyeball.
Seeing the board
Some students can read a book easily but cannot read the writing on a far-away board.
Where does the image of the far board form in their eyes?
- In front of the retina
- Exactly on the retina
- Behind the retina
Compare the eyes
Open every tab. The rays come from a distant object. The pictures are schematic, not to scale.
Short-sighted
A person with myopia sees nearby objects clearly but distant ones look blurred, because the image forms in front of the retina. Two causes are a too-curved lens or a too-long eyeball.
In myopia (near-sightedness) distant objects look blurred: the far point is nearer than infinity and a distant object's image forms in front of the retina, owing to excessive curvature of the eye lens or elongation of the eyeball.
Notes
In myopia (near-sightedness) distant objects look blurred; the far point is nearer than infinity and the image forms in front of the retina (too much curvature of the lens or a long eyeball).
Check yourself
A person with myopia can see…
In a myopic eye, the image of a distant object is formed…
Myopia may arise due to…
Another name for myopia is…
- distant objects clearly, but not nearby objects. That describes hypermetropia. A person with myopia sees nearby objects clearly.
- both nearby and distant objects clearly. A myopic person cannot see distant objects distinctly.
- nearby objects clearly, but not distant objects — correct. Yes!
- in front of the retina — correct. Yes!
- on the retina. That happens in a normal eye. In a myopic eye the image forms in front of the retina.
- behind the retina. In a myopic eye the image of a distant object forms in front of the retina, not behind it.
- a focal length of the eye lens that is too long. A focal length that is too long, or an eyeball that is too small, causes hypermetropia.
- excessive curvature of the eye lens or elongation of the eyeball — correct. Yes!
- weakening of the ciliary muscles with ageing. That causes presbyopia.
- far-sightedness. Far-sightedness is another name for hypermetropia.
- old-sightedness. Presbyopia is the defect that comes with ageing. Myopia is also known as near-sightedness.
- near-sightedness — correct. Yes!