The first thing is proper diet. Use of carrots, beet root, salad etc. improve vision. In Ayurveda there is a drug known as sapat amrit Loh which is used to improve vision. There are some ayurvedic eye hospitals in south they can be contacted. There are specialized ayurvedic techniques in panch karma wherein medicated ghee is kept over eye for some time. This calls for very specialized person.

Hi,
As per Ayurved, Health of eyes depends mainly on 'heat' factor of the body, blood circulation and eye anatomy.
In this case where small children wear big glasses, is really a concern and inconvenience. As a part of treatment, hv to check your niece' birth date . Kindly mail me on drprasadgoa@rediff.com .
Other measures of treatment can include Ayurvedic medicines, Panchakarma therapies, Yog techniques and Diet regimes.
Avoid salted, tinned and ready made products.
Avoid liquid intake such as excessive water and milk after 6.30 pm .
Avoid having hot water pouring on head region while bathing .