a

b

Here are two instruments used for gonioscopy. 

Can you name them?

Answer
Both are for indirect gonioscopy.
a. is a Zeiss goniolens and
b. is a Goldman goniolens

What is the principle of gonioscopy ie. why do you need gonioscope to visualize the trabecular meshwork?

Answer
The angle of the anterior chamber can not be visualize with slilt-lamp
alone because the light from this region undergoes total internal refraction.
The goiniolenses have similar refractive index as the cornea. Therefore, the 
interface between the corneal and air is altered and light could pass from the 
anterior chamber through the cornea into the lens. This allows the image of
the angle to be examined.

When should gonioscopy be used in glaucoma and why?

Answer
Gonioscopy should be used in all patients at risk for primary or secondary open or closed angle glaucoma, in order to identify risk factors and to differentiate the aetiology of the disease.

Gonioscopy is used to grade the angle and can identify patients with or

at risk of angle closure glaucoma
Abnormalities that may be present include:
Peripheral anteiror synechiae following iritis or in anterior cleavage syndrome such as Axenfeld's syndrome
Pigmentation in the trabecular meshwork is associated with pseudoexfoliation syndrome, pigment dispersion syndrome and trauma
Angle recession following trauma
Blood in Schlemm's canal suggests raised episcleral pressure and is seen in carotid-cavernous fistula, superior vena cava syndrome and Sturge-Weber's syndrome.
Tumour or intraocular foreign body may give rise to glaucoma

What are the advantages and disadvantages of the two instruments shown?

Answer
Zeiss lens has a smaller diameter (9 mm) and 4 mirrors angled at 64 degrees. 
The small diameter allows indentation gonioscopy to be performed. 
The 4 mirrors allows all angle to be visualized without excessive manipulation 
of the lens. In addition, it does not require coupling fluid. However, it is 
unstable and cannot be used for argon laser trabeculoplasty.
Goldman has a bigger diameter (12mm) allowing stabilization of the eye during examiantion.This also makes it excellent for argon laser trabeculoplasty. 
However, it can not be used to perform indentation gonioscopy and coupling fluid is needed. The presence of only one mirror also means that the lens need to be rotated to allow visualization of all angle.