This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Examination of the Eye, Subject name: Ophthalmology
Gonioscopy is useful to see details of which of the following? 
Select and explain. 
A. Lens, B. Angle of the anterior chamber, C. Iris, D. Cornea
B: Angle of the anterior chamber
Answer: B: Angle of the anterior chamber 
Explanation: Ans. b (Angle of the anterior chamber) (Ref Basak's ophthalmology 4th/270)The purpose of gonioscopy is to identify abnormal angle structures and to estimate width of chamber angle.Direct (with goniolenses):Provides direct view of angle.Used for diagnostic & operative purposes.Indirect (with gonioprisms):Provides mirror image of opp angle.Can be used only under a slit lamp.# Normal angle structures seen from anterior to posterior:1. Schwalbe's line2. Trabecular meshwork3. Scleral spur4. Ciliary band# Grading of the angle (Schaffer's):GradeAngleGonioscopic ViewClinical interpretationIVWide open (35-45deg)All structures seenClosure improbableIIIOpen (20-35deg)Scleral spur seenClosure improbableIIModerately narrow (10-20deg)Trabecular meshwork seenClosure possibleIExtremely narrow (<10deg)Schwalbe's line visibleClosure imminentOCompletely closed (0deg)Nothing visibleClosure present