It has a separate light source and optical system and is used along with a condensing lens placed in front of the eye. Drops are most often used to dilate the pupil. This instrument provides a high magnification view of the front structures of the eye, including the cornea, iris and lens, and with the use of the condensing lens, it allows a detailed, stereoscopic view of the retina. It also can detect inflammation of the internal structures, cataract changes of the crystalline lens and more. It is used extensively for the fitting of contact lenses and is the instrument of choice for detecting contact lens related tissue changes to the cornea and surrounding tissues.
Most eye doctors use some sort of automated visual field apparatus.
Visual field testing is essential in determining retina disease or neurological deficits in the visual pathways between the eye and the brain. It is the primary tool for detecting visual field loss resulting from glaucoma, retinal tears, artery and vein occlusions and tumors along the optic nerve pathway and brain. These are larger machines that display individual points of light on the inside of hemispherical shell. For all machines, a software program plots the observed targets in the field and uses a database to compare patient responses to expected age-relative normals. This device measures the intraocular fluid pressure.