background. Sclerotic scatter or scattering sclero-corneal illumination With this type of illumination, a wide light beam is directed onto the limbal region of the cornea at an extremely low angle of incidence and with a laterally de-centered illuminating prism. Adjustment must allow the light beam to transmit through the corneal parenchymal layers according to the principle of total reflection allowing the interface with the cornea to be brightly illuminated. The magnification should be selected so that the entire cornea can be seen at a glance. Special techniques Fundus observation and gonioscopy with the slit lamp Fundus observation is known by the ophthalmic and the use of fundus cameras. With the slit lamp, however, direct observation of the fundus is impossible due to the refractive power of the ocular media. In other words: the far point of the eye (punctum remotum) is so distant in front of (myopia) or behind (hyperopia) that the microscope cannot be focused. The use of auxiliary optics - generally as a lens – makes it possible however to bring the far point within the focusing range of the microscope. For this various auxiliary lenses are in use that range in optical properties and practical application. Watzke–Allen test is a test used in diagnosis of a full thickness macular hole and also to assess retinal function after surgical closure of the hole, with the help of slit lamp. Light filters Most slit-lamp use five light filters. Such as Unfiltered, Heat absorption- for increased patient comfort Grey filter, Red free- for better visualisation of nerve fibre layer and haemorrhages and blood vessels. Cobalt blue- after staining with fluorescein dye, for seeing corneal ulcers, contact lens fitting, Seidel's test Cobalt blue light Slit lamps produce light of the wavelength 450 to 500 nm, known as "cobalt blue". This light is specifically useful for looking for problems in the eye once it has been stained with fluorescein. Types There are two distinct slit lamp types based on the location of their illumination system: Zeiss type In the Zeiss type slit lamp, the illumination is located below the microscope. This type of slit lamp is named after the manufacturing company Carl Zeiss. Haag Streit type In the Haag Streit type slit lamp, the illumination is located above the microscope. This type of slit lamp is named after the manufacturing company Haag Streit. Interpretation The slit lamp exam may detect many diseases