At least 100 million in India need spectacles but have no access

Subject : Science and Tech

Section :Msc

Context:

The World Health Assembly, in its meeting, resolved to implement an “integrated people-centered eye care” project.

Global status of people with vision impairment:

According to the WHO, at least 2.2 billion people function with compromised eyesight and at least a billion of these were preventable with access to eye care.
Around 90% of those with vision impairment or blindness live in low- and middle-income countries.
Fourth international conference on ‘Eye health in a changing world’ organised by the India Vision Institute, a non-governmental organisation.

The common defects of the eyes are:

These are called the refractive defects because they are caused by incorrect refraction of light rays by the eye lens.

It is also called shortsightedness
In Myopia:
- Person is able to see nearby objects clearly but is not able to see faraway object
- Image of Faraway objects is formed in front of retina
- Far point of person is nearer than infinity
Causes of Myopia
- Excessive curvature of eye lens (eye lens become more curved)
- Eyeball becomes elongated
Correction of Myopia
- It is corrected by using concave lens of suitable power
- It helps to form image on the retina

It is called long sightedness (or Hyperopia)
In Hypermetropia
- Person is able to see faraway objects but are not able to see nearby objects
- Image of Nearby objects is formed behind the retina
- Near point of person is beyond 25 cm
Causes of Hypermetropia
- Eyeball becomes too small
- Focal Length of Eye lens is too long
Correction of Hypermetropia
- It is corrected by using convex lens of suitable power
- It helps to form image on the retina

It is the defect in which person is not able to see nearby objects clearly
It is formed in old persons whose ciliary muscles become weak with age Hence, they lose their power of accommodation.
Causes
- Weakening of Eye muscles
- Decrease in Flexibility of Eye lens
Correction of Presbyopia
- it is also corrected with the help of convex lens (just like Hypermetropia)

In both Presbyopia and Hypermetropia:

A person cannot see nearby objects clearly but can see far away objects clearly.
The difference is in their causes:
- Presbyopia is caused due to loss of Power of Accommodation
- Hypermetropia is caused due to abnormal shape of the eyeball or abnormal shape of the eye lens

What are Bifocal Lens?

It is a lens whose upper part consists of concave lens and inside part for convex lens
It is used in case of those patients who are suffering from both myopia and hypermetropia

Progressive lens:

Progressive lenses are a type of lens which have no differentiating lines between the focal distances. These have three different levels of focal distances ranging from distance to near.
One looks through the top portion of the lens to see far-away objects, the middle to focus on intermediate objects and the bottom to see things close-up.
This may be especially useful to people who wear single-vision eyeglasses for distance (due to Myopia) in addition to reading glasses for near work (due to presbyopia).

Types of lenses:

Source: TH