Vision defects, also known as refractive errors, occur when the shape of the eye prevents light from focusing directly on the retina, leading to blurred vision. The main types of refractive errors are myopia (near-sightedness), hyperopia (farsightedness), and presbyopia.

1) Myopia (Near-sightedness):

• In myopia, the eyeball is too long, or the cornea is too curved, causing light rays to focus in front of the retina instead of directly on it.
• This results in distant objects appearing blurry, while close objects can be seen clearly.

Correction: Myopia can be corrected with concave lenses, which diverge incoming light before it enters the eye, allowing it to focus correctly on the retina.

2) Hyperopia (Farsightedness):

• Hyperopia occurs when the eyeball is too short, or the cornea has too little curvature, causing light rays to focus behind the retina.
• This leads to difficulty seeing objects up close, while distant objects may be clearer.

Correction: Hyperopia can be corrected with convex lenses, which converge incoming light to bring the focal point forward onto the retina.

3) Presbyopia:

• Presbyopia is an age-related condition where the lens of the eye loses its flexibility, making it difficult to focus on near objects.
• It typically affects individuals over the age of 40 and is characterized by difficulty reading small print or seeing objects up close.

Correction: Presbyopia can be corrected with reading glasses, bifocals, or progressive lenses, which provide different powers of magnification for near and distant vision.