give two possible reasons for this defect of eye in the human beings

It might be due to myopia and hypermetropia.

Why are the shivalik are prone to landslides

The two possible reasons for defect of eyes can be the two desises that occurs,
MYOPIA and HYPERMOPIYA

1 Vitreous humours contain increases
2 Cornea gets scarred
3 Rhodopsin pigement is synthesised as vitamin A deficiencyis there

common types of?eye defects

MYOPIA or NEARSHIGHTED. Myopia occurs when the?eyeball?is too long, relative to the focusing power of the cornea and lens of the?eye. ...HYPEROPIA or FARESIGHTED. This vision problem occurs when light rays entering the?eye?focus behind the retina, rather than directly on it. ...ASTIGMATISM. ...PRESBYOPIA.

Because of short- blindness and long- blindness