Myopia - Queries answered

Why would a near sighted person need glasses for a phone if their prescription is -0.50?

Normal power of eye is 60D . It is sufficient for distant vision but for near more power is required . Our has ability to increase the power of eye to 74D to see near objects clearly ( depending upon how near it is the power varies)

How this power of eye increases ?

By following 4 mechanisms which act together

1. constriction of pupil

2. contraction of ciliary muscle

3. increase in anterior curvature of lens

4. convergence of eyes

With age the accommodative power decreases so we need glasses for near vison after age of 45 yrs generally

In myopia(near sightedness) power of is generally more than 60D . so we use glasses (minus no) to decrease power of eye in order to see clearly . As power is already more there is no need to increase power to see near objects clearly . So for myopes even if age increases generally no need for glasses for near vision

What happens if they use minus no glasses for near vision ?

Near sighted person dont need minus no glasses generally .

If they use glasses(minus no) for near vision their eyes tries to increase more power (even though their eyes having more power )and their eyes get used to minus no glasses . So if they remove glasses they cant see clearly for near vision also . So we advise patients not to use glasses(minus no ) for near vision ,as they can see clearly without glasses.