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What is Gonioscopy is used to study – and explain in detail?
Gonioscopy 

Owing to the lack of transparency of corneoscleral junction and total internal reflection of light at the anterior surface of cornea, it is not possible to visualize the angle of anterior chamber directly.
Therefore, a device (goniolens) is used to divert the beam light and this technique of biomicroscopic examination of the angle of anterior chamber is called gonioscopy.
In many conditions such as glaucoma, foreign bodies or tumours, a close inspection of this region is important.